Patent Publication Number: US-2023136204-A1

Title: Electrically operated linear pump and pump drive

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 63/002,811, filed Mar. 31, 2020, and entitled “ELECTRIC FEED PUMP FOR A PLURAL COMPONENT SPRAY SYSTEM,” and claims the benefit of U.S. Provisional Application No. 63/002,693, filed Mar. 31, 2020, and entitled “ELECTRICALLY OPERATED LINEAR PUMP DRIVE,” the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     This disclosure generally relates to fluid displacement systems. More specifically, this disclosure relates to drives for positive displacement pumps for use in fluid displacement systems, such as spray systems and plural component dispensing systems. 
     A spray fluid, such as paint, is put under pressure by a pump for application to a substrate. Typically, the fluid is placed under pressure by a positive displacement pump. The pump places the fluid under pressure and outputs the fluid under pressure through a flexible hose. A spray gun is used to dispense the fluid, the gun being attached to the end of the hose opposite the pump. The positive displacement pump is typically mounted to a drive housing and driven by a motor. A pump rod is attached to a reciprocating drive that drives reciprocation of the pump rod, thereby pulling fluid from a container into the pump and then driving the fluid downstream from the pump. In some cases, electric motors can power the pump. The motor is attached to the pump via a gear reduction system that increases the torque and reduces the speed generated by the motor. 
     Multiple component (e.g., liquid) applicators often include dispensing systems that receive separate inert material components, mix the components in a predetermined ratio, and then dispense the components as an activated compound. For example, multiple component applicators are often used to dispense epoxies and polyurethanes that solidify after mixing of a resin component and an activating material, which are individually inert. After mixing, an immediate chemical reaction begins that results in the cross-linking, curing, and solidification of the mixture. Therefore, the two components are routed separately in the system so that they can remain segregated as long as possible. A dispensing device, such as a sprayer or other device, receives each component and mixes the components for delivery as an activated compound. A typical multiple component applicator system includes positive displacement pumps that individually draw in component materials from separate hoppers and pump the pressurized component materials (e.g., fluids) to the dispensing device for mixing and application. 
     SUMMARY 
     According to one aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate relative the stator on a pump axis; a pump frame supporting the motor by a first static connection and a first dynamic connection; and a drive mechanism connected to the rotor, the drive mechanism configured to receive a rotational output from the rotor and convert the rotational output into a linear input along the pump axis to cause pumping of the fluid. 
     According to an additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate relative the stator on a pump axis; a pump frame supporting the motor by a first static connection and a first dynamic connection; a drive mechanism connected to the rotor, the drive mechanism configured to receive a rotational output from the rotor and convert the rotational output into a linear input along the pump axis to cause pumping of the fluid; and a displacement pump fixed to the pump frame by a second static connection and connected to the drive mechanism by a second dynamic connection. 
     According to yet another additional or alternative aspect of the present disclosure, a fluid sprayer includes a frame elongate along an axis to have a first end and a second end; a motor mounted on the first end of the frame and configured to output rotational motion, the motor electrically powered and including a rotor rotating about an axis and a stator the motor; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder, the piston reciprocating along the axis within the cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw that is elongate along the axis, the screw only one of linearly translating along or rotating about the axis, the drive mechanism outputting linear reciprocating motion. The piston receives the linear reciprocating motion output by the drive mechanism to reciprocate the piston along the axis while the cylinder is braced by the frame such that the piston reciprocates within the cylinder. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate on a pump axis about the stator to cause reciprocation of a fluid displacement member of a pump on the pump axis; a drive mechanism connected to the rotor, the drive mechanism configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid by the fluid displacement member; and a bearing supporting the rotor and configured to react axial loads in both a first axial direction along the pump axis and a second axial direction along the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid to an applicator to generate a fluid spray includes a motor having a stator and a rotor disposed coaxially about the stator on a pump axis, the rotor including a rotor shaft extending in a first axial direction from a rotor body of the rotor; a pump frame extending in the first axial direction from a first end of the motor such that the rotor shaft extends into the pump frame, wherein the pump frame is connected to the stator to support the motor; a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor to a linear input along the pump axis; and a bearing supporting the motor relative the pump frame and configured to transmit axial forces to the pump frame. 
     According to yet another additional or alternative aspect of the present disclosure, a method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by the rotation of the rotor; reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis, wherein reciprocating the fluid displacement member causes the fluid displacement member to pump fluid; receiving axial loads generated during pumping at the drive mechanism; and transmitting the axial loads to a pump frame by a bearing disposed radially between the pump frame and a rotor shaft connecting the drive mechanism to the rotor. 
     According to yet another additional or alternative aspect of the present disclosure, a portable fluid sprayer includes a frame having a first end and a second end, a motor, a pump, a drive mechanism supported by the frame and located axially between the motor and the pump, and a bearing assembly located between the drive mechanism and the motor. The motor is mounted on the first end of the frame, electrically powered, and has a rotor and a stator. The motor is configured to output rotational motion about an axis. The pump is mounted on the second end of the frame, includes a piston and a cylinder, and is configured to reciprocate along the axis within the cylinder. The drive mechanism includes a screw that is elongate along the axis and configured to only one of linearly translate along or rotate about the axis. The drive mechanism is configured to output linear reciprocating motion. The piston is configured to receive the linear reciprocating motion output by the drive mechanism and to reciprocate within the cylinder through an upstroke and a downstroke. The piston receives a downward reaction force when moving through the upstroke and an upward reaction force when moving through the downstroke. The drive mechanism and the bearing assembly are arranged such that both of the upward reaction force and the downward reaction force transfer through the drive mechanism and to the bearing assembly. The bearing assembly permits rotational motion to pass within the bearing assembly from the motor to the drive mechanism while the bearing assembly prevents some or all of both of the downward reaction force and the upward reaction force from transferring to the rotor. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid. The pumping assembly includes a motor including a stator and a rotor configured to rotate about the stator on a pump axis; and a drive mechanism configured to receive a rotational output from the rotor and generate a linear input along the pump axis to cause pumping of the fluid. The rotor includes a rotor body including a plurality of permanent magnets; and a rotor shaft disposed coaxially on the pump axis and extending in a first axial direction from the rotor body. The drive mechanism is connected to an end of the rotor shaft opposite the rotor body. The rotor shaft defines a cavity, and wherein at least a portion of the drive mechanism is disposed within the cavity. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid to an applicator to generate a fluid spray includes a motor having a stator and a rotor, a pump frame supporting the motor, and a drive mechanism. The rotor is disposed coaxially about the stator on a pump axis and includes a rotor shaft extending in a first axial direction from a rotor body of the rotor. The rotor shaft at least partially defines a cavity. The rotor shaft extends into the pump frame. The drive mechanism is configured to convert a rotational output from the rotor shaft to a linear input along the pump axis. At least a portion of a linear drive element of the drive mechanism axially extends into the cavity of the rotor shaft. 
     According to yet another additional or alternative aspect of the present disclosure, a method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor, the rotor including a rotor shaft coaxial with the pump axis and extending in a first axial direction from a rotor body of the rotor; displacing a screw of a drive mechanism axially along the pump axis by the rotation of the rotor; and reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis to pump a fluid. At least a portion of the screw axially overlaps with the rotor shaft for at least a portion of a reciprocation cycle of the screw. 
     According to yet another additional or alternative aspect of the present disclosure, a fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the rotor rotating about an axis, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw having a first end, the drive mechanism outputting linear reciprocating motion; and a rotor shaft located between the motor and the drive mechanism, the rotor shaft conveying the rotational motion from the motor to the drive mechanism, the rotor shaft comprising a cavity within which the first end of the screw linearly translates. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; a drive mechanism connected the rotor and configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid, wherein the drive mechanism includes a linear drive element configured to displace axially along the pump axis; and a clocking member interfacing with the linear drive element to prevent rotation of the linear drive element about the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid to an applicator to generate a fluid spray includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis, wherein the motor includes a first motor end and a second motor end; a pump frame fixed to the second motor end and including a main body extending in a first axial direction relative the motor, wherein the rotor shaft extends into the main body; a drive mechanism connected to the rotor, the drive mechanism configured to convert a rotational output from the rotor to a linear input along the pump axis; and a clocking member connected to a linear drive element of the drive mechanism and interfacing with the main body to prevent the linear drive element from rotating about the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by rotation of the rotor; reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis, the fluid displacement member pumping a fluid downstream to the spray gun; and preventing rotation of the screw relative a pump frame mechanically fixed to both the stator and a cylinder of a pump by a clocking member interfacing with each of the screw and the pump frame. 
     According to yet another additional or alternative aspect of the present disclosure, a fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw, the drive mechanism outputting linear reciprocating motion, the piston receiving the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder; and a clocking assembly located between the motor and the pump, the clocking assembly configured to resist rotation of the screw due to the rotational motion output by the motor, the clocking assembly comprising a collar fixed about the screw, the clocking assembly further comprising a sleeve fixed with respect to the frame. Both the screw and the collar linearly translate within the sleeve while the sleeve prevents rotation of the collar. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; a drive mechanism connected the rotor and configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid, wherein the drive mechanism includes a linear drive element configured to displace axially along the pump axis; and a clocking member interfacing with the linear drive element to prevent rotation of the linear drive element about the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid to an applicator to generate a fluid spray includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis and including a rotor shaft extending in a first axial direction from a first axial end of the motor; a pump frame extending in the first axial direction such that the rotor shaft extends into the pump frame, wherein the pump frame is fixed to the motor at a second axial end of the motor opposite the first axial end; a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor shaft to a linear input along the pump axis; and a clocking member fixed relative the pump frame and interfacing with a linear drive element of the drive mechanism to prevent the linear drive element from rotating about to the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by rotation of the rotor; reciprocating a fluid displacement member of a displacement pump, the fluid displacement member connected to the screw such that reciprocation of the screw causes reciprocation of the fluid displacement member, wherein reciprocating the fluid displacement member along the pump axis pumps a fluid downstream for spraying; and preventing rotation of the screw relative a pump frame mechanically fixed to the electric motor and the displacement pump by a clocking member telescopically interfacing with the screw. 
     According to yet another additional or alternative aspect of the present disclosure, a fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw, the drive mechanism outputting linear reciprocating motion, the piston receiving the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder; and a clocking assembly, the clocking assembly comprising a telescope member that has a sliding overlapping interface with the screw, the telescope member preventing rotation of the screw by resisting the rotational motion output by the motor as the screw linearly translates relative to the telescope member. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid from an upstream fluid source to a downstream spray applicator for spraying of the fluid includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; and a drive mechanism connected to the rotor disposed coaxially with the rotor, the drive mechanism configured to convert a rotational output from the rotor into a linear input along the pump axis in each of a first axial direction and a second axial direction to cause pumping of the fluid. A screw of the drive mechanism extends into the motor with the screw disposed at a first position associated with an end of a stroke in the second axial direction. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly for pumping a spray fluid to an applicator to generate a fluid spray includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis, wherein the motor includes a first motor end and a second motor end; a rotor shaft extending in a first axial direction from a rotor body of the rotor; a pump frame fixed to the second motor end and including a main body extending in a first axial direction relative the motor, wherein the rotor shaft extends into the main body; and a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor shaft to a linear input along the pump axis. The drive mechanism includes a linear drive element configured to provide the linear input, and wherein at least a portion of the linear drive element is disposed within a motor cavity within the motor with the linear drive element disposed at a first position associated with an end of a stroke in a second axial direction opposite the first axial direction. 
     According to yet another additional or alternative aspect of the present disclosure, a method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the electric motor; displacing a screw of a drive mechanism axially along the pump axis through a first stroke in a first axial direction and a second stroke in a second axial direction by rotation of the rotor; reciprocating a fluid displacement member connected to a first end of the screw along the pump axis by displacement of the screw along the pump axis to pump fluid; and translating a second end of the screw disposed opposite the first end into a motor cavity within the motor during the second stroke. 
     According to yet another additional or alternative aspect of the present disclosure, a fluid sprayer includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the rotor rotating about an axis, the motor configured to output rotational motion, the motor comprising a motor cavity that is coaxial with the axis; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw that is elongate along the axis, the screw having a first end, the first end of the screw linearly translating within the motor cavity along the axis, the drive mechanism outputting linear reciprocating motion. The piston receives the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate on a pump axis; a fluid displacement member operatively connected to the rotor to be reciprocated through an upstroke and a downstroke along the pump axis; and a controller configured to control operation of the motor such that the fluid displacement member displaces according to a first speed profile during the upstroke and according to a second speed profile during the downstroke, the first speed profile different than the second speed profile. 
     According to yet another additional or alternative aspect of the present disclosure, a pumping system includes a first upstream pump having a first electric motor connected to a first fluid displacement member; a first downstream pump having an inlet fluidically connected to an outlet of the first upstream pump; a first sensor disposed downstream from an outlet of the first downstream pump; and a controller in communication with the first electric motor and the first sensor. The controller is configured to receive first parameter data from the first sensor and control operation of the first electric motor based on the first parameter data. 
     According to yet another additional or alternative aspect of the present disclosure, a method of operating a pumping system includes driving rotation of a first rotor of a first electric motor to drive reciprocation of a first fluid displacement member of a first feed pump to pump the first component material to an inlet of a first proportioner pump; increasing a pressure of the first component material via the first proportioner pump; generating first parameter data regarding the first component material downstream of the first proportioner pump by a first sensor; and controlling operation of the first electric motor by a controller based on the first parameter data 
     According to yet another additional or alternative aspect of the present disclosure, a method of operating a pumping system configured to pump different first and second component materials to an applicator for mixing and forming a plural component material includes pumping a first component material, with a first upstream pump including a first electric motor, from a first fluid tank to a first downstream pump; pumping a second component material, with a second upstream pump including a second electric motor, from a first fluid tank to a second downstream pump; controlling, by a controller, pumping by the first upstream pump, the second upstream pump, the first downstream pump, and the second downstream pump in each of a spray mode and a flush mode. The spray mode includes increasing a pressure of the first component material with the first downstream pump and pumping the first component material to an applicator with the first downstream pump; and increasing a pressure of the second component material with the second downstream pump and pumping the second component material to the applicator with the second downstream pump. The flush mode includes pumping the first component material to a first dump tank from the first proportioner pump; and pumping the second component material to a second dump tank from the second proportioner pump. 
     According to yet another additional or alternative aspect of the present disclosure, a pump for a plural component spray system is configured to pump one of first and second component materials to form a plural component spray material and the pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about a pump axis; a drive mechanism connected to the rotor and configured to translate a rotating input from the rotor to a linear output, wherein the drive mechanism is coaxial with the rotor; and a pumping assembly including a piston, wherein the piston is connected to the drive mechanism to receive the linear output and is disposed coaxially with the drive mechanism and the rotor, wherein the piston is configured to reciprocate axially along the pump axis to pump fluid. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump for a plural component spray system configured to receive first and second component materials and output a plural component material includes an electric motor comprising a stator and a rotor disposed within the stator, the rotor configured to rotate about a pump axis; a pumping assembly including a piston, wherein the piston is disposed coaxially with the rotor and is configured to reciprocate axially along the pump axis to pump fluid; a drive mechanism connected to the rotor and the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston, wherein the drive mechanism is coaxial with the piston and the rotor; a fluid outlet manifold positioned axially between the piston and the rotor, the fluid outlet manifold in fluid communication with the pumping assembly; a first check valve axially between a piston head of the piston and a fluid inlet of the feed pump; and a second check valve disposed in the piston to travel axially with the piston. 
     According to yet another additional or alternative aspect of the present disclosure, a drive mechanism for a feed pump that converts a rotational output from an electric motor into a linear input includes a screw having a first end; a second end axially opposite the first end relative the pump axis; and a spiral groove extending on an outer surface of the screw between the first end and the second end. The second end of the screw extends within each of a rotor shaft, a stator, and a housing of the electric motor, and the screw translates axially within the rotor shaft. The drive mechanism further includes a drive nut connected to the rotor and configured to rotate with the rotor. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump apparatus for pumping fluid from a reservoir includes a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump apparatus for pumping fluid from a reservoir includes a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism. The piston is configured to reciprocate within a working zone to build pressure within the cylinder, and wherein the piston can travel into a pressure relief zone to vent pressurized fluid from the cylinder to the reservoir. 
     According to yet another additional or alternative aspect of the present disclosure, a pump for a plural component spray system is configured to pump one of first and second component materials to form a plural component spray material, the pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about a pump axis; a drive mechanism connected to the rotor and configured to translate a rotating input from the rotor to a linear output, wherein the drive mechanism is coaxial with the rotor; and a pumping assembly including a piston and a cylinder, wherein the piston is connected to the drive mechanism to receive the linear output and is disposed coaxially with the drive mechanism and the rotor. The piston is configured to reciprocate axially within a working zone to build pressure within the cylinder, and wherein the piston can travel into a pressure relief zone to vent pressurized fluid from the cylinder to the reservoir. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump for a plural component spray system configured to receive first and second component materials and output a plural component material, the feed pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about an axis; a drive shaft connected to a piston, wherein the drive shaft is configured to reciprocate axially along the pump axis of the feed pump, and wherein the drive shaft is coaxial with the rotor; a drive mechanism connected to the rotor and to the drive shaft, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the drive shaft; a pump including a piston connected to the drive shaft to be reciprocated by the drive shaft and a cylinder surrounding the piston; a fluid outlet manifold positioned axially between the piston and the drive mechanism and including a fluid outlet, the fluid outlet manifold in fluid communication with the pump; and an over-pressurization valve connected to the fluid outlet manifold and fluidically connected to the fluid outlet by an interior passage of the fluid outlet manifold. 
     According to yet another additional or alternative aspect of the present disclosure, a pressure relief assembly for a double ball piston pump, the pressure relief assembly includes a piston housing disposed around a piston, wherein the piston housing extends along an axis and comprises a first end opposite a second end, wherein a piston rod extends through an opening in the first end; a seal housing inside the piston housing, wherein the seal housing is connected to the first end of the piston housing and extends circumferentially around the piston rod and is disposed axially between a piston head and the first end of the piston housing; a seal disposed inside the seal housing and connected to the piston rod, wherein the seal extends radially from the piston rod relative the pump axis and contacts the seal housing; a vent path disposed within the seal housing and in fluid communication with the opening; and at least one port extending through the seal housing. The at least one port fluidically connects the opening in the first end of the piston housing with an interior of the piston housing when the seal is in a pressure relief zone defined by the at least one port. The seal fluidly isolates the at least one port and the vent path when the seal is in a working zone defined between the first end and the at least one port. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump apparatus for pumping fluid from a reservoir includes a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; a clocking assembly disposed axially between the electric motor and the piston wherein the clocking assembly is configured to interface with a linear displacing element of the drive mechanism to prevent rotation of the linear displacement element about the pump axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump for a plural component spray system configured to output a plural component spray material formed from first and second component materials includes an electric motor comprising a stator and a rotor; a pump having a piston configured to reciprocate axially along the pump axis of the feed pump, and wherein the piston is coaxial with the rotor; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston, and a clocking assembly. The drive mechanism includes a drive nut connected to the rotor and configured to rotate with the rotor; and a screw extending through the drive nut and coaxial with the drive nut. The clocking assembly is axially between the electric motor and the piston and around a portion of the screw, wherein the clocking assembly is configured to prevent rotation of the screw relative the pump axis. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump for a plural component spray system configured to receive first and second component materials and output a plural component material includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about an axis; a pump having a piston disposed coaxially with the rotor and configured to reciprocate axially along the axis; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston, wherein the drive mechanism comprises a screw and a nut, wherein each of the screw and the nut one of rotates about the axis or linearly translates along the axis; a bearing assembly axially between the electric motor and the piston and rotationally connecting the rotor of the electric motor to the drive nut. The piston receives a downward reaction force when moving through the upstroke and an upward reaction force when moving through the downstroke, and both of the upward reaction force and the downward reaction force transfer through the drive mechanism and to the bearing assembly. The bearing assembly permits the rotational motion to pass within the drive mechanism from the motor to the drive mechanism while the bearing assembly prevents some or all of both of the downward reaction force and the upward reaction force from transferring to the rotor. 
     According to yet another additional or alternative aspect of the present disclosure, a feed pump for a plural component spray system configured output a plural component spray material includes an electric motor comprising a stator and a rotor, the rotor configured to rotate on an axis; a pump having a piston, wherein the piston is configured to reciprocate axially along the axis of the feed pump, and wherein the piston is coaxial with the rotor; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston; and a bearing assembly rotationally connecting the rotor of the electric motor to the drive mechanism and configured to react axial loads in both a first axial direction along the axis and a second axial direction along the pump axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a front elevational schematic block diagram of a spray system. 
         FIG.  1 B  is a side elevational schematic block diagram of the spray system of FIG. 
         FIG.  2 A  is an isometric view of a pumping assembly for use in the spray system of  FIGS.  1 A and  1 B . 
         FIG.  2 B  is an isometric cross-sectional view taken along line B-B in  FIG.  2 A . 
         FIG.  2 C  is a first elevational cross-sectional view taken along line B-B in  FIG.  2 A . 
         FIG.  2 D  is a second elevational cross-sectional view taken along line D-D in  FIG.  2 B . 
         FIG.  3 A  is an enlarged cross-sectional view of a portion of the pumping assembly shown in  FIG.  2 C  showing a screw at an end of a downstroke. 
         FIG.  3 B  is an enlarged cross-sectional view similar to  FIG.  3 A  showing the screw at an end of an upstroke. 
         FIG.  4 A  is an enlarged cross-sectional view of detail  4  in  FIG.  2 D . 
         FIG.  4 B  is a cross-sectional view taken along line B-B in  FIG.  4 A . 
         FIG.  4 C  is an exploded view of a clocking assembly and portion of a pump frame. 
         FIG.  5    is an elevational cross-sectional view of a second embodiment of a pumping assembly for use in the spray system of  FIGS.  1 A and  1 B . 
         FIG.  6 A  is an enlarged cross-sectional view of a portion of the pumping assembly shown in  FIG.  5    showing a screw at an end of a downstroke. 
         FIG.  6 B  is an enlarged cross-sectional view similar to  FIG.  6 A  showing the screw at an end of an upstroke. 
         FIG.  7    is a cross-sectional view taken along line  7 - 7  in  FIG.  5   . 
         FIG.  8    is a cross-sectional diagram of a screw showing a lubricant fitting mounted on an exterior of the screw. 
         FIG.  9    is a cross-sectional diagram of a screw showing a lubricant fitting mounted within a bore of the screw. 
         FIG.  10 A  is an isometric view of a plural component system. 
         FIG.  10 B  is a block schematic diagram of the plural component system. 
         FIG.  11    is an isometric view of a feed pump and a fluid tank with a partial cross-section of the supply drum. 
         FIG.  12 A  is a cross-sectional view of an upper portion of the feed pump from  FIG.  11    showing an electric motor, a drive mechanism, a bearing assembly, and a clocking assembly of the feed pump. 
         FIG.  12 B  is a cross-sectional view of the upper portion of the feed pump from  FIG.  12 A  rotated 90 degrees and showing the electric motor, the drive mechanism, the bearing assembly, and the clocking assembly of the feed pump. 
         FIG.  13 A  is a cross-sectional view of a lower portion of the feed pump from  FIG.  11    showing a drive shaft, a piston, a seal, and check valves of the feed pump. 
         FIG.  13 B  is another cross-sectional view of the lower portion of the feed pump from  FIG.  13 A  showing the drive shaft, the piston, and the seal in a pressure relief position. 
         FIG.  13 C  is an enlarged cross-sectional view of the lower portion of the feed pump from  FIG.  13 B  showing the seal in a pressure relief position. 
         FIG.  14 A  is a cross-sectional view of a fluid outlet manifold of the feed pump and an over-pressurization relief valve connected to the fluid outlet manifold. 
         FIG.  14 B  is an enlarged cross-sectional view of detail B from  FIG.  14 A . 
         FIG.  15    is an enlarged cross-sectional view of the electric motor, the drive mechanism, and the bearing assembly from  FIG.  12 B . 
         FIG.  16 A  is a cross-sectional view of an embodiment of the bearing assembly with a spring. 
         FIG.  16 B  is an exploded view of an embodiment of the bearing assembly. 
         FIG.  17 A  is an enlarged cross-sectional view of the clocking assembly from  FIG.  12 A . 
         FIG.  17 B  is a cross-sectional view of the clocking assembly taken along line A-A from  FIG.  17 A . 
         FIG.  17 C  is an exploded view of the upper portion of the feed pump from  FIG.  12 A . 
         FIG.  18    is an isometric partial cross-sectional view of a first drive mechanism. 
         FIG.  19    is an isometric view of a second drive mechanism with the body of a drive nut removed. 
         FIG.  20    is a partial cross-sectional view of a third drive mechanism. 
         FIG.  21    is an isometric view of the drive mechanism shown in  FIG.  12    with a portion of a drive nut removed. 
         FIG.  22    is a graph illustrating a piston speed profile for a conventional crank drive overlaid with a piston speed profile for an electrically powered co-linear pumping assembly. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to spray systems that include positive displacement pumps. The pumps include electric motors that are connected to a fluid displacement member to drive reciprocation of the fluid displacement member to cause pumping. The motor is disposed coaxially with the fluid displacement member such that a rotational axis of the rotor and a reciprocation axis of the fluid displacement member are coaxial. A drive can be disposed axially between the rotor and the fluid displacement member to receive the rotational output from the motor and convert that rotational motion into a linear reciprocating input to the fluid displacement member. 
       FIG.  1 A  is a front elevational schematic block diagram of a spray system  10 .  FIG.  1 B  is a side elevational schematic block diagram of spray system  10 .  FIGS.  1 A and  1 B  will be discussed together. Pump assembly  12 , support  14 , spray gun  16 , supply line  18 , and reservoir  20  are shown. Pump assembly  12  includes pump frame  22 , electric motor  24 , drive mechanism  26 , displacement pump  28 , and controller  29 . Support  14  includes support frame  30  and wheels  32 . Fluid displacement member  34  and cylinder  36  of displacement pump  28  are shown. Spray gun  16  includes handle  38  and trigger  40 . 
     Spray system  10  is a system for applying sprays of various fluids, examples of which include paint, water, oil, stains, finishes, aggregate, coatings, and solvents, amongst other options, onto a substrate. Pump assembly  12  can generate high fluid pumping pressures, such as about 3.4-69 megapascal (MPa) (about 500-10,000 pounds per square inch (psi)) or even higher. In some examples, the pumping pressures are in the range of about 20.7-34.5 MPa (about 3,000-5,000 psi). High fluid pumping pressure is useful for atomizing the fluid into a spray for applying the fluid to a surface. 
     Pump assembly  12  is configured to draw spray fluid from reservoir  20  and pump the fluid downstream to spray gun  16  for application on the substrate. Support  14  is connected to pump assembly  12  and supports pump assembly  12  relative reservoir  20 . Support frame  30  is connected to pump frame  22 . Wheels  32  are connected to support frame  30  to facilitate movement between job sites and within a job site. 
     Pump frame  22  supports other components of pump assembly  12 . Motor  24  and displacement pump  28  are connected to pump frame  22 . Motor  24  is an electric motor having a stator and a rotor. The rotor is configured to rotate about pump axis PA in response to current (such as a direct current (DC) signals and/or alternating current (AC) signals) through the stator. Controller  29  is operably connected to motor  24 , electrically or communicatively, to control operation of motor  24  thereby controlling pumping by displacement pump  28 . Controller  29  can be of any desired configuration for controlling pumping by displacement pump  28  and can include control circuitry and memory. Controller  29  is configured to store software, implement functionality, and/or process instructions. Controller  29  is configured to perform any of the functions discussed herein, including receiving an output from any sensor referenced herein, detecting any condition or event referenced herein, and controlling operation of any components referenced herein. Controller  29  can be of any suitable configuration for controlling operation of pump assembly  12 , gathering data, processing data, etc. Controller  29  can include hardware, firmware, and/or stored software, and controller  29  can be entirely or partially mounted on one or more boards. Controller  29  can be of any type suitable for operating in accordance with the techniques described herein. While controller  29  is illustrated as a single unit, it is understood that controller  29  can be disposed across one or more boards. In some examples, controller  29  can be implemented as a plurality of discrete circuitry subassemblies. 
     Drive mechanism  26  is connected to motor  24  to be driven by motor  24 . Drive mechanism  26  receives a rotational output from motor  24  and converts that rotational output into a linear input along pump axis PA. Drive mechanism  26  is connected to fluid displacement member  34  to drive reciprocation of fluid displacement member  34  along pump axis PA. Motor  24 , drive mechanism  26 , and fluid displacement member  34  are disposed coaxially on pump axis PA. Fluid displacement member  34  reciprocates within cylinder  36  to pump spray fluid from reservoir  20  to spray gun  16  through supply line  18 . The fluid displacement member  34  can be cylindrical, elongate along, and coaxial with pump axis PA. The fluid displacement member  34  can be a piston, which can be elongate along and coaxial with pump axis PA. Displacement pump  28  can be configured such that both a static seal and a dynamic seal are disposed between fluid displacement member  34  and cylinder  36 . The static seal is static relative to cylinder  36  and along pump axis PA and the dynamic seal moves relative to cylinder  36  and along pump axis PA during operation. The dynamic seal can be mounted to the piston forming fluid displacement member  34 . The piston forming fluid displacement member  34  can extend out of cylinder  36  through the static seal. 
     During operation, the user can maneuver pump assembly  12  to a desired position relative the target substrate by moving support  14 . For example, the user can maneuver pump assembly  12  by tilting support frame  30  on wheels  32  and rolling pump assembly  12  to a desired location. Displacement pump  28  can extend into reservoir  20 . Motor  24  provides the rotational input to drive mechanism  26  and drive mechanism  26  provides the linear input to fluid displacement member  34  to cause reciprocation of fluid displacement member  34 . Fluid displacement member  34  draws the spray fluid from reservoir  20  and drives the spray fluid downstream through supply line  18  to spray gun  16 . The user can manipulate spray gun  16  by grasping handle  38 , such as with a single hand of the user. The user causes spraying by actuating trigger  40 . In some examples, the pressure generated by pump assembly  12  atomizes the spray fluid exiting spray gun  16  to generate the fluid spray. In some examples, spray gun  16  is an airless sprayer. 
       FIG.  2 A  is an isometric view of pump assembly  12 .  FIG.  2 B  is an isometric cross-sectional view of pump assembly  12  taken along line B-B in  FIG.  2 A .  FIG.  2 C  is an elevational cross-sectional view taken along line B-B in  FIG.  2 A .  FIG.  2 D  is an elevational cross-sectional view taken along line D-D in  FIG.  2 A .  FIGS.  2 A- 2 D  will be discussed together. Pump frame  22 , motor  24 , drive mechanism  26 , displacement pump  28 , rotor shaft  42 , bearing  44 , sensor  48 , lubricant fitting  50 , bumpers  51   a ,  51   b , pump shaft  110 , and clocking member  112  are shown. Pump frame  22  includes main body  52 , connecting member  54 , and frame member  56 . Main body  52  includes first frame body  58 , second frame body  60 , third frame body  62 , mounting flange  64 , posts  66 , and side openings  68 . Frame member  56  includes radial projections  70 . Motor  24  includes stator  72 , rotor  74 , motor bearings  76 , axle  78 , first motor end  80 , and second motor end  82 . Rotor  74  includes rotor body  84  and permanent magnet array  86 . Axle  78  includes outer end  88 . Drive mechanism  26  includes drive nut  90 , screw  92 , and rolling elements  94  ( FIG.  2 B ). Drive nut  90  includes nut threads  91 , nut mounting projection  93 , nut shoulder  95 , and axial extension  97 . Screw  92  includes first screw end  96 , second screw end  98 , screw thread  99 , and bore  100 . Rotor shaft  42  includes first shaft end  102  and second shaft end  104 . Displacement pump  28  includes fluid displacement member  34 , cylinder  36 , and check valves  106   a ,  106   b . Fluid displacement member  34  includes connector  108 . Sensor  48  includes first transducer component  114  and second transducer component  116 . 
     Pump frame  22  supports other components of pump assembly  12 . Main body  52  extends in axial direction AD 1  relative to motor  24 . In the example shown, main body  52  is spaced axially from first motor end  80 . Main body  52  is disposed coaxially with pump axis PA. First frame body  58  forms a portion of main body  52  axially closest to motor  24 . Second frame body  60  is connected to first frame body  58  and extends in first axial direction AD 1  from first frame body  58 . Third frame body  62  is connected to second frame body  60  and extends in first axial direction AD 1  from second frame body  60 . While main body  52  is shown as formed by first frame body  58 , second frame body  60 , and third frame body  62 , it is understood that main body  52  can be formed by as many or as few portions as desired. Posts  66  and side openings  68  are formed in an end of third frame body  62  opposite second frame body  60 . Side openings  68  are formed between posts  66 . Side openings  68  provide access to the connection between fluid displacement member  34  and pump shaft  110  to facilitate mounting and dismounting of displacement pump  28 . Main body  52  being formed from first frame body  58 , second frame body  60 , and third frame body  62  facilitates efficient assembly and servicing of pump assembly  12 . Main body  52  can be disassembled to provide access to various components of pump assembly, including dynamic components. For example, second frame body  60  can be removed from first frame body  58  to facilitate lubrication of drive mechanism  26 . It is understood that, in some examples, drive mechanism  26  can be accessed and serviced without disassembling main body  52 . Bumper  51   b  is disposed in third frame body  62  on an opposite side of pump shaft  110  from drive nut  90 . Bumper  51   b  can be compressible and can interface with pump shaft  110  in case of overtravel. 
     Frame member  56  is disposed on an opposite axial side of motor  24  from main body  52 . Connecting member  54  extends between main body  52  and frame member  56  and fix main body  52  and frame member  56  together to prevent relative movement between frame member  56  and main body  52 . While pump frame  22  is described as formed from multiple parts, it is understood that pump frame  22  functions as a single part to support motor  24  and displacement pump  28  and react loads experienced during pumping. Pump frame  22  can be formed from as many or as few individual parts as desired. 
     Motor  24  is disposed axially between frame member  56  and main body  52 . Motor  24  is an electric motor  24 . Stator  72  includes armature windings (not shown) and rotor  74  includes permanent magnet array  86 . Stator  72  and rotor  74  are disposed coaxially on pump axis PA. Rotor  74  is configured to rotate about pump axis PA in response to current through stator  72 . Motor  24  is a reversible motor in that stator  72  can cause rotation of rotor  74  in either of two rotational directions about pump axis PA (e.g., clockwise or counterclockwise). 
     Rotor  74  is disposed about stator  72  such that motor  24  includes an outer rotator. Permanent magnet array  86  is disposed on an inner circumferential face of rotor body  84  and array circumferentially about pump axis PA. Rotor body  84  can be formed from a single component or from multiple components fixed together. Stator  72  is fixed to axle  78 . Axle  78  extends along and is disposed coaxial with pump axis PA. Outer end  88  of axle  78  extends in second axial direction AD 2  beyond an axial end of stator  72 . Outer end  88  of axle  78  extends in second axial direction AD 2  beyond an axial end of rotor  74 . Outer end  88  projects axially beyond second motor end  82 . Outer end  88  of axle  78  is open such that electric power (e.g., electric cables) is provided to motor  24  through second motor end  82 . As such, motor  24  can receive power through second motor end  82  and provide a rotational output through first motor end  80 . Motor bearings  76  support rotor  74  relative stator  72 . Motor bearings  76  facilitate rotation of rotor  74  relative to stator  72 . Axle  78  extends through the motor bearing  76  disposed at second motor end  82  of motor  24 , such that the motor bearing  76  at second motor end  82  is disposed between rotor body  84  and axle  78 . 
     Frame member  56  is disposed proximate second motor end  82 . Frame member  56  is fixed to outer end  88  of axle  78 . Motor  24  is statically connected to pump frame  22  by the connection of axle  78  and frame member  56 . Pump frame  22  fixes motor  24  on pump axis PA and prevents stator  72  from moving relative pump axis PA by the connection of pump frame  22  and axle  78 . Connecting member  54  is radially spaced from rotor  74  and extends axially between frame member  56  and main body  52 . Connecting member  54  is fixed to radial projections  70  of frame member  56  and to mounting flange  64  of main body  52 . Connecting member  54  fixes frame member  56  and main body  52  together. In some examples, connecting member  54  can fully enclose rotor  74 . In other examples, connecting member  54  can be formed from a plurality of connecting members spaced circumferentially about rotor  74 . In the example shown, connecting member  54  includes a plurality of tie rods extending between and connecting frame member  56  and main body  52 . Pump frame  22  forms an exoskeleton extending around and supporting motor  24  in examples where connecting member  54  is formed by a plurality of connecting members. 
     The portion of pump frame  22  extending circumferentially about rotor  74  is spaced from rotor  74  such that rotor  74  does not contact pump frame  22 . Pump frame  22  can be spaced both axially and radially relative to rotor  74 . Pump frame  22  is spaced from rotor  74  such that air can flow between pump frame  22  and rotor  74 , facilitating additional cooling of motor  24 . For example, main body  52  and frame member  56  can be spaced axially relative to rotor  74  and connecting member  54  can be spaced radially relative to rotor  74 . Connecting member  54  can have a length greater than rotor  74  to connect main body  52  and frame member  56  and facilitate axial spacing between rotor  74  and pump frame  22 . 
     Rotor shaft  42  extends axially from rotor  74  in first axial direction AD 1 . Rotor shaft  42  is disposed coaxially on pump axis PA. Second shaft end  104  is connected to rotor body  84  such that rotor shaft  42  rotates with rotor  74 . Rotor shaft  42  extends into an interior of main body  52  such that at least a portion of rotor shaft  42  overlaps axially with at least a portion of main body  52 . In the example shown, rotor shaft  42  overlaps axially with each of first frame body  58  and second frame body  60 . In the example shown, second shaft end  104  is closed and first shaft end  102  is open. The closed second shaft end  104  is disposed at the interface between rotor shaft  42  and rotor  74 . Rotor shaft  42  can be removably connected to rotor  74 , such as by fasteners. It is understood, however, that rotor shaft  42  can be formed integrally with rotor body  84 . Rotor  74  and rotor shaft  42  function as a single part to power drive mechanism  26 . Bumper  51   a  is disposed in rotor shaft  42  at the closed end of rotor shaft  42 . Bumper  51   a  can be compressible and can interface with second screw end  98  in case of overtravel to prevent damage to screw  92 . 
     Drive mechanism  26  is coaxial with pump axis PA. Drive mechanism  26  is connected to first shaft end  102  of rotor shaft  42 . Drive mechanism  26  receives a rotational output from rotor  74  via rotor shaft  42  and is configured to provide a linear input to fluid displacement member  34 . Drive mechanism  26  is supported by pump frame  22  via bearing  44 . Drive mechanism  26  is located directly between motor  24  and displacement pump  28 . 
     Drive nut  90  of drive mechanism  26  is connected to first shaft end  102  of rotor shaft  42  to rotate about pump axis PA with rotor shaft  42 . Drive nut  90  can be attached to rotor shaft  42  via fasteners (e.g., bolts), adhesive, or press-fitting, among other options. In the example shown, nut mounting projection  93  facilitates mounting of drive nut  90  to rotor shaft  42 . Fasteners can extend through nut mounting projection  93  into rotor shaft  42 . First shaft end  102  interfaces with nut shoulder  95  formed on drive nut  90 . Nut shoulder  95  is formed between nut mounting projection  93  and axial extension  97 , which extends into and axially overlaps with rotor shaft  42 . Screw  92  is disposed radially within drive nut  90 . Screw  92  and drive nut  90  are disposed coaxially on pump axis PA. 
     Components can be considered to axially overlap when the components are disposed at a common position along an axis (e.g., along the axis PA), for example such that a radial line projecting from that axis extends through each of those axially-overlapped components. Similarly, components can be considered to radially overlap when the components are disposed at common positions spaced radially from the axis (e.g., relative to axis PA) such that an axial line parallel to the axis extends through each of those radially-overlapped components. 
     Rolling elements  94  are disposed between screw  92  and drive nut  90  and support screw  92  relative drive nut  90 . Rolling elements  94  are arrayed around, and are arrayed along, an axis that is coaxial with pump axis PA. Rolling elements  94  support screw  92  and drive nut  90  such that gap  118  ( FIGS.  3 A and  3 B ) disposed radially between screw  92  and drive nut  90   i  is maintained. Maintaining the gap  118  prevents screw  92  and drive nut  90  from directly contacting one another. Rolling elements  94  can be of any suitable configuration for supporting drive nut  90  relative screw  92  and driving screw  92  linearly due to rotation of drive nut  90 . For example, rolling elements  94  can be balls or rollers, as discussed in more detail below with regard to  FIGS.  10 - 13   . Rolling elements  94  engage screw thread  99  to exert an axial driving force on screw  92  to cause screw  92  to translate axially along pump axis PA. 
     Screw  92  is configured to reciprocate along pump axis PA during operation. Rotation of drive mechanism  26  causes rolling elements  94  to exert an axial driving force on screw  92  to drive screw  92  linearly. Screw  92  provides the linear output from drive mechanism  26 . Bore  100  extends axially through screw  92 . While screw  92  is described as reciprocating along pump axis PA, it is understood that, in some examples, screw  92  is configured to rotate on pump axis PA to drive linear displacement of fluid displacement member  34 . For example, a nut can be connected to screw  92  to displace linearly along screw  92  due to rotation of screw  92 . For example, pump shaft  110  can be configured to interface with screw  92  and translate along screw  92 . 
     Lubricant fitting  50  is disposed within bore  100 . Lubricant fitting  50  is configured to connect to an applicator of a lubricating device, such as a grease gun. Bore  100  can form a lubricant pathway through screw  92  to provide lubricant to rolling elements  94 . Lubricant fitting  50  can be a grease zerk. 
     In some examples, rotor  74  and drive mechanism  26  are sized to provide a one revolution of rotor  74  results in a full stroke of screw  92 . A full revolution in an opposite rotational direction results in a full stroke of screw  92  in the opposite axial direction. As such, two revolutions in opposite directions can provide a full pump cycle. Pump assembly  12  can thereby provide a 1:1 ratio between revolutions of rotor  74  and pumping strokes. It is understood, however, that rotor  74  and drive mechanism  26  can be sized to provide any desired ratio between revolutions and pump strokes, such as 0.25 revolutions per stroke, 0.5 revolutions per stroke, two revolutions per stroke, three revolutions per stroke, or any other desired number of revolutions per stroke. 
     Bearing  44  is disposed radially between rotor shaft  42  and pump frame  22 . More specifically, bearing  44  is disposed radially between rotor shaft  42  and main body  52 . Bearing  44  is disposed axially between drive nut  90  and motor  24 . Bearing  44  supports motor  24  relative pump frame  22  and facilitates rotation of rotor shaft  42  relative pump frame  22 . As such, bearing  44  forms a dynamic connection between motor  24  and pump frame  22 . 
     Bearing  44  is configured to support both rotational and axial loads generated during pumping. Bearing  44  supports the axial loads to isolate motor  24  from the axial loads, as discussed in more detail below. Bearing  44  can be referred to as a thrust bearing. 
     Bearing  44  can be of any configuration suitable for supporting axial loads generated during pumping. In some examples, bearing  44  can be a single bearing element configured to support axial loads in each of first axial direction AD 1  and second axial direction AD 2 , such as a double row angular contact bearing, among other options. In some examples, bearing  44  can be formed from multiple bearing elements to support axial loads in each of first axial direction AD 1  and second axial direction AD 2 . For example, bearing  44  can be formed by a first tapered roller bearing configured to support axial loads in first axial direction AD 1  and a second tapered roller bearing configured to support axial loads in second axial direction AD 2 . The inner race  45 , outer race  47 , and rolling elements  49  of bearing  44  are shown. 
     Pump shaft  110  is connected to screw  92  and fluid displacement member  34 . Pump shaft  110  is connected to screw  92  to reciprocate with screw  92  and is connected to fluid displacement member  34  to drive reciprocation of fluid displacement member  34 . As such, screw  92  and pump shaft  110  can be considered to form a linear drive element of drive mechanism  26 . In the example shown, mounting projection  122  extends into bore  100  to connect pump shaft  110  to screw  92 . Pump shaft  110  can be connected to screw  92  in any desired manner, such as by interfaced threading, a pin, press-fit, adhesive, or snap lock, among other options. While pump shaft  110  and screw  92  are described as separately formed, it is understood that screw  92  and pump shaft  110  can be formed as a single component. In some examples, fluid displacement member  34  can be directly connected to screw  92  and clocking member  112  can also be mounted to screw  92 . 
     Clocking member  112  is disposed on and supported by pump shaft  110 . Pump shaft  110  and clocking member  112  can be considered to form a clocking assembly to prevent rotation of screw  92  about pump axis PA. Pump shaft  110  forms a support of the clocking assembly  110  as pump shaft  110  supports clocking member  112 . Clocking member  112  reciprocates with screw  92  and pump shaft  110 . Clocking member  112  is clocked to and interfaces with main body  52  such that clocking assembly  46  is prevented from rotating about pump axis PA. Clocking member  112  thereby prevents screw  92  from rotating about axis PA, facilitating translation of screw  92  along pump axis PA. In some examples, the outer surface of clocking member  112  is closely fit to main body  52  to provide a sliding seal at the interface between clocking member  112  and main body  52 . The sliding seal interface prevents dust and other contaminants from migrating through main body  52  to drive mechanism  26 . In some examples, a seal, such as a u-cup seal, is mounted to the radially outer surface of clocking member  112 . In examples where screw  92  rotates about pump axis PA, clocking member  112  can be associated with the nut configured to translate along screw  92  to prevent rotation of the nut about pump axis PA. 
     Sensor bore  120   a  extends into main body  52  of pump frame  22  and is configured to receive first transducer component  114 . Sensor bore  120   b  extends into pump shaft  110  and is configured to receive second transducer component  116 . Sensor  48  is configured to sense an end of a pump stroke in the first axial direction AD 1 . Sensor  48  can generate and provide data to a controller  29  of motor  24  when the linearly displacing elements are at the end of a downstroke, which can be associated with a home position. In some examples, motor  24  is homed on power up. For example, rotor  74  can rotate in a first rotational direction associated with the downstroke until first transducer component  114  senses second transducer component  116 , indicating the end of the downstroke. Rotor  74  can then be controlled to rotate a set number of revolutions associated with a stroke to cause subsequent upstrokes and downstrokes. In some examples, motor  24  is rehomed during operation to prevent creep, such as after a pre-determined number of pump cycles. 
     First transducer component  114  and second transducer component  116  can be of any desired configuration. For example, one of first transducer component  114  and second transducer component  116  can be a magnet while the other of first transducer component  114  and second transducer component  116  can be a magnetic reed switch sensitive to the magnetic field generated by the magnet. For example, first transducer component  114  can be a magnetic field sensor mounted on main body  52  and second transducer component  116  can be a magnet mounted in pump shaft  110 . While the magnetic field sensor of first transducer component  114  is described as located on main body  52  and the magnet of second transducer component  116  is located in pump shaft  110 , it is understood that the locations can be reversed such that the magnet can be in main body  52  while the magnetic field sensor can be mounted on pump shaft  110 . 
     Displacement pump  28  is mounted to pump frame  22  and disposed on pump axis PA. More specifically, cylinder  36  is mounted to an end of pump frame  22  opposite motor  24 . Cylinder  36  is fixedly mounted to pump frame  22 . 
     Fluid displacement member  34  is connected to pump shaft  110 . Fluid displacement member  34  is connected to an end of pump shaft  110  opposite screw  92 . In the example shown, connector  108  of fluid displacement member  34  extends into pump shaft  110 . Connector  108  is secured to pump shaft  110  such that fluid displacement member  34  reciprocates with screw  92  and pump shaft  110 . Connector  108  and pump shaft  110  can be connected in any desired manner. For example, a pin can extend through connector  108  and pump shaft  110  to secure connector  108  to pump shaft  110 . 
     Displacement pump  28  is statically connected to pump frame  22  by the connection between cylinder  36  and main body  52  and dynamically connected to motor  24  by the connection between fluid displacement member  34  and pump shaft  110 . Check valve  106   a  is a one-way valve disposed in cylinder  36 . Check valve  106   b  is a one-way valve disposed in fluid displacement member  34  to reciprocate with fluid displacement member  34 . Displacement pump  28  can be a double displacement pump in that displacement pump  28  outputs fluid during both the upstroke in second axial direction AD 2  and the downstroke in first axial direction AD 1 . 
     An example pump cycle including a downstroke and an upstroke is discussed by way of example. During operation, power is provided to stator  72  to drive rotation of rotor  74  about pump axis PA. Rotor  74  rotates about pump axis PA in a first rotational direction (e.g., one of clockwise and counterclockwise) and causes simultaneous rotation of rotor shaft  42  due to connection between rotor  74  and rotor shaft  42 . Rotor shaft  42  rotates about pump axis PA and drives drive mechanism  26  due to connection between rotor shaft  42  and drive nut  90 . 
     Drive nut  90  rotates about pump axis PA. Drive nut  90  rotating about pump axis PA causes rolling elements  94  to exert an axial driving force on screw  92  in axial direction AD 1  to drive screw  92  linearly along pump axis PA. Screw  92  is driven linearly in first axial direction AD 1 . Screw  92  drives pump shaft  110  and thus fluid displacement member  34  through a downstroke along pump axis PA and in first axial direction AD 1 . During the downstroke, check valve  106   a  is closed and check valve  106   b  is open. Fluid is driven through check valve  106   b  and downstream from displacement pump  28 . Sensor  48  can sense the end of the downstroke and provide that data to the controller. 
     After completing the downstroke, rotor  74  is driven in a second rotational direction opposite the first rotational direction (e.g., the other of clockwise and counterclockwise). Rotor  74  drives rotation of rotor shaft  42 , which drives rotation of drive nut  90 . Rolling elements  94  exert an axial driving force in second axial direction AD 2  on screw  92  to drive screw  92  linearly along pump axis PA. Screw  92  is driven linearly in the second axial direction AD 2 . Screw  92  pulls fluid displacement member  34  through an upstroke along pump axis PA and in second axial direction AD 2 . During the upstroke, check valve  106   a  is open and check valve  106   b  is closed. Fluid is drawn into cylinder through check valve  106   a  and simultaneously driven downstream from displacement pump  28 . Motor  24  thereby causes pumping by displacement pump  28 . Displacement pump  28  outputs fluid during both the upstroke and the downstroke. 
     Axial forces are generated and experienced during pumping. Bearing  44  permits rotational motion to pass within drive mechanism  26  from motor  24  while preventing some or all of the axial forces generated by displacement pump  28  from transferring to rotor  74 . Fluid displacement member  34  moves in a reciprocating linear fashion and experiences axial forces due to fluid resistance experienced during reciprocation. Specifically, fluid displacement member  34  receives a downward reaction force when moving through the upstroke and an upward reaction force when moving through the downstroke, and both of the upward reaction force and the downward reaction force transfer through drive mechanism  26  and to bearing  44 . The axial forces generating during pumping can also be referred to as pump reaction forces. 
     The pump reaction forces are transmitted through fluid displacement member  34  and to the linear drive element of drive mechanism  26 . The pump reaction forces are transmitted through the linear drive element to the rotating element of drive mechanism  26 . The pump reaction forces are transmitted to bearing  44  at a location axially between the rotating elements of drive mechanism  26  and rotor  74 . Bearing  44  supports a sufficient portion of the pump reaction forces and transmits those forces to pump frame  22  and away from motor  24  to protect motor  24  during operation. Bearing  44  can support up to all of the pump reaction forces generated during pumping. Bearing  44  prevents the pump reaction forces from causing axial misalignment between rotor  74  and stator  72 , thereby increasing the life and efficiency of motor  24 . 
     In the example shown, the pump reaction forces are transmitted to pump shaft  110  from fluid displacement member  34  and through pump shaft  110  to screw  92 . The pump reaction forces are transmitted through screw  92  and rolling elements  94  and to drive nut  90 . Drive nut  90  transmits the pump reaction forces to rotor shaft  42 , which interfaces with inner race  45  of bearing  44 . The pump reaction forces are transmitted through bearing  44 , specifically through inner race  45 , rolling elements  49 , and outer race  47 , to pump frame  22 . Pump frame  22  is sufficiently sturdy to handle the pump reaction forces generated during pumping. As such, the axial forces generated during pumping are transferred to and experienced by pump frame  22  prior to those forces being experienced by motor  24 . Motor  24  is thereby isolated from the pump reaction forces. 
     Pump assembly  12  provides significant advantages. Motor  24 , drive mechanism  26 , and displacement pump  28  are disposed coaxially on pump axis PA, providing a compact pumping arrangement that facilitates transport between and within job sites. Bearing  44  reacts pump reaction forces to isolate motor  24  from those pump reaction forces. The pump reaction forces are not transferred to motor  24  to protect components of motor  24  and prevent misalignment between stator  72  and rotor  74 . Rotor  74  is an outer rotator, which provides high inertia and torque, facilitating pumping at the high pressures utilized for generating the fluid spray. Each of motor  24 , drive mechanism  26 , and displacement pump  28  being disposed coaxially on pump axis PA further reduces the number of moving parts of pump assembly  12 , providing a simpler, more robust pumping arrangement. In addition, no speed reduction gearing is present between motor  24  and drive mechanism  26 , which reduces noise generated during operation, providing a safer and more user-friendly spray environment. 
       FIG.  3 A  is an enlarged cross-sectional view of a portion of pump assembly  12  showing screw  92  at the end of a downstroke.  FIG.  3 B  is an enlarged cross-sectional view of the portion of pump assembly  12  shown in  FIG.  3 A  showing screw  92  at the end of an upstroke.  FIGS.  3 A and  3 B  will be discussed together. Drive mechanism  26 , rotor shaft  42 , bearing  44 , main body  52 , rotor  74 , cavity  124 , inner notch  126 , and outer notch  128  are shown. Drive mechanism  26  includes drive nut  90 , screw  92 , and rolling elements  94 . Nut thread  91 , nut mounting projection  93 , nut shoulder  95 , axial extension  97 , first nut end  101 , and second nut end  103  of drive nut  90  are shown. First screw end  96  ( FIG.  3 B ), second screw end  98 , screw thread  99 , and bore  100  of screw  92  are shown. Rotor shaft  42  includes first shaft end  102 , second shaft end  104 , first shaft portion  130 , and second shaft portion  132 . First shaft portion  130  includes radial projection  133 . Second shaft portion  132  includes axial extension  135 . First frame body  58 , second frame body  60 , and mounting flange  64  of main body  52  are shown. Second frame body  60  in includes axial extension  61 . Inner notch  126  includes first inner shoulder  134  and second inner shoulder  136 . Outer notch  128  includes first outer shoulder  138  and second outer shoulder  140 . 
     Main body  52  extends in first axial direction AD 1  relative rotor  74 . First frame body  58  is a part of main body  52  disposed closest to rotor  74  along pump axis PA. Mounting flange  64  extends radially outward from main body  52 . Mounting flange  64  is configured to connect to connecting member  54  (best seen in  FIG.  2 A ) and can further connect to a support frame, such as frame  30  ( FIGS.  1 A and  1 B ). Second frame body  60  is connected to an end of first frame body  58  disposed opposite rotor  74  such that first frame body  58  is disposed axially between second frame body  60  and rotor  74 . In the example shown, first frame body  58  and second frame body  60  are removably connected by fasteners, but it is understood that first frame body  58  and second frame body  60  can be connected in any desired manner. In some examples, main body  52  is formed as a single component unitary component or can be formed from multiple components permanently fixed together, such as by adhesive or welding, among other options. 
     Outer notch  128  is configured to receive a portion of bearing  44 , such as the outer race  47  of bearing  44 , to support bearing  44 . In the example shown, outer notch  128  is formed on main body  52  by first frame body  58  and second frame body  60 . Bearing  44  is retained axially within outer notch  128  between first outer shoulder  138  and second outer shoulder  140 . First outer shoulder  138  is formed on first frame body  58  and second outer shoulder  140  is formed by first frame body  58  and second frame body  60 . Axial extension  61  of second frame body  60  is disposed radially within and axially overlaps a portion of first frame body  58 . Second frame body  60  extending within and axially overlapping first frame body  58  radially locates second frame body  60  on first frame body  58 , maintaining concentricity and facilitating mounting of bearing  44 . In the example shown, first frame body  58  forms a base of outer notch  128 . In some examples, first outer shoulder  138  is formed by first frame body  58  and second frame body  60  while second outer shoulder  140  and the base of outer notch  128  are formed by second frame body  60 . In some examples, first outer shoulder  138  is formed by first frame body  58 , second outer shoulder  140  is formed by second frame body  60 , and the base of outer notch  128  is formed by a combination of first frame body  58  and second frame body  60 . In some examples, outer notch  128  is formed on main body  52  and a separate component, such as a lock nut, is connected to main body  52  to secure bearing  44  within outer notch  128 . 
     Rotor shaft  42  is connected to and extends in first axial direction AD 1  from rotor  74 . Rotor shaft  42  and rotor  74  are disposed coaxially on pump axis PA. A portion of rotor body  84  extends into and axially overlaps with rotor shaft  42 . Rotor body  84  extending into and axially overlapping a portion of rotor shaft  42  maintains concentricity between rotor body  84  and rotor shaft  42 . Rotor shaft  42  extends to and is connected with drive mechanism  26 . Second shaft end  104  of rotor shaft  42  is connected to rotor  74  and first shaft end  102  of rotor shaft  42  is connected to drive nut  90 . In the example shown, second shaft end  104  is formed by first shaft portion  130  and first shaft end  102  is formed by second shaft portion  132 . In the example shown, second shaft end  104  is closed and first shaft end  102  is open. Cavity  124  is formed in rotor shaft  42  and extends between first shaft end  102  and second shaft end  104 . Cavity  124  receives a portion of screw  92  as screw  92  reciprocates during pumping, as discussed in more detail below. 
     In the example shown, rotor shaft  42  includes first shaft portion  130  connected to rotor  74  and second shaft portion  132  connected to an end of first shaft portion  130  opposite rotor  74 . Second shaft portion  132  extends in first axial direction AD 1  from first shaft portion  130  and is connected to drive nut  90 . In the example shown, second shaft portion  132  is connected to first shaft portion by fasteners, but it is understood that first shaft portion  130  and second shaft portion  132  can be connected in any suitable manner, such as by adhesive or press-fitting, among other options. While rotor shaft  42  can be formed from more than one part, it is understood that rotor shaft  42  functions as a single part to provide rotational power to drive mechanism  26 . Furthermore, while rotor shaft  42  is shown as formed by first shaft portion  130  and second shaft portion  132 , rotor shaft  42  can be formed any desired number of parts, such as one or more than two parts. For example, rotor shaft  42  can be formed as a single part. 
     Inner notch  126  is configured to receive a portion of bearing  44 , such as the inner race  45  of bearing  44 , to support bearing  44 . In the example shown, inner notch  126  is formed on rotor shaft  42  between first shaft portion  130  and second shaft portion  132 . Bearing  44  is retained axially within inner notch  126  between first inner shoulder  134  and second inner shoulder  136 . First inner shoulder  134  is formed on first shaft portion  130  and second inner shoulder  136  is formed by first shaft portion  130  and second shaft portion  132 . First inner shoulder  134  is formed by radial projection  133  of first shaft portion  130 , which is a part of first shaft portion  130  extending radially from first shaft portion  130 . Axial extension  135  of second shaft portion  132  extends in second axial direction AD 2  and is disposed around and axially overlaps a portion of first shaft portion  130 . Second shaft portion  132  extending around and axially overlapping first shaft portion  130  radially locates second shaft portion  132  on first shaft portion  130 , maintaining concentricity and facilitating mounting of bearing  44 . In the example shown, first shaft portion  130  forms a base of inner notch  126 . In some examples, first inner shoulder  134  is formed by first shaft portion  130  and second shaft portion  132  while second inner shoulder  136  and the base of inner notch  126  are formed by second shaft portion  132 . In some examples, first inner shoulder  134  is formed by first shaft portion  130 , second inner shoulder  136  is formed by second shaft portion  132 , and the base of inner notch  126  is formed by a combination of first shaft portion  130  and second shaft portion  132 . In some examples, drive nut  90  forms at least a portion of second inner shoulder  136 , such that bearing  44  is axially disposed between rotor shaft  42  and drive nut  90 . 
     Drive nut  90  is connected to rotor shaft  42  to receive rotational power from rotor shaft  42 . More specifically, second nut end  103  is attached to first shaft end  102 . First shaft end  102  interfaces with nut shoulder  95 . It is understood that drive nut  90  can be attached to rotor shaft  42  in any desired manner, such as by fasteners (e.g., bolts), adhesive, or press-fitting, among other options. For example, fasteners can extend through nut mounting projection  93  into rotor shaft  42 . Axial extension  97  of drive nut  90  extends into and axially overlaps with second shaft portion  132 , locating drive nut  90  relative rotor shaft  42  and maintaining concentricity between drive mechanism  26  and rotor shaft  42 . First nut end  101  is disposed at an opposite axial end of drive nut  90  from second nut end  103 . First nut end  101  is free in that first nut end  101  is not mechanically supported by pump frame  22 . Nut thread  91  is formed on an inner radial surface of drive nut  90  between first nut end  101  and second nut end  103 . 
     Screw  92  extends axially through drive nut  90  and is disposed coaxially with drive nut  90  on pump axis PA. Screw thread  99  is formed on an outer radial surface of screw  92 . Rolling elements  94  are disposed between screw  92  and drive nut  90  and support screw  92  and drive nut  90  relative each other. Rolling elements  94  maintain radial gap  118  between screw  92  and drive nut  90  such that screw  92  does not directly contact drive nut  90 . Rolling elements  94  engage screw thread  99  to exert an axial driving force on screw  92  at screw thread  99  to cause screw  92  to translate along pump axis PA. In the example shown, rolling elements  94  are balls that ride in raceways formed by nut thread  91  and screw thread  99 . It is understood, however, that rolling elements  94  can be of any suitable configuration for driving linear displacement of screw  92  due to rotation of drive nut  90 . 
     Screw  92  is elongate along pump axis PA between first screw end  96  and second screw end  98 . Second screw end  98  forms a distal end of screw  92  oriented towards rotor  74 . In the example shown, second screw end  98  is unsupported such that second screw end  98  is free relative rotor shaft  42  as screw  92  reciprocates during operation. For example, no bearing, bushing, or other support element may be disposed between second screw end  98  and rotor shaft  42 . Second screw end  98  reciprocates within cavity  124  during operation. Second screw end  98  axially overlaps with a portion of rotor shaft  42 . In some examples, second screw end  98  axially overlaps with rotor shaft  42  both with screw  92  at the end of a downstroke ( FIG.  3 A ) and with screw  92  and the end of an upstroke ( FIG.  3 B ). It is understood, however, that in some examples screw  92  does not axially overlap any portion of rotor shaft  42  with screw  92  at the end of the downstroke. For example, drive nut  90  can be axially elongate in second axial direction AD 2  such that second screw end  98  axially overlaps drive nut  90  but not rotor shaft  42 . The axial overlap between screw  92  and rotor shaft  42  increases as screw  92  shifts in second axial direction AD 2  through the upstroke. The axial overlap between screw  92  and rotor shaft  42  decreases as screw  92  shifts in first axial direction AD 1  through the downstroke. During at least a portion of a pump cycle, which includes both the upstroke and the downstroke, each of screw  92 , rotor shaft  42 , bearing  44 , and main body  52  axially overlap with one another. 
     Bearing  44  is disposed proximate drive mechanism  26  to support alignment of drive mechanism  26  on pump axis PA. In the example shown, distance D 1  between second nut end  103  and bearing  44  is smaller than distance D 2  between first motor end  80  and bearing  44 . Bearing  44  being disposed proximate drive mechanism  26  further maintains concentricity between pump frame  22 , rotor shaft  42 , drive nut  90 , and screw  92 . Minimizing an axial distance between bearing  44  and drive mechanism  26  prevents wobbling of screw  92  relative pump axis PA. 
     During operation, rotor  74  is rotated in a first rotational direction (e.g., one of clockwise and counterclockwise) drives rotation of rotor shaft  42  in the first rotational direction. Rotor shaft  42  drives rotation of drive nut  90 . Rotation of drive nut  90  causes rolling elements  94  to exert an axial driving force on screw  92  to cause linear displacement of screw  92 . Beginning from the position shown in  FIG.  3 A , where screw  92  is at the end of the downstroke rotation of rotor  74  causes screw  92  to displace linearly in second axial direction AD 2  towards rotor  74 . Second screw end  98  displaces axially into cavity  124  and towards first shaft end  102  and rotor  74 . Screw  92  continues to displace into cavity  124 , thereby reducing an axial distance between second screw end  98  and first shaft end  102  and increasing an axial overlap between screw  92  and rotor shaft  42  until screw  92  reaches the end of the upstroke, as shown in  FIG.  3 B . 
     With screw  92  at the end of the upstroke, screw  92  is displaced a maximum distance into cavity  124 . In some examples, a majority of the volume of cavity  124  is occupied by screw  92 . It is understood, however, that screw  92  can occupy any desired portion of the volume of cavity  124  with screw  92  at the end of the upstroke. In the example shown, no portion of screw  92  contacts rotor shaft  42  such that a radial gap is disposed between an inner radial surface of rotor shaft  42  and an outer radial surface of screw  92 . Second screw end  98  is axially spaced from the closed first shaft end  102  at the end of the upstroke. 
     After completing the upstroke, rotor  74  is rotated in a second rotational direction opposite the first rotational direction (e.g., the other of clockwise and counterclockwise) to drive screw  92  through a downstroke. Rotor  74  drives rotation of rotor shaft  42  in the second rotational direction. Rotor shaft  42  drives rotation of drive nut  90  in the second rotational direction. Drive nut  90  causes rolling elements  94  to exert an axial force on screw  92  to linearly displace screw  92  in first axial direction AD 1 . Screw  92  displaces through a downstroke from the position shown in  FIG.  3 B  towards the position shown in  FIG.  3 A . The axial overlap between rotor shaft  42  and screw  92  decrease as screw  92  displaces through the downstroke. The axial overlap between screw  92  and rotor shaft  42  is at a minimum when screw  92  reaches the end of the downstroke, thereby completing a pump cycle. After screw  92  reaches the end of the downstroke, rotor  74  can be driven in the first rotational to drive screw  92  back through an upstroke. Screw  92  continues to be reciprocated throughout pumping. 
     Screw  92  reciprocating within rotor shaft  42  provides significant advantages. Screw  92  reciprocating within cavity  124  provides an axially compact pump assembly  12 . The axially compact pump assembly  12  facilitates ease of transport, set up, and use. Screw  92  reciprocating within cavity  124  facilitates mounting of bearing  44  proximate drive nut  90 , maintaining concentricity and alignment between drive mechanism  29  and motor  24  during operation. 
     Pump reaction forces are experienced by fluid displacement member  34  and transmitted to drive mechanism  26  via screw  92  as fluid displacement member  34  displaces axially during each stroke of the pump cycle. The axial forces are experienced by fluid displacement member  34  at least in part due to fluid resistance during each of the upstroke and the downstroke, and are transferred to screw  92  via pump shaft  110 . The axial forces experienced by screw  92  are transferred to rolling elements  94  and from rolling elements  94  to drive nut  90 . The axial forces experienced by drive nut  90  are transferred to rotor shaft  42 . The axial forces experienced by rotor shaft  42  are transferred to bearing  44  and through bearing  44  to main body  52  of pump frame  22 . Bearing  44  transfers the pump reaction forces to pump frame  22  thereby isolating rotor  74  from those pump reaction forces and reducing dynamic axial loading on motor  24 . 
       FIG.  4 A  is an enlarged view of detail  4  shown in  FIG.  2 D .  FIG.  4 B  is a cross-sectional view taken along line B-B in  FIG.  4 A .  FIG.  4 C  is an exploded view showing clocking assembly  46  and main body  52 .  FIGS.  4 A- 4 C  will be discussed together. Fluid displacement member  34  ( FIG.  4 A ), cylinder  36  ( FIG.  4 A ), third frame body  62 , screw  92  ( FIG.  4 A ), pump shaft  110 , clocking member  112 , and pin  142 . Pump shaft  110 , clocking member  112 , and pin  142  form clocking assembly  46 . Pump shaft  110  includes mounting projection  122  ( FIGS.  4 A and  4 C ), sensor bore  120   b  ( FIG.  4 C ), pump shaft body  144 , first body end  146  ( FIGS.  4 A and  4 C ), second body end  148  ( FIGS.  4 A and  4 C ), receiver  150  ( FIGS.  4 A and  4 C ), and support flange  152  ( FIGS.  4 A and  4 C ). Clocking member  112  includes collar  154  and clocking projections  156 . Collar  154  includes radial groove  155 . First screw end  96 , screw thread  99 , and bore  100  of screw  92  are shown. Third frame body  62  includes posts  66  ( FIGS.  4 A and  4 C ), side openings  68  ( FIGS.  4 A and  4 C ), sensor bore  120   a  ( FIG.  4 C ), pump opening  158  ( FIGS.  4 A and  4 C ), and axial slots  160 . 
     Clocking assembly  46  is disposed coaxially with screw  92  on pump axis PA. Clocking assembly  46  is configured to prevent screw  92  from rotating about pump axis PA. More specifically, pump shaft  110  is directly connected to screw  92  and clocking member  112  is mounted to pump shaft  110 . Pump shaft body  144  is elongate along pump axis PA. Support flange  152  extends radially from pump shaft body  144 . In the example shown, support flange  152  extends from pump shaft body  144  such that pump shaft body  144  extends axially in both the first axial direction AD 1  and the second axial direction AD 2  relative support flange  152 . Mounting projection  122  extends axially from second body end  148 . Mounting projection  122  extends in second axial direction AD 2  from second body end  148 . Mounting projection  122  has a smaller diameter than pump shaft body  144 . Mounting projection  122  connects to first screw end  96  to mount pump shaft  110  to screw  92 . In the example shown, mounting projection  122  extends into screw bore  100  to connect pump shaft  110  to screw  92 . In some examples, mounting projection  122  and shaft bore  100  include interfaced threading. It is understood, however, that pump shaft  110  can be connected to screw  92  in any desired manner, such as by fasteners, adhesive, or press-fitting, among other options. 
     Receiver  150  extends in first axial direction AD 1  from first body end  146 . Receiver  150  is configured to connect to fluid displacement member  34 . In the example shown, receiver  150  receives a portion of fluid displacement member  34  to connect to fluid displacement member  34 . Connector  108  of fluid displacement member  34  extends into receiving bore  162  formed in receiver  150 . A fastener, such as a pin, extends through receiver  150  and connector  108  to secure fluid displacement member  34  to pump shaft  110 . While fluid displacement member  34  is described as connecting to pump shaft  110  by a pinned connection, it is understood that fluid displacement member  34  can be connected to pump shaft  110  in any manner suitable for pump shaft  110  driving reciprocation of fluid displacement member  34 . 
     Clocking member  112  is supported by and connected to pump shaft  110 . Clocking member  112  is disposed around pump shaft body  144  adjacent support flange  152 . In the example shown, clocking member  112  is disposed axially between support flange  152  and first screw end  96 . Collar  154  extends around pump shaft body  144 . In the example shown, collar  154  extends around second body end  148  of pump shaft body  144 . Clocking member  112  forms a collar extending around pump shaft body  144 . While clocking member  112  is shown as a single piece, it is understood that anti-rotation element can be formed from multiple parts. For example, clocking member  112  can be formed from multiple components disposed in a clamshell configuration about pump shaft body  144 . 
     Clocking projections  156  extend radially from collar  154 . Clocking projections  156  project radially beyond an outer radial edge of support flange  152 . In the example shown, clocking member  112  includes two clocking projections  156 , but it is understood that anti-rotation element can include as many or as few clocking projections  156  as desired. In the example shown, clocking projections  156  are formed by rounded projections extending from collar  154 . It is understood that clocking projections  156  can be of any suitable configuration for interfacing with main body  52  and preventing rotation relative main body  52 , such as cylindrical projections, rectangular projections, or triangular projections, among other options. 
     Clocking member  112  is secured to pump shaft  110  to prevent relative rotation between pump shaft  110  and clocking member  112 . In the example shown, clocking member  112  is secured to pump shaft  110  by a pinned connection. Pin  142  extends through clocking member  112  and pump shaft  110  to connect clocking member  112  to pump shaft  110 . Pin  142  extends into each clocking projection  156  of clocking member  112 . To assemble clocking assembly  46 , clocking member  112  is shifted in first axial direction AD 1  over second shaft body end  148  of pump shaft  110 . The radial bores through clocking member  112  are aligned with the radial bore through pump shaft  110  and pin  142  in inserted therethrough to secure clocking member  112  to pump shaft  110 . While clocking member  112  and pump shaft  110  are described as being connected by pin  142 , it is understood that clocking member  112  and pump shaft  110  can be secured in any desired manner, such as by adhesive or press-fitting, among other options. In some examples, the outer radial surface of pump shaft body  144  and the inner radial surface of collar  154  can have mating contours to prevent relative rotation. 
     Clocking assembly  46  is configured such that the portions fixed to screw  92  reciprocate relative to main body  52  with screw  92 . Axial slots  160  are formed on an inner surface of main body  52 . Axial slots  160  extend axially and are configured to receive clocking projections  156  of clocking member  112 . Clocking projections  156  being received in axial slots  160  prevents clocking assembly  46 , and thus screw  92 , from rotating relative to pump frame  22  and about pump axis PA. Clocking assembly  46  can be considered to include both the projections  156  and the slots  160  as the projections  156  interface with slots  160  to prevent relative rotation. Clocking assembly  46  can thereby be considered to include both a collar formed by clocking member  112  and a sleeve on which the axial slots  160  are formed. The sleeve is fixed with respect to pump frame  22 , and in the example shown is formed by third frame body  62 . Both screw  92  and clocking member  112  translate within the sleeve along pump axis PA while the sleeve prevents rotation of clocking member  112  about pump axis PA. 
     Pump opening  158  extends through main body  52  and is disposed coaxially on pump axis PA. Fluid displacement member  34  extends through pump opening  158  to connect to pump shaft  110 . Cylinder  36  (best seen in  FIGS.  2 A and  2 B ) of displacement pump  28  can be connected to main body  52  at pump opening  158 . Side openings  68  extend radially through main body  52 . Posts  66  are disposed between side openings  68 . Side openings  68  provide the user access to the connection between pump shaft  110  and fluid displacement member  34  to facilitate mounting and dismounting of fluid displacement member  34  to pump shaft  110 . Sensor bore  120   b  extends into first body end  146 . Sensor bore  120   b  is configured to receive a component of sensor  48  ( FIGS.  2 B and  2 C ) (e.g., one of first transducer component  114  ( FIGS.  2 B and  2 C ) and second transducer component  116  ( FIGS.  2 B and  2 C )). Sensor bore  120   a  extends into third frame body  62 . Sensor bore  120   a  is configured to receive a component of sensor  48  (e.g., the other one of first transducer component  114  and second transducer component  116 ). 
     During operation, screw  92  reciprocates along pump axis PA to drive reciprocation of fluid displacement member  34 . Clocking assembly  46  is disposed axially between screw  92  and fluid displacement member  34 . Pump shaft  110  connects fluid displacement member  34  to screw  92  to cause reciprocation of fluid displacement member  34 . Clocking member  112  interfaces with main body  52  to prevent rotation of screw  92  about pump axis PA as screw  92  reciprocates along pump axis PA. Clocking projections  156  of clocking member  112  are disposed in axial slots  160  and reciprocate axially within axial slots  160 . Clocking projections  156  interfacing with axial slots  160  prevents relative rotation about pump axis PA. 
     In some examples, both the outer radial surface of collar  154  and the outer radial surface of clocking projections  156  interface with the inner radial surface of third frame body  62 . The outer radial surface of clocking member  112  interfacing with the inner radial surface of third frame body  62  can form a sliding seal to prevent contaminants, such as dust or overspray, from migrating past clocking member  112  in second axial direction AD 2 . For example, radial groove  155  can form a u-cup to seal against third frame body  62 . As such, clocking member  112  prevents the contaminants from reaching screw  92  and other elements of drive mechanism  26  (best seen in  FIGS.  2 B- 3 B ). 
     Clocking assembly  46  provides significant advantages. Clocking assembly  46  prevents screw  92  from rotating about pump axis PA, thereby causing screw  92  to reciprocate along pump axis PA due to rotation of drive nut  90  (best seen in  FIGS.  2 B- 3 B ). Clocking member  112  both clocks screw  92  to pump frame  22  to prevent rotation and provides a sliding seal to prevent contaminants from reaching lubricated portions of drive mechanism  26 . 
       FIG.  5    is a cross-sectional view of pump assembly  12 ′. Pump assembly  12 ′ is substantially similar to pump assembly  12  (best seen in  FIGS.  2 A- 2 D ) and is configured to generate a rotational output by motor  24  and provide a linear driving input to displacement pump  28  to pump fluid. Pump assembly  12 ′ can be utilized in spray system  10  ( FIGS.  1 A and  1 B ). Pump frame  22 ′, motor  24 , drive mechanism  26 ′, displacement pump  28 , rotor shaft  42 ′, bearing  44 , pump shaft  110 ′, clocking member  112 ′, and cavity  124 ′ are shown. Pump frame  22 ′ includes main body  52 ′, connecting member  54 , and frame member  56 . Main body  52 ′ includes first frame body  58 ′ and second frame body  60 ′. Frame member  56  includes radial projections  70 . Motor  24  includes stator  72 , rotor  74 , motor bearings  76 , axle  78 , first motor end  80 , and second motor end  82 . Rotor  74  includes rotor body  84  and permanent magnet array  86 . Drive mechanism  26 ′ includes drive nut  90 ′, screw  92 ′, and rolling elements  94 ′. Drive nut  90 ′ includes axial extension  97 ′, first nut end  101 ′, and second nut end  103 ′. Screw  92 ′ includes first screw end  96 ′, second screw end  98 ′, and bore  100 ′. Rotor shaft  42 ′ includes first shaft end  102 ′, second shaft end  104 ′, and shaft flange  164 . Displacement pump  28  includes fluid displacement member  34 , cylinder  36 , and check valves  106   a ,  106   b . Fluid displacement member  34  includes connector  108 . Cavity  124 ′ includes shaft cavity  164  and motor cavity  168 . 
     Pump frame  22 ′ supports other components of pump assembly  12 ′. Main body  52 ′ extends in axial direction AD 1  relative to motor  24 . In the example shown, main body  52 ′ is spaced in first axial direction AD 1  from first motor end  80  of motor  24 . Frame member  56  is disposed on an opposite axial side of motor  24  from main body  52 ′ and is adjacent second motor end  82 . Frame member  56  is fixed to motor  24 . Connecting member  54  extends axially between main body  52 ′ and frame member  56  and fixes main body  52 ′ and frame member  56  together. More specifically, connecting member  54  is attached to mounting flange  64 ′ of main body  52 ′ and radial projections  70  of frame member  56 . Connecting member  54  is spaced radially from motor  24 . Connecting member  54  can fully enclose rotor  74  or be formed from a plurality of connecting members  52  spaced circumferentially about rotor  74 . In the example shown, connecting member  54  includes tie rods extending between and connecting frame member  56  and main body  52 ′. Pump frame  22 ′ forms an exoskeleton extending around and supporting motor  24  in examples where connecting member  54  formed by a plurality of connecting members. 
     Motor  24  is an electric motor statically and dynamically connected to pump frame  22 ′. Motor  24  is disposed axially between frame member  56  and main body  52 ′. Motor  24  is an electric motor. Stator  72  includes armature windings (not shown) and rotor  74  includes permanent magnet array  86 . Rotor  74  is configured to rotate about pump axis PA in response to current through stator  72 . Motor  24  is a reversible motor in that stator  72  can cause rotation of rotor  74  in either of two rotational directions about pump axis PA (e.g., clockwise or counterclockwise). 
     Rotor  74  is disposed about stator  72  such that motor  24  includes an outer rotator. The permanent magnets forming permanent magnet array  86  are disposed on an inner circumferential face of rotor body  84 . Stator  72  is fixed to axle  78 . Outer end  88  of axle  78  extends in second axial direction AD 2  beyond second motor end  82 . Outer end  88  extends through rotor body  84 . Outer end  88  of axle  78  is connected to frame member  56  such that axle  78  is fixed to frame member  56 . Outer end  88  connecting to frame member  56  forms the static connection between motor  24  and pump frame  22 ′. Motor bearings  76  support rotor  74  relative stator  72 . Motor bearings  76  facilitate rotation of rotor  74  relative to stator  72 . Axle  78  extends through the motor bearing  76  disposed at second motor end  82  of motor  24 , such that the motor bearing  76  at second motor end  82  is disposed between rotor body  84  and axle  78 . 
     Rotor shaft  42 ′ extends axially from rotor  74  in first axial direction AD 1  and is connected to rotor  74  to rotate with rotor  74 . Rotor shaft  42 ′ is disposed coaxially with rotor  74  on pump axis PA. Rotor shaft  42 ′ extends into an interior of main body  52 ′ such that at least a portion of rotor shaft  42 ′ overlaps axially with at least a portion of main body  52 ′. In the example shown, rotor shaft  42 ′ overlaps axially with each of first frame body  58 ′ and second frame body  60 ′. Rotor shaft  42 ′ overlaps axially with a full axial length of first frame body  58 ′. Rotor shaft  42 ′ is open at each of first shaft end  102 ′ and second shaft end  104 ′. Second shaft end  104 ′ extends through rotor body  84  and into an interior of motor  24 . Second shaft end  104 ′ overlaps axially with axle  78 . The motor bearing  76  disposed at first motor end  80  is disposed radially between axle  78  and rotor shaft  42 ′. In the example shown, second shaft end  104 ′ is disposed on a radially inner side of the motor bearing  76  and axle  78  is disposed on a radially outer side of the motor bearing  76 . 
     Cavity  124 ′ is elongated along pump axis PA. Cavity  124 ′ is formed by shaft cavity  166  extending within rotor shaft  42 ′ and motor cavity  168  extending within motor  24 . More specifically, motor cavity  168  is formed within axle  78 . 
     Clocking member  112 ′ interfaces with pump frame  22 ′ such that clocking member  112 ′ is held static relative to pump frame  22 ′ during pumping. In the example shown, clocking member  112 ′ is fixed to frame member  56 . Clocking member  112 ′ can be formed separately from frame member  56  and be connected to frame member  56  or can be integrally formed with frame member  56 . Clocking member  112 ′ can be removably or permanently fixed to frame member  56 . Clocking member  112 ′ extends in first axial direction AD 1  from frame member  56  and through cavity  124 ′ to interface with screw  92 ′. Clocking member  112 ′ is cantilevered from frame member  56 . In the example shown, clocking member  112 ′ extends through a full axial length of motor cavity  168  such that clocking member  112 ′ axially overlaps with the full axial length of each of axle  78 , stator  72 , and rotor  74 . Clocking member  112 ′ is connected to frame member  56  at a location spaced in second axial direction AD 2  from second motor end  82 . In the example shown, clocking member  112 ′ extends through a full axial length of shaft cavity  166  such that clocking member  112 ′ axially overlaps a full axial length of rotor shaft  42 ′. It is understood, however, that clocking member  112 ′ can extend any desired distance into cavity  124 ′ such that clocking member  112 ′ interfaces with screw  92 ′ when screw  92 ′ is at the end of a downstroke, as discussed in more detail below. 
     Clocking member  112 ′ interfaces with screw  92 ′ to prevent screw  92 ′ from rotating about pump axis PA. Clocking member  112 ′ is disposed coaxially with screw  92 ′ on pump axis PA. In the example shown, clocking member  112 ′ is a rod elongate along pump axis PA. Clocking member  112 ′ includes a contoured outer surface configured to interface with a contoured surface of screw  92 ′ within bore  100 ′ to prevent rotation of screw  92 ′ about pump axis PA. Clocking member  112 ′ and bore  100 ′ can have any desired contours suitable for mating and preventing rotation of screw  92 ′ about clocking member  112 ′. For example, one or both of clocking member  112 ′ and screw  92 ′ can have contours that are triangular, rectangular, pentagonal, or hexagonal, among other options. Screw  92 ′ translates axially relative to and along clocking member  112 ′ during operation. 
     Drive mechanism  26 ′ is connected to rotor shaft  42 ′. Drive mechanism  26 ′ receives a rotational output from rotor  74  via rotor shaft  42 ′ and is configured to provide a linear input to fluid displacement member  34 . More specifically, second nut end  103 ′ of drive nut  90 ′ is connected to first shaft end  102 ′ of rotor shaft  42 ′. Drive nut  90 ′ is disposed coaxially with rotor shaft  42 ′ to rotate about pump axis PA with rotor shaft  42 ′. Drive nut  90 ′ can be attached to rotor shaft  42 ′ via fasteners (e.g., bolts), adhesive, or press-fitting, among other options. In the example shown, drive nut  90 ′ is connected to rotor shaft  42 ′ by fasteners oriented on axes transverse and non-orthogonal to pump axis PA. It is understood, however, that the fasteners can be disposed at any desired orientation suitable for fixing drive nut  90 ′ to rotor shaft  42 ′. First nut end  101 ′ is disposed at an opposite axial end of drive nut  90 ′ from second nut end  103 ′. First nut end  101 ′ is free in that first nut end  101 ′ is not mechanically supported by pump frame  22 ′. Axial extension  97 ′ extends in second axial direction AD 2  from second nut end  103 ′ and is disposed around a portion of rotor shaft  42 ′. Axial extension  97 ′ interfaces with shaft flange  164  and is disposed on an opposite axial side of shaft flange  164  from bearing  44 . 
     Screw  92 ′ is disposed coaxially with drive nut  90 ′ on pump axis PA and is elongate along pump axis PA. Screw  92 ′ is reciprocates along pump axis PA during operation. Screw  92 ′ provides the linear input to fluid displacement member  34  to drive fluid displacement member  34  linearly along pump axis PA. Second screw end  98 ′ is oriented towards motor  24 . Bore  100 ′ extends axially into screw  92 ′ from second screw end  98 ′. Pump shaft  110 ′ is attached to first screw end  96 ′ and to fluid displacement member  34 . Pump shaft  110 ′ can be connected to each of screw  92 ′ and fluid displacement member  34  in any desired manner, such as by pinned connections, among other options. Screw  92 ′ and pump shaft  110 ′ form a linear drive element of drive mechanism  26 ′. It is understood that, in some examples, screw  92 ′ and pump shaft  110 ′ are formed as a single component. Screw  92 ′ and pump shaft  110 ′ function as a single part to drive linear reciprocation of fluid displacement member  34  on pump axis PA. 
     Rolling elements  94 ′ are disposed radially between screw  92 ′ and drive nut  90 ′ and support screw  92 ′ relative drive nut  90 ′ such that gap  118  is disposed between screw  92 ′ and drive nut  90 ′. Rolling elements  94 ′ thereby prevent screw  92 ′ and drive nut  90 ′ from directly contacting one another during operation. Rolling elements  94 ′ are arrayed around, and are arrayed along, an axis that is coaxial with pump axis PA. Rolling elements  94 ′ are rollers arrayed circumferentially around screw  92 ′. In the example shown, rolling elements  94 ′ are rollers that are elongate between first nut end  101 ′ and second nut end  103 ′. It is understood, however, that rolling elements  94 ′ can be of any suitable configuration for maintaining gap  118  between drive nut  90 ′ and screw  92 ′ and for causing axial translation of screw  92 ′ due to rotation of drive nut  90 ′, such as balls, among other options. 
     Bearing  44  is disposed radially between rotor shaft  42 ′ and pump frame  22 ′. More specifically, bearing  44  is disposed radially between rotor shaft  42 ′ and main body  52 ′. Bearing  44  is disposed axially between drive nut  90 ′ and motor  24 . Bearing  44  is retained axially on rotor shaft  42 ′ between shaft flange  164  and rotor body  84 . In the example shown, shaft flange  164  contacts each of bearing  44  and drive mechanism  26 ′. More specifically, shaft flange  164  contacts each of bearing  44  and drive nut  90 ′. Bearing  44  is retained axially on main body  52 ′ between first frame body  58 ′ and second frame body  60 ′. Bearing  44  is disposed axially between drive nut  90 ′ and motor  24 . Bearing  44  supports motor  24  relative pump frame  22 ′ and facilitates rotation of rotor shaft  42 ′ relative pump frame  22 ′. Bearing  44  thereby forms a dynamic connection between motor  24  and pump frame  22 ′. Bearing  44  is configured to support both rotational and axial loads generated during pumping. Bearing  44  supports the axial loads and transfers the axial loads to pump frame  22 ′ to isolate motor  24  from the axial loads. 
     Displacement pump  28  is mounted to pump frame  22 ′. Displacement pump  28  is disposed coaxially on pump axis PA. More specifically, cylinder  36  is mounted to main body  52 ′ at an end of main body  52 ′ disposed axially opposite motor  24 . Cylinder  36  is fixed to main body  52 ′ thereby forming a static connection between displacement pump  28  and pump frame  22 ′. Fluid displacement member  34  is connected to screw  92 ′ by pump shaft  110 ′. Fluid displacement member  34  is connected to an end of pump shaft  110 ′ opposite screw  92 ′. While fluid displacement member  34  is described as connected to screw  92 ′ by pump shaft  110 ′, it is understood that fluid displacement member  34  can be directly connected to screw  92 ′. Displacement pump  28  is dynamically connected to motor  24  by the connection between fluid displacement member  34  and pump shaft  110 ′. Check valve  106   a  is a one-way valve disposed in cylinder  36 . Check valve  106   b  is a one-way valve disposed in fluid displacement member  34  to reciprocate with fluid displacement member  34 . Displacement pump  28  can be a double displacement pump in that displacement pump  28  outputs fluid during both of the upstroke in second axial direction AD 2  and the downstroke in first axial direction AD 1 . 
     An example pump cycle including an initial downstroke and a subsequent upstroke is discussed by way of example. During operation, power is provided to stator  72  to drive rotation of rotor  74  about pump axis PA. Rotor  74  rotates about pump axis PA in a first rotational direction (e.g., one of clockwise and counterclockwise) and causes simultaneous rotation of rotor shaft  42 ′ due to connection between rotor  74  and rotor shaft  42 ′. Rotor shaft  42 ′ rotates about pump axis PA and drives rotation of drive nut  90 ′ about pump axis PA. Rotor shaft  42 ′ provides the rotational output from motor  24  to drive mechanism  26 ′. 
     Drive nut  90  rotates about pump axis PA. Drive nut  90  rotating about pump axis PA causes rolling elements  94  to exert an axial driving force on screw  92  in axial direction AD 1  to drive screw  92  linearly along pump axis PA. Screw  92  is driven linearly in first axial direction AD 1 . Screw  92  drives pump shaft  110 ′ and thus fluid displacement member  34  through a downstroke along pump axis PA and in first axial direction AD 1 . During the downstroke, check valve  106   a  is closed and check valve  106   b  is open. Fluid is driven through check valve  106   b  and downstream from displacement pump  28 . 
     After completing the downstroke, rotor  74  is driven in a second rotational direction opposite the first rotational direction (e.g., the other of clockwise and counterclockwise). Rotor  74  drives rotation of rotor shaft  42 , which drives rotation of drive nut  90 . Rolling elements  94  exert an axial driving force in second axial direction AD 2  on screw  92  to drive screw  92  linearly along pump axis PA. Screw  92  is driven linearly in the second axial direction AD 2 . Screw  92  pulls fluid displacement member  34  through an upstroke along pump axis PA and in second axial direction AD 2 . During the upstroke, check valve  106   a  is open and check valve  106   b  is closed. Fluid is drawn into cylinder through check valve  106   a  and simultaneously driven downstream from displacement pump  28 . Motor  24  thereby causes pumping by displacement pump  28 . Displacement pump  28  outputs fluid during both the upstroke and the downstroke. 
     In some examples, rotor  74  and drive mechanism  26 ′ are sized to provide a one revolution of rotor  74  results in a full stroke of screw  92 ′. A full revolution in an opposite rotational direction results in a full stroke of screw  92 ′ in the opposite axial direction. As such, two revolutions in opposite directions can provide a full pump cycle. Pump assembly  12 ′ can thereby provide a 1:1 ratio between revolutions of rotor  74  and pumping strokes. It is understood, however, that rotor  74  and drive mechanism  26 ′ can be sized to provide any desired ratio between revolutions and pump strokes, such as 0.25 revolutions per stroke, 0.5 revolutions per stroke, two revolutions per stroke, three revolutions per stroke, or any other desired number of revolutions per stroke. 
     Axial forces are experienced by drive mechanism  26  as screw  92  displaces linearly along pump axis PA during each of the downstroke and the upstroke. The axial forces experienced by fluid displacement member  34 , at least in part due to fluid resistance during each of the upstroke and the downstroke, are transferred to screw  92  via pump shaft  110 ′. The axial forces experienced by screw  92  are transferred to rolling elements  94  and from rolling elements  94  to drive nut  90 . The axial forces experienced by drive nut  90  are transferred to rotor shaft  42 . The axial forces experienced by rotor shaft  42  are transferred to bearing  44  and through bearing  44  to main body  52  of pump frame  22 . As such, the axial forces generated during pumping, which can also be referred to as pump reaction forces, are transferred to and experienced by pump frame  22  prior to those forces being experienced by motor  24 . Motor  24  is thereby isolated from the pump reaction forces. 
     Pump assembly  12 ′ provides significant advantages. Motor  24 , drive mechanism  26 ′, and displacement pump  28  are disposed coaxially on pump axis PA, providing a compact pumping arrangement that facilitates transport between and within job sites. Screw  92 ′ translates within each of rotor shaft  42 ′ and motor  24 , facilitating the compact axial arrangement. Bearing  44  reacts pump reaction forces to isolate motor  24  from those pump reaction forces. The pump reaction forces are not transferred to motor  24  to protect components of motor  24  and prevent misalignment between stator  72  and rotor  74 . Rotor  74  is an outer rotator, which provides high inertia and torque, facilitating pumping at the high pressures utilized for generating the fluid spray. Each of motor  24 , drive mechanism  26 ′, and displacement pump  28  being disposed coaxially on pump axis PA further reduces the number of moving parts of pump assembly  12 ′, providing a simpler, more robust pumping arrangement. In addition, no speed reduction gearing is present between motor  24  and drive mechanism  26 ′, which reduces noise generated during operation, providing a safer and more user-friendly spray environment. 
       FIG.  6 A  is an enlarged cross-sectional view of a portion of pump assembly  12 ′ showing screw  92 ′ at the end of a downstroke.  FIG.  6 B  is an enlarged cross-sectional view of pump assembly  12 ′ showing screw  92 ′ at the end of an upstroke.  FIGS.  6 A and  6 B  will be discussed together. Pump frame  22 ′, motor  24 , drive mechanism  26 ′, rotor shaft  42 ′, bearing  44 , lubricant fittings  50 , clocking member  112 ′, cavity  124 ′, inner notch  126 ′, and outer notch  128 ′ are shown. Main body  52 ′, connecting member  54 , and frame member  56  of pump frame  22 ′ are shown. First frame body  58 ′, second frame body  60 ′, and mounting flange  64 ′ of main body  52 ′ are shown. Motor  24  includes stator  72 , rotor  74 , motor bearings  76 , axle  78 , first motor end  80 , and second motor end  82 . Rotor  74  includes rotor body  84  and permanent magnet array  86 . Axle  78  includes outer end  88 . Drive mechanism  26 ′ includes drive nut  90 ′, screw  92 ′, and rolling elements  94 ′. Drive nut  90 ′ includes axial extension  97 ′, first nut end  101 ′, and second nut end  103 ′. Second screw end  98 ′, screw thread  99 , bore  100 ′, and contoured opening  170  of screw  92 ′ are shown. Rotor shaft  42 ′ includes first shaft end  102 ′, second shaft end  104 ′, and shaft flange  164 . Cavity  124 ′ is formed by shaft cavity  166 ′ and motor cavity  168 ′. 
     Motor  24  is supported by pump frame  22 ′ and disposed axially between frame member  56  and main body  52 ′. Motor  24  is an electric motor. Stator  72  is fixed to axle  78  and rotor  74  is disposed about stator  72 . Outer end  88  of axle  78  extends in second axial direction AD 2  beyond second motor end  82  and is fixed to frame member  56 . Outer end  88  connecting to frame member  56  forms the static connection between motor  24  and pump frame  22 ′. Motor bearings  76  support rotor  74  relative stator  72 . Motor bearings  76  facilitate rotation of rotor  74  relative to stator  72 . 
     Main body  52 ′ extends axially in first axial direction AD 1  relative motor  24 . First frame body  58 ′ is a part of main body  52 ′ disposed closest to rotor  74  along pump axis PA. Second frame body  60 ′ is connected to an end of first frame body  58 ′ disposed opposite motor  24  such that first frame body  58 ′ is disposed axially between second frame body  60 ′ and motor  24 . First frame body  58 ′ and second frame body  60 ′ can be removably connected, such as by fasteners, or can be permanently connected, such as by adhesive or welding. In some examples, main body  52 ′ can be formed as a single unitary component. 
     Outer notch  128 ′ is formed on main body  52 ′. Outer notch  128 ′ supports an outer race  47  of bearing  44 . In the example shown, outer notch  128 ′ is formed by first frame body  58 ′ and second frame body  60 ′. Bearing  44  is received by outer notch  128 ′. Bearing  44  is retained axially within outer notch  128 ′ between first outer shoulder  138 ′ and second outer shoulder  140 ′. First outer shoulder  138 ′ is formed on first frame body  58 ′ and second outer shoulder  140 ′ is formed by first frame body  58 ′ and second frame body  60 ′. An axially extending flange of second frame body  60 ′ is disposed within and axially overlaps a portion of first frame body  58 ′. The axially extending flange forms a portion of second frame body  60 ′ forms part of second outer shoulder  140 ′. Second frame body  60 ′ extending within and axially overlapping first frame body  58 ′ further radially locates second frame body  60 ′ on first frame body  58 ′, maintaining concentricity and facilitating mounting of bearing  44 . First frame body  58 ′ forms a base of outer notch  128 ′. In some examples, first outer shoulder  138 ′ is formed by first frame body  58 ′ and second frame body  60 ′ while second outer shoulder  140 ′ and the base of outer notch  128 ′ are formed by second frame body  60 ′. In some examples, first outer shoulder  138 ′ is formed by first frame body  58 ′, second outer shoulder  140 ′ is formed by second frame body  60 ′, and the base of outer notch  128 ′ is formed by a combination of first frame body  58 ′ and second frame body  60 ′. It is understood that outer notch  128 ′ can be formed in any suitable manner for supporting bearing  44  on pump frame  22 ′. 
     Rotor shaft  42 ′ is connected to and extends in first axial direction AD 1  from rotor body  84 . Rotor shaft  42 ′ extends to and is connected with drive mechanism  26 ′. Second shaft end  104 ′ of rotor shaft  42 ′ is connected to rotor body  84 . Second shaft end  104 ′ extends into motor  24 . Second shaft end  104 ′ axially overlaps with axle  78 . Second shaft end  104 ′ extends through rotor body  84  and into axle  78 . The motor bearing  76  disposed at first motor end  80  is disposed between rotor shaft  42 ′ and axle  78 . First shaft end  102 ′ of rotor shaft  42 ′ is connected to drive nut  90 ′. In the example shown, rotor shaft  42 ′ is connected to drive nut  90 ′ by fasteners, but it is understood that rotor shaft  42 ′ and drive nut  90 ′ can be connected in any suitable manner, such as by adhesive or press-fitting, among other options. Second shaft end  104 ′ is open such that screw  92 ′ can reciprocate through second shaft end  104 ′ during operation. 
     Inner notch  126 ′ supports an inner race  45  of bearing  44 . In the example shown, inner notch  126 ′ is formed axially between rotor shaft  42 ′ and rotor body  84 . Bearing  44  is retained axially within inner notch  126 ′ between first inner shoulder  134 ′ and second inner shoulder  136 ′. First inner shoulder  134 ′ is formed by rotor shaft  42 ′ and rotor body and second inner shoulder  136 ′ is formed on rotor shaft  42 ′. Shaft flange  164  forms a portion of second inner shoulder  136 ′. Rotor shaft  42 ′ forms a base of inner notch  126 ′. In some examples, first inner shoulder  134 ′ is formed by rotor body  84  and second inner shoulder  136 ′ is formed by rotor shaft  42 ′ and rotor body  84 . In some examples, first inner shoulder  134 ′ is formed by rotor body  84 , second inner shoulder  136 ′ is formed by rotor shaft  42 ′, and the base of inner notch  126 ′ is formed by a combination of rotor shaft  42 ′ and rotor body  84 . It is understood that inner notch  126 ′ can be formed in any suitable manner for supporting bearing  44  on rotating components of pump assembly  12 ′. 
     Cavity  124 ′ is formed in rotor shaft  42 ′ and motor  24 . Shaft cavity  166 ′ is defined by rotor shaft  42 ′ and motor cavity  168 ′ is defined by motor  24 . More specifically, shaft cavity  166 ′ is disposed within and defined by axle  78 . Screw  92 ′ is configured to reciprocate within cavity  124 ′ during pumping, as discussed in more detail below. 
     Drive nut  90 ′ is connected to first shaft end  102 ′. It is understood that drive nut  90 ′ can be attached to rotor shaft  42 ′ in any desired manner, such as by fasteners (e.g., bolts), adhesive or press-fitting, among other options. First nut end  101 ′ is disposed at an opposite axial end of drive nut  90 ′ from second nut end  103 ′. First nut end  101 ′ is free in that first nut end  101 ′ is not mechanically supported by pump frame  22 ′. Axial extension  97 ′ extends in second axial direction AD 2  from second nut end  103 ′ and is disposed around a portion of rotor shaft  42 ′. Axial extension  97 ′ interfaces with shaft flange  164  and is disposed on an opposite axial side of shaft flange  164  from bearing  44 . Shaft flange  164  is disposed axially between bearing  44  and drive nut  90 ′. Each of drive nut  90 ′ and bearing  44  contact shaft flange  164 . 
     Screw  92 ′ extends axially through drive nut  90 ′ and is disposed coaxially on pump axis PA with drive nut  90 ′. Rolling elements  94 ′ are disposed between screw  92 ′ and drive nut  90 ′ and support screw  92 ′ and drive mechanism  26 ′. Rolling elements  94 ′ maintain a radial gap between screw  92 ′ and drive nut  90 ′ such that screw  92 ′ does not directly contact drive nut  90 ′. In the example shown, rolling elements  94 ′ are rollers, but it is understood that rolling elements  94 ′ can be of any suitable configuration for driving axial displacement of screw  92 ′, such as balls. Lubricant fittings  50  are mounted on drive nut  90 ′ and extends into an outer radial surface of drive nut  90 ′. Lubricant fittings  50  facilitates lubrication of rolling elements  94 ′. In the example shown, two lubricant fittings  50  are disposed on opposite sides of drive nut  90 ′, spaced 180-degrees from each other. The two lubricant fittings  50  balance to prevent wobbling of drive nut  90 ′ as drive nut  90 ′ rotates about pump axis PA. 
     Second screw end  98 ′ forms a distal end of screw  92 ′ oriented in second axial direction AD 2  and that translates within cavity  124 ′ during operation. In some examples, second screw end  98 ′ is unsupported such that second screw end  98 ′ is free relative rotor shaft  42 ′ and axle  78  as screw  92 ′ reciprocates within cavity  124 ′ during operation. For example, no bearing, bushing, or other support element may be disposed between second screw end  98 ′ and either of rotor shaft  42 ′ and axle  78 . Bore  100 ′ extends axially into screw  92 ′ from second screw end  98 ′. Contoured opening  170  is formed at second screw end  98 ′ and defines a portion of bore  100 ′. Contoured opening  170  is an axial opening through second screw end  98 ′ aligned on pump axis PA. Contoured opening  170  is a non-circular opening configured to receive clocking member  112 ′. In the example shown, contoured opening  170  forms a portion bore  100 ′ disposed furthest in second axial direction AD 2 . It is understood that the contouring of contoured opening  170  can extend any desired axial distance into bore  100 ′, including up to a full axial length of bore  100 ′. 
     Screw  92 ′ axially overlaps with a portion of rotor shaft  42 ′. In some examples, second screw end  98 ′ axially overlaps with rotor shaft  42 ′ with screw  92 ′ at the end of the downstroke ( FIG.  6 A ). It is understood, however, that in some examples screw  92 ′ does not axially overlap any portion of rotor shaft  42 ′ with screw  92 ′ at the end of the downstroke. For example, drive nut  90 ′ can be axially elongated in second axial direction AD 2  such that second screw end  98 ′ axially overlaps drive nut  90 ′ but not rotor shaft  42 ′. The axial overlap between screw  92 ′ and rotor shaft  42 ′ increases through a portion of the upstroke as screw  92 ′ shifts in second axial direction AD 2 . The axial overlap between screw  92 ′ and rotor shaft  42 ′ decreases through a portion of the downstroke as screw  92 ′ shifts in first axial direction AD 1 . 
     Screw  92 ′ axially overlaps with motor  24  during at least a portion of the pump cycle. Screw  92 ′ extends into motor cavity  168 ′ with screw  92 ′ at the end of the upstroke ( FIG.  6 B ). At the end of the upstroke, screw  92 ′ fully occupies shaft cavity  166 ′ and extends into motor cavity  168 ′. As such, screw  92 ′ axially overlaps with each of motor  24  and rotor shaft  42 ′ at the end of the upstroke. 
     Clocking member  112 ′ is elongate along pump axis PA and disposed coaxially on pump axis PA with screw  92 ′. Clocking member  112 ′ is connected to frame member  56  and extends in first axial direction AD 1  from frame member  56 . Clocking member  112 ′ is at least partially disposed in cavity  124 ′. In the example shown, clocking member  112 ′ extends fully through each of motor cavity  168 ′ and shaft cavity  166 ′. Clocking member  112 ′ interfaces with screw  92 ′ to prevent screw  92 ′ from rotating about pump axis PA. In the example shown, clocking member  112 ′ is a rod extending into bore  100 ′ through contoured opening  170 . The outer surface of clocking member  112 ′ interfaces with contoured opening  170  such that the interface between clocking member  112 ′ and contoured opening  170  prevents rotation of screw  92 ′. In some examples, the outer surface of clocking member  112 ′ is contoured similar to contoured opening  170 . Clocking member  112 ′ and screw  92 ′ are telescopically connected such that the axial overlap between clocking member  112 ′ and screw  92 ′ varies during operation. Screw  92 ′ and clocking member  112 ′ have a sliding overlapping interface, which interface prevents rotation of screw  92 ′ by resisting the rotational motion output by motor  24  as screw  92 ′ linearly translates relative to clocking member  112 ′. 
     While clocking member  112 ′ is described as extending into bore  100 ′ such that screw  92 ′ is disposed around and receives clocking member  112 ′, it is understood that clocking member  112 ′ and screw  92 ′ can interface in any manner suitable for preventing screw  92 ′ from rotating relative to pump axis PA. For example, clocking member  112 ′ can include a contoured bore and the second screw end  98 ′ can extend into and interface with that contoured bore. Second screw end  98 ′ can include a radially extending portion, such as a flange, that projects radially beyond the threads of screw  92 ′. The radially extending portion can be contoured to mate with the contoured bore to prevent rotation of screw  92 ′ as screw  92 ′ translate along pump axis PA. 
     During operation, power is provided to stator  72 , such as through second motor end  82 , to cause rotation of rotor  74  about pump axis PA. Rotor  74  drives rotation of rotor shaft  42 ′ about pump axis PA. Rotor shaft  42 ′ drives rotation of drive nut  90 ′ about pump axis PA. Rotation of drive nut  90 ′ causes rolling elements  94 ′ to exert an axial driving force on screw  92 ′ to cause linear displacement of screw  92 ′. 
     By way of example, a pump cycle beginning from the position associated with the end of the downstroke shown in  FIG.  6 A  is discussed in more detail. Rotor  74  is rotated in a first rotational direction (e.g., one of clockwise and counterclockwise) and causes screw  92 ′ to displace linearly in second axial direction AD 2  through an upstroke. Screw  92 ′ shifts in second axial direction AD 2  through cavity  124 ′. The axial overlap between screw  92 ′ and rotor shaft  42 ′ increases as screw  92 ′ shifts in second axial direction AD 2 . The axial overlap between screw  92 ′ and clocking member  112 ′ increases as screw  92 ′ shifts through the upstroke such that clocking member  112 ′ extends further into bore  100 ′ as screw  92 ′ shifts in second axial direction AD 2 . Screw  92 ′ shifts axially through shaft cavity  166 ′ such that screw  92 ′ axially overlaps with bearing  44 . Screw  92 ′ shifts fully through shaft cavity  166 ′ and enters motor cavity  168 ′. Screw  92 ′ translates into motor  24  through first motor end  80 . Screw  92 ′ extends into motor cavity  168 ′ through the opening in rotor body  84  where rotor body  84  connects to first shaft end  102 ′. Screw  92 ′ translates in second axial direction AD 2  within motor cavity  168 ′ and towards second motor end  82 . The axial overlap between screw  92 ′ and rotor shaft  42 ′ increase during a first portion of the upstroke, as second screw end  98 ′ translates axially through motor cavity  168 ′, and remains constant during a second portion of the upstroke, when second screw end  98 ′ is disposed within and translates through motor cavity  168 ′. Screw  92 ′ continues to translate in second axial direction AD 2  until reaching the end of the upstroke, which position is shown in  FIG.  6 B . 
     Screw  92 ′ is displaced a maximum distance in second axial direction AD 2  into cavity  124 ′ when screw  92 ′ is at the end of the upstroke. Second screw end  98 ′ of screw  92 ′ is disposed within motor  24  with screw  92 ′ at the end of the upstroke. Screw  92 ′ fully extends through shaft cavity  166 ′ and occupies at least a portion of motor cavity  168 ′. Screw  92 ′ axially overlaps with portions of motor  24  at the end of the upstroke, including with the motor bearing  76  disposed between axle  78  and rotor shaft  42 ′, with rotor body  84 , with axle  78 , and with stator  72 . 
     After completing the upstroke, rotor  74  is rotated in a second rotational direction (e.g., the other of clockwise and counterclockwise) and causes screw  92 ′ to translate in first axial direction AD 1  through the downstroke. During the downstroke, screw  92 ′ translates from the position shown in  FIG.  6 B  to the position shown in  FIG.  6 A . Rotor  74  drive rotation of rotor shaft  42 ′, which drives rotation of drive nut  90 ′. Drive nut  90 ′ causes rolling elements  94 ′ to exert an axial force on screw  92 ′ to linearly displace screw  92 ′ in first axial direction AD 1 . The axial overlap between motor  24  and screw  92 ′ decreases as screw  92 ′ translates through the downstroke. Screw  92 ′ is fully withdrawn form motor cavity  168 ′ and continues to translate in first axial direction AD 1  away from second motor end  82 . Clocking member  112 ′ withdraws from bore  100 ′ as screw  92 ′ shifts in first axial direction AD 1 , such that the axial overlap between screw  92 ′ and clocking member  112 ′ decreases as screw  92 ′ translates through the downstroke. The axial overlap between screw  92 ′ and rotor shaft  42 ′ remains constant through a first portion of the downstroke, where at least a portion of screw  92 ′ is disposed in motor cavity  168 ′, and decreases through a second portion of the downstroke. After completing the downstroke, rotor  74  is rotated in the first rotational direction to drive screw  92 ′ back through the upstroke, thereby reciprocating screw  92 ′ for pumping. 
     Screw  92 ′ reciprocating within cavity  124 ′ provides significant advantages. Screw  92 ′ reciprocates within each of rotor shaft  42 ′ and motor  24  during operation. Screw  92 ′ extending into motor  24  to axially overlap with portions of motor  24  facilitates a more compact axial arrangement of pump assembly  12 ′. An axially compact pump assembly  12 ′ provides more efficient spray operations by facilitating transport to and within a job site. Screw  92 ′ telescopically interfacing with clocking member  112 ′ further facilitates a compact pump assembly  12 ′ as the axial overlap between screw  92 ′ and clocking member  112 ′ can vary throughout operation. 
       FIG.  7    is a cross-sectional view taken along line  7 - 7  in  FIG.  5   . Pump frame  22 ′, drive nut  90 ′, screw  92 ′, and clocking member  112 ′ are shown. Contoured opening  170  of screw  92 ′ is shown, and contoured opening  170  includes first contour  172 . Clocking member  112 ′ includes second contour  174 . Drive nut  90 ′, screw  92 ′, and clocking member  112 ′ are disposed coaxially on pump axis PA. Drive nut  90 ′ is disposed about screw  92 ′ and screw  92 ′ is disposed about clocking member  112 ′. Clocking member  112 ′ extends into bore  100 ′ (best seen in  FIG.  6 B ) of screw  92 ′ through contoured opening  170 . First contour  172  is formed on an outer radial surface of clocking member  112 ′. Second contour  174  is formed on an inner radial surface of contoured opening  170 . 
     Second contour  174  interfaces with first contour  172  to clock screw  92 ′ relative clocking member  112 ′ and prevent screw  92 ′ from rotating relative to clocking member  112 ′ about pump axis PA. Clocking member  112 ′ thereby rotationally locks screw  92 ′ on pump axis PA. As discussed above, the interface between screw  92 ′ and clocking member  112 ′ can be telescopic such that screw  92 ′ reciprocates along pump axis PA relative clocking member  112 ′. In the examples shown, first contour  172  and second contour  174  each have hexagonal cross-sectional profiles. It is understood, however, that first contour  172  and second contour  174  can be of any desired shape suitable for clocking screw  92 ′ to clocking member  112 ′ to prevent rotation of screw  92 ′ about pump axis PA. 
       FIG.  8    is a cross-sectional diagram of screw  92  showing lubricant fitting  50  mounted on an exterior of screw  92 . First screw end  96 , screw thread  99 , bore  100 , and outlet passage  176  of screw  92  are shown. 
     Bore  100  is elongate along pump axis PA and disposed axially on pump axis PA. Bore  100  extends axially into screw  92  from first screw end  96 . Lubricant fitting  50  is mounted on an exterior of screw  92 . Lubricant fitting  50  projects radially from the exterior of screw  92  such that lubricant fitting  50  can be accessed without disconnecting other components from screw  92 . For example, lubricant fitting  50  can be accessed without disconnecting fluid displacement member  34  (best seen in  FIG.  2 B ) from screw  92 . 
     Lubricant fitting  50  is fluidly connected to bore  100  to provide lubricant to bore  100 . Outlet passage  176  extends from bore  100  to an exterior of screw  92 . Outlet passage  176  extends along an axis transverse to pump axis PA. In some examples, outlet passage  176  extends along an axis orthogonal to pump axis PA. Outlet passage  176  provides a flowpath for lubricant in bore  100  to flow to an exterior of screw  92 . Outlet passage  176  extends to the exterior of screw  92  at a location where the exterior of screw  92  is disposed within drive nut  90  (best seen in  FIGS.  2 B- 3 B ) to provide lubricant to rolling elements  94  (best seen in  FIG.  10   ) disposed between screw  92  and drive nut  90 . In some examples, lubricant fitting  50  is a grease zerk. Bore  100  can act as a lubricant reservoir to store lubricant during operation. 
     To lubricate the rolling elements  94  an applicator of a lubricating device, such as a grease gun, is connected to lubricant fitting  50 . The applicator supplies lubricant, such as oil or grease, to bore  100 . The lubricant flows through bore  100  to outlet passage  176  and through outlet passage  176  to the gap disposed between screw  92  and drive nut  90 . The lubricant is thereby provided to the rolling elements  94  disposed in and maintaining the gap between screw  92  and drive nut  90  via bore  100  and outlet passage  176 . 
       FIG.  9    is a cross-sectional diagram of screw  92  showing lubricant fitting  50  mounted within screw  92 . First screw end  96 , screw thread  99 , bore  100 , and outlet passage  176  of screw  92  are shown. Bore  100  includes first diameter portion  178  and second diameter portion  180 . 
     Bore  100  is elongate along pump axis PA and disposed axially on pump axis PA. Bore  100  extends axially into screw  92  from first screw end  96 . First diameter portion  178  of bore  100  extends axially into screw  92  from first screw end  96 . Second diameter portion  180  of bore  100  extends axially into screw  92  from first diameter portion  178 . Lubricant fitting  50  is disposed in bore  100  at the interface between first diameter portion  178  and second diameter portion  180 . Lubricant fitting  50  is secured to screw  92  within bore  100 . Lubricant fitting  50  can be secured within second diameter portion  180  and a portion of lubricant fitting  50  can extend into first diameter portion  178 . Lubricant fitting  50  can be a grease zerk. Second diameter portion  180  of bore  100  can act as a lubricant reservoir to store lubricant during operation. 
     Outlet passage  176  extends from bore  100  to an exterior of screw  92 . Outlet passage  176  provides a flowpath for lubricant in bore  100  to flow to an exterior of screw  92 . Outlet passage  176  extends along an axis transverse to pump axis PA. In some examples, outlet passage  176  extends along an axis orthogonal to pump axis PA. Outlet passage  176  provides a flowpath for lubricant in bore  100  to flow to an exterior of screw  92 . Outlet passage  176  extends to the exterior of screw  92  at a location where the exterior of screw  92  is disposed within drive nut  90  (best seen in  FIGS.  2 B- 3 B ) to provide lubricant to rolling elements  94  (best seen in  FIG.  10   ) disposed between screw  92  and drive nut  90 . In some examples, lubricant fitting  50  is a grease zerk. Bore  100  can act as a lubricant reservoir to store lubricant during operation. 
     First diameter portion  178  of bore  100  is sized to receive an applicator of a lubricating device, such as a grease gun. To lubricate the rolling elements  94  an applicator of the lubricating device is inserted into first diameter portion  178  and connected to lubricant fitting  50 . The applicator supplies lubricant, such as oil or grease, to second diameter portion  180  through lubricant fitting  50 . The lubricant flows through bore  100  to outlet passage  176  and through outlet passage  176  to the gap disposed between screw  92  and drive nut  90 . The lubricant is thereby provided to the rolling elements  94  disposed in and maintaining the gap between screw  92  and drive nut  90  via bore  100  and outlet passage  176 . 
     In any of the examples discussed above in  FIGS.  1 - 9   , rotor  74  and drive mechanism  26 ,  26 ′ are sized to provide a desired revolution to stoke ratio. In some examples, rotor  74  and drive mechanism  26 ,  26 ′ are sized such that one revolution of rotor  74  results in a full stroke of fluid displacement member  34  in one of first axial direction AD 1  and second axial direction AD 2 . A full revolution in an opposite rotational direction results in a full stroke of fluid displacement member  34  in the opposite axial direction. As such, two revolutions in opposite directions can provide a full pump cycle of fluid displacement member  34 . Pump assembly  12 ,  12 ′ can thereby provide a 1:1 ratio between revolutions of rotor  74  and pumping strokes. 
     It is understood, however, that rotor  74  and drive mechanism  26 ,  26 ′ can be sized to provide any desired revolution to stroke ratio. It is further understood that controller  29  can control operation of motor  24  such that the actual stroke length is dynamic and varies can during operation. Controller  29  can cause the stroke length to vary between the downstroke and the upstroke. In some examples, controller  29  is configured to control operation between a maximum revolution to stroke ratio and a minimum revolution to stroke ratio. Pump assembly  12 ,  12 ′ can be configured to provide any desired revolution to stroke ratio. In some examples, pump assembly  12 ,  12 ′ provides a revolution to stroke ratio of up to about 4:1. It is understood that other maximum revolution to stroke ratios are possible, such as about 1:1, 2:1, 3:1, or 5:1, among other options. In some examples, pump assembly  12 ,  12 ′ can provide a revolution to stroke ratio between about 0.25:1-7:1. It is understood that any of the ranges discussed can be an inclusive range such that the boundary values are included within the range. It is further understood that each of the ranges discussed can vary from the specified range while still falling within the scope of this disclosure. 
     Motor  24  and drive mechanism  26 ,  26 ′ can be configured to displace fluid displacement member  34  at least about 6.35 mm (about 0.25 in.) per rotor revolution. In some examples, motor  24  and drive mechanism  26 ,  26 ′ are configured to displace fluid displacement member  34  between about 8.9-30.5 mm (about 0.35-1.2 in.) per rotor revolution. In some examples, motor  24  and drive mechanism  26 ,  26 ′ are configured to displace fluid displacement member  34  between about 8.9-11.4 mm (about 0.35-0.45 in.). In some examples, motor  24  and drive mechanism  26 ,  26 ′ are configured to displace fluid displacement member  34  between about 19-21.6 mm (about 0.75-0.85 in.). In some examples, motor  24  and drive mechanism  26 ,  26 ′ are configured to displace fluid displacement member  34  between about 24.1-26.7 mm (about 0.95-1.05 in.). The axial displacement per rotor revolution provided by pump assembly  12 ,  12 ′ facilitates precise control and quick responsiveness during pumping. The axial displacement per rotor revolution facilitates quick changeover and provides more efficient pumping while reducing wear on components of pump assembly  12 ,  12 ′. 
     Pump assembly  12 ,  12 ′ is configured to pump according to a revolution to displacement ratio. More specifically, motor  24  and drive mechanism  26 ,  26 ′ are configured to provide a desired revolution to displacement ratio between revolutions of rotor  74  and the linear travel distance of fluid displacement member  34 , as measured in inches, for each revolution of rotor  74 . In some examples, the revolution to displacement ratio (rev/in.) is less than about 4:1. In some examples, the revolution to displacement ratio is between about 0.85:1 and 3.25:1. In some examples, the revolution to displacement ratio is between about 1:1-3:1. In some examples, the revolution to displacement ratio is between about 1:1-2.75:1. In some examples, the revolution to displacement ratio between is about 1:1-2.55:1. In some examples, the revolution to displacement ratio is between about 1:1-1.3:1. In some examples, the revolution to displacement ratio is between about 0.9:1-1.1:1. In some examples, the revolution to displacement ratio is between about 2.4:1-2.6:1. The low revolution to displacement ratio provided by pump assembly  12 ,  12 ′ relative to other electrically-powered pumps, such as crank-powered pumps that require reduction gearing to generate sufficient pumping torque and typically have revolution to displacement ratios of about 8:1 or higher, facilitates more efficient pumping, generates less wear, and provides quick responsiveness for changing stroke direction. Rotor  74  can be driven at a lower rotational speed to generate the same linear speed, thereby generating less heat during operation. 
       FIGS.  10 A and  10 B  will be discussed concurrently.  FIG.  10 A  is an isometric view of spray system  1010 .  FIG.  10 B  is a block schematic diagram of spray system  1010 . Spray system  1010  is a plural component system that receives separate inert material components, mixes the components in a predetermined ratio, and then dispenses the components as an activated compound. As shown in  FIGS.  1 A and  1 B , spray system  1010  includes proportioner  1016 ; motor  1014 ; controller  1029 ; user interface  1018 ; fluid tanks  1020   a ,  1020   b ; feed pumps  1012   a ,  1012   b ; feed lines  1024   a ,  1024   b , proportioner pumps  1022   a ,  1022   b ; supply lines  1028   a ,  1028   b ; upstream sensors  1030   a ,  1030   b ; downstream sensors  1032   a ,  1032   b ; and applicator  1034 . Controller  1029  includes memory  1036  and control circuitry  1038 . Applicator  1034  includes mixer  1040 , handle  1042 , and trigger  1044 . Spray system  1010  also includes primary heaters  1045   a ,  1045   b  (shown in  FIG.  10 B ). Heated portion  1046  of supply lines  1028   a ,  1028   b  and heat controller  1047  are shown. 
     Spray system  1010  is a system configured to pump a first component material and a second component material to applicator  1034  to form a plural component spray material. The component materials are pumped according to target parameters, such as ratio, temperature, flow rate and/or pressure. The first and second component materials are mixed at applicator  1034  to form the spray material that is sprayed onto a substrate by applicator  1034 . For example, one of the first and second component materials can be a catalyst, such as isocyanate, and the other one of the first and second component materials can be a resin, such as polyol resin, that combine to form a plural component material, such as a spray foam. 
     Fluid tanks  1020   a ,  1020   b  hold the individual component materials during spraying. In some examples, fluid tanks  1020   a ,  1020   b  are portable and can be moved between and around job sites. In some examples, fluid tanks  1020   a ,  1020   b  can be drums, such as 55-gallon drums, among other options. 
     Feed pumps  1012   a ,  1012   b  are respectively mounted to fluid tanks  1020   a ,  1020   b . One or both of feed pumps  1012  can be substantially similar to pump apparatus  12  (best seen in  FIGS.  2 A- 2 D ). Feed lines  1024   a ,  1024   b  respectively extend from feed pumps  1012   a ,  1012   b  to proportioner pumps  1022   a ,  1022   b . Feed line  1024   a  fluidically connects an outlet of feed pump  1012   a  to an inlet of proportioner pump  1022   a , and feed line  1024   b  fluidically connects an outlet of feed pump  1012   b  to an inlet of proportioner pump  1022   b . Feed pumps  1012   a ,  1012   b  draw the first and second component materials from fluid tanks  1020   a ,  1020   b  and pump the component materials through feed lines  1024   a ,  1024   b  to proportioner pumps  1022   a ,  1022   b . In some examples, feed pumps  1012   a ,  1012   b  can be referred to as drum pumps. Feed pumps  1012   a ,  1012   b  provide the component materials to proportioner pumps  1022   a ,  1022   b  under pressure. In some examples, feed pumps  1012   a ,  1012   b  are configured to pump the component materials to proportioner pumps  1022   a ,  1022   b  at pressures of at least about 0.35 Megapascal (MPa) (about 50 pounds per square inch (psi)). In some examples, feed pumps  1012   a ,  1012   b  are configured to pump the component materials at pressures of up to about 1.75 MPa (about 250 psi). 
     Feed pumps  1012   a ,  1012   b  provide the component materials to proportioner pumps  1022   a ,  1022   b  under pressure to fully fill proportioner pumps  1022   a ,  1022   b  during pumping. Fully filling proportioner pumps  1022   a ,  1022   b  prevents proportioner pumps  1022   a ,  1022   b  from starving and maintains the desired balance between the first and second component materials being pumped to applicator  1034 . Feeding proportioner pumps  1022   a ,  1022   b  under pressure prevents the component materials from being pumped downstream at a ratio other than the target ratio due to insufficient fill of proportioner pumps  1022   a ,  1022   b . As discussed further herein with particular reference to  FIGS.  11 - 12 B , each of feed pumps  1012   a ,  1012   b  comprises an electric motor to drive feed pumps  1012   a ,  1012   b.    
     Proportioner  1016  supports various components of system  1010 . In some examples, controller  1029  is supported by proportioner  1016 . It is understood that controller  1029  can be formed by more than one discrete component operatively connected together, such as electrically and/or communicatively. Proportioner  1016  can further support proportioner pumps  1022   a ,  1022   b  and motor  1014 . Primary heaters  1045   a ,  1045   b  can be disposed in and supported by proportioner  1016 . 
     Proportioner pumps  1022   a ,  1022   b  receive the first and second component materials from feed pumps  1012   a ,  1012   b  and pump the component materials downstream to applicator  1034 . Proportioner pumps  1022   a ,  1022   b  increase the pressure of the first and second component materials from the feed pressure to a spray pressure. The spray pressure is greater than the feed pressure generated by feed pumps  1012   a ,  1012   b . In some examples, proportioner pumps  1022   a ,  1022   b  can pump the component materials at pressures between about 3.45 MPa (about 500 psi) and about 35.5 MPa (about 5000 psi). In some examples, proportioner pumps  1022   a ,  1022   b  can pump the component materials at pressures between about 6.9 MPa (about 1000 psi) and about 25.6 MPa (about 4000 psi). In some examples, proportioner pumps  1022   a ,  1026   b  are configured to pump at pressures between about 11.7 MPa (1700 psi) and about 24.1 MPa (about 3500 psi). While proportioner pumps  1022   a ,  1022   b  are described as generating the spray pressures, it is understood that feed pumps  1012   a ,  1012   b  can, in some examples, generate sufficient spray pressure, such as in applications other than plural component spray systems. In some examples, a feed pump  1012  can be utilized in a transfer system to transfer material to a downstream location. In some examples, a feed pump  1012  can be utilized in a spray system similar to spray system  10  ( FIGS.  1 A and  1 B ). 
     Flush valves  1033   a ,  1033   b  are disposed downstream of proportioner pumps  1022   a ,  1022   b  and are configured to control flow from proportioner pumps  1022   a ,  1022   b . In some examples, flush valves  1033   a ,  1033   b  are disposed at the outlets of proportioner pumps  1022   a ,  1022   b . Flush valves  1033   a ,  1033   b  are fluidly connected to flush lines  1035   a ,  1035   b , which provide return paths for fluid to return to fluid tanks  1020   a ,  1020   b . While flush lines  1035   a ,  1035   b  are shown as fluidly connected to fluid tanks  1020   a ,  1020   b , it is understood that flush lines  1035   a ,  1035   b  can be connected to any external vessel to flush fluid and air before operation. In some examples, flush valves  1033   a ,  1033   b  can be fluidly connected to each of flush lines  1035   a ,  1035   b  and supply lines  1028   a ,  1028   b  to control flow to one or both of flush lines  1035   a ,  1035   b  and supply lines  1028   a ,  1028   b.    
     Motor  1014  can be mechanically connected to both proportioner pump  1022   a  and proportioner pump  1022   b . Motor  1014  can be a pneumatic, hydraulic, or electric motor. Motor  1014  is connected to proportioner pumps  1022   a ,  1022   b  such that motor  1014  simultaneously causes displacement of the fluid displacement members of each of proportioner pumps  1022   a ,  1022   b . Proportioner pumps  1022   a ,  1022   b  are linked to motor  1014  for simultaneous displacement of the fluid displacement members of proportioner pumps  1022   a ,  1022   b . In some examples, proportioner pumps  1022   a ,  1022   b  are fixed to a displacement component of motor  1014  such that the fluid displacement members proportioner pumps  1022   a ,  1022   b  are linked together for simultaneous displacement. In some examples, the fluid displacement members of proportioner pumps  1022   a ,  1022   b  are fixed together such that each fluid displacement member displaces the same distance for each stroke. 
     Primary heaters  1045   a ,  1045   b  are disposed downstream from proportioner pumps  1022   a ,  1022   b  respectively, and receive the component materials from proportioner pumps  1022   a ,  1022   b . Primary heaters  1045   a ,  1045   b  include heating elements configured to raise a temperature of the first and second component materials to an operating temperature above the ambient temperature during spraying. In some examples, primary heaters  1045   a ,  1045   b  are configured to heat the component materials to temperatures between about 37 degrees C. (about 100 degrees F.) and 82 degrees C. (about 180 degrees F.). 
     Supply lines  1028   a ,  1028   b  respectively extend from proportioner pumps  1022   a ,  1022   b  to applicator  1034 . Supply line  1028   a  fluidically connects an outlet of proportioner pump  1022   a  to applicator  1034 , and supply line  1028   b  fluidically connects an outlet of proportioner pump  1022   b  to applicator  1034 . Heated portion  1046  of supply lines  1028   a ,  1028   b  includes heating elements configured to maintain the temperature of the component materials above ambient as the component materials travel through supply lines  1028   a ,  1028   b . Heated portion  1046  can form up to the full length of supply lines  1028   a ,  1028   b . Supply lines  1028   a ,  1028   b  can also be referred to as a heated hose. In some examples, heated portion  1046  can operate at temperatures up to about 82 degrees C. (about 180 degrees F.). Maintaining the first and second component materials at elevated temperatures facilitates proper mixing and the formation of desired material characteristics in the spray material. Heat controller  1047  can communicate with primary heaters  1045   a ,  1045   b  and/or heated portion  1046  of supply lines  1028   a ,  1028   b . Heat controller  1047  can provide an interface for an operator to view the temperature of the component materials while at the position of the applicator and to input commands to adjust the heating of the component materials by primary heaters  1045   a ,  1045   b  and/or heated portion  1046 . Heat controller  1047  can form a portion of controller  1029 . 
     Applicator  1034  receives the first and second component materials from outlets of supply lines  1028   a ,  1028   b . The first and second component materials are mixed in mixer  1040 , which is connected to and, in some examples, disposed within applicator  1034 . The component materials mix within a chamber in mixer  1040  to form the plural component spray material. Mixer  1040  is the first location within system  1010  where the first and second component materials mix. The first and second component materials are isolated from each other at all locations upstream of mixer  1040 . The spray material is ejected through a spray orifice of applicator  1034  and applied to the substrate. For example, the user can grasp handle  1042  and actuate trigger  1044  to cause spraying by applicator  1034 . 
     Upstream sensors  1030   a ,  1030   b  are disposed upstream of proportioner pumps  1022   a ,  1022   b  respectively. Upstream sensors  1030   a ,  1030   b  are disposed downstream of feed pumps  12   a ,  12   b . Upstream sensors  1030   a ,  1030   b  are disposed fluidically between feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b . Upstream sensors  1030   a ,  1030   b  can be disposed proximate the inlets of proportioner pumps  1022   a ,  1022   b . Upstream sensors  1030   a ,  1030   b  are parameter sensors configured to generate data regarding parameters of the component materials feeding proportioner pumps  1022   a ,  1022   b . The data generated by upstream sensors  1030   a ,  1030   b  indicates the parameters of the fluids after exiting feed pumps  1012   a ,  1012   b  and prior to entering proportioner pumps  1022   a ,  1022   b . For example, upstream sensors  1030   a ,  1030   b  can include any one or more of pressure sensors, flow rate sensors, and temperature sensors, among other options. Upstream sensors  1030   a ,  1030   b  are configured to provide the upstream parameter data to controller  1029 . 
     Downstream sensors  1032   a ,  1032   b  are disposed downstream of proportioner pumps  1022   a ,  1022   b  respectively. Downstream sensors  1032   a ,  1032   b  are disposed fluidically between proportioner pumps  1022   a ,  1022   b  and applicator  1034 . Downstream sensors  1032   a ,  1032   b  can be disposed proximate the outlets of proportioner pumps  1022   a ,  1022   b . Downstream sensors  1032   a ,  1032   b  are parameter sensors configured to generate data regarding parameters of the component materials at a location downstream of proportioner pumps  1022   a ,  1022   b . The fluid sensed by downstream sensors  1032   a ,  1032   b  flows downstream through supply lines  1028   a ,  1028   b . Downstream sensors  1032   a ,  1032   b  can include any one or more of pressure sensors, flow rate sensors, and temperature sensors, among other options. In some examples, pressure and flow rate sensors of downstream sensors  1032   a ,  1032   b  are disposed proximate the outlets of proportioner pumps  1022   a ,  1022   b  and temperature sensors of downstream sensors  1032   a ,  1032   b  are disposed within heated portion  1046 . Downstream sensors  1032   a ,  1032   b  are configured to provide the downstream parameter data to controller  1029 . In some examples, downstream sensors  1032   a ,  1032   b  are disposed downstream of proportioner pumps  1022   a ,  1022   b    
     Controller  1029  is configured to store software, implement functionality, and/or process instructions. Controller  1029  can be substantially similar to controller  29  ( FIGS.  1 A and  1 B ). Controller  1029  is configured to perform any of the functions discussed herein, including receiving an output from any sensor referenced herein, detecting any condition or event referenced herein, and controlling operation of any components referenced herein. Controller  1029  can be of any suitable configuration for controlling operation of the pumps within system  1010 , gathering data, processing data, etc. Controller  1029  can include hardware, firmware, and/or stored software, and controller  1029  can be entirely or partially mounted on one or more boards. Controller  1029  can be of any type suitable for operating in accordance with the techniques described herein. While controller  1029  is illustrated as a single unit, it is understood that controller  1029  can be disposed across one or more boards. In some examples, controller  1029  can be implemented as a plurality of discrete circuitry subassemblies. For example, controller  1029  can be disposed across each of proportioner  1016  and heat controller  1047 . 
     Controller  1029  is operatively connected to the electric motors of feed pumps  1012   a ,  1012   b , either electrically or communicatively, to control pumping by feed pumps  1012   a ,  1012   b . In some examples, controller  1029  can also be operatively connected to motor  1014 , either electrically or communicatively, to control pumping by portioner pumps  1022   a ,  1022   b . Controller  1029  can be connected to motor  1014  and feed pumps  1012   a ,  1012   b  via either wired or wireless connections to provide commands to and cause operation of feed pumps  1012   a ,  1012   b  and motor  1014 . Controller  1029  is operatively connected to upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b , either electrically or communicatively. Controller  29  can be connected to upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b  by either wired or wireless connections. Controller  1029  receives data regarding the sensed parameters for the first component material and the second component material from upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b . Controller  1029  can control operation of any one or more of motor  1014  and feed pumps  1012   a ,  1012   b  based on the data received from one or more of upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b.    
     Memory  1036  is configured to store software that, when executed by control circuitry  1038 , controls operation of feed pumps  12   a ,  12   b . For example, control circuitry  1038  can include one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. Memory  1036 , in some examples, is described as computer-readable storage media. In some examples, a computer-readable storage medium can include a non-transitory medium. The term “non-transitory” can indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). In some examples, memory  1036  is a temporary memory, meaning that a primary purpose of memory  1036  is not long-term storage. Memory  1036 , in some examples, is described as volatile memory, meaning that memory  1036  does not maintain stored contents when power to controller  1029  is turned off. Examples of volatile memories can include random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), and other forms of volatile memories. Memory  1036 , in one example, is used by software or applications running on control circuitry  1038  to temporarily store information during program execution. Memory  1036 , in some examples, also includes one or more computer-readable storage media. Memory  1036  can further be configured for long-term storage of information. Memory  1036  can be configured to store larger amounts of information than volatile memory. In some examples, memory  1036  includes non-volatile storage elements. Examples of such non-volatile storage elements can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. 
     User interface  1018  can be any graphical and/or mechanical interface that enables user interaction with controller  1029 . For example, user interface  1018  can implement a graphical user interface displayed at a display device of user interface  1018  for presenting information to and/or receiving input from a user. User interface  1018  can include graphical navigation and control elements, such as graphical buttons or other graphical control elements presented at the display device. User interface  1018 , in some examples, includes physical navigation and control elements, such as physically actuated buttons or other physical navigation and control elements. In general, user interface  1018  can include any input and/or output devices and control elements that can enable user interaction with controller  1029 . 
     During operation, the first and second component materials are pumped to applicator  1034  from fluid tanks  1020   a ,  1020   b  by feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b , and are mixed at applicator  1034  to form the plural component spray material. Flows of the first component material and the second component material to the applicator  1034  are controlled based on one or more target operating parameters, such as fluid ratio, pressure, and temperature. 
     Controller  1029  controls operation of feed pumps  1012   a ,  1012   b  based on at least one of the target operating parameters. The electric current to the electric motors of feed pumps  1012   a ,  1012   b  controls the pressure output by feed pumps  1012   a ,  1012   b . It is understood that a reference to the term “current” can be replaced with a different measure of power such as voltage or the term “power” itself. Controller  1029  can also control operation of motor  1014  based on at least one of the target operating parameters. Controlling the flow based on the target operating parameters generates a spray material having desired material properties, such as porosity, expansion rate, expansion volume, thermal resistivity, etc. Spraying according to the target operating parameters further provides an even spray pattern, fine droplet size, adequate flow, and good mixing. Spraying according to the target operating parameters further prevents excessive overspray, undesirably high flow rates, difficult control, and excessive wear. 
     Controller  1029  controls electric current flow to the electric motors of feed pumps  1012   a ,  1012   b  to pump the component materials to proportioner pumps  1022   a ,  1022   b  according to target feed parameters. Controller  1029  can be configured to operate feed pumps  1012   a ,  1012   b  at or below a maximum operating parameter and/or current level. Controller  1029  can control the current provided to the electric motors of feed pumps  1012   a ,  1012   b  based on parameter data received from one or more of upstream sensors  1030   a ,  1030   b  and/or downstream sensors  1032   a ,  1032   b.    
     Controller  1029  can control operation of motor  1014  to cause proportioner pumps  1022   a ,  1022   b  to pump the component materials according to target spray parameters. For example, controller  1029  can control flows of working fluid or electricity to motor  1014 . Controller  1029  can be configured to operate proportioner pumps  1022   a ,  1022   b  according to the target spray parameter. Controller  1029  can control operation of motor  1014  based on parameter data received from downstream sensors  1032   a ,  1032   b  and/or operation of applicator  1034   
     To apply the spray material, the user manipulates applicator  1034  by grasping handle  1042 . The user depresses trigger  1044  to cause flow through applicator  1034  and mixing within mixer  1040 . The upstream pressures generated by proportioner pumps  1022   a ,  1022   b  drive the component materials through mixer  1040 , causing mixing of the component materials within mixer  1040  to form the spray material. The pressures upstream of applicator  1034  drive the material out through the orifice of applicator  1034  to cause spraying by applicator  1034 . As such, proportioner pumps  1022   a ,  1022   b  drive the component materials through mixer  1040  and generate the spray ejected from applicator  1034 . The pressures and flow rates generated by proportioner pumps  1022   a ,  1022   b  affect flow to and through mixer  1040 . 
     Feed pump  1012   a  draws the first component material from fluid tank  1020   a  and pumps the first component material through feed line  1024   a  to proportioner pump  1026   a . Upstream sensor  1030   a  generates data regarding one or more operating parameters of the first component material and provides that data to controller  1029 . Feed pump  1012   b  draws the second component material from fluid tank  1020   b  and pumps the second component material through feed line  1024   b  to proportioner pump  1026   b . Upstream sensor  1030   b  generates data regarding one or more operating parameters of the second component material and provides that data to controller  1029 . 
     Motor  1014  drives linear displacement of the fluid displacement members of proportioner pumps  1022   a ,  1022   b . Motor  1014  can simultaneously drive proportioner pumps  1022   a ,  1022   b , causing proportioner pumps  1022   a ,  1022   b  to simultaneously pump the first and second component materials downstream to applicator  1034 . While proportioner pumps  1022   a ,  1022   b  are described as connected to a common motor  1014 , it is understood that proportioner pumps  1022   a ,  1022   b  can, in some examples, be individually powered. Proportioner pumps  1022   a ,  1022   b  can be double displacement pumps, such that proportioner pumps  1022   a ,  1022   b  output fluid during both strokes of a pump cycle. While proportioner pumps  1022   a ,  1022   b  output fluid during both strokes of the pump cycle, proportioner pumps  1022   a ,  1022   b  receive fluid from feed pumps  1012   a ,  1012   b  during only one stroke of the pump cycle, which stroke can be referred to as a fill stroke. Controller  1029  can control motor  1014  to control pumping by proportioner pumps  1022   a ,  1022   b  and control the downstream parameters of the flows generated by proportioner pumps  1022   a ,  1022   b . Downstream sensors  1032   a ,  1032   b  generate parameter data regarding the individual component material in supply lines  1028   a ,  1028   b , respectively. Controller  1029  can adjust the current provided to the electric motors of feed pumps  1012   a ,  1012   b  based on the parameter data received from one or both of downstream sensors  1032   a ,  1032   b  and one or both of upstream sensors  1030   a ,  1030   b  to maintain a desired parameter ratio across proportioner pumps  1022   a ,  1022   b  and to ultimately maintain the supply parameters at the target supply parameters. 
     The component materials are pumped downstream through supply lines  1028   a ,  1028   b  disposed between proportioner pumps  1022   a ,  1022   b  and applicator  1034 . Primary heaters  1045   a ,  1045   b  increase the temperature of the component materials after the component materials exit proportioner pumps  1022   a ,  1022   b  and prior to entering supply lines  1028   a ,  1028   b  to temperatures above ambient. Heated portion  1046  of supply lines  1028   a ,  1028   b  maintains the temperature of the materials flowing through supply lines  1028   a ,  1028   b  above ambient. Heating the component materials reduces the viscosity of the component materials and enhances mixing to cause the formation of desired characteristics in the spray material. The first and second component materials combine within mixer  1040  of applicator  1034  to form the spray material that is sprayed from applicator  1034  onto the substrate. 
     The user can depress and release trigger  1044  multiple times during any spray job. The user releasing trigger  1044  deadheads proportioner pumps  1022   a ,  1022   b , meaning that the flowpaths through supply lines  1028   a ,  1028   b  are closed and material is not flowing downstream from proportioner pumps  1022   a ,  1022   b . Controller  1029  is configured to control current flow to the electric motors of feed pumps  1012   a ,  1012   b  and current flow to motor  1014  both when proportioner pumps  1022   a ,  1022   b  are actively pumping and when proportioner pumps  1022   a ,  1022   b  are stalled. 
     In a stalled state, feed pumps  1012   a ,  1012   b  are prevented from pumping due to downstream pressure extending the target operating pressure. With feed pumps  1012   a ,  1012   b  in stalled states, controller  1029  can maintain, reduce, or stop the current to the electric motors of feed pumps  1012   a ,  1012   b . System  1010  can include multiple check valves (not shown) to maintain the feed pressure within feed lines  1024   a ,  1024   b  and the downstream pressure in supply lines  1028   a ,  1028   b  when feed pumps  1012   a ,  1012   b  and/or proportioner pumps  1022   a ,  1022   b  are stalled. Feed pumps  1012   a ,  1012   b  resume pumping once the downstream pressure falls below the pumping pressure, such as when the user actuates trigger  1044  and resumes spraying. Continuing to apply power to feed pumps  1012   a ,  1012   b  during a stall provides quick reaction when the user resumes spraying, as proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  can resume pumping as soon as the downstream pressure drops, increasing spray efficiency and avoiding undesired pressure loss. In some examples, controller  1029  can reduce or stop current flow to feed pumps  1012   a ,  1012   b  while in the stalled state, to conserve energy and reduce heat generation. Controller  1029  can increase the current to cause feed pumps  1012   a ,  1012   b  to resume pumping at the target operating current based on any one of upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b  indicating a drop in the pressure downstream of feed pumps  1012   a ,  1012   b.    
     During pumping and spraying, controller  1029  can control operation of feed pumps  1012   a ,  1012   b  to maintain the component materials at desired fluid parameters in supply lines  1028   a ,  1028   b . Controller  1029  can control operation of feed pumps  1012   a ,  1012   b  by adjusting the speeds of the electric motors of feed pumps  1012   a ,  1012   b . Controller  1029  can independently control each feed pump  1012   a ,  1012   b . For example, downstream sensors  1032   a ,  1032   b  can indicate that the sensed downstream parameters in supply lines  1028   a ,  1028   b  are imbalanced. In an example where the desired output of component materials is at a 1:1 ratio, controller  1029  can monitor the sensed downstream parameters to ensure that the materials are provided according to that ratio. If controller  1029  detects that the parameter, such as pressure, in supply line  1028   a  differs from the parameter in supply line  1028   b , then controller  29  can control operation of feed pumps  1012   a ,  1012   b  to correct the imbalance, as discussed in more detail below. Controller  1029  can control operation of each feed pump  1012   a ,  1012   b  based on data received from one or more of upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b . Controller  1029  can individually control operation of each feed pump  1012   a ,  1012   b  based on the data received. Controller  1029  controls operation of feed pumps  1012   a ,  1012   b  to ensure that proportioner pumps  1022   a ,  1022   b  fully fill during the fill stroke of each proportioner pump  1022   a ,  1022   b . Ensuring that proportioner pumps  1022   a ,  1022   b  fully fill prevents proportioner pumps  1022   a ,  1022   b  from starving and maintains the material ratio at applicator  1034 , thereby generating a material spray having desired material characteristics. Factors such as ambient temperature, clogging, leakage, seal failure, etc. can affect material flows. For example, cooler ambient temperatures increase the viscosity of the component materials. One material may be more viscous than the other such that the feed pump  1012   a ,  1012   b  associated with the more viscous material requires more power to achieve similar flows. Controller  1029  discretely controlling operation of each feed pump  1012   a ,  1012   b  facilitates fine control when such factors affect the flow. Controller  1029  individually controls each feed pump  1012   a ,  1012   b  to address any flow issues that may arise regarding the flow of the component material associated with that feed pump  1012   a ,  1012   b . As such, controller  1029  provides discrete A-side control (for the component material from fluid tank  1020   a ) and B-side control (for the component material from fluid tank  1020   b ). 
     An example ratio of 1:1 between the first and second component materials is discussed by way of example. It is understood that system  1010  and pumps  1012   a ,  1012   b ,  1022   a ,  1022   b  can be configured to provide materials at any desired ratio. Controller  1029  can further controls operation of each feed pump  1012   a ,  1012   b  based on data generated downstream of a pump other than the feed pump  1012   a ,  1012   b . Specifically, can controller  1029  controls operation of each feed pump  1012   a ,  1012   b  based on data regarding flows downstream of and generated by proportioner pumps  1022   a ,  1022   b.    
     In one example, if downstream sensors  1032   a ,  1032   b  communicate to controller  1029  that the downstream pressures in supply lines  1028   a ,  1028   b  are out of ratio, such that the flow is imbalanced, controller  1029  can determine that additional flow is required to one of proportioner pumps  1022   a ,  1022   b  to correct the imbalance. For example, downstream sensors  1032   a  can indicate an unexpected pressure drop or rise, or a comparison between the data from downstream sensors  1032   a ,  1032   b  can indicate that the pressure in supply line  1028   a  is lower than the supply line  1028   b . Such a pressure variation can indicate that proportioner pump  1026   a  is not fully filling on the fill stroke (i.e., proportioner pump  1026   a  is being starved). In response, controller  1029  can increase power to the electric motor of feed pump  1012   a  to increase the pumping speed and/or pressure output of feed pump  1012   a . Increasing power to feed pump  1012   a  will increase the flow through and feed pressure in feed line  1024   a  and provide an increased volume of the component material to proportioner pump  1026   a  to ensure that proportioner pump  1026   a  fully fills on the fill stroke. Proportioner pump  1026   a  can thereby generate increased flow and downstream pressure in supply line  1028   a . Controller  1029  can thus control operation of an individual feed pump  1012   a  based on the data from downstream sensor  1032   a  or both downstream sensors  1032   a ,  1032   b , even though only one of those sensors (downstream sensor  1032   a ) is in-line with feed pump  1012   a.    
     Similarly, controller  1029  can increase power to feed pump  1012   b  based on any one of downstream sensor  1032   b  indicating a spike or drop in the downstream pressure of the component material in supply line  1028   b  or the comparison between the data from downstream sensors  1032   a ,  1032   b  indicating that the pressure in supply line  1028   b  is lower than the supply line  1028   a . Increasing power to feed pump  1012   b  increases flow and pressure generated by feed pump  1012   b , thereby providing additional material to proportioner pump  1026   b . Controller  1029  can ramp the power increase such that controller  1029  continues to increase power to feed pump  1012   b  until the parameter variation is smoothed and/or the parameter imbalance is alleviated. In some examples, controller  1029  can decrease power to feed pump  1012   a  to decrease pressure in supply line  1028   a  and alleviate the parameter imbalance. 
     In another example, if downstream sensor  1032   a  measures a downstream pressure in supply line  1028   a  that matches a downstream pressure in supply line  1028   b , however, downstream sensor  1032   a  measures a flow in supply line  1028   a  that is lower than a flow in supply line  1028   b , controller  1029  can determine that feed pump  1012   a  is not supplying enough of the component material to proportioner pump  26   a  based on the flow imbalance. In response, controller  1029  can increase the power to the electric motor of feed pump  1012   a  to increase the flow and the feed pressure of the component material to proportioner pump  1026   a , and ultimately increase the flow of the component material in supply line  1028   a . Alternatively, controller  1029  can determine supply line  1028   a  contains a blockage that is decreasing the flow in supply line  1028   a . For example, upstream sensor  1030   a  can indicate expected pressures and low/no flow. In response to detecting an error, controller  1029  can shut down proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  and/or send an alert to the user, such as via user interface  1018 , communicating the existence of the blockage to the user. 
     In some examples, controller  1029  can detect an error based on data from downstream sensors  1032   a ,  1032   b  indicating a drop in the downstream pressure while upstream sensors  1030   a ,  1030   b  indicate an increase in feed pressure. In response to detecting the malfunction, controller  1029  can stop operation of each of proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  to prevent damage to system  1010  and to reduce waste of the component materials. Controller  1029  can send a prompt to user interface  1018  to communicate the malfunction to the user. For example, the prompt can be audio, visual, or a combination of audio and visual, among other options. 
     Controller  1029  can further control operation of feed pumps  1012   a ,  1012   b  based on data generated by upstream sensors  1030   a ,  1030   b . Controller  1029  can control operation of feed pumps  1012   a ,  1012   b  based on the upstream parameter data or a combination of the upstream parameter data and the downstream parameter data generated by downstream sensors  1032   a ,  1032   b . For example, upstream sensor  1030   a  can indicate a change in flow and/or pressure and controller  1029  can increase or decrease power to feed pump  1012   a  based on that indication. 
     Controller  1029  can further control operation of each feed pump  1012   a ,  1012   b  based on the operating state of each proportioner pump  1022   a ,  1022   b . Controller  1029  can control operation of feed pumps  1012   a ,  1012   b  such that feed pumps  1012   a ,  1012   b  changeover (change stroke direction) in coordination with the strokes of proportioner pumps  1022   a ,  1022   b . As such, the changeover point of each feed pump  1012   a ,  1012   b , which is the point where the piston of the feed pumps  1012   a ,  1012   b  changes between a first stroke direction (in one of the first axial direction AD 1  and the second axial direction AD 2 ) and a second stroke direction (in the other one of the first axial direction AD 1  and the second axial direction AD 2 ), is dynamic in that the changeover point and the stroke length can each vary. Unlike fluid-powered motors, such as pneumatic motors, that have a set changeover point such as when a shuttle valve is actuated to direct compressed air to an opposite side of the motor, the electric motors of feed pumps  1012   a ,  1012   b  can be controlled to have a dynamic changeover point. Fluid-powered motors require a full stroke in one direction prior to actuating the shuttle valve, such that changeover points are fixed. 
     Controller  1029  controls operation of feed pumps  1012   a ,  1012   b  to coordinate the changeover of feed pumps  1012   a ,  1012   b  with the fill strokes of proportioner pumps  1022   a ,  1022   b . Feed pumps  1012   a ,  1012   b  are controlled such that feed pumps  1012   a ,  1012   b  do not changeover during the fill stroke of proportioner pumps  1022   a ,  1022   b  or changeover during a predetermined portion of the fill stroke. 
     When proportioner pumps  1022   a ,  1022   b  are undergoing a fill stroke (i.e., when component materials enter proportioner pumps  1022   a ,  1022   b  from feed lines  1024   a ,  1024   b ), feed pumps  1012   a ,  1012   b  are undergoing a stroke to supply component material to proportioner pumps  1022   a ,  1022   b  under pressure. In some examples, proportioner pumps  1022   a ,  1022   b  are arranged out-of-phase, such that only one of proportioner pumps  1022   a ,  1022   b  is proceeding through a fill stroke while the other is proceeding through a return stroke. As such, controller  29  can control each feed pump  1012   a ,  1012   b  such that the feed pump  1012   a ,  1012   b  associated with the proportioner pump  1022   a ,  1022   b  proceeding through the fill stroke drives fluid while the other feed pump  1012   a ,  1012   b  is stalled or inactive. It is understood that controller  1029  can continue to provide power to the feed pump  1012   a ,  1012   b  associated with the proportioner pump  1022   a ,  1022   b  proceeding through the return stroke, but that feed pump  1012   a ,  1012   b  is stalled as the pressures generated by proportioner pumps  1022   a ,  1022   b  are greater than the pressures generated by feed pumps  1012   a ,  1012   b . In some examples, proportioner pumps  1022   a ,  1022   b  operated in-phase such that each proportioner pump  1022   a ,  1022   b  proceeds through concurrent fill strokes and return strokes. Controller  1029  can thus control feed pumps  1012   a ,  1012   b  such that each feed pump  1012   a ,  1012   b  concurrently pumps fluid to fill proportioner pumps  1022   a ,  1022   b.    
     Feed pumps  1012   a ,  1012   b  are configured such that each stroke (both up and down) of feed pumps  1012   a ,  1012   b  supplies component material to proportioner pumps  1022   a ,  1022   b . Feed pumps  1012   a ,  1012   b  are thus double displacement pumps. Feed pumps  1012   a ,  1012   b  can be sized such that each stroke of a feed pump  1012   a ,  1012   b  has sufficient displacement so that a single stroke of the feed pump  1012   a ,  1012   b  fully fills the proportioner pump  1022   a ,  1022   b  associated with the feed pump  1012   a ,  1012   b . In some examples, feed pumps  1012   a ,  1012   b  are oversized by a buffer volume such that the feed pump displacement for a full stroke is at least 40% larger than the fill volume of the proportioner pump  1022   a ,  1022   b . In some examples, feed pumps  1012   a ,  1012   b  are sized such that the feed pump displacement for a full stroke is at least one of 10%, 20%, or 30% larger than the fill volume of the proportioner pump  1022   a ,  1022   b . In some examples, feed pumps  1012   a ,  1012   b  are sized such that the feed pump displacement for a full stroke is up to 40% larger than the fill volume of the proportioner pump  1022   a ,  1022   b . Sizing the feed pumps  1012   a ,  1012   b  to have a buffer volume such that the displacement is larger than the fill volume of proportioner pumps  1022   a ,  1022   b  ensures sufficient room for feed pump  1012   a ,  1012   b  to complete a full stroke in one direction while avoiding changeover. Feed pumps  1012   a ,  1012   b  can be configured such that the piston floats between buffer zones on either end of each stroke. As such, feed pumps  1012   a ,  1012   b  have a buffer for both a stroke in first axial direction AD 1  and second axial direction AD 2 . 
     Feed pumps  1012   a ,  1012   b  provide fluid to proportioner pumps  1022   a ,  1022   b  during each stroke of the pump cycle and are controlled such that feed pumps  1012   a ,  1012   b  do not changeover from one stroke to another while proportioner pumps  1022   a ,  1022   b  are filling. Changeover occurs for feed pumps  1012   a ,  1012   b  between fill strokes of proportioner pumps  1022   a ,  1022   b . An example of a pump cycle for feed pumps  1012   a ,  1012   b  is discussed in more detail. Initially, proportioner pump  1022   a  proceeds through a fill stroke and proportioner pump  1022   b  proceeds through a return stroke. Feed pump  1012   a  is powered through a first stroke in one of the first axial direction AD 1  and second axial direction AD 2  and feed pump  1012   b  does not pump (e.g., stalls or is depowered). Feed pump  1012   a  continues through the first stroke until proportioner pump  1026   a  completes the fill stroke. Proportioner pumps  1022   a ,  1022   b  reverse direction, feed pump  1012   b  begins to pump fluid to proportioner pump  1022   b  and feed pump  1012   a  stops pumping. Feed pump  1012   b  is powered through a first stroke in one of the first axial direction AD 1  and second axial direction AD 2 . Feed pump  1012   b  continues through the first stroke until proportioner pump  1022   b  completes the fill stroke. 
     After proportioner pumps  1022   a ,  1022   b  complete the first pump cycle, proportioner pumps  1022   a ,  1022   b  proceed through a second pump cycle. Proportioner pump  1022   a  proceeds through a fill stroke and proportioner pumps  1022   b  proceeds through a return stroke. Feed pump  1012   a  is powered through a second stroke in an opposite axial direction from the first stroke of feed pump  1012   a  and feed pump  1012   b  stops pumping. Feed pump  1012   a  has thereby changed stroke direction outside of the fill stroke of proportioner pump  1022   a . Feed pump  1012   a  continues through the second stroke until proportioner pump  1022   a  completes the fill stroke. Proportioner pumps  1022   a ,  1022   b  reverse direction, feed pump  1012   b  begins to pump fluid to proportioner pump  1022   b , and feed pump  1012   a  stops pumping. Feed pump  1012   b  is powered through a second stroke in an opposite axial direction from the first stroke of feed pump  1012   b . Feed pump  1012   b  continues through the second stroke until proportioner pump  1022   b  completes the fill stroke. Feed pump  1012   b  has thereby changed stroke direction outside of the fill stroke of proportioner pump  1022   b.    
     Each feed pump  1012   a ,  1012   b  completes half of a feed pump cycle (e.g., a single stroke) for the first pump cycle of proportioner pumps  1022   a ,  1022   b . Each feed pump  1012   a ,  1012   b  completes a full feed pump cycle (e.g., two opposite strokes) for two pump cycles of proportioner pumps  1022   a ,  1022   b . Feed pumps  1012   a ,  1012   b  fully fill proportioner pumps  1022   a ,  1022   b  twice for each feed pump cycle completed. In the example discussed, feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b  have a feed pump cycle to proportioner pump cycle ratio of 1:2. In some examples, feed pumps  1012   a ,  1012   b  can be sized such that a single feed stroke can fully fill more than one fill stroke of the proportioner pump  1022   a ,  1022   b . As such, feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b  can have any desired feed pump cycle to proportioner pump cycle ratio. For example, feed pump  1012   a ,  1012   b  can be sized such that a single stroke provides sufficient fluid for two fill cycles of proportioner pump  1022   a ,  1022   b , providing a 1:4 ratio of feed pump cycles to proportioner pump cycles. 
     In some examples, each feed pump  1012   a ,  1012   b  completes two strokes with a single changeover for every two proportioner pump cycles. In some examples, each feed pump  1012   a ,  1012   b  completes a single stroke without changing over for a single proportioner pump fill stroke. In some examples, controller  1029  causes feed pumps  1012   a ,  1012   b  to reverse stroke direction between each proportioner pump cycle. In some examples, the first feed stroke of a feed pump  1012   a ,  1012   b  is the only stroke that pumps fluid during a first fill stroke of proportioner pump  1022   a ,  1022   b  and the second feed stroke of feed pump  1012   a ,  1012   b  is the only stroke that pumps fluid during a second, immediately subsequent fill stroke of proportioner pump  1022   a ,  1022   b . As such, no two immediately subsequent fill strokes of the proportioner pump  1022   a ,  1022   b  is filled by strokes of its associated feed pump  1012   a ,  1012   b  in the same axial direction. 
     Reducing power to feed pumps  1012   a ,  1012   b  between fill strokes of proportioner pumps  1022   a ,  1022   b  reduces pressure on the feed lines  1024   a ,  1024   b  and the inlets of proportioner pumps  1022   a ,  1022   b  between fill strokes of proportioner pumps  1022   a ,  1022   b . Furthermore, timing the changeover of strokes for feed pumps  1012   a ,  1012   b  to correspond with the changeover of proportioner pumps  1022   a ,  1022   b  ensures that proportioner pumps  1022   a ,  1022   b  are receiving a consistent supply of component material at a smooth and steady pressure. Preventing changeover of feed pumps  1012   a ,  1012   b  during the fill stroke prevents undesired pressure spikes from occurring that can inhibit filling of proportioner pumps  1022   a ,  1022   b  and cause inaccurate readings from upstream sensors  1030   a ,  1030   b  and downstream sensors  1032   a ,  1032   b.    
     In some examples, feed pumps  1012   a ,  1012   b  are sized such that a full fill stroke requires feed pumps  1012   a ,  1012   b  to changeover during the fill stroke. In such an example, controller  1029  controls operation of feed pumps  1012   a ,  1012   b  to cause the changeover to occur during a predetermined portion of the feed pump stroke. For example, controller  1029  can determine the relative location of the feed pump piston prior to initiating the feed stroke and can drive the piston of feed pump  1012   a ,  1012   b  in one of the two axial directions AD 1 , AD 2  based on the predetermined portion and the relative location. For example, the predetermined portion can be the first 50% of a fill stroke. Controller  1029  will initially cause the piston to displace in the axial direction that will cause the changeover to occur within the predetermined portion of the stroke. 
     For example, assuming a maximum stroke length of feed pump  1012   a ,  1012   b  is 5.08 centimeters (cm) (2 inches (in.)), the stroke required to fill proportioner pump  1022   a ,  1022   b  is 1.8 inches, and the piston traveled 1.6 inches through a stroke in the second axial direction AD 2  on the previous stroke. The piston is thus 0.4 inches from completing the stroke in the second axial direction AD 2  and 1.6 inches from completing the stroke in the first axial direction AD 1 . Controller  1029  will thus cause the piston to displace in the second axial direction AD 2  to complete a first portion of the fill stroke and then displace in the first axial direction AD 1  to complete the fill stroke to cause the changeover to occur within the predetermined portion of the stroke. In some examples, controller  1029  is configured to minimize the number of changeovers during a fill stroke. For example, if the stroke required to fill proportioner pump  1022   a ,  1022   b  is instead 2.5 inches, then feed pump  1012   a ,  1012   b  must complete two changeovers if the piston first displaces in second axial direction AD 2 . As such, controller  1029  can instead cause the piston to displace in first axial direction AD 1  which will cause a single changeover. That single changeover is also earlier in the fill stroke than the second changeover, providing additional benefits. 
     Controller  1029  can also synchronize feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b  respectively during a flush mode of system  1010 . Feed pumps  1012   a ,  1012   b  can run dry and draw air into feed lines  1024   a ,  1024   b  when fluid tanks  1020   a ,  1020   b  empty and when feed pumps  1012   a ,  1012   b  are attached to a new set of fluid tanks  1020   a ,  1020   b . The air pockets need to be flushed from feed pumps  1012   a ,  1012   b , feed lines  1024   a ,  1024   b , and proportioner pumps  1022   a ,  1022   b  prior to operation. The user can cause system  1010  to enter the flush mode via user interface  1018  and/or controller  1029  can cause system  1010  to automatically enter the flush mode based on the detection of parameters indicating air in the system. During flush mode, controller  1029  causes feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b  to deactivate. Controller  1029  can alert the user that the flush mode has been activated and can prompt the user to actuate flush valves  1033   a ,  1033   b  to dump positions. The dump position can also be referred to as a recirculation position where flush lines  1035   a ,  1035   b  are connected to fluid tanks  1020   a ,  1020   b . The user can provide an input to controller  1029  to indicate that the flush valves  1033   a ,  1033   b  are in the dump positions. In some examples, flush valves  1033   a ,  1033   b  can be activated by controller  1029 . 
     Controller  1029  activates the electric motors of feed pumps  1012   a ,  1012   b  causes feed pumps  1012   a ,  1012   b  to build pressure in supply lines  1028   a ,  1028   b . Proportioner pumps  1022   a ,  1022   b  are activated to generate constant flow. In some examples, controller  1029  activates proportioner pumps  1022   a ,  1022   b  based on upstream sensors  1030   a ,  1030   b  indicating sufficient pressure in feed lines  1024   a ,  1024   b . Feed pumps  1012   a ,  1012   b  and proportioner pumps  1022   a ,  1022   b  actuate at synchronized and periodic stokes to drive air pockets inside system  1010  out of system  1010  via flush valves  1033   a ,  1033   b . Flush lines  1035   a ,  1035   b  are connected to flush valves  1033   a ,  1033   b  and to fluid tanks  1020   a ,  1020   b  respectively. Any component material that exits flush valves  1033   a ,  1033   b  during the flushing of system  1010  can be returned to fluid tanks  1020   a ,  1020   b  via flush lines  1035   a ,  1035   b  to avoid waste of the component materials. Controller  1029  can be configured to control a duration of the flush pumping during the flush mode based on any suitable parameter, such as a count of pump cycles, a time duration, a volume pumped, etc. In one example, controller  1029  can base the duration of the flush mode on a count of pump cycles for any one of proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b . For example, controller  1029  can cause operation in the flush mode for thirty proportioner pump cycles. It is understood, however, that any desired number of proportioner pump or fill pump cycles can be utilized. In some examples, proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  continue to pump after the flush pumping duration is reached. 
     After completing the flush pumping, flush valves  1033   a ,  1033   b  are returned to the spray position, such that feed lines  1024   a ,  1024   b  are fluidly connected to supply lines  1028   a ,  1028   b . For example, controller  29  can alert the user to actuate flush valves  1033   a ,  1033   b  and the user can actuate flush valves  1033   a ,  1033   b . In other examples, controller  1029  can cause feed valves  1033   a ,  1033   b  to return to respective spray positions. With the flush valves  1033   a ,  1033   b  in the respective spray positions and applicator  1034  deactivated, each of proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  stall. With the proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  stalled, each of supply lines  1028   a ,  1028   b  and feed lines  1024   a ,  1024   b  are pressurized. 
     Controller  1029  deactivates proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  based on flush valves  1033   a ,  1033   b  returning to the spray positions. For example, controller  1029  can deactivate proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  based on a user input indicating that the flush valves  1033   a ,  1033   b  are in the spray positions. Controller  1029  can deactivate proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  based on parameter data from downstream sensors  1032   a ,  1032   b  and upstream sensors  1030   a ,  1030   b . Such as where the data indicates pressure and no flow in supply lines  1028   a ,  1028   b  and feed lines  1024   a ,  1024   b.    
     After proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  are deactivated, flush valves  1033   a ,  1033   b  are returned to respective dump positions. Controller  1029  can prompt the user to actuate flush valves  1033   a ,  1033   b  or automatically actuate flush valves  1033   a ,  1033   b . With flush valves again returned to the dump positions, the pressure in feed lines  1024   a ,  1024   b  can drive the fluid through return lines  1035   a ,  1035   b . Flow through return lines  1035   a ,  1035   b  is observed to determine if air is still present in the fluid. Such observation can be audio or visual. For example, spitting of the fluid can indicate that air is still present. Such spitting can be detected audibly by the user or by an audio sensor connected to controller  1029 . In some examples, flush lines  1035   a ,  1035   b  can be formed from a transparent material to facilitate visual inspection of the return flow. The user can visually determine if air is still present or a sensor can be associated with a return lines  1035   a ,  1035   b  to monitor the return lines  1035   a ,  1035   b  for the presence of air pockets. In some examples, a flow meter can be associated with return lines  1035   a ,  1035   b , and controller  1029  can determine if air is present based on data received from the flow meter. For example, fluid flow without air can show a steady flow while the presence of air can cause the flow rate to suddenly change. 
     If air is still present, the flush mode is repeated until all air is purged. In some examples, controller  1029  can automatically restart the purge process based on the detection of air in return lines  1035   a ,  1035   b . Once all air is purged, system  1010  can return to the operating mode to apply the spray material. For example, each of the A-side and B-side can include dedicated dump valve to prevent undesired mixing of the component materials. 
     System  1010  provides significant advantages. Controller  1029  can control the pressure output by proportioner pumps  1022   a ,  1022   b  by controlling operation of feed pumps  1012   a ,  1012   b . The user can control the downstream pressure by simply setting a target spray pressure. Controller  1029  controls operation of the electric motors of feed pumps  1012   a ,  1012   b  based on feedback from downstream sensor  1032   a ,  1032   b  and/or upstream sensors  1030   a ,  1030   b  to achieve the desired downstream pressure in supply lines  1028   a ,  1028   b  and the desired target spray pressure in applicator  1034 . Feed pumps  1012   a ,  1012   b  ensure that proportioner pumps  1022   a ,  1022   b  fully fill on each fill stroke, preventing proportioner pumps  1022   a ,  1022   b  from starving, preventing parameter imbalance, and providing proper mixing such that the spray material has desired material properties. Unlike feed pumps with a hydraulic or pneumatic drive, the user is not required to adjust the pressure at the feed pumps  1012   a ,  1012   b  such as by a series of knobs to set the downstream pressure. Instead, controller  1029  adjusts the current flow to the electric motors of feed pumps  1012   a ,  1012   b  to maintain the desired downstream pressure and spray pressure. Maintaining the desired downstream pressure and the desired spray pressure provides the individual component materials downstream according to the desired ratio. Controller  1029  further controls operation of feed pumps  1012   a ,  1012   b  to prevent changeover during the fill stroke of proportioner pumps  1022   a ,  1022   b , thereby avoiding undesired pressure variations caused by the changeover. Controller  1029  further coordinates operation of proportioner pumps  1022   a ,  1022   b  and feed pumps  1012   a ,  1012   b  to ensure air is purged from system  1010  during the flush mode. 
       FIG.  11    is an isometric view of feed pump  1012  and a fluid tank  1020  with a partial cross-section of fluid tank  1020 . Feed pump  1012  is an example of feed pumps  1012   a ,  1012   b  shown in  FIGS.  10 A and  10 B . Fluid tank  1020  is an example of fluid tanks  1020   a ,  1020   b  shown in  FIGS.  10 A and  10 B . As shown in  FIG.  11   , fluid tank  1020  includes body  1047 , interior  1048 , and top  1050 . Feed pump  1012  includes upper portion  1052  and lower portion  1054 . Upper portion  1052  of feed pump  1012  includes electric motor  1056 , bearing assembly  1058 , clocking assembly  1060 , fluid outlet manifold  1062  with outlet  1063 , mounting collar  1064 , handles  1065 , and tie rods  1066 . Lower portion  1054  of feed pump  1012  includes drive shaft  1068 , displacement assembly  1070 , and tubes  1072 . Axis PA of feed pump  1012  is shown. 
     Feed pump  1012  is configured to draw fluid from fluid tank  1020  and pump the fluid downstream from fluid tank  1020 . Feed pump  1012  can be a two ball piston pump including first and second one-way check valves within displacement assembly  1070 . In some examples, feed pump  1012  can be referred to as a drum pump. Displacement assembly  1070  can be configured to output fluid during each of an upstroke and downstroke of its piston such that feed pump  1012  is a double displacement pump. 
     Upper portion  1052  and lower portion  1054  are disposed coaxially on axis PA. Lower portion  1054  of feed pump  1012  is disposed within interior  48  of fluid tank  1020  and can be inserted into interior  48  through top  50  of fluid tank  1020 . In some examples, fluid tank  1020  contains one of the component materials discussed above in the discussion of  FIGS.  10 A and  10 B . In some examples fluid tank  1020  can be similar to reservoir  20  ( FIGS.  1 A and  1 B ) and can store a supply of a material for spraying without combining with another component, such as paints, coatings, varnishes, etc. Displacement assembly  1070  can be at least partially submerged in the material stored within tank  1020 . Mounting collar  1064  connects feed pump  1012  to top  1050  of fluid tank  1020 . Below mounting collar  1064  (e.g., in axial direction AD 1 ), lower portion  1054  of feed pump  1012  extends axially into fluid tank  1020  along axis PA. Above mounting collar  1064  (e.g., in axial direction AD 2 ), upper portion  1052  of feed pump  1012  extends axially above fluid tank  1020  and away from the interior  1048  of fluid tank  1020  along axis PA. In some examples, mounting collar  1064  can be threaded onto top  1050  of fluid tank  1020  to connect feed pump  1012  to fluid tank  1020 . It is understood, however, that feed pump  1012  can be supported relative to fluid tank  1020  in any desired manner Handles  1065  extend radially outward from mounting collar  1064  relative axis PA. A user can use handles  1065  to grip and turn feed pump  1012  while threading mounting collar  1064  onto top  1050 . 
     Fluid outlet manifold  1062  is disposed axially between electric motor  1056  and displacement assembly  1070  relative to axis PA. Tubes  1072  attach displacement assembly  1070  to fluid outlet manifold  1062  and provide fluid passages that allow displacement assembly  1070  to fluidically communicate with fluid outlet manifold  1062 . Tubes  1072  receive fluid from displacement assembly  1070  and provide the fluid to outlet manifold  1062 . In some examples, tie rods  1066  mechanically attach fluid outlet manifold  1062  directly to a housing of electric motor  1056 . In other examples, tie rods  1066  attach fluid outlet manifold  1062  to a portion of bearing assembly  1058  that is connected to the housing of electric motor  1056 . Bearing assembly  1058  is axially between electric motor  1056  and fluid outlet manifold  1062  and is disposed coaxially on axis PA with electric motor  1056 . 
     Bearing assembly  1058  is disposed axially between electric motor  1056  and fluid tank  1020 . Bearing assembly  1058  is configured to receive axial thrust loads generated during pumping, which loads can also be referred to as pump reaction loads transmit those loads to structural components, such as tie rods  1066 , to isolate electric motor  1056  from those loads. Clocking assembly  1060  is axially between bearing assembly  1058  and fluid outlet manifold  1062  and is disposed coaxially with bearing assembly  1058  on axis PA. Clocking assembly  1060  is axially between electric motor  1056  and top  1050  of fluid tank  1020 . Clocking assembly  1060  is configured to prevent rotation of the linearly displacing components of feed pump  1012  about axis PA. As discussed below with reference to  FIGS.  12 A and  12 B , a drive mechanism connects drive shaft  1068  with a rotor shaft of electric motor  1056 . 
       FIG.  12 A  is a cross-sectional view of upper portion  1052  of feed pump  1012  taken along line  12 - 12  in  FIG.  11   , and  FIG.  12 B  is a cross-sectional view of upper portion  1052  rotated 90-degrees from the view shown in  FIG.  12 A .  FIGS.  12 A and  12 B  will be discussed together. As shown in  FIGS.  12 A and  12 B , electric motor  1056  includes housing  1074  with first end cap  1076 , second end cap  1078 , and side wall  1080 . Electric motor  1056  also includes stator  1082 , rotor  1084 , rotor shaft  1086 , and bearings  1088 . Feed pump  1012  also includes drive mechanism  1026 . Drive mechanism  1026  includes drive nut  1090 , screw  1092 , and rolling elements  1094 . Screw  1092  includes second end  1093  and first end  1091 . Spacer  1097  is disposed about second end  1093  of screw  1092 . Bearing assembly  1058  includes sleeve coupler  1095 , first roller bearing subassembly  1096 , second roller bearing subassembly  1098 , first housing  1099   a , and second housing  1099   b . Clocking assembly  1060  includes clocking housing  1100 , collar  1102 , anti-rotation pin  1104 , and link pin  1106 . Collar  1102 , anti-rotation pin  1104 , and screw  1092  can be considered to form a clocking mechanism. Drive shaft  1068  includes hollow end  1108 . Feed pump  1012  also includes switch pin  1110  and direction control switch  1112 . 
     Electric motor  1056  includes stator  1082  and rotor  1084 . Electric motor  1056  is substantially similar to electric motor  24  ( FIGS.  1 A- 2 D and  5 - 6 B ) except that electric motor  1056  includes an inner rotator where rotor  1084  is disposed within stator  1082 . It is understood, however, that some examples of electric motor  1056  include an outer rotator similar to electric motor  24 . 
     Stator  1082  and rotor  1084  are disposed within housing  1074 . Stator  1082  includes armature windings (not shown) and is fixed to housing  1074  such that stator  1082  does not rotate about axis PA. Rotor  1084  includes permanent magnet array  1087  disposed on and extending circumferentially about rotor body  1085 . Rotor  1084  is configured to rotate about axis PA within housing  1074  in response to a current (such as a direct current (DC) signals and/or alternating current (AC) signals) through stator  1082 . Rotor  1084  is configured to rotate about axis PA in response to the current through stator  1082 . Each of stator  1082  and rotor  1084  are coaxial with axis PA. Rotor  1084  is disposed within stator  1082  such that electric motor  1056  includes an inner rotator. As such, the permanent magnet array  1087  is disposed on the radially outer side of rotor body  1085  relative to axis PA. It is understood, however, that electric motor  1056  could be configured similar to electric motor  24  such that rotor  1084  is disposed around stator  1082  and electric motor  1056  is an outer rotator. In such an example, permanent magnet array  1087  is mounted on a radially inner side of rotor body  1085  relative to axis PA. 
     Electric motor  1056  is a reversible motor in that stator  1082  can cause rotor  1084  to rotate in either of two rotational directions about axis PA (e.g., clockwise and counterclockwise). Rotor  1084  is connected to rotor shaft  1086  such that rotor shaft  1086  rotates with rotor  1084 . Rotor shaft  1086  extends axially on axis PA from first end cap  1076  and through second end cap  1078 . Rotor shaft  1086  is disposed coaxially with rotor  1084  and extends through body  1085  of rotor  1084 . Rotor shaft  1086  is disposed coaxially with drive shaft  1068  on axis PA. Rotor shaft  1086  is disposed coaxially with an axis of reciprocation of the fluid displacement member of feed pump  1012  (e.g., piston  1115 ). Rotor shaft  1086  can have a greater axial length than body  1085  of rotor  1084  along axis PA. Rotor shaft  1086  can be fixed to rotor body  1085  for simultaneous rotation, such as by press-fitting, adhesive, or fasteners, among other options. 
     Side wall  1080  axially spaces first end cap  1076  from second end cap  1078  along axis PA and extends circumferentially around stator  1082 , rotor  1084 , and rotor shaft  1086 . Bearings  1088  interface with and support rotor shaft  1086 . In the example shown, bearings  1088  are supported by housing  1074 . More specifically, bearings  1088  are supported by first end cap  1076  and second end cap  1078  of housing  1074 . Bearings  1088  support rotation of rotor  1084 . In the example shown, bearings  1088  are connected to rotor shaft  1086  and housing  1074  and facilitate relative rotation between the rotating components of electric motor  1056  (rotor  1084  and rotor shaft  1086 ) and the static components of electric motor  1056  (e.g., stator  1082 , housing  1080 , and end caps  1076 ,  1078 ). 
     Rotor shaft  1086  is connected to drive shaft  1068  by drive mechanism  1026  and bearing assembly  1058 . Drive mechanism  1026  is configured to receive the rotational output from motor  1056  via rotor shaft  1086  and to convert that rotational output into a linear input to drive shaft  1068 . As described in greater detail in the discussion of  FIGS.  13 A- 13 C , drive shaft  1068  is connected to a fluid displacement member (e.g., a piston) in displacement assembly  1070  such that drive shaft  1068  drives reciprocation of the fluid displacement member along axis PA due to the linear input from drive mechanism  1026 . Drive shaft  1068  reciprocates axially along axis PA of feed pump  1012  and is coaxial with rotor shaft  1086  and drive mechanism  1026 . The axis of rotation of rotor  1084  and the axis of reciprocation of drive shaft  1068  are coaxial with each other and coaxial with the axis PA. 
     Bearing assembly  1058  connects rotor shaft  1086  to drive mechanism  1026 . Bearing assembly  1058  isolates electric motor  1056  (including rotor shaft  1086  and rotor  1084 ) from axial thrust loads generated by displacement assembly  1070  during operation and transmitted along drive shaft  1068  and drive mechanism  1026 , which thrust loads form pump reaction forces. Bearing assembly  1058  isolates rotor shaft  1086  and rotor  1084  from these thrust loads by transferring the thrust loads to the stationary, structural portions of feed pump  1012  (e.g., tie rods  1066  and fluid outlet manifold  1062 ) and thus to fluid tank  1020 . Isolating rotor shaft  1086  from the thrust loads of displacement assembly  1070  reduces wear on electric motor  1056  and increases the operational life of electric motor  1056 . Bearing assembly  1058  is described in greater detail in the discussion referencing  FIGS.  15 - 16 B . 
     As shown in  FIGS.  12 A and  12 B , drive mechanism  1026  includes drive nut  1090 , rolling elements  1094 , and screw  1092 . Drive nut  1090  is coaxial with rotor shaft  1086  and is connected to rotor shaft  1086  by bearing assembly  1058 . More specifically, drive nut  1090  and rotor shaft  1086  are each coupled to sleeve coupler  1095 . In the example shown, drive nut  1090  is cantilevered from sleeve coupler  1095  and extends axially along axis PA. Sleeve coupler  1095 , drive nut  1090 , and rotor shaft  1086  are rotationally fixed relative to one another such that sleeve coupler  1095 , drive nut  1090 , and rotor shaft  1086  rotate in unison. Sleeve coupler  1095  is coupled to rotor shaft  1086  such that rotor shaft  1086  drives rotation of sleeve coupler  1095  when rotor  1084  rotates about axis PA. Drive nut  1090  is coupled to sleeve coupler  1095  such that sleeve coupler  1095  drives rotation of drive nut  1090  about axis PA. Rotor  1084 , rotor shaft  1086 , sleeve coupler  1095 , and drive nut  1090  are disposed coaxially on axis PA. 
     Drive nut  1090  is axially spaced from rotor shaft  1086  along axis PA such that axial gap AG exists between drive nut  1090  and rotor shaft  1086  during operation. Drive nut  1090  does not directly contact rotor shaft  1086 . In some examples, drive nut  1090  is fixed to sleeve coupler  1095  such that drive nut  1090  is prevented from moving axially along axis PA relative to sleeve coupler  1095 . In some examples, rotor shaft  1086  is not axially fixed to sleeve coupler  1095  such that rotor shaft  1086  can instead float relative to sleeve coupler  1095 . However, rotor shaft  1086  is rotationally fixed to sleeve coupler  1095  such that rotor shaft  1086  and sleeve coupler  1095  rotate together on axis PA. Axial gap AG is a variable gap that can expand and contract axially, such that the axial distance between rotor shaft  1086  and drive nut  1090  can grow and shrink during operation. However, sleeve coupler  1095  is configured such that axial gap AG is present throughout operation such that rotor shaft  1086  and drive nut  1090  do not contact. Drive nut  1090  forms a rotating element of drive mechanism  90 . Maintaining axial gap AG prevents drive nut  1090  from transferring pump reaction forces to rotor shaft  1086 , and thus to rotor  1084 , during operation. 
     Screw  1092  is elongate along axis PA and disposed on axis PA. Screw  1092  extends axially through drive nut  1090  and is coaxial with drive nut  1090  on axis PA. Screw  1092  extends in both first axial direction AD 1  and second axial direction AD 2  relative to drive nut  1090 . Screw  1092  is configured to only one of linearly translate along or rotate on axis PA. While screw  1092  is generally discussed as linearly translating along axis PA, it is understood that, in some examples, screw  1092  can on about axis PA without translating along axis PA. For example, a nut can be connected to the rotating screw  1092  and the nut can be clocked to prevent the nut from rotating about axis PA, such as by clocking assembly  1060 . Rotation of screw  1092  causes the nut to translate axially along axis PA. The nut can be connected to piston  1113  to cause reciprocation of piston  1113  along axis PA. The nut can translate in each of first axial direction AD 1  and second axial direction AD 2  based on the rotational direction of screw  1092  such that reversing screw  1092  causes the nut to translate in a different axial direction. 
     Rolling elements  1094  are disposed radially between screw  1092  and drive nut  1090 . Rolling elements  1094  can be of any configuration suitable for causing linear displacement of screw  1092  based on rotation of drive nut  1090 . For example, rolling elements  1094  can be formed by balls or elongate rollers, among other options. Rolling elements  1094  engage the thread of screw  1092  to drive linear displacement of screw  1092  along axis PA. In some examples, rolling elements  1094  are disposed in raceways formed by opposing threads on drive nut  1090  and screw  1092 . Rolling elements  1094  are disposed circumferentially about screw  1092  and evenly arrayed around screw  1092 . Rolling elements  1094  maintain a radial gap between drive nut  1090  and screw  1092  such that drive nut  1090  does not directly contact screw  1092 . Instead, both drive nut  1090  and screw  1092  ride on rolling elements  1094 . Rolling elements  1094  maintain the radial gap, such as gap  118  ( FIG.  18   , between drive nut  1090  and screw  1092 . Drive nut  1090  receives the rotational output from electric motor  1056  and screw  1092  provides the linear output from drive mechanism  1026 . 
     Rotor shaft  1086 , bearing assembly  1058 , drive nut  1090 , screw  1092 , and drive shaft  1068  are all coaxially aligned on axis PA of feed pump  1012 . Screw  1092  extends axially on axis PA from first end  92  to first end  1091 . Screw  1092  extends through drive nut  1090 , through bearing assembly  1058 , and into electric motor  1056 . Screw  1092  axially overlaps with bearing assembly  1058  and reciprocates relative to bearing assembly  1058 . 
     As shown in  FIGS.  12 A and  12 B , rotor shaft  1086  is a hollow tube, and screw  1092  extends into the cavity of rotor shaft  1086  such that second end  1093  of screw  1092  is disposed within the center cavity of rotor shaft  1086 . Screw  1092  thus extends into a cavity within electric motor  1056 . At least a portion of screw  1092  is disposed within the central cavity of motor  1056 . Spacer  1097  is disposed on second end  1093  of screw  1092  and is radially between screw  1092  and rotor shaft  1086 . Spacer  1097  contacts each of screw  1092  and rotor shaft  1086 . Spacer  1097  is disposed axially between the two motor bearings  1088 . The axial distance between spacer  1097  and each motor bearing  88  changes throughout operation. One of the motor bearings  1088  and bearing assembly  1058  are spaced in first axial direction AD 1  from spacer  1097  and the other motor bearing  88  is spaced in second axial direction AD 2  from spacer  1097 . 
     Spacer  1097  can be a damper, bumper, bushing, or linear bearing that prevents second end  1093  from wobbling inside rotor shaft  1086  as screw  1092  reciprocates axially up and down along axis PA. Spacer  1097  forms a low friction interface configured to not transfer rotational moment from rotor shaft  1086  to screw  1092 . Spacer  1097  supports second end  1093  relative to rotor shaft  1086  to minimize any unsupported length of screw  1092 . Screw  1092  is supported on axis PA by spacer  1097  and drive nut  1090  and spans between spacer  1097  and drive nut  1090 . Screw  1092  extends though drive nut  1090  such that driver nut  1090  is disposed axially between second end  1093  and first end  1091 . In the example shown, spacer  1097  is fixed to screw  1092  such that spacer  1097  reciprocates with screw  1092  along axis PA. Spacer  1097  is disposed between screw  1092  and rotor shaft  1086  such that screw  1092  does not directly contact rotor shaft  1086 . As such, drive mechanism  1026  does not directly contact any portion of rotor  1084  during operation. Spacer  1097  can be formed from a non-ferrous material to prevent interference with operation of motor  1056 . In some examples, spacer  1097  is formed from a plastic. In one example, spacer  1097  is formed from polyether ether ketone (PEEK). 
     Screw  1092  reciprocates within rotor shaft  1086  during operation. Screw  1092  displaces in each of first axial direction AD 1  and second axial direction AD 2  along axis PA. The axial overlap between screw  1092  and rotor shaft  1086  increases as screw  1092  displaces in second axial direction AD 2  and decreases as screw  1092  displaces in first axial direction AD 1 . During at least a portion of the stroke of screw  1092 , at least a portion of screw  1092  axially overlaps with each of rotor  1084 , rotor shaft  1086 , and stator  1082  such that a radial line extending from axis PA would pass through each of screw  1092 , rotor shaft  1086 , rotor  1084 , permanent magnet array  1087 , and stator  1082 . 
     First end  1091  of screw  1092  is connected to drive shaft  1068 . Drive shaft  1068  can form a piston shaft of piston  1113 . Screw  1092  is connected to drive shaft  1068  to cause axial displacement of drive shaft  1068  along axis PA. Drive shaft  1068  is elongate along axis PA and disposed coaxially with screw  1092  on axis PA. As shown in  FIGS.  12 A and  12 B , end  1108  of drive shaft  1068  is hollow and is sized to be received by first end  1091  of screw  1092 . Link pin  1106  extends through hollow end  1108  of drive shaft  1068  and first end  1091  of screw  1092  to fasten drive shaft  1068  to screw  1092 . In other embodiments, first end  1091  of screw  1092  can be hollow and sized to receive end  1108  of drive shaft  1068 . In the example shown, link pin  1106  extends through and connects screw  1092  and drive shaft  1068 . It is understood that screw  1092  and drive shaft  1068  can be connected in any desired manner, such as by press-fitting, fasteners, or adhesive, among other options. 
     Clocking assembly  1060  is connected to screw  1092  and configured to prevent screw  1092  from rotating about axis PA. Rotation of drive nut  1090  generates a rotational force on screw  1092  that is resisted by clocking assembly  1060 . Clocking assembly  1060  preventing rotation of screw  1092  on axis PA causes screw  1092  to displace linearly along axis PA due to rotation of drive nut  1090 . 
     Clocking assembly  1060  is disposed axially between fluid outlet manifold  1062  and bearing assembly  1058 . Clocking assembly  1060  is disposed axially between drive nut  1090  and displacement assembly  1070  (best seen in  FIGS.  13 A and  13 B ). Clocking assembly  1060  is disposed around screw  1092  proximate first end  1091  of screw  1092 . Clocking assembly  1060  is connected to screw  1092  to prevent rotation of screw  1092  and drive shaft  1068  about axis PA. Collar  1102  is connected to screw  1092  such that collar  1102  and screw  1092  are rotationally fixed together relative axis PA. The interface between screw  1092  and drive shaft  1068  is covered by collar  1102 . Collar  1102  further covers the ends of link pin  1106  to secure link pin  1106  in position and thus secure the connection between screw  1092  and drive shaft  1068  by link pin  1106 . 
     Clocking assembly  1060  includes clocking housing  1100  that is connected to a housing of bearing assembly  1058  and/or fluid outlet manifold  1062 . Clocking housing  1100  is stationary and does not rotate or move relative axis PA. A chamber is formed inside clocking housing  1100  and collar  1102  of clocking assembly  1060  is disposed inside the chamber. Collar  1102  is configured to slide axially along axis PA within the chamber. As shown in  FIGS.  12 A and  12 B , the chamber can also extend into a portion of fluid outlet manifold  1062  to make the chamber longer and allow collar  1102  to slide a longer distance along axis PA. 
     Anti-rotation pin  1104  extends through collar  1102  and screw  1092  transverse to axis PA. Anti-rotation pin  1104  rotationally fixes screw  1092  to collar  1102  to prevent rotation of screw  1092  relative to collar  1102 . As described in greater detail below with reference to  FIGS.  17 A- 17 C , clocking assembly  1060  includes an anti-rotation interface between collar  1102  and clocking housing  1100  that prevents collar  1102  from rotating relative clocking housing  1100  and about axis PA. Clocking assembly  1060  ensures that screw  1092  and drive shaft  1068  reciprocate axially on axis PA and do not rotate with drive nut  1090  and rotor shaft  1086  because screw  1092  is connected to collar  1102  and is unable to rotate relative to collar  1102 , because collar  1102  interfaces with clocking housing  1100  and is unable to rotate relative to clocking housing  1100 , and because clocking housing  1100  is fixed and unable to rotate relative axis PA. 
     Switch pin  1110  is connected to second end  1093  of screw  1092  and is disposed at least partially inside rotor shaft  1086 . Switch pin  1110  can extend axially beyond the end of rotor shaft  1086  oriented towards first end cap  1076 . As such, the linear displacement member of drive mechanism  1026  can be considered to extend beyond each axial end of rotor shaft  1086 , in some examples. Direction control switch  1112  is disposed in first end cap  1076  of housing  1074  of electric motor  1056 . During operation, the electrical current in stator  1082  causes rotor  1084  (and thus rotor shaft  1086 , sleeve coupler  1095 , and drive nut  1090 ) to rotate in a first rotational direction (e.g., in one of the clockwise and counterclockwise direction). Rotor  1084  rotates and drives rotation of rotor shaft  1086  due to the connection of rotor  1084  and rotor shaft  1086 . Rotor shaft  1086  drives rotation of sleeve coupler  1095  due to the interface between rotor shaft  1086  and sleeve coupler  1095 . Sleeve coupler  1095  drives rotation of drive nut  1090  due to the connection between sleeve coupler  1095  and drive nut  1090 . Drive nut  1090  exerts axial force on screw  1092  via rolling elements  1094  to drive screw  1092  linearly along axis PA. Screw  1092  causes drive shaft  1068  to move axially due to the connection between screw  1092  and drive shaft  92 . 
     Rotor  1084  rotating in the first rotational direction cause screw  1092  to shift upward in the second axial direction AD 2  along axis PA and towards first end cap  1076 . As screw  1092  and drive shaft  1068  move axially upward on axis PA toward first end cap  1076 , switch pin  1110  can contact direction control switch  1112 . When switch pin  1110  contacts direction control switch  1112 , direction control switch  1112  generates a signal and provides that signal to controller  1029  ( FIG.  10 B ) causing controller  1029  to provide current to stator  1082  to cause rotor  1084  to rotate in a second rotational direction opposite the first rotational direction (e.g., the other of clockwise and counterclockwise). Rotating rotor  1084  in the second rotational direction causes rotor shaft  1086 , sleeve coupler  1095  and drive nut  1090  to rotate in the second rotational direction. With the direction of rotation changed for drive nut  1090 , drive nut  1090  exerts an axial force on screw  1092  via rolling elements  1094  to drive screw  1092  linearly along axis PA and in first axial direction AD 1 . Screw  1092  and drive shaft  1068  are driven axially downward on axis PA and away from first end cap  1076  of housing  1074  of electric motor  1056 . The direction of rotation will change again (e.g., back to the first one of clockwise and counterclockwise) when screw  1092  and drive shaft  1068  reach a bottom of a downstroke of feed pump  1012 . Switch pin  110  and switch  1112  form a position sensor configured to indicate when the fluid displacement member is at the end of an upstroke. 
     The bottom of a stroke in first axial direction AD 1  can be set and adjusted by controller  1029 . Controller  1029  can determine when screw  1092  and drive shaft  1068  have reached the bottom of the pump stroke based on a count of the rotations of rotor  1084 , drive nut  1090 , and/or rotor shaft  1086  (via a position sensor, such as an encoder or Hall-effect sensor, among other options). Each rotation of rotor  1084  is associated with a set axial displacement of screw  1092  such that the total axial displacement can be calculated based on the rotations (full or partial) of rotor  1084 . In some examples, controller  1029  determines the axial distance traveled by screw  1092  based on the number of rotations since the last instance switch pin  1110  contacted direction control switch  1112 . 
     As discussed in more detail below, screw  1092  actuates piston  1113  to cause pumping by displacement assembly  1070 . Drive shaft  1068  extends between screw  1092  and piston  1113  and can be considered to form at least a portion of a piston rod  1127  of piston  1113 . 
     Rotor  1084  and drive mechanism  1026  are sized to provide a desired revolution to stoke ratio. In some examples, rotor  1084  and drive mechanism  1026  are sized such that one revolution of rotor  1084  results in a full stroke of piston  1113  in one of first axial direction AD 1  and second axial direction AD 2 . A full revolution in an opposite rotational direction results in a full stroke of piston  1113  in the opposite axial direction. As such, two revolutions in opposite directions can provide a full pump cycle of piston  1113 . Feed pump  1012  can thereby provide a 1:1 ratio between revolutions of rotor  1084  and pumping strokes. 
     It is understood, however, that rotor  1084  and drive mechanism  1026  can be sized to provide any desired revolution to stroke ratio. It is further understood that controller  1029  can control operation of motor  1056  such that the actual stroke length is dynamic and varies can during operation. Controller  1029  can cause the stroke length to vary between the downstroke and the upstroke. In some examples, controller  1029  is configured to control operation between a maximum revolution to stroke ratio and a minimum revolution to stroke ratio. Feed pump  1012  can be configured to provide any desired revolution to stroke ratio. In some examples, feed pump  1012  provides a revolution to stroke ratio of up to about 4:1. It is understood, however, that other maximum revolution to stroke ratios are possible, such as about 1:1, 2:1, 3:1, or 5:1, among other options. In some examples, feed pump  1012  can provide a revolution to stroke ratio between about 0.25:1-7:1. It is understood that any of the ranges discussed can be an inclusive range such that the boundary values are included within the range. It is further understood that each of the ranges discussed can vary from the specified range while still falling within the scope of this disclosure. 
     Motor  1056  and drive mechanism  1026  can be configured to displace piston  1113  at least about 6.35 mm (about 0.25 in.) per rotor revolution. In some examples, motor  1056  and drive mechanism  1026  are configured to displace piston  1113  between about 8.9-30.5 mm (about 0.35-1.2 in.) per rotor revolution. In some examples, motor  1056  and drive mechanism  1026  are configured to displace piston  1113  between about 8.9-11.4 mm (about 0.35-0.45 in.) per rotor revolution. In some examples, motor  1056  and drive mechanism  1026  are configured to displace piston  1113  between about 19-21.6 mm (about 0.75-0.85 in.). In some examples, motor  1056  and drive mechanism  1026  are configured to displace piston  1113  between about 24.1-26.7 mm (about 0.95-1.05 in.). The axial displacement per rotor revolution provided by feed pump  1012  facilitates precise control and quick responsiveness during pumping. The axial displacement per rotor revolution facilitates quick changeover and provides more efficient pumping while reducing wear on components of feed pump  1012 . 
     Feed pump  1012  is configured to pump according to a revolution to displacement ratio. More specifically, motor  1056  and drive mechanism  1026  are configured to provide a desired revolution to displacement ratio between revolutions of rotor  1084  and the linear travel distance of piston  1113 , as measured in inches, for each revolution of rotor  1084 . In some examples, the revolution to displacement ratio (rev/in.) is less than about 4:1. In some examples, the revolution to displacement ratio is between about 0.85:1 and 3.25:1. In some examples, the revolution to displacement ratio is between about 1:1-3:1. In some examples, the revolution to displacement ratio is between about 1:1-2.75:1. In some examples, the revolution to displacement ratio between is about 1:1-2.55:1. In some examples, the revolution to displacement ratio is between about 1:1-1.3:1. In some examples, the revolution to displacement ratio is between about 0.9:1-1.1:1. In some examples, the revolution to displacement ratio is between about 2.4:1-2.6:1. The low revolution to displacement ratio provided by feed pump  1012  relative to other electrically-powered pumps, such as crank-powered pumps that require reduction gearing to generate sufficient pumping torque and typically have revolution to displacement ratios of about 8:1 or higher, facilitates more efficient pumping, generates less wear, and provides quick responsiveness for changing stroke direction. Rotor  1084  can be driven at a lower rotational speed to generate the same linear speed, thereby generating less heat during operation. 
       FIGS.  13 A and  13 B  are cross-sectional views of lower portion  1054  of feed pump  1012 .  FIG.  13 C  is an enlarged cross-sectional view of lower portion  1054 .  FIGS.  13 A- 13 C  will be discussed concurrently. As shown in  FIGS.  13 A and  13 B , displacement assembly  1070  of feed pump  1012  includes piston  1113 , piston housing  1114 , and pump inlet  1116 . Piston housing  1114  includes upper end  1118  and lower end  1120 . Piston  1113  includes piston head  1115  and piston rod  1127 . Displacement assembly  1070  also includes seal housing  1122 , seal  1124 , first check valve  1126 , and second check valve  1128 . Seal housing  1122  includes pressure relief ports  1130 , top end  1135 , bottom end  1137 , working zone WZ, and pressure release zone PRZ. Opening  132  is formed in upper end  1118  of piston housing  1114 . As discussed below, pressure relief ports  1130  facilitate depressurizing feed pump  1012 , such as when feed pump  1012  requires maintenance or storage. 
     Piston housing  1114  extends axially on axis PA of feed pump  1012  and provides a piston chamber that encloses piston  113 . Piston housing  1114  extends axially between upper end  1118  and lower end  1120 . Piston housing  1114  can be cylindrical and be disposed coaxially with rotor  1084 . Opening  1132  extends axially through upper end  1118  and is disposed coaxially on axis PA. Piston rod  1127  extends axially between screw  1092  and piston head  1115 . Drive shaft  1068  extends through opening  1132  to connect with piston head  1115 . As discussed above, drive shaft  1068  can be considered to form part of piston rod  1127 . As such, piston rod  1127  extends out of displacement assembly  1070  to connect with drive mechanism  1026 . Opening  1132  is sufficiently larger in diameter than drive shaft  1068  to form a radial gap between drive shaft  1068  and upper end  1118  of piston housing  1114 . As such, drive shaft  1068  does not directly or indirectly contact piston housing  1114  along the axial length of opening  132 . 
     Pump inlet  1116  is formed in lower end  1120  of piston housing  1114 . First check valve  1126  is disposed at pump inlet  1116 . In the example shown, first check valve  1126  is a one-way ball valve that is configured to prevent back flow through pump inlet  1116 . It is understood, however, that check valve  1126  can be formed in any desired manner, such as by a flapper valve, disk valve, etc. Piston  1113  is disposed inside piston housing  1114  between upper end  1118  and lower end  1120 . Piston  1113  is connected to drive shaft  1068  and reciprocates inside piston housing  1114  along axis PA when drive shaft  1068  is actuated by electric motor  1056  and drive mechanism  1026  as discussed above with reference to  FIGS.  12 A and  12 B . Second check valve  1128  is integrated into piston  1113  and moves axially along axis PA with piston  1113 . In the example shown, second check valve  1128  is a one-way ball valve that is configured to allow flow across piston  1113  toward upper end  1118  of piston housing  1114  and prevent back flow towards lower end  1120  of piston housing  1114 . It is understood, however, that second check valve  1128  can be of any desired configuration, such as a flapper valve or disk valve, among other options. First check valve  1126  and second check valve  1128  are disposed coaxially on axis PA with piston  1113 . First check valve  1126  and second check valve  1128  are thereby disposed coaxially on axis PA with electric motor  1056 . 
     Displacement assembly  1070  is a double displacement pump such that displacement assembly  1070  outputs fluid during both an upstroke in second axial direction AD 2  and a downstroke in first axial direction AD 1 . During the upstroke, first check valve  1126  is open and second check valve  1128  is closed. During the downstroke, first check valve  1126  is closed and second check valve  1128  is open. Piston  1113  reciprocates on axis PA and can be elongate along, cylindrical, and coaxial with axis PA. 
     Lower shaft  1117  extends from drive shaft  1068  and is disposed coaxially with drive shaft  1068  on axis PA. More specifically, lower shaft  1117  and drive shaft  1068  are each connected to seal support  1125 . Piston head  1115  is disposed at an end of lower shaft  1117  axially opposite drive shaft  1068 . Piston head  1115  interfaces with piston housing  1114  to form a sliding seal. In some examples, a sealing element is mounted on piston head  1115  to travel with piston head  1115  and create the fluid tight seal between piston head  1115  and piston housing  1114 . Piston head  1115  divides piston housing  1114  into an upstream chamber, between lower end  1120  and piston head  1115 , and a downstream chamber, between piston head  1115  and upper end  1118 . The volumes of the upstream and downstream chambers vary during pumping as piston  1113  reciprocates on axis PA. As such, the interface between piston head  1115  and piston housing  1114  can form a first dynamic seal of displacement assembly  1070 . Second check valve  1128  is disposed in piston head  1115 . 
     Seal housing  1122  is disposed inside piston housing  1114  and is positioned axially between piston head  1115  and upper end  1118  of piston housing  1114 . Piston  1113  extends through seal housing  1122 . Seal housing  1122  is tubular and extends axially between top end  1135  and bottom end  1137  and is coaxially aligned with piston housing  1114  on axis PA. Top end  1135  of seal housing  1122  is connected to upper end  1118  of piston housing  1114 . Seal housing  1122  is smaller in diameter than piston housing  1114  and piston  1113  so as to form an annular flow path between seal housing  1122  and piston housing  1114 . Seal housing  1122  is larger in diameter than opening  1132  and is coaxial with opening  1132 . Seal housing  1122  extends circumferentially around drive shaft  1068  and piston  1113 . The linearly displacing elements of feed pump  1012  extend fully through seal housing  1122  between top end  1135  and bottom end  1137  to connect drive mechanism  1026  to piston  1113 . Seal  1124  is disposed inside seal housing  1122  and is connected to linearly displacing components of feed pump  1012 . In the example shown, seal  1124  is mounted to seal support  1125  that is connected to each drive shaft  1068  and lower shaft  1117 . Seal  1124  reciprocates relative seal housing  1122  during operation. As such, the interface between seal  1124  and seal housing  1122  can form a second dynamic seal of displacement assembly  1070 . 
     Seal  1124  extends radially outward from seal support  1125  to contact an inner surface of seal housing  1122 . Seal  1124  forms a fluid-tight seal with seal housing  1122  to prevent pressurized fluid in the downstream chamber of piston housing  1114  from flowing around seal  1124  to outlet  1132 . For example, seal  1124  can be an elastomeric cup seal with flanges extending generally axially from a base. In the example shown, the flanges extend generally axially towards lower end  1120  such that the cup of seal  1124  is oriented in first axial direction AD 1  towards piston head  1115 . Flange  1129  extends radially from a body of seal support  1125 . Seal  1124  is disposed on a side of flange  1129  facing top end  1135  and portions of seal  1124  extend axially over and surround at least a portion of an exterior radial surface of flange  1129 . Mounting ring  1131  is disposed on seal support  1125  and secures seal  1124  on seal support  1125 . For example, mounting ring  1131  can be a threaded ring configured to connect to seal support  1125  by interfacing threading. In some examples, mounting ring  1131  is fixed to seal support  1125  by a set screw or other fastener. Seal  1124  can be sandwiched axially between mounting ring  1131  and flange  1129 . 
     Pressure relief ports  1130  extend radially through seal housing  1122  proximate bottom end  1137  of seal housing  1122 . Working zone WZ is formed in the portion of seal housing  1122  that extends from top end  1135  to just above pressure relief ports  1130 . Pressure release zone PRZ is formed in the portion of seal housing  1122  that extends from pressure relief ports  1130  to bottom end  1137  of seal housing  1122 . Seal  1124  is configured to reciprocate within working zone WZ during typical operation, preventing venting of fluid to pressure relief ports  1130  and maintaining pressure in the downstream chamber of piston housing  1114 . 
     Tubes  1072  are connected to upper end  1118  of piston housing  1114  and fluidically communicate with the annular flow path  1142  ( FIG.  14 A ) between seal housing  1122  and piston housing  1114 . Tubes  1072  fluidly connect displacement assembly  1070  to fluid outlet manifold  1062  to provide flowpaths for fluid to flow to fluid outlet manifold  1062  from displacement assembly  1070  to be output by feed pump  1012 . Tubes  1072  can connect displacement assembly  1070  to outlet manifold  1062  and can support displacement assembly  1070  relative to outlet manifold  1062 . 
     During regular operation, electric motor  1056  and drive mechanism  1026  drive displacement of drive shaft  1068  to cause drive shaft  1068  to reciprocate axially along and on axis PA. As drive shaft  1068  reciprocates on axis PA, drive shaft  1068  moves piston  1113  axially upward in second axial direction AD 2  and axially downward in first axial direction AD 1  inside piston housing  1114 . Seal  1124  reciprocates axially with drive shaft  1068  and piston  1113  due to the connection of seal support  1125  with drive shaft  1068  and piston  1113 . During regulator operation, the stroke length of feed pump  1012  is controlled such that seal  1124  reciprocates inside seal housing  1122  within working zone WZ. 
     As drive shaft  1068  moves axially upward in second axial direction AD 2  on axis PA, piston  1113  moves upward toward upper end  1118  of piston housing. As piston  1113  moves upward, second check valve  1128  closes and first check valve  1126  opens. Fluid is drawn into the upstream chamber through first check valve  1126 . Piston head  1115  moves through piston housing  1114  in first axial direction AD 1 , decreasing the volume of the downstream chamber and driving fluid through tubes  1072  and to outlet manifold  1062 . Second check valve  1128  prevents retrograde flow from the downstream chamber to the upstream chamber. As piston  1113  moves upward, seal  1124  also moves upward inside seal housing  1122  toward upper end  1118  of piston housing  1114 . Seal  1124  prevents pressurized fluid from leaking out of piston housing  1114  via opening  1132  around drive shaft  1068 . 
     As drive shaft  1068  moves axially downward in first axial direction AD 1  on axis PA, piston  1113  moves downward, second check valve  1128  opens and first check valve  1126  closes. First check valve  1126  being closed prevents retrograde flow from the upstream chamber and back into the interior  1048  of fluid tank  1020 . Piston head  1115  moves through piston housing  1114  in first axial direction AD 1 , decreasing a volume of the upstream chamber and increasing a volume of the downstream chamber. Fluid is driven through piston head  1115  and second check valve  1128  and from the upstream chamber into the downstream chamber. Fluid is driven downstream from the downstream chamber through tubes  1072  and downstream from pump  1012  through the outlet  1063  of pump  1012  during both of the upstroke and the downstream. As such, displacement assembly  1070  is a double displacement pump that outputs fluid during each of the upstroke and the downstroke. As piston  1113  moves downward, seal  1124  moves axially downward inside seal housing  1122  within working zone WZ. Seal  1124  continues to block fluid from escaping piston housing  1114  via opening  1132 . Seal  1124  does not move into pressure release zone PRZ or into contact with pressure relief ports  1130  during regular cycling of piston  1113  for pumping by feed pump  1012 . Displacement assembly  1070  can include both the first dynamic seal formed by the interface between piston head  1115  and piston housing  1114  and the second dynamic seal formed by the interface between seal  1124  and seal housing  1122 . In the example shown, displacement assembly  1070  does not include a static seal, which is a seal that remains static relative to axis PA, though it is understood that not all examples may be so limited. 
     Controller  1029  can control operation of feed pump  1012  to depressurize feed pump  1012 . During the depressurization routine, controller  1029  causes over-travel of piston  1113  in first axial direction AD 1  to open a vent path through displacement assembly  1070  and relieve pressure from within displacement assembly  1070 . Opening the vent path allows pressurized components of and connected to feed pump  1012  to be depressurized. For example, feed lines  1024   a ,  1024   b  can vent pressure to fluid tank  1020  through outlet manifold  1062 , fluid tube  1072 , piston housing  1114 , seal housing  1122 , and outlet  1132 . 
     When feed pump  1012  needs to be depressurized, such as during maintenance or before storage of feed pump  1012 , controller  1029  can send a command to feed pump  1012  to cause rotation of rotor  1084  such that drive shaft  1068  and piston  1113  displace axially downward in first axial direction AD 1 . Drive shaft  1086  and piston  1113  continue to displace in first axial direction AD 1  such that seal  1124  shifts in first axial direction AD 1  out of working zone WZ and in to pressure release zone PRZ. Seal  1124  thus overtravels and shifts axially beyond the regular pump cycling range. With seal  1124  in pressure release zone PRZ, an edge of seal  1124  encounters and, in some examples, moves axially beyond relief ports  1130 , as shown in  FIGS.  13 B and  13 C . Seal  1124  can thereby axially overlap with relief ports  1130  during depressurization. When the edge of seal  1124  encounters relief ports  1130 , pressurized fluid PF (shown by arrows in  FIG.  13 C ) in piston housing  1114  is able to push past seal  1124 , enter the portion of seal housing  1122  above seal  1124  and axially between seal  1124  and opening  1132 , and exit displacement assembly  1070  through opening  1132 . The pressure of the fluid in piston housing  1114  drives the pressurized fluid PF through opening  1132 . The pressurized fluid PF exiting displacement assembly  1070  through opening  1132  returns to fluid tank  1020 . The pressurized fluid PF dumping back to fluid tank  1020  relieves pressure within piston housing  1114  thereby depressurizing feed pump  1012 . 
     Additional pressure is generated in piston housing  1114 , fluid lines  1072 , and outlet housing  1062  as piston  1113  moves through the pressure relief stroke. An over-pressurization valve  1134  is disposed on the fluid pathway between piston housing  1114  and the outlet  1063  of outlet housing  6102 . Over-pressurization valve  1134  is a one-way pressure actuated valve configured to actuate to an open state to dump fluid back to the interior  1048  of fluid tank  1020 , thereby preventing pressures from building to undesired levels in the fluid paths through feed pump  1012 . The over-pressurization valve  1134  is discussed below with reference to  FIGS.  14 A and  14 B . 
     Venting pressure by overtravel of piston  1113  provides significant advantages. Venting pressure by overtravel of piston  1113  provides a simple and safe pressure relief procedure for feed pump  1012 . In addition, venting pressure from feed pump  1012  allows maintenance to be performed on those components upstream of proportioner pumps  1022   a ,  1022   b  ( FIGS.  10 A and  10 B ) without venting pressure from the full system. Relieving pressure through a vent path in displacement assembly  1070  ensures that all pressure is relieved within and downstream of displacement assembly  1070 , preventing unexpected, sudden pressure release when disconnecting components. Venting pressure through displacement assembly  1070  thereby prevents sputtering and waste of fluid and provides a safer work environment. Depressurizing feed pump  1012  further removes pressure from the inlets of proportioner pumps  1022   a ,  1022   b , thereby preventing the upstream pressure from exerting undesired pressure on the motor driving proportioner pumps  1022   a ,  1022   b.    
       FIG.  14 A  is a cross-sectional view of fluid outlet manifold  1062  of feed pump  1012  and over-pressurization valve  1134 .  FIG.  14 B  is an enlarged cross-sectional view of detail B in  FIG.  14 A .  FIGS.  14 A and  14 B  will be discussed concurrently. As shown in  FIGS.  14 A and  14 B , fluid outlet manifold  1062  includes outer housing  1136 , inner housing  1138 , O-ring  1140 , manifold passage  1142 , manifold inlets  1144 , over-pressure outlet  1146 , base end  1148 , and top end  1150 . Over-pressurization valve  1134  includes, as shown best in  FIG.  14 B , valve housing  1152 , ball  1154 , valve seat  1155 , spring  1156 , spring seat  1158 , first end  1160 , second end  1162 , inlet  1164 , and outlet  1166 . 
     Fluid outlet manifold  1062  extends axially between base end  1148  and top end  1150 . Outer housing  1136  of fluid outlet manifold  1062  extends axially from base end  1148  to top end  1150 . Outer housing  1136  includes a cavity extending axially into outer housing  1136  from top end  1150 . Inner housing  1138  of fluid outlet manifold  1062  is received by the cavity of outer housing  1136 . As such, inner housing  1138  is disposed radially inward of outer housing  1136 . Outer housing  1136  extends circumferentially about inner housing  1138 . Inner housing  1138  can form a portion of clocking housing  1100 . Inner housing  1138  can interface with collar  1102  to prevent rotation of collar  1102  about axis PA. Collar  1102  can extend axially into and reciprocate within inner housing  1138  during at least a portion of a stroke. At the end of a stroke in first axial direction AD 1 , collar  1102 , and thus a portion of screw  1092  about which collar  1102  extends, can be disposed within inner housing  1138  such that collar  1102  and a portion of screw  1092  axially overlap with the fluid flowpath formed by manifold passage  1142 . As such, at least a portion of collar  1102  axially overlaps with a portion of the fluid flowpath of the fluid being pumped by feed pump  1012 . Collar  1102  is disposed radially inside of the annular flowpath formed by manifold passage  1142 . Moreover, at least a portion of the drive mechanism  1026  that causes linear reciprocation of piston  1113  axially overlaps with a portion of the fluid path (e.g., the portion of screw  1092  within inner housing  1138 ). At least a portion of the drive mechanism  1026  (e.g., that portion of screw  1092  within inner housing  1138 ) can be disposed radially within a portion of the fluid path. For example, a radial line extending from axis PA can intersect with a portion of screw  1092  and with the portion of the fluid passage  1142 . The radial line intersects first with the portion of the screw  1092 , then with the inner housing  1138 , then with the fluid passage  1142 . 
     O-ring  1140  is disposed between outer housing  1136  and inner housing  1138  at top end  1150 . O-ring  1140  provides a seal between outer housing  1136  and inner housing  1138  to prevent fluid from leaking out of fluid outlet manifold  1062  at top end  1150 . Manifold passage  1142  is formed between outer housing  1136  and inner housing  1138 . Manifold passage  1142  is in fluidic communication with outlet  1063  of feed pump  1012  (shown in  FIGS.  11  and  12 B ) and with flow tubes  1072 . Manifold inlets  1144 , only one of which is shown in  FIGS.  14 A and  14 B , extend axially through base end  1148  of fluid outlet manifold  1062  and intersect with manifold passage  1142 . Each of manifold inlets  1144  is connected to one of tubes  1072 . 
     Tubes  1072  attach displacement assembly  1070  to fluid outlet manifold  1062  and provide fluid passages that provide fluid from displacement assembly  1070  to fluid outlet manifold  1062 . Over-pressure outlet  1146  extends axially through base end  1148  of fluid outlet manifold  1062  and intersects with manifold passage  1142 . Over-pressurization valve  1134  is attached to base end  1148  at over-pressure outlet  1146 . Over-pressurization valve  1134  and over-pressure outlet  1146  are both radially offset from axis PA of feed pump  1012 . Mounting collar  1064  extends circumferentially around base end  1148  and is configured to connect feed pump  1012  to top  1050  of fluid tank  1020 , such as by interfaced threading, among other options. With feed pump  1012  mounted on fluid tank  1020 , base end  1148  of fluid outlet manifold  1062  and over-pressurization valve  1134  are disposed within fluid tank  1020  and exposed to the interior  48  of fluid tank  1020 . 
     Valve housing  1152  of over-pressurization valve  1134  extends axially from first end  1160  to second end  1162 . Inlet  1164  is formed in first end  1160  and outlet  1166  is formed in second end  1162 . Inlet  1164  is smaller in diameter than outlet  1166  to form valve seat  1155  between inlet  1164  and outlet  1166 . Ball  1154  is disposed inside valve housing  1152  between valve seat  1155  and outlet  1166 . Ball  1154  forms a valve member of over-pressurization valve  1134 . It is understood, however, that over-pressurization valve  1134  can include any desired form of valve member. Spring seat  1158  is disposed inside valve housing  1152  between ball  1154  and outlet  1166 . Spring seat  1158  includes at least one passage to allow fluid to flow past spring seat  1158  when ball  1154  is in an open position away from valve seat  1155 . Spring  1156  is disposed inside valve housing  1152  between spring seat  1158  and ball  1154 . Spring  1156  is compressed between spring seat  1158  and ball  1154  and biases ball  1154  against valve seat  1155  into a closed position such that over-pressurization valve  1134  is a normally-closed valve. 
     First end  1160  of over-pressurization valve  1134  is connected to over-pressure outlet  1146  of fluid outlet manifold  1062  (e.g., by interfaced threading, among other mounting options). The spring force generated by spring  1156  is set such that over-pressurization valve  1134  does not open with fluid pressures at or below the maximum operating pressure. The spring force is set such that over-pressurization valve  1134  opens only in response to an over-pressure event. Over-pressurization valve  1134  can be configured to open in response to the pressure reaching a level above the maximum operating pressure to prevent unintended dumping during operation, such as at 10%, 20%, 30% or any desired level greater than the maximum operating pressure. 
     During operation of feed pump  1012 , whenever the internal pressure of the fluid inside feed pump  1012  exceeds a predetermined threshold, the internal pressure of the fluid acting on ball  1154  can overcome the biasing force of spring  1156  and move ball  1154  away from valve seat  1155 . When ball  1154  is pushed away from valve seat  1155 , the fluid exits fluid outlet manifold  1062  through outlet  1166  of over-pressurization valve  1134  and flows into fluid tank  1020  that feed pump  1012  is mounted to. Over-pressurization valve  1134  closes when the internal pressure of the fluid inside feed pump  1012  decreases below the predetermined pressure threshold. In this way, over-pressurization valve  1134  prevents the internal pressure of the fluid inside feed pump  1012  from increasing to a level that could cause damage to feed pump  1012  or system  1010 . 
       FIG.  15    is an enlarged cross-sectional view of electric motor  1056 , drive mechanism  1026 , and bearing assembly  1058  from  FIG.  12 B .  FIG.  16 A  is a cross-sectional view of bearing assembly  1058 .  FIG.  16 B  is an exploded view of bearing assembly  1058 .  FIGS.  15 - 16 B  will be discussed together. Electric motor  1056  and drive mechanism  1026  are as described above. Bearing assembly  1058  includes sleeve coupler  1095 , first roller bearing subassembly  1096 , second roller bearing subassembly  1098 , first housing piece  1099   a , and second housing piece  1099   b . First fasteners  1168  are shown. Bearing assembly  1058  also includes second fasteners  1170 , first end  1172 , second end  1174 , and spring  1176 . Sleeve coupler  1095  includes first end  1178 , second end  1180 , body  1182 , bore  1184 , shoulder  1185 , and flange  1186 . Flange  1186  includes first surface  1188  and second surface  1190 . First housing piece  1099   a  includes first opening  1192 , and second housing piece  1099   b  includes second opening  1194 . First roller bearing subassembly  1096  includes first race  1196 , first rolling elements  1198 , and second race  1200 . Second roller bearing subassembly  1098  includes third race  1202 , second rolling elements  1204 , and fourth race  1206 . First housing piece  1099   a  includes first diameter portion  1101 , second diameter portion  1103 , and third diameter portion  1105 . Second housing piece  1099   b  includes mounting depression  1107 , bearing shoulder  1109 , and seating shoulder  1111 . 
     Bearing assembly  1058  connects rotor  1084  to drive mechanism  1026 . Bearing assembly  1058  permits rotational motion to pass within drive mechanism  1026  from motor  1056  while preventing some or all of the axial forces generated by displacement assembly  1070  from transferring to rotor  1084 . Piston  1113  moves in a reciprocating linear fashion and experiences axial forces due to fluid resistance experienced during reciprocation. Specifically, piston  1113  experiences a downward axial reaction force (e.g., in axial direction AD 1 ) when moving through the upstroke and an upward axial reaction force (e.g., in axial direction AD 2 ) when moving through the downstroke, and both of the upward reaction force and the downward reaction force transfer through drive mechanism  1026  and to bearing assembly  1058 . 
     Bearing assembly  1058  is configured to react the axial loads generated during pumping to isolate electric motor  1056  (including rotor shaft  1086  and rotor  1084 ) from those axial loads generated by displacement assembly  1070  and transmitted to and through drive mechanism  1026 . Bearing assembly  1058  isolates rotor  1084  from these thrust loads by transferring the thrust loads to the stationary, structural portions of feed pump  1012  (e.g., tie rods  1066 , and fluid outlet manifold  1062 ) and to fluid tank  1020 . 
     The pump reaction forces are transmitted through piston  1113  and to the linear drive element of drive mechanism  1026  (e.g., through drive shaft  1068  and screw  1092 ). The pump reaction forces are transmitted through the linear drive element to the rotating element of drive mechanism  1026 . The pump reaction forces are transmitted to bearing assembly  1058  at a location axially between the rotating elements of drive mechanism  1026  and rotor  1084 . Bearing assembly  1058  supports a sufficient portion of the pump reaction forces and transmits those forces to stationary frame components of feed pump  1012  (e.g., tie rods  1066 , and fluid outlet manifold  1062 ) and away from motor  1056  to protect motor  1056  during operation. Bearing assembly  1058  can support up to all of the pump reaction forces generated during pumping. Bearing assembly  1058  prevents the pump reaction forces from causing axial misalignment between rotor  1084  and stator  1082 , thereby increasing the life and efficiency of motor  1056 . 
     First housing member  1099   a  is coaxially aligned with electric motor  1056  on axis PA and includes first opening  1192  extending through first housing member  1099   a  along axis PA. First housing member  1099   a  includes first diameter portion  1101  that is the part of first housing member  1099   a  furthest in first axial direction AD 1 . Second diameter portion  1103  is adjacent first diameter portion  1101  and has a larger inner diameter than first diameter portion  1101 . The larger diameter of second diameter portion  1103  forms a radial shelf RS 1  that supports at least a portion of wave spring  1176 . Third diameter portion  1105  is adjacent second diameter portion  1103  such that second diameter portion  1103  is disposed axially between first diameter portion  1101  and third diameter portion  1105 . Third diameter portion  1105  has an inner diameter larger than the inner diameter of second diameter portion  1103 . The larger diameter of third diameter portion  1105  facilitates third diameter portion  1105  receiving a portion of first roller bearing subassembly  1096 . More specifically, third diameter portion  1105  receives and radially supports first race  1196 . First housing member  1099   a  further includes axial projection  1133 . A portion of clocking housing  1100  extends around and interfaces with axial projection  1133 , facilitating axial alignment between bearing assembly  1058  and clocking assembly  1060 . 
     Second housing member  1099   b  is positioned axially between first housing member  1099   a  and electric motor  1056  and is disposed coaxially with first housing member  1099   a  and electric motor  1056  on axis PA. First housing member  1099   a  is connected to second housing member  1099   b . In the example shown, second housing member  1099   b  is connected to first housing member  1099   a  by second fasteners  1170 . It is understood, however, that first housing member  1099   a  and second housing member  1099   b  can be fixed in any suitable manner, such as by press-fitting or adhesive, among other options. A portion of first housing member  1099   a  extends into a portion of second housing member  1099   b . More specifically, third diameter portion  1105  extends into second housing member  1099   b  and interfaces with seating shoulder  1111 . Axial flange  1121  extends partially over an exterior of third diameter portion  1105 . First housing member  1099   a  extending into and being received by second housing member  1099   b  assists in aligning and maintaining alignment between first housing member  1099   a  and second housing member  1099   b  on axis PA. 
     Second housing member  1099   b  further includes second opening  1194  extending through second housing member  1099   b  along axis PA. Second housing member  1099   b  interfaces with the housing of electric motor  1056 . Mounting depression  1107  is formed at second end  1174  of bearing assembly  1058  and is configured to receive a portion of the housing of electric motor  1056 . For example, mounting depression  1107  can receive a portion of second end cap  1078 . Mounting depression  1107  receiving a portion of the housing of motor  1056  assists in aligning bearing assembly  1058  and electric motor  1056  coaxially on axis PA. In some examples, second housing member  1099   b  can be fixed to second end cap  1078 . Second housing member  1099   b  is further configured to connect to tie rods  1066 , such as by fasteners extending through mounting openings  1119 . As such, bearing assembly  1058  is rigidly connected to components forming the frame of feed pump  1012 . 
     First end  1172  of bearing assembly  1058  is formed by first housing member  1099   a , and second end  1174  of bearing assembly  1058  is formed by second housing member  1099   b . First housing member  1099   a  and second housing member  1099   b  are stationary relative axis PA and do not rotate about axis PA. Second housing member  1099   b  is fixed to frame components of feed pump  1012  to fix second housing member  1099   b  relative to axis PA. First housing member  1099   a  is connected to second housing member  1099   b  to fix first housing member  1099   a  relative second housing member  1099   b  on axis PA. Together, first housing member  1099   a  and second housing member  1099   b  enclose other components of bearing assembly  1058 . First housing member  1099   a  and second housing member  1099   b  radially surround the rotating components of bearing assembly  1058 . 
     Sleeve coupler  1095  is the radially innermost component of bearing assembly  1058 . Portions of sleeve coupler  1095  are disposed axially between first housing member  1099   a  and second housing member  1099   b . Sleeve coupler  1095 , first housing member  1099   a , and second housing member  1099   b  are all coaxial with axis PA of feed pump  1012 . Body  1182  of sleeve coupler  1095  extends axially from first end  1178  to second end  1180 . 
     Flange  1186  is an annular flange that extends radially outward from body  1182  between first end  1178  and second end  1180 . First surface  1188  of flange  1186  faces toward first housing member  1099   a . First surface  1188  contacts and supports first roller bearing subassembly  1096 . More specifically, first surface  1188  contacts and supports second race  1200 . Second race  1200  is supported by sleeve coupler  1095  such that second race  1200  rotates with sleeve coupler  1095 . Coupler shoulder  1189  is formed on sleeve coupler  1095  and interfaces with first roller bearing subassembly  1096 . Coupler shoulder  1189  is formed at the interface between first surface  1188  and first portion  1183 . Coupler shoulder  1189  axially and radially interfaces with first roller bearing subassembly  1096 . Second surface  1190  of flange  1186  faces toward second housing member  1099   b . Second surface  1190  contacts and supports second roller bearing subassembly  1098 . More specifically, second surface  1190  contacts and supports third race  1202 . Third race  1202  is supported by sleeve coupler  1095  such that third race  1202  rotates with sleeve coupler  1095 . Coupler shoulder  1191  is formed on sleeve coupler  1095  and interfaces with second roller bearing subassembly  1098 . Coupler shoulder  1191  axially and radially interfaces with second roller bearing subassembly  1098 . Coupler shoulder  1191  is formed at the interface between second surface  1190  and second portion  1187 . In the example shown, coupler shoulder  1191  is disposed radially closer to axis PA than coupler shoulder  1189 . 
     Bore  1184  extends axially through body  1182  from first end  1178  to second end  1180 . As shown best in  FIG.  16 A , body  1182  of sleeve coupler  1095  incudes first portion  1183  extending axially from first end  1178  to first surface  1188  of flange  1186 . Body  1182  of sleeve coupler  1095  includes second portion  1187  extending axially from second end  1180  to second surface  1190  of flange  1186 . The first portion  1183  of body  1182  comprises an inner diameter D 1  that is larger than an inner diameter D 2  of the second portion  1187 . First portion  1183  is configured to receive an axial projection of drive nut  1090 , facilitating coaxial alignment of drive nut  1090  and bearing assembly  1058 . The inner diameter D 1  of the first portion  1183  of body  1182  is larger than inner diameter D 2  forming shoulder  1185  at the interface between first portion  1183  and second portion  1187 . Shoulder  1185  interfaces with the end of the axial projection of drive nut  1090  to limit the extent that drive nut  1090  extends into bore  1184 . Second portion  1187  facilitates connection with rotor  1084 . More specifically, second portion  1187  is configured to receive an end of rotor shaft  1086 . 
     First roller bearing subassembly  1096  is disposed axially between sleeve coupler  1095  and first housing member  1099   a . In the example shown, first roller bearing subassembly  1096  is disposed axially between flange  1186  of sleeve coupler  1095  and first housing member  1099   a . First roller bearing subassembly  1096  radially overlaps with each of second diameter portion  1103  and third diameter portion  1105 . Second roller bearing subassembly  1098  is disposed axially between sleeve coupler  1095  and second housing member  1099   b . In the example shown, second roller bearing subassembly  1098  is disposed axially between flange  1186  of sleeve coupler  1095  and second housing member  1099   b . Flange  1186  is disposed axially between each of first roller bearing subassembly  1096  and second roller bearing subassembly  1098 . Flange  1186  contacts both first roller bearing subassembly  1096  and second roller bearing subassembly  1098 . In the example shown, flange  1186  contacts both second race  1200  and third race  1202 , which races  1200 ,  1202  form the rotating races of first bearing subassembly  1096  and second bearing subassembly  1098 , respectively. 
     Spring  1176 , shown only in  FIG.  16 A , is a damper spring that can be positioned axially between first housing member  1099   a  and first roller bearing subassembly  1096 . In the example shown, spring  1176  is supported on radial shelf RS 1 . Spring  1176  can be an annular wave spring formed by one or more spring components. Spring  1176  is coaxially aligned with axis PA. Spring  1176  is coaxial with bore  1184 , first opening  1192 , and second opening  1194 . Spring  1176  axially loads first roller bearing subassembly  1096  against sleeve coupler  1095 . Spring  1176  interfaces with first race  1196  of first roller bearing subassembly  1096  to axially load first roller bearing subassembly  1096 . Spring  1176  can prevent direct contact between first race  1196  and the radial shelf RS 2  extending radially inward from shoulder  1123 . In some examples, spring  1176  holds first bearing assembly  1096  axially away from radial shelf RS 2  but can allow contact during operation. First race  1196  is a non-rotating race of first roller bearing subassembly  1096 . The axial force exerted by spring  1176  is transmitted through sleeve coupler  1095  and further axially loads second roller bearing subassembly  1098 . Spring  1176  is configured to dampen vibrations inside bearing assembly  1058 . While spring  1176  is shown as interfacing with first roller bearing subassembly  1096 , it is understood that spring  1176  can be disposed on an opposite side of flange  1186  such that spring  1176  interfaces with second roller bearing subassembly  1098 . For example, spring can be disposed axially between second bearing housing  1099   b  and fourth race  1206 . In such an example, first race  1196  can seat on the shoulder  1123  of third diameter portion  1121 . 
     First roller bearing subassembly  1096  is configured to react to and transmit axial loads when drive shaft  1068  and screw  1092  are moving axially. For example, first roller bearing subassembly  1096  can react downward axial loads when drive shaft  1068  and screw  1092  move axially upward in second axial direction AD 2  through an upstroke and towards electric motor  1056 . First roller bearing subassembly  1096  includes first race  1196 , first rolling elements  1198 , and second race  1200 . In first roller bearing subassembly  1096 , first race  1196  is adjacent first housing member  1099   a  and spring  1176 . Second race  1200  is adjacent first surface  1188  of flange  1186  and interfaces with coupler shoulder  1189 . First rolling elements  1198  are axially between first race  1196  and second race  1200 . Rolling elements  1198  can be of any suitable configuration for supporting and transferring axial loads from sleeve coupler  1095  to first housing member  1099   a . For example, rolling elements  1198  can be elongate rollers that are elongate along axes transverse to axis PA. In some examples, the axes of rolling elements  1198  are orthogonal to axis PA. In some examples, rolling elements  1198  can be cylindrical rollers, tapered rollers, balls, or of any other configuration suitable for transmitting axial forces and facilitating rotation of sleeve coupler  1095 . First bearing subassembly  1096  is loaded axially between spring  1176  and sleeve coupler  1095 . 
     Second roller bearing subassembly  1098  is configured to react to and transmit axial loads when drive shaft  1068  and screw  1092  are moving axially. For example, second roller bearing subassembly  1098  can react downward axial loads when drive shaft  1068  and screw  1092  move axially downward in first axial direction AD 1  through a downstroke and away from electric motor  1056 . Second roller bearing subassembly  1098  includes third race  1202 , second rolling elements  1204 , and fourth race  1206 . In second roller bearing subassembly  1098 , third race  1202  is adjacent second surface  1190  of flange  1186  and interfaces with coupler shoulder  1191 . Fourth race  1206  is adjacent second housing member  1099   b  and interfaces with bearing shoulder  1109  of second housing member  1099   b . Second rolling elements  1204  are disposed axially between third race  1202  and fourth race  1206 . Rolling elements  1204  can be of any suitable configuration for supporting and transferring axial loads from sleeve coupler  1095  to second housing member  1099   b . For example, rolling elements  1204  can be elongate rollers that are elongate along axes transverse to axis PA. In some examples, the axes of rolling elements  1204  are orthogonal to axis PA. In some examples, rolling elements  1204  can be cylindrical rollers, tapered rollers, balls, or of any other configuration suitable for transmitting axial forces and facilitating rotation of sleeve coupler  1095 . Second bearing subassembly  1098  is loaded axially between second housing member  1099   b  and sleeve coupler  1095 . 
     As shown in  FIG.  15   , drive mechanism  1026  is mounted to bearing assembly  1058  and includes drive nut  1090  and screw  1092 . Drive nut  1090  is coaxial with rotor shaft  1086  and is connected to rotor shaft  1086  by sleeve coupler  1095  of bearing assembly  1058 . Drive nut  1090  extends through first opening  1192  of first housing member  1099   a  and is connected to first end  1178  of sleeve coupler  1095  by first fasteners  1168 . A portion of drive nut  1090  extends into bore  1184  between first end  1178  and shoulder  1185  of sleeve coupler  1095 , thereby axially aligning drive nut  1090  with sleeve coupler  1095  on axis PA. A radial flange of drive nut  1090  abuts against first end  1178  to limit the extent that drive nut  1090  can axially extend into bore  1184 . Fasteners  1168  extend through the flange of drive nut  1090  can into sleeve coupler  1095 , though it is understood that other forms of connecting can be used, such as press-fitting or adhesive, among other options. 
     The radial flange of drive nut  1090  is sized to not contact spring  1176 . The portion of drive nut  1090  extending into bearing assembly  1058  can axially overlap with some or all of first roller bearing subassembly  1096 . The portion of drive nut  1090  extending into bearing assembly  1058  can extend further in second axial direction AD 2  than first housing member  1099   a . As such, drive nut  1090  can axially overlap with a full axial extent of first housing member  1099   a  and can axially overlap with at least a part of second housing member  1099   b.    
     Rotor shaft  1086  is disposed coaxially with bearing assembly  1058  on axis PA and rotationally fixed to bearing assembly  1058 . Rotor shaft  1086  extends into bearing assembly  1058  through second opening  1194  of second housing member  1099   b  and extends into bore  1184  of sleeve coupler  1095  to interface with sleeve coupler  1095 . Bore  1184  axially aligns rotor shaft  1086  with sleeve coupler  1095  and drive nut  1090 . 
     Sleeve coupler  1095 , drive nut  1090 , and rotor shaft  1086  are rotationally fixed relative to one another such that sleeve coupler  1095 , drive nut  1090 , and the rotor shaft  1086  rotate in unison when electric motor  1056  rotates rotor shaft  1086 . Rotor shaft  1086  is rotationally fixed to sleeve coupler  1095  by interface components  1151   a ,  1151   b . For example, one of interface components  1151   a ,  1151   b  can be a tab and the other one of interface components  1151   a ,  1151   b  can be a groove configured to receive the tab. One of rotor shaft  1086  and sleeve coupler  1095  can include a first one of interface components  1151   a ,  1151   b  that interlocks with a second one of interface components  1151   a ,  1151   b  formed in the other one of rotor shaft  1086  and sleeve coupler  1095 . For example, a groove can be formed in one of sleeve coupler  1095  and rotor shaft  1086  and a tab configured to interface within the groove can extend from the other of sleeve coupler  1095  and rotor shaft  1086 . It is understood, however, that interface components  1151   a ,  1151   b  can be of any configuration suitable for rotationally locking sleeve coupler  1095  and rotor shaft  1086  for simultaneous rotation while allowing for relative axial movement. 
     Interface components  1151   a ,  1151   b  interface within bore  1184 . The interface between interface components  1151   a ,  1151   b  facilitates rotor shaft  1086  transmitting torque to sleeve coupler  1095  while still allowing relative axial movement between sleeve coupler  1095  and rotor shaft  1086 . Allowing relative axial movement between sleeve coupler  1095  and rotor shaft  1086  prevents bearing assembly  1058  from transferring axial thrust loads from drive mechanism  1026  to rotor  1084 . Rather, bearing assembly  1058  transfers the thrust loads to the stationary portions of feed pump  1012  (i.e., tie rods  1066 , clocking housing  1100 , and fluid outlet manifold  1062 ) via first roller bearing subassembly  1096 , shaft coupler  1095 , second roller bearing subassembly  1098 , and housing portions  1099   a ,  1099   b . Isolating rotor  1084  from the thrust loads generated by displacement assembly  1070  reduces wear on electric motor  1056  and increases the operational life of electric motor  1056 . 
     For example, when piston  1113  is moving axially upward in an upstroke toward electric motor  1056 , drive mechanism  1026  experiences a downward reaction force pulling axially downward on drive mechanism  1026 . This downward reaction force is transferred from piston  1113  to drive shaft  1068  and through drive shaft  1068  to screw  1092 . The pump reaction force is transmitted through screw  1092  and rolling elements  1094  to drive nut  1090 . The forces are transmitted through drive nut  1090  to sleeve coupler  1095 . The downward reaction force is transferred within sleeve coupler  1095  from first end  1178  to flange  1186  and from flange  1186  to first roller bearing subassembly  1096 . The axial force is transmitted through first roller bearing subassembly  1096  to first housing member  1099   a . More specifically, the axial force is transmitted through second race  1200 , rolling elements  1198 , and first race  1196  to first housing member  1099   a . The axial forces can be transmitted through spring  1176 . The axial forces are transmitted from first housing member  1099   a  to second housing member  1099   b  due to the rigid connection between first housing member  99   a  and second housing member  1099   b . From second housing member  1099   b , the downward reaction force is transferred to tie rods  1066 , from tie rods  1066  to fluid outlet manifold  1062 , and from fluid outlet manifold  1062  to fluid tank  1020 . In this manner, reaction forces are transmitted out of feed pump  1012  to fluid tank  1020  without transferring the reaction forces through electric motor  1056 . 
     When piston  1113  moves axially downward in a downstroke away from electric motor  1056 , drive mechanism  1026  experiences an upward reaction force pushing axially upward on drive mechanism  1026 . This upward reaction force is transferred from piston  1113  to drive shaft  1068  and through drive shaft  1068  to screw  1092 . The pump reaction force is transmitted through screw  1092  and rolling elements  1094  to drive nut  1090 . The forces are transmitted through drive nut  1090  to sleeve coupler  1095 . The upward reaction force is transferred within sleeve coupler  1095  from first end  1178  to flange  1186  and from flange  1186  to second roller bearing subassembly  1098 . The axial force is transmitted through second roller bearing subassembly  1098  then to second housing member  1099   b . More specifically, the axial force is transmitted through third race  1202 , rolling elements  1204 , and fourth race  1206  to second housing member  1099   b . From second housing member  1099   b , the upward reaction force is transferred to tie rods  1066 , from tie rods  1066  to fluid outlet manifold  1062 , and from fluid outlet manifold  1062  to fluid tank  1020 . In this manner, upward reaction forces are transmitted out of feed pump  1012  to fluid tank  1020  without transferring the upward reaction forces through electric motor  1056 . 
     Bearing assembly  1058  provides significant advantages. Bearing assembly  1058  facilitates the transmission of torque from motor  1056  to drive mechanism  1026  while inhibiting transmission of axial forces from drive mechanism  1026  to motor  1056 . Bearing assembly  1058  allows for relative axial movement between rotor shaft  1086  and bearing assembly  1058  and maintains an axial gap AG between drive nut  1090  and rotor shaft  1086  preventing direct contact therebetween and further preventing transmission of axial forces. Bearing assembly  1058  isolates motor  1056  from pump reaction forces, maintaining alignment between stator  1082  and rotor  1084 , preventing undesired wear and facilitating efficient operation. 
       FIG.  17 A  is an enlarged cross-sectional view of clocking assembly  1060 .  FIG.  17 B  is a cross-sectional view of clocking assembly  1060  taken along line A-A from  FIG.  17 A .  FIG.  17 C  is an exploded view of a portion of feed pump  1012  for an additional view of clocking assembly  1060 .  FIGS.  17 A- 17 C  will be discussed together. As discussed above with regard to  FIGS.  12 A and  12 B , clocking assembly  1060  is disposed axially between fluid outlet manifold  1062  and bearing assembly  1058 . Clocking assembly  1060  is disposed axially between drive nut  1090  and fluid outlet manifold  1062 . Bearing assembly  1058  is disposed axially between clocking assembly  1060  and motor  1056 . Drive nut  1090  is disposed axially between clocking assembly  1060  and motor  1056 . 
     Clocking assembly  1060  is disposed around screw  1092  proximate first end  1091  of screw  1092 . Clocking assembly  1060  is connected to screw  1092  to prevent rotation of screw  1092  and drive shaft  1068  about axis PA. Because of clocking assembly  1060 , screw  1092  and drive shaft  1068  move axially along axis PA and do not rotate about axis PA. Clocking assembly  1060  includes clocking housing  1100 , collar  1102 , anti-rotation pin  1104 , and link pin  1106 . Clocking assembly  1060  can further include lower bumper  1208 ; upper bumper  1210 ; slots  1212   a ,  1212   b ; housing segments  1214   a ,  1214   b ; chamber  1215 ; collar segments  1216   a ,  1216   b ; tabs  1218   a ,  1218   b ; fasteners  1220 ; and fasteners  1222 . 
     Clocking housing  1100  includes housing segments  1214   a ,  1214   b . Housing segments  1214   a ,  1214   b  come together around screw  1092  and axis PA of feed pump  1012  to form chamber  1215 . As such, clocking housing  1100  can be considered to be of a clamshell configuration. It is understood, however, that in other examples clocking housing  1100  can be formed as a single part or as more than two parts connected together. Fasteners  1220  connect housing segment  1214   a  to housing segment  1214   b . Clocking housing  1100  is fastened to fluid outlet manifold  1062  by fasteners  1222 . By fastening clocking housing to fluid outlet manifold  1062 , clocking housing  1100  is stationary and does not rotate or move relative axis PA. In some embodiments, clocking housing  1100  can be fastened to the housing of bearing assembly  1058 . Clocking housing  1100  can transmit axial forces from bearing assembly  1058  to outlet manifold  1062 . 
     Collar  1102  includes collar segments  1216   a ,  1216   b  that come together to form collar  1102 . As such, collar  1102  can be considered to be of a clamshell configuration. It is understood, however, that collar  1102  can be formed as a single part or as more than two parts connected together. Collar segments  1216   a ,  1216   b  are disposed inside chamber  1215  of clocking housing  1100 . Collar  1102  can slide axially within chamber  1215  along axis PA with screw  1092 . As shown in  FIGS.  12 A,  12 B, and  17 A , chamber  1215  can also extend into a top of fluid outlet manifold  1062  to make chamber  1215  longer and allow collar  1102  to slide a longer distance along axis PA. For example, chamber  1215  can be at least partially defined by inner housing  1138  ( FIG.  14 A ). Chamber  1215  can thus axially overlap with a portion of the fluid flowpath through feed pump  1012  (e.g., the portion disposed radially between inner housing  1138  and outer housing  1136 ). 
     Upper bumper  1210  is connected to a first axial end of collar  1102 . Lower bumper  1208  is connected to a second axial end of collar  1102  opposite upper bumper  1210 . Upper bumper  1210  and lower bumper  1208  protect collar  1102  from impacting a top and a bottom of chamber  1215  and provide damping in the event such contact occurs. Anti-rotation pin  1104  extends through collar  1102  and screw  1092  transverse to axis PA to connect screw  1092  to collar  1102  and to prevent rotation of screw  1092  relative collar  1102 . Anti-rotation pin  1104  also connects collar segments  1216   a ,  1216   b  together. Anti-rotation pin  1104  thereby locks collar  1102  to screw  1092 , preventing relative movement therebetween. 
     Slots  1212   a ,  1212   b  and tabs  1218   a ,  1218   b  provide an anti-rotation interface between collar  1102  and clocking housing  1100  that prevents collar  1102  from rotating relative clocking housing  1100 . Slots  1212   a ,  1212   b , shown best in  FIG.  17 B , are formed on interior surfaces of housing segments  1214   a ,  1214   b  and can extend up to a full axial length of chamber  1215 . Slots  1212   a ,  1212   b  can be open on both axial ends of chamber  1215  or on at least one common axial end of chamber  1215  to facilitate insertion of collar  1102  into clocking housing  1100 . In some examples, such as where clocking housing  1100  is formed from multiple components fastened together, slots  1212   a ,  1212   b  can be closed at each axial end. Tabs  1218   a ,  1218   b  are formed on collar segments  1216   a ,  1216   b , respectively, and extend radially outward from collar  1102  relative axis PA. Tabs  1218   a ,  1218   b  are sized to mate with slots  1212   a ,  1212   b  and thereby prevent rotation between collar  1102  and clocking housing  1100 . Tabs  1218   a ,  1218   b  are further sized to mate with slots  1212   a ,  1212   b  while still allowing collar  1102  to slide axially relative axis PA with screw  1092 . Because screw  1092  is connected to collar  1102  and is unable to rotate relative collar  1102 , and because collar  1102  and clocking housing  1100  are unable to rotate relative axis PA, clocking assembly  1060  ensures that screw  1092  and drive shaft  1068  reciprocate axially on axis PA and do not rotate with drive nut  1090  and rotor shaft  1086 . 
     First end  1091  of screw  1092  is connected to drive shaft  1068  inside clocking housing  1100 . Link pin  1106  extends through screw  1092  and drive shaft  1068  to connect screw  1092  and drive shaft  1068  together. Collar segments  1216   a ,  1216   b  sandwich first end  1091  of screw  1092  and end  1108  of drive shaft  1068 . As shown in  FIG.  17 A , collar  1102  is disposed around the connection between drive shaft  1068  and screw  1092 . By surrounding the connection between drive shaft  1068  and screw  1092 , collar  1102  can protect the connection between drive shaft  1068  and screw  1092  by holding link pin  1106  in place. 
     Clocking housing  1100  can extend axially between fluid outlet manifold  1062  to the housing of bearing assembly  1058 . By extending completely between fluid outlet manifold  1062  and bearing assembly  1058 , clocking housing  1100  can cover drive nut  1090 , screw  1092 , and collar  1102  and protect those components from dust and dirt. Furthermore, clocking housing  1100  increases the safety of feed pump  1012  by covering moving parts (e.g., drive nut  1090 , screw  1092 , and collar  1102 ) and shielding these moving parts from hands and fingers of users during use of feed pump  1012 . Clocking housing  1100  thereby provides pinch protection. 
     The gaps between adjacent tie rods  1066  are larger than the width of clocking housing  1100 . The arrangement of tie rods  1066  and clamshell configuration of clocking housing  1100  facilitate disassembly of clocking housing  1100  without requiring disassembly of feed pump  1012 . The user can remove fasteners  1222  and fasteners  1220  and pull housing segments  1214   a ,  1214   b  radially away from axis PA, thereby removing clocking housing  1100  between tie rods  1066 . Removing clocking housing  1100  provides user access to drive mechanism  1026 , collar  1102 , and the connection between screw  1092  and drive shaft  1068 . The user can thereby access and service various components of feed pump  1012  without disassembling feed pump  1012  or even removing feed pump  1012  from fluid tank  1020 . Such servicing saves time and cost and reduces downtime of system  1010 . 
     Clocking assembly  1060  provides significant advantages. Clocking assembly  1060  facilitates pumping by locking screw  1092  rotationally relative axis PA such that screw  1092  translates along axis PA. Clocking assembly  1060  travels with screw  1092  to provide a compact arrangement for feed pump  1012 . Clocking housing  1100  completely encloses collar  1102 , preventing contaminants from reaching drive mechanism  1026  and protecting the user. The user can disassemble clocking assembly  1060  to access and service various components of feed pump  1012  without disassembling feed pump  1012  or even removing feed pump  1012  from fluid tank  1020 . Such servicing saves time and cost and reduces downtime of system  1010 . 
       FIG.  18    is an isometric partial cross-sectional view of drive mechanism  26 .  FIG.  19    is an isometric partial cross-sectional view of drive mechanism  26 .  FIGS.  18  and  19    will be discussed together. Drive nut  90 , screw  92 , and rolling elements  94  of drive mechanism  26  are shown. Nut thread  91  and screw thread  99  are shown. Drive mechanism  26  is substantially similar to drive mechanism  1026  (best seen in  FIGS.  12 A,  12 B, and  15   ). Drive nut  90  is substantially similar to drive nut  1090  (best seen in  FIGS.  12 A,  12 B, and  15   ). Screw  92  is substantially similar to screw  1092  (best seen in  FIGS.  12 A,  12 B, and  15   ). Rolling elements  94  are substantially similar to rolling elements  1094  ( FIGS.  12 A,  12 B, and  15   ). 
     Drive mechanism  26  receives a rotational output at drive nut  90  and provides a linear input along pump axis PA via screw  92 . Drive nut  90  is disposed coaxially on pump axis PA with screw  92 . Drive nut  90  is configured to rotate about pump axis PA. A hole or bore is formed axially through drive nut  90  to form an inner radial surface of drive nut  90 . Nut thread  91  is formed on an inner radial surface of drive nut  90 . Nut thread  91  can be formed by a single helical or spiral groove that extends circumferentially and axially along the inner radial surface of drive nut  90 . In other examples, nut thread  91  can be formed by multiple spiral grooves that extend circumferentially along the inner radial surface of drive nut  90 . Screw  92  extends axially through the central bore in drive nut  90 . Screw thread  99  is formed on an exterior surface of screw  92 . Together, nut thread  91  and screw thread  99  define a raceway that interfaces with rolling elements  94 . 
     Rolling elements  94  are disposed in raceways formed by screw thread  99  and nut thread  91 . Rolling elements  94  are disposed in radial gap  118  formed between drive nut  90  and screw  92 . In the example shown in  FIGS.  18  and  19   , rolling elements  94  are balls that are guided between screw  92  and drive nut  90  by screw thread  99  and nut thread  91 . As such, drive mechanism  26  can be considered to be a ball screw. Ball return  184  is configured to pick up rolling elements  94  and recirculate the rolling elements  94  within the raceway formed by screw thread  99  and nut thread  91 . Ball return  184  can be of any type suitable for circulating rolling elements  94 . In some examples, ball return  184  is an internal ball return such that rolling elements  94  not within the raceway pass through the body of drive nut  90 . 
     Rolling elements  94  support screw  92  relative drive nut  90  such that each of drive nut  90  and screw  92  ride on rolling elements  94 . Rolling elements  94  support screw  92  relative drive nut  90  to maintain gap  118  between drive nut  90  and screw  92  and such that drive nut  90  and screw  92  are not in direct contact during operation. Rolling elements  94  are arrayed around, and are arrayed along, an axis that is coaxial with pump axis PA. Drive nut  90  is configured to rotate relative to screw  92  about the axis. Nut thread  91  rotates with drive nut  90 , while screw thread  99  travels axially with screw  92  without rotating. Rolling elements  94  exert axial driving forces on screw  92  at screw thread  99  to cause axial displacement of screw  92  along the axis (e.g., along pump axis PA). Drive mechanism  26  can thereby convert a rotational input to a linear output. Rolling elements  94  allow drive nut  90  to rotate relative to screw  92  with less friction loss and greater efficiency than if drive nut  90  was in direct contact with screw  92 . 
     Drive nut  90  can be driven in a first rotational direction by a rotor shaft, such as rotor shaft  1086  (best seen in  FIG.  15   ) or rotor shaft  42  (best seen in  FIGS.  3 A and  3 B ) to drive screw  92  in a first axial direction. For example, the first rotational direction can be the clockwise direction about axis PA and the first axial direction can be axially upward relative axis PA and gravity. Drive nut  90  can be driven by the rotor shaft in a second rotational direction opposite the first rotational direction to drive screw  92  in a second axial direction opposite the first axial direction. For example, the second rotational direction can be the counterclockwise direction about axis PA and the second axial direction can be axially downward relative to axis PA and gravity. While the above description provides drive mechanism  228  with a ball screw, another embodiment of drive mechanism is described below with reference to  FIGS.  20  and  21   . 
       FIG.  20    is an isometric view of drive mechanism  26 ′ with the body of drive nut  90 ′ removed to show rolling elements  94 ′.  FIG.  21    is an isometric view of drive mechanism  26 ′ with a portion of drive nut  90 ′ removed. Drive mechanism  26 ′ is substantially similar to drive mechanism  26  (best seen in  FIGS.  3 A and  3 B ) and drive mechanism  1026  (best seen in  FIGS.  12 A,  12 B, and  15   ). Drive mechanism  26  includes drive nut  90 ′, screw  92 , and rolling elements  94 ′. Screw thread  99  of screw  92  is shown. Drive nut  90 ′ includes drive rings  186   a ,  186   b  and support member  187 . Each of rolling elements  94 ′ include roller shafts  182  and end rollers  188   a ,  188   b.    
     Screw  92  and drive nut  90 ′ are disposed coaxially. Screw  92  extends axially through each of drive ring  186   a  and drive ring  186   b . Rolling elements  94 ′ are disposed radially between drive nut  90 ′ and screw  92 . Rolling elements  94 ′ are arrayed around, and are arrayed along, an axis that is coaxial with pump axis PA. Drive ring  186   a  is spaced axially from drive ring  186   b  along the axis PA. Support member  187  is connected to both drive ring  186   a  and drive ring  186   b  and axially spaces drive ring  186   a  apart from drive ring  186   b . Support member also rotationally locks first drive ring  186   a  to second drive ring  186   b  such that the drive rings  186   a ,  186   b  are unable to rotate relative to each other. Each drive ring  186   a ,  186   b  includes a plurality of gear teeth formed on a radially inner surface of that drive ring  186   a ,  186   b . Drive rings  186   a ,  186   b  are the same shape and size and include the same number and size of gear teeth. Drive rings  186   a ,  186   b  can be considered to be rings gears. 
     Rolling elements  94 ′ each include a common design. In the example shown, rolling elements  94 ′ are rollers including end rollers  188   a ,  188   b  and roller shafts  182 . As such, drive mechanism  26 ′ can be considered to be a roller screw. Roller shafts  182  have threaded bodies that extend between the axial ends of each rolling element  94 ′. End rollers  188   a ,  188   b  are disposed at opposite axial ends of each roller shaft  182 . End rollers  188   a ,  188   b  each include a plurality of gear teeth formed on an exterior surface of the rolling element  94 ′. Rolling elements  94 ′ support drive nut  90 ′ relative screw  92  such that each of drive nut  90 ′ and screw  92  ride on rolling elements  94 ′ and such that radial gap  118  is maintained between drive nut  90 ′ and screw  92 . Rolling elements  94 ′ are disposed circumferentially and symmetrically about screw  92 . Rolling elements  94 ′ maintain radial gap  118  between drive nut  90 ′ and screw  92  such that drive nut  90 ′ and screw  92  are not in direct contact during operation. The teeth of end rollers  188   a ,  188   b  mesh with the teeth of drive rings  186   a ,  186   b . End rollers  188   a ,  188   b  can be considered to be planetary gears. End rollers  188   a ,  188   b  do not directly engage with screw  92 . Instead, each roller shaft  182  includes threading configured to mate with screw thread  99  to exert driving force on screw  92  by that threaded interface. As drive nut  90 ′ rotates, engagement between end rollers  188   a ,  188   b  and drive rings  186   a ,  186   b  causes each rolling element  94 ′ to rotate about its own axis and causes the array of rolling elements  94 ′ to rotate about pump axis PA. Roller shafts  182  engage screw thread  99  and exert an axial driving force on screw thread  99  to linearly displace screw  92  along pump axis PA. 
       FIG.  22    is a graph illustrating a piston speed profile SP 1  for a conventional crank drive overlaid with piston speed profile SP 2  for pumps  12 ,  12 ′,  1012 . The lower horizontal axis relates to crank angle for piston speed profile SP 1 , which crank angle is not applicable to pumps  12 ,  12 ′,  1012  as pumps  12 ,  12 ′,  1012  linearly displace its associated fluid displacement member (e.g., fluid displacement members  34 ,  1113 ) without a crank. Downstroke profile DSP is associated with a downstroke of the fluid displacement member and upstroke profile USP is associated with an upstroke of the fluid displacement member. Pump  12 ,  12 ′,  1012  displaces fluid already within the pump during the downstroke and both displaces fluid from the pump and intakes additional fluid during the upstroke. The downstroke can also be referred to as a pumping stroke and the upstroke can also be referred to as a suction stroke. 
     Piston speed profile SP 1  shows a speed profile for a typical crank drive that consists of an offset crankshaft, a connecting link that connects the offset portion of the crankshaft to a linear slider that slides in a bearing, and the slider is connect to the top of a pump rod. As the crankshaft rotates, the connecting link oscillates side to side, typically from +30° to −30°, which creates a side load on the bearing. The linear slider and the pump rod motions are purely axial and reciprocate up and down. 
     Piston speed profile SP 1  is a skewed sinusoid. If the connecting link length were infinite, the profile would approach a perfect sinusoid, and the two peaks would occur at 90° and 270°. But because the connecting link length is limited, the first peak is delayed to ˜110°, and the second peak occurs sooner at ˜250°. Because these peaks are not in the middle of either the upstroke or down stroke, the accelerations and side loads are higher; the piston speed is higher, which result in higher wear and undesirable pump filling speed, which may result in undesirable cavitation. 
     Piston speed profile SP 2  is overlaid on piston speed profile SP 2  for illustrative purposes. It is understood that the slopes and plateau values can vary from those shown. Furthermore, pump  12 ,  12 ′,  1012 , for which piston speed profile SP 2  applies, does not include a crank, so the lower Crank Angle horizontal axis applies only to piston speed profile SP 1 , while the areas associated with a downstroke ADS and upstroke AUS are shown along the upper horizontal axis and apply to both piston speed profiles SP 1  and SP 2 . 
     Controller  29 ,  1029  is configured to control operation of motor  24 ,  1056  to control the speed, acceleration rate, and deceleration rate of the fluid displacement member through each of the upstroke and the downstroke. Controller  29 ,  1029  can control the rotational speed and acceleration of the rotor  74 ,  1084  such that rotor  74 ,  1084  accelerates slower on the upstroke than on the downstroke. The slower acceleration on the upstroke prevents formation of a vacuum within the pump, thereby preventing undesired cavitation during the upstroke. Controller  29 ,  1029  can further control rotation of rotor  74 ,  1084  such that the steady state speed on the upstroke is less than the steady state speed on the downstroke, further avoiding cavitation. Piston speed profile SP 2  can thereby be asymmetric, with different profiles for the upstroke and the downstroke. It is understood that controller  29 ,  1029  can adjust the slope and plateau values for each of the pressure stroke and the suction stroke based on feedback from any one or more sensors and/or from motor  24 ,  1056 . 
     The downstroke profile DSP includes acceleration segment S 1 , steady speed segment S 2 , and deceleration segment S 3 . The upstroke profile USP includes acceleration segment S 4 , steady speed segment S 5 , and deceleration segment S 6 . Controller  29 ,  1029  is capable of controlling the speed of rotation of rotor  74 ,  1084  and thus the speed of reciprocation of the fluid displacement member to provide any desired piston speed profile SP 2 . Piston speed profile SP 2  reduces wear and provides greater pumping efficiency and can provide greater flow through a single pump cycle. Piston speed profile SP 2  reduces pressure drop at changeover, reduces the chance of cavitation, and causes the pump to output fluid at consistent pressure and/or flow rate. The reciprocation of the fluid displacement member is controlled such that the pump powered by the electric motor  24 ,  1056  can provide an output similar to that of a pneumatically powered pump, but at higher pressures and with greater responsiveness and control. 
     During acceleration segment S 1 , the fluid displacement member is moving through the downstroke and accelerating. For pumps  12 ,  12 ′, check valve  106   a  closes and check valve  106   b  opens during the downstroke. For pump  1012 , check valve  1126  closes and check valve  1128  opens. After accelerating, the fluid displacement member moves at a set, steady speed. In steady speed segment S 2 , the motor  24 ,  1056  causes the fluid displacement member to move through the downstroke but at a steady linear speed. The constant speed of the fluid displacement member results in stable pressure that maintains a constant spray pattern width as fluid is emitted from the sprayer (e.g., spray gun  16  or applicator  1034 ). In deceleration segment S 3 , the fluid displacement member decelerates as the fluid displacement member approaches the end of the downstroke. The fluid displacement member changes over from the downstroke to the upstroke at the intersection between deceleration segment S 3  and acceleration segment S 4 , where the speed of the fluid displacement member is zero. 
     After completing the downstroke, the fluid displacement member is driven through an upstroke. During acceleration segment S 4 , fluid the displacement member is moving through the upstroke and accelerating. In pumps  12 ,  12 ′, check valve  106   a  opens and check valve  106   b  closes during the upstroke. In pump  1012 , check valve  1126  opens and check valve  1128  closes. It is desirable to have check valve  106   b ,  1128  close in the shortest time period possible to minimize any flow retrograde flow through that check valve  106   a ,  1126  and to minimize pressure drop. Acceleration segment S 4  has a more gradual slope than acceleration profile S 1 , such that the fluid displacement member can take a longer portion of the upstroke to accelerate to the steady speed than used to accelerate to the steady speed during the downstroke. Acceleration segment S 4  has a more gradual slope than acceleration segment S 1  to ensure that the fluid flows into the pump without generating a vacuum that could cause the fluid to cavitate. The gentler acceleration profile S 4  relative to acceleration profile S 1  avoids such cavitation. Cavitation is not an issue during the downstroke as additional fluid is not being drawn into the pump. 
     After accelerating, the fluid displacement member moves at a set, steady speed. In steady speed segment S 5 , the fluid displacement member continues to displace through the upstroke and moves at a steady speed. In some examples, the speed of steady speed segment S 5  is less than the speed of steady speed segment S 2 , to further avoid cavitation. The slower acceleration of acceleration profile S 1  and the lower speed of steady speed segment S 5  provides additional time for fluids to move into the pumping chamber of displacement pump  28 , reducing vacuum pressure and avoiding cavitation. In examples of plural component spray systems, such as system  1010 , reducing vacuum pressure also helps maintain the component materials at desired ratios. 
     The constant speed of the fluid displacement member during steady speed segment S 5  also results in stable pressure that maintains a constant spray pattern width as fluid is emitted from the sprayer. In deceleration segment S 6 , the fluid displacement member decelerates as the fluid displacement member approaches the end of the upstroke. The fluid displacement member changes over from the upstroke to the downstroke at the end of deceleration segment S 6 . 
     Acceleration segments S 1  and S 4  and deceleration segments S 3  and S 6  are periods of time where the fluid displacement member is changing speed, which can also be referred to as periods of changeover. The changeover periods can reduce flow from the pump, thereby resulting in lower pressures and flowrates. A reduced pressure reduces the spray fan width and makes it more difficult to atomize the fluid, which can result in coarser droplets and unatomized fluid at the extreme ends of the spray pattern. Reduced pressure from a feed pump  1012  in a plural component spray system can also increase the chance of cavitation in the downstream proportioner pumps  1022   a ,  1022   b . Piston speed profile SP 2  provides significantly less changeover time for acceleration and deceleration as compared to piston speed profile SP 1 , providing greater pump efficiency, a more consistent spray pattern, a more consistent pressure and flow rate, improved spray quality, and reduced pump wear, among other benefits. 
     Steady speed segments S 2  and S 4  are periods of time where the piston speed, and therefore the pump flow and pressure, is constant. The electric motor  24 ,  1056  provides quick reaction to accelerate back to the speed of steady speed segments S 2 , S 4  if the pump stalls mid-stroke due to the sprayer being detriggered. The peak speeds of piston speed profile SP 2  are substantially lower than the peak speeds of piston speed profile SP 1 . This reduces the wear on the pump, provides enhanced pressure stabilization, and prevents cavitation. 
     The area of the curves of each of piston speed profile SP 1  and piston speed profile SP 2  are proportional to the total flow from the pump. The areas under the curves of each of piston speed profile SP 1  and piston speed profile SP 2  are approximately equal, such that the pumps  12 ,  12 ′,  1012  reduce undesired acceleration and deceleration and provides lower peak forces while providing the same or similar flow and pressure. 
     While the pumping assemblies of this disclosure are discussed in the context of a spraying system, it is understood that the pumping assemblies and controls can be utilized in a variety of fluid handing contexts and systems and are not limited to those discussed. Any one or more of the pumping assemblies discussed can be utilized alone or in unison with one or more additional pumps to transfer fluid for any desired purpose, such as location transfer, spraying, metering, application, etc. 
     DISCUSSION OF NON-EXCLUSIVE EXAMPLES 
     The following are non-exclusive descriptions of possible embodiments of the present disclosure. 
     A pumping assembly for pumping a fluid from an upstream fluid source to a downstream location includes a motor including a stator and a rotor, the rotor configured to rotate relative the stator on a pump axis; a pump frame supporting the motor by a first static connection and a first dynamic connection; and a drive mechanism connected to the rotor, the drive mechanism configured to receive a rotational output from the rotor and convert the rotational output into a linear input along the pump axis to cause pumping of the fluid. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism includes a drive nut connected to the rotor to rotate with the rotor; a screw elongated along the pump axis and disposed coaxially on the pump axis; and a plurality of rolling elements disposed radially between the drive nut and the screw and supporting the drive nut relative the screw to maintain a radial gap between the drive nut and the screw. 
     The plurality of rolling elements are formed by one of balls and rollers. 
     A lubricant fitting connected to one of the drive nut and the screw. 
     The lubricant fitting is fluidly connected to a bore extending axially through the screw. 
     The lubricant fitting is disposed within the bore. 
     A main body of the pump frame extends in a first axial direction relative a first axial end of the motor, and wherein the first static connection is formed between the pump frame and a second axial end of the motor disposed opposite the first axial end. 
     The pump frame further comprises a frame member disposed at the second axial end of the motor and fixed to the motor; and a connecting member extending between the frame member and the main body and fixing the frame member to the main body. The motor is disposed axially between the main body and the frame member. 
     The connecting member includes a plurality of connecting members forming an exoskeleton about the motor. 
     The exoskeleton is formed by a plurality of tie rods. 
     At least a portion of the drive mechanism is disposed within the main body. 
     The main body is formed from a plurality of component parts fastened together. 
     The first dynamic connection is formed by a bearing supporting the motor on the pump frame, the bearing configured to react axial loads in each of a first axial direction and a second axial direction. 
     The bearing is disposed radially between and a rotor shaft and the pump frame, wherein the rotor shaft extends in the first axial direction from the rotor and is disposed at least partially within the pump frame. 
     The rotor shaft extends in the first axial direction on the pump axis, and wherein the rotor shaft includes a first shaft end connected to the drive mechanism and a second shaft end connected to a rotor body of the rotor. 
     The rotor shaft is disposed radially between the main body and a screw of the drive mechanism with the screw disposed in a first position associated with an end of an upstroke. 
     The rotor shaft is disposed radially between the screw and the bearing with the screw disposed in the first position. 
     The first static connection is formed at a second axial end of the motor disposed opposite a first axial end of the motor, and wherein a permanent magnet array of the rotor is disposed axially between the first static connection and the bearing. 
     The pump frame includes a frame member connected to the motor at the second axial end to form the first static connection. 
     A main body of the pump frame extends in the first axial direction relative the motor, and wherein the motor is disposed axially between the main body and the first static connection. 
     The bearing is disposed axially between a rotating component of the drive mechanism and the motor. 
     The drive mechanism comprises a drive nut connected to an end of the rotor shaft to rotate with the rotor; a screw elongate along the pump axis and disposed coaxially on the pump axis; and a plurality of rolling elements disposed radially between the drive nut and the screw and supporting the drive nut relative the screw to maintain a radial gap between the drive nut and the screw. The bearing is disposed axially between the drive nut and the motor. 
     The rotor is disposed about the stator such that the motor includes an outer rotator A displacement pump having a pump body and a piston. The pump body is connected to the pump frame by a second static connection; and the piston is connected to the drive mechanism by a second dynamic connection. 
     The first dynamic connection is disposed axially between the first static connection and the second static connection. 
     The pump frame is mounted to a support frame having wheels. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray and the pumping assembly of any of the previous examples disposed upstream of and fluidly connected to the spray applicator to pump spray fluid to the spray applicator. 
     A pumping assembly for pumping a fluid includes a motor including a stator and a rotor, the rotor configured to rotate relative the stator on a pump axis; a pump frame supporting the motor by a first static connection and a first dynamic connection; a drive mechanism connected to the rotor, the drive mechanism configured to receive a rotational output from the rotor and convert the rotational output into a linear input along the pump axis to cause pumping of the fluid; and a displacement pump fixed to the pump frame by a second static connection and connected to the drive mechanism by a second dynamic connection. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The first dynamic connection is disposed axially between the first static connection and the second static connection. 
     The first dynamic connection is formed by a bearing configured to transfer axial loads generated by the displacement pump in each of a first axial direction and a second axial direction to the pump frame, thereby isolating the motor from the axial loads. 
     The second dynamic connection is formed between a screw of the drive mechanism and a fluid displacement member of the displacement member, wherein the screw and the fluid displacement member are disposed coaxially on the pump axis. 
     A fluid sprayer includes a frame elongate along an axis to have a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the rotor rotating about an axis, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder, the piston reciprocating along the axis within the cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw that is elongate along the axis, the screw only one of linearly translating along or rotating about the axis, the drive mechanism outputting linear reciprocating motion, wherein the piston receives the linear reciprocating motion output by the drive mechanism to reciprocate the piston along the axis while the cylinder is braced by the frame such that the piston reciprocates within the cylinder. 
     The fluid sprayer of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism includes a drive nut connected to the rotor to rotate with the rotor; a screw elongated along the pump axis and disposed coaxially on the pump axis; and a plurality of rolling elements disposed radially between the drive nut and the screw and supporting the drive nut relative the screw to maintain a radial gap between the drive nut and the screw. 
     A lubricant fitting connected to one of the drive nut and the screw. 
     The lubricant fitting is fluidly connected to a bore extending axially through the screw. 
     A main body of the frame extends in a first axial direction relative the motor, and wherein a first static connection is formed between the frame and an end of the motor disposed opposite the first end of the frame. 
     The pump frame further includes a frame member disposed at the second axial end of the motor and fixed to the motor; and a connecting member extending between the frame member and the main body and fixing the frame member to the main body. The motor is disposed axially between the main body and the frame member. 
     The connecting member includes a plurality of connecting members forming an exoskeleton about the motor. 
     At least a portion of the drive mechanism is disposed within the main body. 
     The main body is formed from a plurality of component parts fastened together. 
     A first dynamic connection is formed by a bearing supporting the motor on the frame, the bearing configured to react axial loads in each of a first axial direction and a second axial direction. 
     The bearing is disposed radially between and a rotor shaft and the frame, wherein the rotor shaft extends in the first axial direction from the rotor and is disposed at least partially within the frame. 
     The rotor shaft extends in the first axial direction on the axis, and wherein the rotor shaft includes a first shaft end connected to the drive mechanism and a second shaft end connected to a rotor body of the rotor. 
     The rotor shaft is disposed radially between the main body and a screw of the drive mechanism with the screw disposed in a first position associated with an end of an upstroke. 
     The rotor shaft is disposed radially between the screw and the bearing with the screw disposed in the first position. 
     A first static connection is formed at an end of the motor disposed opposite the first end of the frame, and wherein a permanent magnet array of the rotor is disposed axially between the first static connection and the bearing. 
     A main body of the frame extends in the first axial direction relative the motor, and wherein the motor is disposed axially between the main body and the first static connection. 
     The bearing is disposed axially between a rotating component of the drive mechanism and the motor. 
     The drive mechanism includes a drive nut connected to an end of the rotor shaft to rotate with the rotor; a screw elongate along the pump axis and disposed coaxially on the pump axis; and a plurality of rolling elements disposed radially between the drive nut and the screw and supporting the drive nut relative the screw to maintain a radial gap between the drive nut and the screw. The bearing is disposed axially between the drive nut and the motor. 
     The rotor is disposed about the stator such that the motor includes an outer rotator. 
     The cylinder is connected to the frame by a second static connection and the piston is connected to the drive mechanism by a second dynamic connection. 
     The first dynamic connection is disposed axially between the first static connection and the second static connection. 
     The pump frame is mounted to a support frame having wheels. 
     A pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate on a pump axis about the stator to cause reciprocation of a fluid displacement member of a pump on the pump axis; a drive mechanism connected to the rotor, the drive mechanism configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid by the fluid displacement member; and a bearing supporting the rotor and configured to react axial loads in both a first axial direction along the pump axis and a second axial direction along the pump axis. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The rotor is supported on an axle of the motor by a first bearing disposed at a first axial end of the motor and a second bearing disposed at a second axial end of the motor. 
     The rotor includes a rotor body supporting a plurality of permanent magnets and a rotor shaft extending in the first axial direction from the rotor body. 
     The rotor shaft extends into a pump frame and the bearing is disposed radially between the rotor shaft and the pump frame. 
     The motor is disposed at a first end of the pump frame. 
     A displacement pump mounted to a second send of the pump frame disposed opposite the first end of the pump frame, wherein the displacement pump includes a piston connected to the drive mechanism to be translated along the pump axis by the drive mechanism. 
     The displacement pump is a double displacement pump such that the displacement pump is configured to output fluid during an upstroke of the piston and during a downstroke of the piston. 
     The rotor shaft includes a first shaft component extending in the first axial direction from a first end of the rotor body; and a second shaft component extending in the first axial direction from the first shaft component. The bearing is disposed in a first notch formed by the first shaft component and the second shaft component. 
     The pump frame includes a first body component at least partially axially overlapping the first shaft component; and a second body component at least partially axially overlapping the second shaft component. The bearing is disposed in a second notch formed by the first body component and the second body component. 
     The bearing extends radially between a first notch formed on the rotor shaft and a second notch formed on the pump frame. 
     The rotor body contacts the bearing. 
     The bearing is disposed axially between a drive nut of the drive mechanism and the motor. 
     The drive mechanism includes a drive nut connected to the rotor to be rotatably driven by the rotor; a screw disposed coaxially with the drive nut on the pump axis and configured to be driven linearly by rotation of the drive nut; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The drive nut is spaced from the bearing in the first axial direction and the motor is spaced from the bearing in the second axial direction. 
     The screw axially overlaps with the bearing with the screw in a first position associated with the end of an upstroke. 
     The rotor includes a rotor shaft extending in the first axial direction from the rotor into a pump frame; the bearing is disposed between the rotor shaft and the pump frame; and the drive nut is mounted to an end of the rotor shaft disposed opposite the motor. 
     The end of the rotor shaft includes a radial flange, wherein a first side of the radial flange forms at least a part of an inner groove supporting the bearing. 
     The drive nut contacts a second side of the radial flange. 
     The bearing comprises a double row angular contact bearing. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any one of the previous examples disposed upstream of and fluidly connected to the spray applicator to pump spray fluid to the spray applicator. 
     A pumping assembly includes a motor having a stator and a rotor disposed coaxially about the stator on a pump axis, the rotor including a rotor shaft extending in a first axial direction from a rotor body of the rotor; a pump frame extending in the first axial direction from a first end of the motor such that the rotor shaft extends into the pump frame, wherein the pump frame is connected to the stator to support the motor; a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor to a linear input along the pump axis; and a bearing supporting the motor relative the pump frame and configured to transmit axial forces to the pump frame. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A fluid displacement member connected to a screw of the drive mechanism to be driven in the first axial direction and a second axial direction by the screw. 
     The drive mechanism includes a drive nut disposed coaxially with the screw on the pump axis, the drive nut connected to the rotor shaft to receive the rotational output. 
     The bearing is disposed axially between the drive nut and the rotor body. 
     A method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by the rotation of the rotor; reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis, wherein reciprocating the fluid displacement member causes the fluid displacement member to pump fluid; receiving axial loads generated during pumping at the drive mechanism; and transmitting the axial loads to a pump frame by a bearing disposed radially between the pump frame and a rotor shaft connecting the drive mechanism to the rotor. 
     A portable fluid sprayer includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered and having a rotor and a stator, wherein the motor is configured to output rotational motion about an axis; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder, wherein the piston is configured to reciprocate along the axis within the cylinder; a drive mechanism supported by the frame and located axially between the motor and the pump, the drive mechanism comprising a screw that is elongate along the axis, the screw configured to only one of linearly translate along or rotate about the axis, the drive mechanism configured to output linear reciprocating motion; a bearing assembly located between the drive mechanism and the motor. The piston is configured to receive the linear reciprocating motion output by the drive mechanism and to reciprocate within the cylinder through an upstroke and a downstroke. The piston receives a downward reaction force when moving through the upstroke and an upward reaction force when moving through the downstroke. The drive mechanism and the bearing assembly are arranged such that both of the upward reaction force and the downward reaction force transfer through the drive mechanism and to the bearing assembly. The bearing assembly permits rotational motion to pass within the bearing assembly from the motor to the drive mechanism while the bearing assembly prevents some or all of both of the downward reaction force and the upward reaction force from transferring to the rotor. 
     The fluid sprayer of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The bearing assembly transfers the downward reaction force and the upward reaction force to the rotor frame. 
     The bearing assembly comprises a double row angular contact bearing. 
     The bearing assembly includes an inner race, an outer race, and a plurality of rolling elements disposed between the inner race and the outer race. 
     The inner race is supported by a rotor shaft extending between and connecting the rotor and the drive mechanism. 
     The outer race is supported by the frame. 
     The bearing assembly includes a first annular array of rolling elements and a second annular array of rolling elements spaced axially from the first annular array of rolling elements. 
     The rolling elements include balls. 
     The rolling elements include rollers. 
     The rotor is supported on an axle of the motor by a first motor bearing disposed at a first axial end of the motor and a second motor bearing disposed at a second axial end of the motor. 
     The rotor includes a rotor body supporting a plurality of permanent magnets and a rotor shaft extending in the first axial direction from the rotor body. 
     The rotor shaft extends into the frame and the bearing assembly is disposed radially between the rotor shaft and the frame. 
     The pump is a double displacement pump such that the pump is configured to output fluid during both the upstroke of the piston and the downstroke of the piston. 
     The rotor shaft includes a first shaft component extending in the first axial direction from a first end of the rotor body; and a second shaft component extending in the first axial direction from the first shaft component. The bearing is disposed in a first notch formed by the first shaft component and the second shaft component. 
     The frame includes a first body component at least partially axially overlapping the first shaft component; and a second body component at least partially axially overlapping the second shaft component. The bearing is disposed in a second notch formed by the first body component and the second body component. 
     The bearing extends radially between a first notch formed on the rotor shaft and a second notch formed on the pump frame. 
     A rotor body of the rotor contacts the bearing assembly. 
     The bearing is disposed axially between a drive nut of the drive mechanism and the motor. 
     The drive mechanism includes a drive nut connected to the rotor to be rotatably driven by the rotor; a screw disposed coaxially with the drive nut on the pump axis and configured to be driven linearly by rotation of the drive nut; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The drive nut is spaced from the bearing in the first axial direction and the motor is spaced from the bearing in the second axial direction. 
     The screw axially overlaps with the bearing assembly with the screw in a first position associated with the end of the upstroke. 
     The rotor includes a rotor shaft extending in a first axial direction from the rotor into the frame; the bearing assembly is disposed between the rotor shaft and the frame; and the drive nut is mounted to an end of the rotor shaft disposed opposite the motor. 
     The end of the rotor shaft includes a radial flange, wherein a first side of the radial flange forms at least a part of an inner groove supporting the bearing. 
     The drive nut contacts a second side of the radial flange. 
     A pumping assembly includes a motor and a drive mechanism. The motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis. The rotor includes a rotor body including a plurality of permanent magnets; and a rotor shaft disposed coaxially on the pump axis and extending in a first axial direction from the rotor body. The drive mechanism connected to an end of the rotor shaft opposite the rotor body, wherein the drive mechanism is configured to receive a rotational output from the rotor and generate a linear input along the pump axis to cause pumping of the fluid. The rotor shaft defines a cavity, and wherein at least a portion of the drive mechanism is disposed within the cavity. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism comprises a drive nut connected to the end of the rotor shaft to be rotatably driven by the rotor; and a screw disposed coaxially with the drive nut on the pump axis, the screw configured to be driven linearly on the pump axis by rotation of the drive nut. 
     The drive mechanism further comprises a plurality of rolling elements disposed radially between the screw and the drive nut and supporting the drive nut relative the screw. 
     The screw includes a first end oriented towards the motor and a second end disposed opposite the first end, wherein the first end is disposed within the cavity. 
     The cavity extends in a second axial direction into the rotor shaft from a first shaft end of the rotor shaft, wherein the first shaft end is connected to the drive nut, and wherein the screw extends into the cavity through the first shaft end. 
     The cavity extends in the second axial direction to a second shaft end of the rotor shaft. 
     The second shaft end is connected to the rotor body. 
     The second shaft end is closed. 
     The second cavity end is open. 
     The screw extends through the second cavity end with the screw disposed in a first position associated with the end of a stroke in the second axial direction. 
     The screw occupies a majority of a volume of the cavity with the screw disposed in a first position associated with the end of a stroke in the second axial direction. 
     The screw includes a first end oriented towards the motor and a second end disposed opposite the first end, wherein the first end axially overlaps with the rotor shaft for at least a portion of a stroke of the screw. 
     The second end does not axially overlap with the rotor shaft during the stroke. 
     The first end of the screw axially overlaps with the rotor shaft with the screw disposed in a first position associated with an end of a stroke in the second axial direction. 
     The first end of the screw does not axially overlap with the rotor shaft with the screw disposed in a second position associated with an end of a stroke in the first axial direction. 
     The rotor shaft includes a first shaft component extending in the first axial direction from the rotor body; and a second shaft component extending in the first axial direction from the first shaft component. The drive nut is connected to the second shaft component. 
     The rotor shaft does not axially overlap with the stator. 
     A first static connection is formed between a pump frame and the stator at a second end of the motor, wherein the rotor shaft extends axially from a first end of the motor disposed opposite the second end. 
     A first dynamic connection is formed between the rotor shaft and the pump frame, the first dynamic connection allowing for relative rotational movement between the rotor shaft and the pump frame and preventing relative axial movement between the rotor shaft and the pump frame. 
     The rotor shaft, the drive mechanism, and a fluid displacement member of a pump are disposed coaxially on the pump axis. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any of the preceding paragraphs disposed upstream of and fluidly connected to the spray applicator to pump spray fluid to the spray applicator. 
     A pumping assembly includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis and including a rotor shaft extending in a first axial direction from a rotor body of the rotor, wherein the rotor shaft at least partially defines a cavity; a pump frame supporting the motor, wherein the rotor shaft extends into the pump frame; a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor shaft to a linear input along the pump axis, wherein at least a portion of a linear drive element of the drive mechanism axially extends into the cavity of the rotor shaft. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism further comprises a drive nut connected to the rotor shaft to rotate with the rotor shaft, and wherein the linear drive element includes a screw configured to be driven linearly by rotation of the drive nut. 
     The screw occupies a majority of a volume of the cavity with the screw in a first position associated with an end of a stroke in a second axial direction opposite the first axial direction. 
     A method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor, the rotor including a rotor shaft coaxial with the pump axis and extending in a first axial direction from a rotor body of the rotor; displacing a screw of a drive mechanism axially along the pump axis by the rotation of the rotor; and reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis to pump a fluid. At least a portion of the screw axially overlaps with the rotor shaft for at least a portion of a reciprocation cycle of the screw. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Displacing the screw of the drive mechanism axially along the pump axis includes displacing the screw in a second axial direction opposite the first axial direction and within a cavity defined by the rotor shaft thereby increasing an axial overlap between the screw and the rotor shaft. 
     Displacing the screw in the second axial direction includes displacing the screw within the cavity and to a first position associated with an end of a stroke in the second axial direction. 
     Displacing the screw of the drive mechanism axially along the pump axis further comprises decreasing the axial overlap between the screw and the rotor shaft by displacing the screw in the first axial direction and to a second position associated with an end of a stroke in the first axial direction. 
     A fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the rotor rotating about an axis, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw having a first end, the drive mechanism outputting linear reciprocating motion; and a rotor shaft located between the motor and the drive mechanism, the rotor shaft conveying the rotational motion from the motor to the drive mechanism, the rotor shaft comprising a cavity within which the first end of the screw linearly translates. 
     The fluid pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism further includes a drive nut connected to the rotor shaft to be rotatably driven by the rotor; and wherein the screw is disposed coaxially with the drive nut on the pump axis, the screw configured to be driven linearly on the pump axis by rotation of the drive nut. 
     The drive mechanism further comprises a plurality of rolling elements disposed radially between the screw and the drive nut and supporting the drive nut relative the screw. 
     The cavity extends in a second axial direction into the rotor shaft from a first shaft end of the rotor shaft, wherein the first shaft end is connected to the drive nut, and wherein the screw extends into the cavity through the first shaft end. 
     The cavity extends in the second axial direction to a second shaft end of the rotor shaft. 
     The second shaft end is connected to the rotor body. 
     The second shaft end is closed. 
     The second cavity end is open. 
     The screw extends through the second cavity end with the screw disposed in a first position associated with the end of a stroke in the second axial direction. 
     The screw occupies a majority of a volume of the cavity with the screw disposed in a first position associated with the end of a stroke in the second axial direction. 
     The screw includes a second end disposed opposite the first end, wherein the first end axially overlaps with the rotor shaft for at least a portion of a stroke of the screw. 
     The second end does not axially overlap with the rotor shaft during the stroke. 
     The first end of the screw axially overlaps with the rotor shaft with the screw disposed in a first position associated with an end of a stroke in the second axial direction. 
     The first end of the screw does not axially overlap with the rotor shaft with the screw disposed in a second position associated with an end of a stroke in the first axial direction. 
     The rotor shaft includes a first shaft component extending in the first axial direction from the rotor body; and a second shaft component extending in the first axial direction from the first shaft component. The drive nut is connected to the second shaft component. 
     The rotor shaft does not axially overlap with the stator. 
     A first static connection is formed between a pump frame and the stator at a second end of the motor, wherein the rotor shaft extends axially from a first end of the motor disposed opposite the second end. 
     A first dynamic connection is formed between the rotor shaft and the pump frame, the first dynamic connection allowing for relative rotational movement between the rotor shaft and the pump frame and preventing relative axial movement between the rotor shaft and the pump frame. 
     The rotor shaft, the drive mechanism, and a fluid displacement member of a pump are disposed coaxially on the pump axis. 
     A pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; a drive mechanism connected the rotor and configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid, wherein the drive mechanism includes a linear drive element configured to displace axially along the pump axis; and a clocking member interfacing with the linear drive element to prevent rotation of the linear drive element about the pump axis. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The clocking member is fixed to the linear drive element. 
     The clocking member interfaces with a pump frame mechanically fixed to the stator. 
     The clocking member is configured to move linearly relative to the pump frame with the linear drive element. 
     The pump frame includes an axially elongate slot and the clocking member includes a projection disposed in the slot. 
     The drive mechanism includes a drive nut connected to the rotor to be rotatably driven by the rotor; a screw disposed on the pump axis and forming at least a portion of the linear drive element; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The clocking member is disposed at a first end of the screw and fixed relative the screw to reciprocate with the screw. 
     The drive nut is disposed axially between the first end of the screw and the motor. 
     A clocking assembly mounted to the first end of the screw, the clocking assembly includes a support fixed to the first end of the screw and disposed coaxially with the screw; and the clocking member mounted to the support. 
     The clocking member includes a collar disposed around a body of the support; and at least one projection extending radially from the collar. 
     A pin fixes the clocking member to the support. 
     The support includes a support body extending axially along the pump axis; and a radial support flange extending from the support body. The clocking member is disposed adjacent the radial support flange. 
     The clocking member is disposed axially between the radial support flange and the screw. 
     The support further includes a mounting projection extending axially from a first end of the support body and into a bore of the screw to secure the clocking assembly to the screw. 
     The support further includes a receiver disposed at a second end of the support body, the receiver configured to connect to a fluid displacement member of a displacement pump. 
     The clocking member interfaces with a pump frame mechanically fixed to the motor, and wherein the clocking member seals against the pump frame to form a sliding seal with the pump frame. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any one of the previous examples disposed upstream of and fluidly connected to the spray applicator to pump spray fluid to the spray applicator. 
     A pumping assembly includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis, wherein the motor includes a first motor end and a second motor end; a pump frame fixed to the second motor end and including a main body extending in a first axial direction relative the motor, wherein the rotor shaft extends into the main body; a drive mechanism connected to the rotor, the drive mechanism configured to convert a rotational output from the rotor to a linear input along the pump axis; and a clocking member connected to a linear drive element of the drive mechanism and interfacing with the main body to prevent the linear drive element from rotating about the pump axis. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The motor is disposed axially between a portion of the pump frame fixed to the second motor end and the main body. 
     The drive mechanism includes a drive nut spaced in the first axial direction from the motor, and wherein the clocking member is spaced in the first axial direction from the drive nut. 
     The linear drive element includes a screw disposed coaxially with the drive nut. 
     The clocking member includes at least one radial projection disposed within an axial slot formed on the main body. 
     A method of pumping fluid to a spray gun to generate an atomized fluid spray includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by rotation of the rotor; reciprocating a fluid displacement member connected to the screw along the pump axis by displacing the screw along the pump axis, the fluid displacement member pumping a fluid downstream to the spray gun; and preventing rotation of the screw relative a pump frame mechanically fixed to both the stator and a cylinder of a pump by a clocking member interfacing with each of the screw and the pump frame. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Preventing rotation of the screw relative the pump frame includes disposing a projection of the clocking member within a slot formed in the pump frame, the projection interfacing with the slot to prevent rotation of the screw relative the pump frame. 
     Preventing rotation of the screw relative the pump frame further includes reciprocating the clocking member with the screw such that the clocking member shifts axially relative the pump frame with the screw. 
     A fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw, the drive mechanism outputting linear reciprocating motion, the piston receiving the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder; and a clocking assembly located between the motor and the pump, the clocking assembly configured to resist rotation of the screw due to the rotational motion output by the motor, the clocking assembly comprising a collar fixed about the screw, the clocking assembly further comprising a sleeve fixed with respect to the frame. Both the screw and the collar linearly translate within the sleeve while the sleeve prevents rotation of the collar. 
     The fluid pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The sleeve includes an axially elongate slot and the collar includes a projection disposed in the slot. 
     The drive mechanism further includes a drive nut connected to the rotor to be rotatably driven by the rotor; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The drive nut is disposed axially between the collar and the motor. 
     A support fixed to a first end of the screw and disposed coaxially with the screw. The collar is mounted to the support. 
     A pin fixes the collar to the support. 
     The support includes a support body extending axially along the pump axis; and a radial support flange extending from the support body. The collar is disposed adjacent the radial support flange. 
     The support further includes a mounting projection extending axially from a first end of the support body and into a bore of the screw to secure the clocking assembly to the screw. 
     The collar seals against the sleeve to form a sliding seal with the sleeve. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the fluid pump of any one of the preceding examples disposed upstream of and fluidly connected to the spray applicator to pump spray fluid to the spray applicator. 
     A pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; a drive mechanism connected the rotor and configured to convert a rotational output from the rotor into a linear input along the pump axis to cause pumping of the fluid, wherein the drive mechanism includes a linear drive element configured to displace axially along the pump axis; and a clocking member interfacing with the linear drive element to prevent rotation of the linear drive element about the pump axis. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The linear drive element is movable relative to the clocking member. 
     The clocking member is elongate along the pump axis. 
     The clocking member axially overlaps with at least a portion of the stator. 
     The clocking member is fixed to a pump frame supporting the motor. 
     The clocking member telescopically interfaces with the linear drive element. 
     The rotor includes a rotor body supporting a plurality of permanent magnets and a rotor shaft extending in a first axial direction from the rotor body and disposed coaxially with the rotor. 
     The drive mechanism includes a drive nut connected to the rotor shaft to receive a rotational output from the rotor via the rotor shaft; a screw disposed coaxially on the pump axis with the drive nut and forming at least a portion of the linear drive element; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The clocking member extends into the rotor shaft. 
     The clocking member includes a rod extending into a bore of the screw, the rod having an exterior surface contour configured to mate with an interior surface contour of the bore. 
     An axial overlap between the clocking member and the screw is larger with the screw disposed at a first position associated with an end of a stroke in a second axial direction than with the screw disposed at a second position associated with an end of a stroke in the first axial direction. 
     A bearing is disposed between the rotor shaft and a pump frame fixed to the stator, and wherein the clocking member at least partially axially overlaps with the bearing. 
     The clocking member extends axially through the bearing such that a first portion of the clocking member extends in the first axial direction relative to the bearing and a second portion of the clocking member extends in a second axial direction relative the bearing, the second axial direction being opposite the first axial direction. 
     The drive mechanism includes a drive nut connected to the rotor shaft to be rotatably driven by the rotor shaft; a screw disposed on the pump axis and forming at least a portion of the linear drive element; and a plurality of rolling elements disposed radially between the screw and the drive nut. The clocking member does not extend in the first axial direction beyond the drive nut. 
     A pump frame including a frame member fixed to the motor; and a main body extending in a first axial direction relative the motor, wherein the motor is disposed axially between the frame member and the main body. The clocking member is fixed to the frame member and extends in the first axial direction from the frame member and through the motor. 
     The clocking member telescopically interfaces with the linear drive element. 
     The clocking member includes a contoured rod elongate along the pump axis, and wherein the clocking member extends into a bore of a screw, the screw forming at least a portion of the linear drive element. 
     The bore includes a contoured opening receiving and interfacing with the contoured rod. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any one of the preceding examples disposed upstream of and fluidly connected to the spray gun to pump spray fluid to the spray gun. 
     A pumping assembly includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis and including a rotor shaft extending in a first axial direction from a first axial end of the motor; a pump frame extending in the first axial direction such that the rotor shaft extends into the pump frame, wherein the pump frame is fixed to the motor at a second axial end of the motor opposite the first axial end; a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor shaft to a linear input along the pump axis; and a clocking member fixed relative the pump frame and interfacing with a linear drive element of the drive mechanism to prevent the linear drive element from rotating about to the pump axis. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A double displacement pump fixed to the pump frame, wherein a fluid displacement member of the double displacement pump is connected to the linear drive element to be reciprocated by the linear drive element. 
     The rotor, the rotor shaft, the clocking member, the drive mechanism, and the fluid displacement member are disposed coaxially. 
     The clocking member includes a rod extending through the motor from the second end of the motor and into the rotor shaft, wherein the rod extends into a bore formed in a screw of the drive mechanism, wherein the screw forms at least a portion of the linear drive element, and wherein an exterior surface of the rod includes a first contour interfaces with a second contour formed on an interior surface of the bore to prevent the screw from rotating relative to the pump frame. 
     The second contour extends less than a full axial length of the bore. 
     The clocking member is cantilevered from the pump frame. 
     A method of pumping fluid includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the motor; displacing a screw of a drive mechanism axially along the pump axis by rotation of the rotor; reciprocating a fluid displacement member of a displacement pump, the fluid displacement member connected to the screw such that reciprocation of the screw causes reciprocation of the fluid displacement member, wherein reciprocating the fluid displacement member along the pump axis pumps a fluid downstream for spraying; and preventing rotation of the screw relative a pump frame mechanically fixed to the electric motor and the displacement pump by a clocking member telescopically interfacing with the screw. 
     A fluid pump apparatus includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the motor configured to output rotational motion; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw, the drive mechanism outputting linear reciprocating motion, the piston receiving the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder; and a clocking assembly, the clocking assembly comprising a telescope member that has a sliding overlapping interface with the screw, the telescope member preventing rotation of the screw by resisting the rotational motion output by the motor as the screw linearly translates relative to the telescope member. 
     The fluid pump apparatus of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The telescope member is elongate along the pump axis. 
     The telescope member axially overlaps with at least a portion of the stator. 
     The telescope member is fixed to a pump frame supporting the motor. 
     The rotor includes a rotor body supporting a plurality of permanent magnets and a rotor shaft extending in a first axial direction from the rotor body and disposed coaxially with the rotor. 
     The drive mechanism includes a drive nut connected to the rotor shaft to receive a rotational output from the rotor via the rotor shaft; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The telescope member extends into the rotor shaft. 
     The telescope member includes a rod extending into a bore of the screw, the rod having an exterior surface contour configured to mate with an interior surface contour of the bore. 
     An axial overlap between the telescope member and the screw is larger with the screw disposed at a first position associated with an end of a stroke in a second axial direction than with the screw disposed at a second position associated with an end of a stroke in the first axial direction. 
     A bearing is disposed between the rotor shaft and a pump frame fixed to the stator, and wherein the telescope member at least partially axially overlaps with the bearing. 
     The telescope member extends axially through the bearing such that a first portion of the telescope member extends in the first axial direction relative to the bearing and a second portion of the telescope member extends in a second axial direction relative the bearing, the second axial direction being opposite the first axial direction. 
     The telescope member includes a contoured rod elongate along the pump axis, and wherein the telescope member extends into a bore of the screw. 
     The bore includes a contoured opening receiving and interfacing with the contoured rod. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any of the preceding claims upstream of and fluidly connected to the spray gun to pump spray fluid to the spray gun. 
     A pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate about the stator on a pump axis; and a drive mechanism connected to the rotor disposed coaxially with the rotor, the drive mechanism configured to convert a rotational output from the rotor into a linear input along the pump axis in each of a first axial direction and a second axial direction to cause pumping of the fluid. A screw of the drive mechanism extends into the motor with the screw disposed at a first position associated with an end of a stroke in the second axial direction. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The screw is movable relative to the rotor. 
     The drive mechanism further includes a drive nut connected to the rotor to be rotatably driven by the rotor, the drive nut disposed around and disposed coaxially with the screw; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The screw is configured to translate within the motor in the first axial direction and the second axial direction. 
     The drive nut is spaced in the first axial direction from the rotor such that the drive nut does not axially overlap with the rotor. 
     The screw is not disposed within the motor with the screw disposed at a second position associated with an end of a stroke in the first axial direction. 
     The motor includes an axle supporting the stator and at least partially defining a motor cavity, wherein the screw extends into the motor cavity with the screw in the first position. 
     A rotor shaft extends in the first axial direction from a rotor body of the rotor, the rotor shaft at least partially defining a shaft cavity, and wherein the screw extends fully through the shaft cavity with the screw in the first position. 
     The drive nut is connected to an end of the rotor shaft opposite the rotor body. 
     A displacement pump supported by a pump frame, wherein the pump frame fixed to the motor; the displacement pump includes a fluid displacement member connected to the screw to be reciprocated by the screw. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly any one of the preceding paragraphs disposed upstream of and fluidly connected to the spray gun to pump spray fluid to the spray gun. 
     A pumping assembly includes a motor having a stator and a rotor, the rotor disposed coaxially about the stator on a pump axis, wherein the motor includes a first motor end and a second motor end; a rotor shaft extending in a first axial direction from a rotor body of the rotor; a pump frame fixed to the second motor end and including a main body extending in a first axial direction relative the motor, wherein the rotor shaft extends into the main body; and a drive mechanism connected to the rotor shaft, the drive mechanism configured to convert a rotational output from the rotor shaft to a linear input along the pump axis. The drive mechanism includes a linear drive element configured to provide the linear input, and wherein at least a portion of the linear drive element is disposed within a motor cavity within the motor with the linear drive element disposed at a first position associated with an end of a stroke in a second axial direction opposite the first axial direction. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The first portion of the linear drive element does not axially overlap with the rotor with the linear drive element in a second position associated with an end of a stroke in the first axial direction. 
     The linear drive element is a screw connected to a drive nut of the drive mechanism and disposed coaxially with the drive nut, wherein the drive nut is fixed to the rotor shaft. 
     The screw extends axially through a shaft cavity within the rotor shaft and into the motor cavity with the screw in the first position. 
     A displacement pump fixed to the pump frame by a static connection and attached to the motor by a dynamic connection between the drive mechanism and a fluid displacement member of the displacement pump. 
     A method of pumping fluid includes driving rotation of a rotor of an electric motor about a pump axis and about a stator of the electric motor; displacing a screw of a drive mechanism axially along the pump axis through a first stroke in a first axial direction and a second stroke in a second axial direction by rotation of the rotor; reciprocating a fluid displacement member connected to a first end of the screw along the pump axis by displacement of the screw along the pump axis to pump fluid; and translating a second end of the screw disposed opposite the first end into a motor cavity within the motor during the second stroke. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Translating the second end of the screw disposed opposite the first end into the motor cavity within the motor during the second stroke includes translating the screw in the second axial direction through a shaft cavity defined by a rotor shaft extending axially between the rotor and a drive nut of the drive mechanism and into the motor cavity. 
     Increasing an axial overlap between the screw and the rotor shaft as the screw translates in the second axial direction; and decreasing an axial overlap between the screw and the rotor shaft as the screw translates in the first axial direction. 
     Increasing an axial overlap between the screw and the motor as the screw translates in the second axial direction; and decreasing an axial overlap between the screw and the motor as the screw translates in the first axial direction. 
     Withdrawing the second end of the screw from the motor cavity during the first stroke. 
     A fluid sprayer includes a frame having a first end and a second end; a motor mounted on the first end of the frame, the motor electrically powered, the motor comprising a rotor and a stator, the rotor rotating about an axis, the motor configured to output rotational motion, the motor comprising a motor cavity that is coaxial with the axis; a pump mounted on the second end of the frame, the pump comprising a piston and a cylinder; a drive mechanism supported by the frame and located directly between the motor and the pump, the drive mechanism comprising a screw that is elongate along the axis, the screw having a first end, the first end of the screw linearly translating within the motor cavity along the axis, the drive mechanism outputting linear reciprocating motion, wherein the piston receives the linear reciprocating motion output by the drive mechanism to reciprocate the piston within the cylinder. 
     The fluid sprayer of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The screw is movable relative to the rotor. 
     The drive mechanism further includes a drive nut connected to the rotor to be rotatably driven by the rotor, the drive nut disposed around and disposed coaxially with the screw; and a plurality of rolling elements disposed radially between the screw and the drive nut. 
     The drive nut is spaced in the first axial direction from the rotor such that the drive nut does not axially overlap with the rotor. 
     The screw is not disposed within the motor with the screw disposed at a second position associated with an end of a stroke in a first axial direction. 
     The motor includes an axle supporting the stator and at least partially defining the motor cavity. 
     A rotor shaft extends in the first axial direction from a rotor body of the rotor, the rotor shaft at least partially defining a shaft cavity, and wherein the screw extends fully through the shaft cavity with the screw disposed at an end of a first stroke. 
     The drive nut is connected to an end of the rotor shaft opposite the rotor body. 
     A pumping assembly includes a motor including a stator and a rotor, the rotor configured to rotate on a pump axis; a fluid displacement member operatively connected to the rotor to be reciprocated through an upstroke and a downstroke along the pump axis; and a controller configured to control operation of the motor such that the fluid displacement member displaces according to a first speed profile during the upstroke and according to a second speed profile during the downstroke, the first speed profile different than the second speed profile. 
     The pumping assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The first speed profile has a first acceleration profile and the second speed profile has a second acceleration profile different than the first acceleration profile. 
     A difference between the first speed profile and the second speed profile is when accelerating out of a changeover. 
     A fluid spray system includes a handheld spray gun configured to atomize a pumped fluid into a fluid spray; and the pumping assembly of any of the preceding paragraphs disposed upstream of and fluidly connected to the spray gun to pump spray fluid to the spray gun. 
     A pumping system includes a first upstream pump having a first electric motor connected to a first fluid displacement member; a first downstream pump having an inlet fluidically connected to an outlet of the first upstream pump; a first sensor disposed downstream from an outlet of the first downstream pump; and a controller in communication with the first electric motor and the first sensor. The controller is configured to receive first parameter data from the first sensor and control operation of the first electric motor based on the first parameter data. 
     The pumping system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A second upstream pump having a second electric motor connected to a second fluid displacement member; a second downstream pump having an inlet fluidically connected to an outlet of the second upstream pump; a second sensor disposed downstream from an outlet of the second downstream pump; a controller in communication with the first electric motor, the second electric motor, the first sensor, and the second sensor. The controller is configured to receive first parameter data from the first sensor and control operation of at least one of the first electric motor and the second electric motor based on the first parameter data. 
     The controller is configured to receive second parameter data from the second sensor and to control operation of at least one of the first electric motor and the second electric motor based on to at least one of the first parameter data, the second parameter data, and a comparison of the first parameter data and the second parameter data. 
     The controller is configured to adjust power to at least one of the first electric motor and the second electric motor based on the comparison indicating that a ratio between a first parameter indicated by the first parameter data and a second parameter indicated by the second parameter data differs from a target ratio between the first parameter and the second parameter. 
     The first pump is sized to fill the third pump during a fill stroke of the third pump with a single stroke of the first pump such that the first pump does not change stroke direction during the fill stroke of the third pump. 
     The second pump is sized to fill the fourth pump during a fill stroke of the fourth pump a single stroke of the second pump such that the second pump does not change stroke direction during the fill stroke of the fourth pump. 
     The controller is configured to stop rotation of the first electric motor during a return stroke of the third pump, the return stroke being in an opposite stroke direction from the fill stroke of the third pump. 
     The controller is configured to control a stroke direction of the first upstream pump such that a changeover of the stroke direction occurs during a predetermined portion of a fill stroke of the first downstream pump. 
     The first sensor comprises a first pressure sensor and the second sensor comprises a second pressure sensor. 
     The first sensor comprises a first flow sensor and the second sensor comprises a second flow sensor. 
     The controller is configured to adjust power to the first electric based on the first parameter data. 
     The controller is configured to adjust a speed of the first electric motor based on the first parameter data. 
     The controller is configured to adjust a pressure output by the first feed pump based on the first parameter data. 
     An applicator comprising a mixing chamber fluidically connected to the outlet of the first downstream pump and fluidic ally connected to the outlet of the second downstream pump. 
     A first heated hose disposed between the outlet of the third pump and to the mixing chamber of the applicator; and a second heated hose disposed between the outlet of the fourth pump and to the mixing chamber of the applicator. 
     The first pump includes a piston configured to reciprocate axially along a pump axis of the first pump; and a drive mechanism connected to the piston. The drive mechanism is connected to a first rotor of the first electric motor. The drive mechanism is configured to receive a rotational output from the first rotor and provide a linear input to the piston to cause the piston to displace axially along the pump axis. The piston, the drive mechanism, and the first rotor are disposed coaxially. 
     The drive mechanism includes a drive nut connected to the rotor of the first electric motor and configured to rotate with the rotor of the first electric motor; and a screw connected with the drive nut and connected to a piston shaft of the piston of the first pump. 
     A third sensor disposed downstream from the first upstream pump and upstream from the first downstream pump; and a fourth sensor disposed downstream from the second upstream pump and upstream from the second downstream pump. The controller is in communication with the third sensor and the fourth sensor. The controller is configured to receive third parameter data from the third sensor and control operation of at least one of the first electric motor and the second electric motor based on the third parameter data. 
     The controller is configured to receive fourth parameter data from the fourth sensor and to control operation of at least one of the first electric motor and the second electric motor based on to at least one of the third parameter data, the fourth parameter data, and a comparison of the third parameter data and the fourth parameter data. 
     A method of operating a pumping system includes driving rotation of a first rotor of a first electric motor to drive reciprocation of a first fluid displacement member of a first feed pump to pump the first component material to an inlet of a first proportioner pump; increasing a pressure of the first component material via the first proportioner pump; generating first parameter data regarding the first component material downstream of the first proportioner pump by a first sensor; and controlling operation of the first electric motor by a controller based on the first parameter data. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Driving rotation of a second rotor of a second electric motor to drive reciprocation of a second fluid displacement member of a second feed pump to pump the second component material to an inlet of a second proportioner pump; increasing a pressure of the second component material via the second proportioner pump; generating second parameter data regarding the second component material downstream of the second proportioner pump by a second sensor; and controlling operation of at least one of the first electric motor and the second electric motor based on a comparison of the first parameter data and the second parameter data. 
     Measuring a pressure of the first component material downstream of the first proportioner pump by the first sensor; measuring a pressure of the second component material downstream of the second proportioner pump by the second sensor; communicating the measured pressure of the first component material and the measured pressure of the second component material to the controller; and adjusting power to at least one of the first electric motor and the second electric motor by the controller based on at least one of the measured pressure of the first component material and the measured pressure of the second component material. 
     Measuring a flow rate of the first component material downstream of the first proportioner pump by the first sensor; measuring a flow rate of the second component material downstream of the second proportioner pump by the second sensor; communicating the measured flow rate of the first component material and the measured flow rate of the second component material to the controller; and adjusting power to at least one of the first electric motor and the second electric motor by the controller based on at least one of the measured flow rate of the first component material and the measured flow rate of the second component material. 
     The controller adjusts the rotational speed of at least one of the first electric motor and the second electric motor by modulating an electrical current to at least one of the first electric motor and the second electric motor. 
     Controlling the first electric motor such that the first feed pump pumps fluid to the first proportioner pump during a fill stroke of the first proportioner pump. 
     Controlling the first electric motor such that the first feed pump does not pump fluid to the first proportioner pump during a return stroke of the first proportioner pump, the return stroke being an opposite stroke from the fill stroke. 
     Outputting fluid by the proportioner pump during each of the fill stroke and the return stroke. 
     Controlling the first electric motor such that the first piston does not change stroke direction during the fill stroke. 
     A method of operating a pumping system configured to pump different first and second component materials to an applicator for mixing and forming a plural component material, the method includes pumping a first component material, with a first upstream pump including a first electric motor, from a first fluid tank to a first downstream pump; pumping a second component material, with a second upstream pump including a second electric motor, from a first fluid tank to a second downstream pump; controlling, by a controller, pumping by the first upstream pump, the second upstream pump, the first downstream pump, and the second downstream pump in each of a spray mode and a flush mode. The spray mode includes increasing a pressure of the first component material with the first downstream pump and pumping the first component material to an applicator with the first downstream pump; and increasing a pressure of the second component material with the second downstream pump and pumping the second component material to the applicator with the second downstream pump. The flush mode includes pumping the first component material to a first dump tank from the first proportioner pump; and pumping the second component material to a second dump tank from the second proportioner pump. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Initiating a flush routine to enter the flush mode from the operating mode; and depowering each of the first upstream pump, second upstream pump, first downstream pump, and second downstream pump based on the flush routine being initiated. 
     Actuating a first flush valve from a first position to a second position, the second position of the first flush valve fluidly connecting an outlet of the first downstream pump with a first flush line configured to provide the first component material to the first dump tank; and actuating a second flush valve from a first position to a second position, the second position of the second flush valve fluidly connecting an outlet of the second downstream pump with a second flush line configured to provide the second component material to the second dump tank. 
     Powering the first electric motor with the first flush valve in the second position and powering the second electric motor with the second flush valve in the second position. 
     Activating the first downstream pump with the first flush valve in the second position and activating the second downstream pump with the second flush valve in the second position. 
     Causing pumping by the first upstream pump, the second upstream pump, the first downstream pump, and the second downstream pump for a flush duration based on a flush parameter. 
     The flush parameter is a count of pump cycles and the flush duration is a number of pump cycles. 
     Actuating the first flush valve from the second position to the first position; and actuating the second flush valve from the second position to the second position. 
     Depowering each of the first upstream pump, second upstream pump, first downstream pump, and second downstream pump based on the first flush valve returning to the first position and on the second flush valve returning to the first position. 
     Actuating the first flush valve from the first position to the second position based on the first upstream pump and the first downstream pump being depowered; and actuating the second flush valve from the first position to the second position based on the second upstream pump and the second downstream pump being depowered. 
     Determining a completion status of the flush mode based on detection of air in one of the first component material entering the first dump tank and the second component material entering the second dump tank; and exiting the flush mode based on an absence of air in each of the first component material and the second component material. 
     Recirculating the first component material during the flush mode such that the first fluid tank is the first dump tank; and recirculating the second component material during the flush mode such that the second fluid tank is the second dump tank. 
     A pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about a pump axis; a drive mechanism connected to the rotor and configured to translate a rotating input from the rotor to a linear output, wherein the drive mechanism is coaxial with the rotor; and a displacement assembly including a piston, wherein the piston is connected to the drive mechanism to receive the linear output and is disposed coaxially with the drive mechanism and the rotor, wherein the piston is configured to reciprocate axially along the pump axis to pump fluid. 
     The pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism includes a drive nut connected to the rotor and configured to rotate with the rotor; and a screw connected with the drive nut and the piston, wherein the screw and the drive nut are coaxially aligned with the rotor and the piston. 
     The drive mechanism includes a plurality of rolling elements disposed within a gap between the screw and the drive nut. The plurality of rolling elements axially align the screw inside the drive nut and are configured to be driven by rotation of drive nut to drive the screw axially. The plurality of rolling elements maintain the gap and prevent direct contact between the drive nut and the screw. 
     The drive mechanism further includes a drive nut bore extending axially through the drive nut and inner threading formed on a surface of the hole, wherein the inner threading rotates with the drive nut; and outer threading on the screw, wherein the outer threading moves axially with the screw. Each rolling element of the plurality of rolling elements interfaces with both the inner threading and the outer threading. 
     The plurality of rolling elements includes one of balls and elongate rollers. 
     The rolling elements are mechanically attached to the drive nut and are configured to rotate with the drive nut and configured to rotate relative the drive nut. 
     A rotor shaft connected to the rotor and coaxial with the rotor, wherein the rotor shaft rotates with the rotor and connects the rotor to the drive mechanism. 
     The screw extends into the rotor shaft. 
     The rotor shaft is at least partially disposed within and surrounded by the rotor. 
     A spacer is disposed on the screw and radially between the screw and the rotor shaft, wherein the spacer prevents the screw from directly contacting the rotor shaft. 
     The spacer is connected to the screw to translate axially with the screw. 
     The spacer is disposed at an end of the screw opposite the piston. 
     The spacer is disposed coaxially on the central axis and aligns the screw on the central axis. 
     The spacer is formed from a non-ferrous material. 
     The spacer is formed from a plastic. 
     The screw extends within each of the rotor and the stator of the electric motor. 
     The screw axially overlaps with a permanent magnet array of the rotor. 
     A rotor shaft connected to and disposed coaxially within a rotor body of the rotor. The rotor shaft rotates with the rotor body and connects the rotor body to the drive mechanism. The rotor shaft is hollow and receives the screw. 
     The screw extends within the electric motor such that a radial line extending from the central axis passes through, in order, the screw, the rotor shaft, the rotor, and the stator. 
     An axial overlap between the rotor shaft and the screw is larger with the screw disposed at a first position associated with an end of a stroke in a first axial direction than with the screw disposed at a second position associated with an end of a stroke in a second axial direction. 
     A spacer mounted on the screw and supporting the screw relative the rotor shaft. 
     An axial overlap between the screw and the rotor shaft is configured to vary during reciprocation of the piston. 
     The displacement assembly includes a first check valve disposed on the central axis; and a second check valve disposed on the central axis. The second check valve is disposed in the piston to travel with the piston. 
     A bearing assembly connecting the rotor of the electric motor to the drive mechanism, wherein the bearing assembly is configured to react axial loads. 
     A fluid outlet manifold positioned axially between the piston and the bearing assembly; and a plurality of tie rods extending axially between the bearing assembly and the fluid outlet manifold and connecting the bearing assembly and the fluid outlet manifold. 
     A clocking assembly disposed axially between the fluid outlet manifold and the bearing assembly, the clocking assembly interfacing with the screw to prevent the screw from rotating about the pump axis. 
     The rotor is an inner rotor disposed radially within the stator. 
     A pump includes an electric motor comprising a stator and a rotor disposed within the stator, the rotor configured to rotate about a pump axis; a displacement assembly including a piston, wherein the piston is disposed coaxially with the rotor and is configured to reciprocate axially along the pump axis to pump fluid; a drive mechanism connected to the rotor and the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston, wherein the drive mechanism is coaxial with the piston and the rotor; a fluid outlet manifold positioned axially between the piston and the rotor, the fluid outlet manifold in fluid communication with the displacement assembly; a first check valve axially between a piston head of the piston and a fluid inlet of the feed pump; and a second check valve disposed in the piston to travel axially with the piston. 
     The pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The drive mechanism includes a drive nut connected to the rotor and configured to rotate with the rotor; a screw extending through the drive nut and coaxial with the drive nut, wherein the screw is connected to the piston and is coaxial with both the piston and the rotor; and a plurality of rolling elements disposed within a gap between the screw and the drive nut, wherein the plurality of rolling elements support the screw relative the drive nut to prevent contact between the screw and the drive nut, and wherein the plurality of rolling elements are configured to be driven by rotation of the rotor shaft and the drive nut to drive the screw axially. 
     The fluid outlet manifold is disposed axially between the drive nut and the piston head. 
     A bearing assembly connecting the rotor to the drive mechanism. The bearing assembly is disposed axially between the rotor and the drive nut. 
     A plurality of tie rods extending axially between the fluid outlet manifold and a housing of the bearing assembly and connecting the bearing assembly and the fluid outlet manifold. 
     A drive mechanism for a feed pump that converts a rotational output from an electric motor into a linear input, wherein the drive mechanism includes a screw and a drive nut. The screw having a first end; a second end axially opposite the first end relative the pump axis; and a spiral groove extending on an outer surface of the screw between the first end and the second end, wherein the second end of the screw extends within each of a rotor shaft, a stator, and a housing of the electric motor, and wherein the screw translates axially within the rotor shaft. The drive nut connected to the rotor and configured to rotate with the rotor. 
     The drive mechanism of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A plurality of rolling elements disposed within a gap between the screw and the drive nut, wherein the plurality of rolling elements support the screw relative the drive nut and are configured to be driven by rotation of the rotor shaft and the drive nut to drive the screw axially. 
     A spacer bearing connected to the second end of the screw and radially between the second end of the screw and the rotor shaft relative the pump axis. 
     The screw does not directly contact the rotor shaft. 
     An axial overlap between the screw and the rotor shaft is largest at an end of an upstroke of the feed pump and smallest at an end of a downstroke of the feed pump. 
     A plural component spray system comprising a first feed pump, wherein the first feed pump comprises the pump of any preceding paragraph; a second feed pump; a first proportioner pump fluidically connected to an outlet of the first feed pump; a second proportioner pump fluidically connected to an outlet of the second feed pump; and an applicator connected to an outlet of the first proportioner pump and to an outlet of the second proportioner pump to output a plural component material formed from materials pumped by the first feed pump, the second feed pump, the first proportioner pump, and the second proportioner pump. 
     The plural component spray system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The second feed pump comprises the pump of any one of the preceding claims. 
     A pump apparatus for pumping fluid from a reservoir, the pump apparatus including a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism. 
     The pump apparatus of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A drive shaft connected to a piston and the drive mechanism, wherein the drive shaft is configured to reciprocate axially along the pump axis of; a bearing assembly rotationally connecting a rotor shaft to the drive mechanism, wherein the rotor shaft is disposed within a rotor body of the rotor and is coaxial with the screw and the rotor; a fluid outlet manifold positioned axially between the cylinder and the bearing assembly. 
     A plurality of tie rods extending axially between the fluid outlet manifold and a housing of the bearing assembly and connecting the bearing assembly and the fluid outlet manifold. 
     The rotor includes a rotor shaft extending axially along the axis and connected to the drive mechanism. 
     A first check valve disposed axially between the piston and a fluid inlet of the cylinder; and a second check valve disposed within the piston to travel axially with the piston. 
     A plurality of rolling elements disposed within a gap between the screw and the drive nut, wherein the plurality of rolling elements support the screw relative the drive nut and are configured to be driven by rotation of the rotor shaft and the drive nut to drive the screw axially. 
     The nut is connected to the rotor and configured to rotate with the rotor; the screw extends through the nut and is coaxial with the nut; and the screw is connected to the piston and is coaxial with both the piston and the rotor. 
     The bearing assembly further includes a first housing member comprising a first opening; a second housing member positioned axially between the first housing member and the electric motor and comprising a second opening, wherein the second housing member is connected to a housing of the electric motor and to the first housing member; a sleeve coupler position axially between the first housing member and the second housing member and coaxial with the first housing member and the second housing member; a first plurality of roller bearings disposed between the sleeve coupler and the first housing member; and a second plurality of roller bearings disposed between the sleeve coupler and the second housing member, wherein the nut extends through the first opening and is connected to the sleeve coupler, and wherein the rotor is connected to the sleeve coupler through the second opening. 
     The sleeve coupler, the drive nut, and the rotor shaft are rotationally fixed relative one another such that the sleeve coupler, the drive nut, and the rotor shaft rotate in unison when the electric motor rotates the rotor shaft. 
     The screw includes a first end; a second end axially opposite the first end relative the pump axis; a spiral groove extending on an outer surface of the screw between the first end and the second end, wherein the first end of the screw is connected to a drive shaft extending between the screw and the piston, and wherein the second end of the screw extends within each of the rotor shaft, the stator, and a housing of the electric motor. 
     A spacer bearing connected to the second end of the screw and disposed radially between the second end of the screw and the rotor shaft. 
     A clocking assembly disposed axially between the fluid outlet manifold and the bearing assembly and disposed around the screw, wherein the clocking assembly prevents the screw from rotating about the axis. 
     The clocking assembly includes a clocking housing extending axially from the first housing member of the bearing assembly to the fluid outlet manifold, wherein the clocking housing is fastened to at least one of the fluid outlet manifold and the first housing member of the bearing assembly; a chamber inside the clocking housing; a collar inside the chamber and around the first end of the screw, wherein the collar is configured to slide inside the chamber relative the clocking housing; an anti-rotation pin extending through the collar and the screw to couple the screw to the collar; and an anti-rotation interface between the collar and the clocking housing and configured to prevent rotation of the collar relative the clocking housing. 
     A feed pump apparatus for pumping fluid from a reservoir, the feed pump includes a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism; wherein the piston is configured to reciprocate within a working zone to build pressure within the cylinder, and wherein the piston can travel into a pressure relief zone to vent pressurized fluid from the cylinder to the reservoir. 
     The feed pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The piston includes a vent seal mounted on the piston shaft, the vent seal disposed axially between a piston head of the piston and the drive mechanism, wherein the vent seal is configured to control flow through a vent path in fluid communication with the reservoir. 
     The piston head seals against a side wall of the cylinder to divide the cylinder into an upstream chamber and a downstream chamber, wherein the vent seal provides a seal between the downstream chamber and the vent path. 
     A portion of the downstream chamber is formed between a seal housing and the cylinder, wherein the vent seal is disposed within the seal housing and at the vent path extends through the seal housing. 
     A seal housing disposed within the cylinder, wherein the vent seal is disposed within the seal housing. 
     The seal housing is disposed coaxially with the cylinder. 
     The seal housing extends from a first end of the cylinder towards a second end of the cylinder, wherein the piston extends into the cylinder through the first end. 
     A fluid outlet of the cylinder extends through the first end. 
     The seal housing includes at least one port through the seal housing. 
     The at least one port is disposed at a convergence of the working zone and the pressure relief zone. 
     The vent seal enters the pressure relief zone to fluidly connect an interior of the cylinder to the vent with a lower edge of the vent seal extending over the at least one port. 
     The vent seal enters the pressure relief zone to fluidly connect an interior of the cylinder to the vent path when the vent seal is moved axially between the at least one port and a bottom end of the seal housing. 
     The vent seal includes a seal support connected to the piston; and a seal member mounted on the seal support. 
     The seal support forms a portion of a piston shaft of the piston. 
     The seal support includes a radial flange, and wherein the seal member is disposed on a side of the radial flange facing the vent path. 
     The seal member is a cup seal. 
     A pressure-actuated relief valve disposed downstream from the cylinder. 
     The pressure-actuated relief valve is configured to output fluid to the reservoir. 
     A fluid outlet manifold disposed axially between the piston and the drive mechanism, wherein the fluid outlet manifold is in fluid communication with the pump; 
     The fluid outlet manifold is connected to the cylinder by at least one axially elongate tube, the tube providing a flowpath for fluid between the cylinder and the fluid outlet manifold. 
     The pressure-actuated relief valve is mounted to the fluid outlet manifold. 
     The reservoir is a drum, an outlet of the fluid outlet manifold is disposed outside of the drum, and the pressure-actuated relief valve provides fluid to an interior of the drum. 
     A pump including an electric motor comprising a stator and a rotor, the rotor configured to rotate about a pump axis; a drive mechanism connected to the rotor and configured to translate a rotating input from the rotor to a linear output, wherein the drive mechanism is coaxial with the rotor; and a displacement assembly including a piston and a cylinder, wherein the piston is connected to the drive mechanism to receive the linear output and is disposed coaxially with the drive mechanism and the rotor; wherein the piston is configured to reciprocate axially within a working zone to build pressure within the cylinder, and wherein the piston can travel into a pressure relief zone to vent pressurized fluid from the cylinder to the reservoir. 
     A feed pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about an axis; a drive shaft connected to a piston, wherein the drive shaft is configured to reciprocate axially along the pump axis of the feed pump, and wherein the drive shaft is coaxial with the rotor; a drive mechanism connected to the rotor and to the drive shaft, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the drive shaft; a pump including a piston connected to the drive shaft to be reciprocated by the drive shaft and a cylinder surrounding the piston; a fluid outlet manifold positioned axially between the piston and the drive mechanism and including a fluid outlet, the fluid outlet manifold in fluid communication with the pump; and an over-pressurization valve connected to the fluid outlet manifold and fluidically connected to the fluid outlet by an interior passage of the fluid outlet manifold. 
     The feed pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A rotor shaft connected to the rotor and coaxial with the rotor, wherein the rotor shaft rotates with the rotor, wherein the rotor shaft is coaxial with the drive shaft and connects the rotor to the drive mechanism. 
     The over-pressurization valve extends axially from the fluid outlet manifold away from the electric motor and is not coaxial with the pump axis of the feed pump. 
     The over-pressurization valve includes a ball; a seat; and a spring biasing the ball against the seat in a closed position. 
     A seal housing inside the cylinder, wherein the seal housing is connected to a first end of the seal housing and extends circumferentially around the drive shaft and is disposed axially between the piston and the first end of the cylinder; a seal inside the seal housing and connected to the drive shaft, wherein the seal extends radially from the drive shaft relative the pump axis and contacts the seal housing; and at least one port extending through the seal housing, wherein the at least one port fluidically connects an opening in the first end of the cylinder with an interior of the cylinder when the seal is moved into contact with the at least one port. 
     The seal housing includes a top end connected to the first end of the cylinder; a bottom end axially spaced from the top end and axially between the top end and the piston; and a tubular body extending from the top end to the bottom end, wherein the tubular body is spaced radially from the cylinder relative the pump axis to form an annular gap between the seal housing and the cylinder, wherein the at least one port extends radially through the tubular body proximate the bottom end of the seal housing. 
     A pressure relief assembly for a double ball piston pump, the pressure relief assembly includes a piston housing disposed around a piston, wherein the piston housing extends along an axis and comprises a first end opposite a second end, wherein a piston rod extends through an opening in the first end; a seal housing inside the piston housing, wherein the seal housing is connected to the first end of the piston housing and extends circumferentially around the piston rod and is disposed axially between a piston head and the first end of the piston housing; a seal disposed inside the seal housing and connected to the piston rod, wherein the seal extends radially from the piston rod relative the pump axis and contacts the seal housing; a vent path disposed within the seal housing and in fluid communication with the opening; and at least one port extending through the seal housing; wherein the at least one port fluidically connects the opening in the first end of the piston housing with an interior of the piston housing when the seal is in a pressure relief zone defined by the at least one port; and wherein the seal fluidly isolates the at least one port and the vent path when the seal is in a working zone defined between the first end and the at least one port. 
     A method of depressurizing a feed pump includes actuating a drive shaft connected to a piston to move the piston inside of a piston housing below a bottom of a downstroke of the piston; and moving a seal element disposed inside of the piston housing and connected to the drive shaft such that the seal element moves axially with the piston from a working zone into a pressure relief zone to fluidically connect a gap between the drive shaft and the piston housing with an interior of the piston housing such that fluid vents from the interior through the gap. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Opening an over-pressurization valve connected to the feed pump when an internal pressure of the feed pump exceeds a predetermined pressure value. 
     A feed pump apparatus for pumping fluid from a reservoir includes a frame for mounting on the reservoir; an electric motor mounted on the frame, the electric motor comprising a stator and a rotor, the rotor rotating about an axis to output rotational motion; a drive mechanism supported by the frame, the drive mechanism comprising a screw and a nut, the drive mechanism configured to receive the rotational motion output by the motor and convert the rotational motion into linear reciprocating motion, each of the screw and the nut one of rotating about the axis or linearly translating along the axis; a clocking assembly disposed axially between the electric motor and the piston wherein the clocking assembly is configured to interface with a linear displacing element of the drive mechanism to prevent rotation of the linear displacement element about the pump axis; and a pump comprising a cylinder and a piston within the cylinder, the piston configured to be linearly reciprocated along the axis by the drive mechanism. 
     The clocking assembly includes a clocking housing forming a chamber, wherein the clocking housing is stationary relative the pump axis. 
     The clocking assembly includes a collar disposed inside the chamber and around the screw, wherein the collar is configured to interface with the clocking housing to prevent rotation of the screw about the axis. 
     The collar is configured to move axially inside the chamber relative the clocking housing. 
     The collar is fixed to the screw. 
     The clocking assembly further includes an anti-rotation element extending through the collar and the screw and coupling the screw to the collar. 
     An end of the screw is connected to an end of a drive shaft extending between the screw and the piston, and wherein the collar is disposed around an interface between the end of the screw and the end of the drive shaft. 
     The collar comprises a clamshell configuration with a first half that is separable with a second half. 
     The clocking housing comprises a clamshell configuration with a first half that is separable with a second half. 
     The clocking assembly includes a clocking housing forming a chamber, wherein the clocking housing is stationary relative the pump axis; a collar disposed inside the chamber and fixed to the screw, wherein the collar is configured to interface with the clocking housing to prevent rotation of the screw about the axis; wherein the interface is formed by at least one projection extending into at least one slot. 
     The at least one projection extends from the collar and the at least one slot is formed on the clocking housing. 
     A fluid outlet manifold positioned axially between the piston and the rotor. 
     The fluid outlet manifold defines an outlet flowpath between the pump and an outlet formed in the fluid outlet manifold, wherein a manifold portion of the outlet flowpath is disposed between an outer housing and an inner housing. 
     The clocking assembly includes a collar configured to reciprocate along the axis, wherein the collar is disposed within the inner housing and interfaces with the inner housing to prevent rotation about the axis. 
     The collar axially overlaps with the manifold portion of the outlet flowpath with the piston at an end of a first stroke, the first stroke being away from the motor. 
     The feed pump further includes a plurality of tie rods extending axially and disposed circumferentially about the clocking housing. 
     The clocking housing encloses at least a portion of the nut. 
     A feed pump includes an electric motor comprising a stator and a rotor; a pump having a piston configured to reciprocate axially along the pump axis of the feed pump, and wherein the piston is coaxial with the rotor; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston; and a clocking assembly. The drive mechanism comprises a drive nut connected to the rotor and configured to rotate with the rotor; and a screw extending through the drive nut and coaxial with the drive nut. The clocking assembly axially between the electric motor and the piston and around a portion of the screw, wherein the clocking assembly is configured to prevent rotation of the screw relative the pump axis. 
     The feed pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The clocking assembly includes a clocking housing forming a chamber, wherein the clocking housing is stationary relative the pump axis; a collar inside the chamber and around the screw, wherein the collar is configured to slide inside the chamber relative the clocking housing, and wherein the collar interlocks with the clocking housing such that the collar does not rotate relative the clocking housing; and an anti-rotation pin extending through the collar and the screw and coupling the screw to the collar. 
     The clocking housing includes a slot extending radially into an inner surface of the clocking housing relative the pump axis and extending axially on the inner surface of the clocking housing relative the pump axis. 
     The collar includes a tab extending radially from the collar relative the pump axis of the feed pump and into the slot to provide anti-rotation between the collar and the clocking housing. 
     The clocking mechanism further includes a first bumper connected to a first end of the collar; and a second bumper connected to a second end of the collar and opposite the first bumper. 
     The clocking housing includes a second slot extending radially into the inner surface of the clocking housing relative the pump axis and extending axially on the inner surface of the clocking housing relative the pump axis. 
     The collar includes a second tab extending radially from the collar relative the pump axis of the feed pump and into the second slot to provide anti-rotation between the collar and the clocking housing. 
     A plural component spray system includes a first feed pump, wherein the first feed pump comprises the feed pump of any one of the preceding examples; a second feed pump; a first proportioner pump fluidically connected to an outlet of the first feed pump; a second proportioner pump fluidically connected to an outlet of the second feed pump; and an applicator connected to an outlet of the first proportioner pump and to an outlet of the second proportioner pump to output a plural component material formed from materials pumped by the first feed pump, the second feed pump, the first proportioner pump, and the second proportioner pump. 
     The plural component spray system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     Wherein the second feed pump comprises the pump of any one of the preceding examples. 
     A feed pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate about an axis; a pump having a piston disposed coaxially with the rotor and configured to reciprocate axially along the axis; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston, wherein the drive mechanism comprises a screw and a nut, wherein each of the screw and the nut one of rotates about the axis or linearly translates along the axis; a bearing assembly axially between the electric motor and the piston and rotationally connecting the rotor of the electric motor to the drive nut; wherein the piston receives a downward reaction force when moving through the upstroke and an upward reaction force when moving through the downstroke, and both of the upward reaction force and the downward reaction force transfer through the drive mechanism and to the bearing assembly, and wherein the bearing assembly permits the rotational motion to pass within the drive mechanism from the motor to the drive mechanism while the bearing assembly prevents some or all of both of the downward reaction force and the upward reaction force from transferring to the rotor. 
     The feed pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     The bearing assembly is fixed to a frame supporting the electric motor. 
     The frame includes a support extending axially between and connecting the bearing assembly to a fluid outlet manifold. 
     The support includes a plurality of tie rods. 
     A rotor shaft connected to the rotor to rotate with the rotor and disposed coaxial with the rotor, wherein connects the rotor to the drive mechanism. 
     The rotor shaft is rotationally fixed to the bearing assembly and axially free relative the bearing assembly. 
     The bearing assembly includes a first roller bearing assembly disposed axially between the nut and the electric motor; a second roller bearing assembly disposed axially between the first roller bearing assembly and the electric motor; a sleeve coupler connected to the drive nut and positioned axially between the first roller bearing assembly and the second roller bearing assembly; wherein the rotor is connected to the sleeve coupler. 
     The first roller bearing assembly is disposed on a first side of a radial flange of the sleeve coupler and the second roller bearing assembly is disposed on a second side of the radial flange such that the radial flange is disposed axially between the first roller bearing assembly and the second roller bearing assembly. 
     The bearing assembly further includes a first housing member axially aligned with the electric motor and comprising a first opening; and a second housing member connected to the first housing member and positioned axially between the first housing member and the electric motor and comprising a second opening, and wherein the drive nut extends through the first opening and is connected to the sleeve coupler, and wherein a rotor shaft of the rotor extends through the second opening and is connected to the sleeve coupler. 
     A portion of the drive nut extends into a bore of the sleeve coupler and an end of the rotor shaft extends into the bore. 
     The nut does not directly contact the rotor shaft. 
     The sleeve coupler is connected to the drive nut and the rotor shaft such that an axial gap is disposed between the drive nut and the rotor shaft. 
     The sleeve coupler, the drive nut, and the rotor shaft are rotationally fixed relative one another such that the sleeve coupler, the drive nut, and the rotor shaft rotate in unison. 
     The nut is axially fixed to the sleeve coupler and the rotor shaft is axially free relative the sleeve coupler. 
     The bearing assembly further includes a damper spring disposed axially between the first housing member and the first plurality of roller bearings. 
     The damper spring is an annular wave spring that is axially between the first housing member and the first plurality of roller bearings, and is coaxially aligned with the pump axis and the first opening in the first housing member. 
     The sleeve coupler includes a body extending axially from a first end to a second end axially opposite the first end; a flange extending radially outward from the body between the first end and the second end; and a bore. The flange includes a first surface supports the first roller bearing assembly; and a second surface axially opposite the first surface, wherein the second surface supports the second roller bearing assembly. The bore extending axially through the body from the first end to the second end of the body. 
     The body of the sleeve coupler further includes a first portion extending axially from the first end of the body to the first surface of the flange; and a second portion extending axially from the second end of the body to the second surface of the flange, wherein the first portion comprises an inner radius larger than an inner radius of the second portion. 
     The drive nut is connected to the first end of the body by at least one fastener, and the rotor shaft of the electric motor extends into the bore. 
     A feed pump includes an electric motor comprising a stator and a rotor, the rotor configured to rotate on an axis; a pump having a piston, wherein the piston is configured to reciprocate axially along the axis of the feed pump, and wherein the piston is coaxial with the rotor; a drive mechanism connected to the rotor and to the piston, the drive mechanism configured to convert a rotational output from the rotor into a linear input to the piston; and a bearing assembly rotationally connecting the rotor of the electric motor to the drive mechanism and configured to react axial loads in both a first axial direction along the axis and a second axial direction along the pump axis. 
     The feed pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A rotor shaft connected to the rotor and coaxial with the rotor, wherein the rotor shaft rotates with the rotor, wherein the rotor shaft is coaxial with the drive shaft and connects the rotor to the drive mechanism. 
     A fluid outlet manifold positioned axially between the piston and the bearing assembly; a plurality of tie rods extending axially between the fluid outlet manifold and a housing of the bearing assembly and connecting the bearing assembly and the fluid outlet manifold; a first check valve axially between the piston and a fluid inlet of the feed pump; and a second check valve axially between the piston and the first check valve. 
     The drive mechanism includes a drive nut connected to the rotor shaft and configured to rotate with the rotor shaft; a screw extending through the drive nut and coaxial with the drive nut, wherein the screw is connected to the drive shaft and is coaxial with both the drive shaft and the rotor shaft; and a plurality of rolling elements disposed within a gap between the screw and the drive nut, wherein the plurality of rolling elements support the screw relative the drive nut and are configured to be driven by rotation of the rotor shaft and the drive nut to drive the screw axially. 
     The bearing assembly rotationally connects the rotor shaft of the electric motor to the drive nut. 
     The bearing assembly includes a first roller bearing subassembly disposed axially between the drive nut and the electric motor; a second roller bearing subassembly disposed axially between the first plurality of roller bearings and the electric motor; a sleeve coupler position axially between the first roller bearing subassembly and the second roller bearing subassembly; wherein the drive nut is connected to the sleeve coupler, and wherein the rotor shaft of the electric motor is connected to the sleeve coupler. 
     The bearing assembly further includes a first housing member axially aligned with the electric motor and comprising a first opening; and a second housing member positioned axially between the first housing member and the electric motor and comprising a second opening, wherein the second housing member is connected to a housing of the electric motor and to the first housing member, wherein the sleeve coupler position axially between the first housing member and the second housing member and coaxial with the first housing member and the second housing member, wherein the first roller bearing subassembly is disposed between the sleeve coupler and the first housing member, wherein the second roller bearing subassembly is disposed between the sleeve coupler and the second housing member, wherein the drive nut extends through the first opening and is connected to the sleeve coupler, and wherein the rotor shaft of the electric motor extends through the second opening and is connected to the sleeve coupler. 
     The sleeve coupler, the drive nut, and the rotor shaft are rotationally fixed relative one another such that the sleeve coupler, the drive nut, and the rotor shaft rotate in unison when the electric motor rotates the rotor shaft. 
     The rotor shaft is not axially fixed to the sleeve coupler such that the sleeve coupler can axially move relative the rotor shaft. 
     The rotor shaft does not directly contact the drive nut. 
     The bearing assembly further includes a damper spring disposed axially between the first housing member and the first roller bearing subassembly. 
     The damper spring is an annular wave spring that is axially between the first housing member and the first roller bearing subassembly, and is coaxially aligned with the pump axis and the first opening in the first housing member. 
     The sleeve coupler includes a body extending axially from a first end to a second end axially opposite the first end; a flange extending radially outward from the body between the first end and the second end; and a bore. The flange includes a first surface contacting the first roller bearing subassembly; and a second surface axially opposite the first surface, wherein the second surface contacts the second roller bearing subassembly. The bore extending axially through the body from the first end to the second end of the body. 
     The body of the sleeve coupler further includes a first portion extending axially from the first end of the body to the first surface of the flange; a second portion extending axially from the second end of the body to the second surface of the flange, wherein the first portion comprises an inner radius larger than an inner radius of the second portion; and a shoulder in the bore axially between the inner radius of the first portion and the inner radius of the second portion, wherein an axial gap is formed between the shoulder and the drive nut. 
     The drive nut is connected to the first end of the body by at least one fastener, and the rotor shaft of the electric motor extends into the bore. 
     The first roller bearing subassembly includes a first race adjacent the first housing member; a second race adjacent the first surface of the flange; and a first plurality of bearing elements axially between the first race and the second race. 
     The second roller bearing subassembly includes a third race adjacent the second surface of the flange; a fourth race adjacent the second housing member; and a second plurality of bearing elements axially between the third race and the fourth race. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.