Abstract:
A hydraulic pumping system is provided for delivering a compressible fluid material from a hopper to an outlet. A primary hydraulically driven pumping unit has a first interior volume for receiving the fluid material from the hopper. A secondary hydraulically driven pumping unit is interconnected with the primary hydraulically driven pumping unit and has a second interior volume less than the first interior volume for receiving fluid material from the primary hydraulically driven pumping unit. The primary and secondary hydraulically driven pumping units have hydraulically driven reciprocating piston units with unequal stroke lengths. The piston units are alternately reciprocated to fill the first interior volume of fluid material from the hopper, pump a portion of the first interior volume of fluid material into the second interior volume and the remainder of the first interior volume to the outlet, and pump the second interior volume of fluid material to the outlet while fluid material is being pulled into the first interior volume in a sequential and simultaneous manner which will produce substantially continuous delivery of fluid material to the outlet.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of pumps, and more particularly, pertains to a positive displacement pump arrangement designed to produce substantially continuous delivery of a compressible fluid material. 
       BACKGROUND OF THE INVENTION 
       [0002]    Constant delivery fluid pumps find useful application in many fields. One field in which the pumps of this character are presently employed to advantage is the construction industry wherein it is relatively common practice to apply cement and plaster to building surfaces by means of spray nozzles. If a relatively uniform layer of plaster or cement material is to be applied to a building surface, the rate of flow of material from the spray nozzle of the spray unit must be relatively constant. This, in turn, requires a constant delivery pump capable of producing substantially a constant rate of material flow to the spray nozzle. 
         [0003]    Prior art pumps are, of course, known in the art, and are generally comprised of a pair of pumping units actuated in such a manner that the pumping discharges from the pumping units overlap in a manner to produce a substantially constant flow delivery at an outlet. Valve members are typically provided so that one pumping unit serves as a primary unit to initially discharge pumped material concurrently into a delivery line and into a cylinder of the other pumping unit which then operates as a secondary pumping unit to discharge its previously received material into the delivery line. 
         [0004]    One such prior art arrangement is embodied in a pair of equal stroke length material cylinders alternately driven by equal stroke length hydraulic cylinders. This arrangement requires either four separate ball and seat valves or the switching of a tube, commonly referred to as an S-tube, that changes between the material cylinders. 
         [0005]    Another prior art arrangement is formed by a pair of unequal stroke length material cylinders driven by a mechanical pumping assembly, in which the pumping action of the primary and secondary pumping units is effected mechanically by the interaction of a crank arm and a cam with follower. The mechanical pumping assembly can be variously driven by an engine or electric motor via a clutch, belts or chains, pulleys or sprockets, and a gearbox, all of which is undesirably complex. This design requires an external mechanical pressure limiting device. In addition, the pumping output rate is sometimes limited to preset pulley or sprocket ratios. The mechanical pumping assembly can also be variously driven by an engine or electric motor via a hydraulic pump and motor combination, but this retains the complexity and the high number of wearing components inherent to the mechanical pumping assembly. 
         [0006]    Accordingly, the present invention is concerned more particularly with a new and improved design of pumping apparatus in which the inherent draw backs of the prior art have been overcome. There is a need for a hydraulic equivalent to the prior art mechanical system wherein the unequal stroke length of the two material cylinders reduces the number of and simplifies components required for the pumping system, while allowing the material pressure to be equalized by controlling the pressure of the hydraulic fluid and the appropriate size combination of hydraulic cylinders. 
       SUMMARY OF THE INVENTION 
       [0007]    It is a general object of the present invention to provide a positive displacement pump in which operatively associated pumping units are interconnected hydraulically for alternating operation such that a substantially constant flow of material will be produced at an outlet. 
         [0008]    It is also an object of the present invention to provide a constant delivery hydraulically driven pump having primary and secondary piston/cylinder units with unequal stroke lengths, and a pair of valve members for controlling the supply of material into the pumping units and into a delivery outlet. 
         [0009]    It is another object of the present invention to provide a hydraulically driven pumping system having unequal stroke length material cylinders with equal material output pressure. 
         [0010]    It is a further object of the present invention to provide a pump apparatus which is especially suited to the pumping of cement, plastic and other abrasive materials. 
         [0011]    It is an additional object of the present invention to provide a hydraulically driven pumping arrangement for abrasive materials which offers improved performance, reliability and cost in installation and service. 
         [0012]    The present invention relates to a hydraulically driven pumping system for delivering a compressible fluid material from a hopper to an outlet. The system includes a primary hydraulically driven pumping unit having a first interior volume for receiving the fluid material from the hopper. A secondary hydraulically driven pumping unit is interconnected with the primary pumping unit and has a second interior volume less than the first interior volume for receiving fluid material from the primary hydraulically driven pumping unit. The primary and secondary hydraulically driven pumping units have hydraulically driven reciprocating piston units with unequal stroke lengths. The piston units are alternately reciprocated to fill the first interior volume with fluid material from the hopper, pump a portion of the first interior volume of fluid material into the second interior volume and the remainder of the first interior volume to the outlet, and pump the second interior volume of fluid material to the outlet while fluid material is being pulled into the first interior volume in a simultaneous and sequential manner which will produce substantially continuous delivery of fluid material to the outlet. 
         [0013]    In the preferred embodiment, the piston units are reciprocated in primary and secondary hydraulic cylinders of unequal lengths. The piston units are reciprocated in primary and secondary material cylinders of unequal lengths that have substantially equal output pressures. A single ball and seat combination, functioning as a check valve is positioned between the hopper and the primary hydraulically driven pumping unit. An additional single ball and seat combination functioning as a check valve is positioned between the primary hydraulically driven pumping unit and the secondary hydraulically driven pumping unit. 
         [0014]    In another aspect of the invention, a hydraulically driven pumping system for delivering a compressible fluid material from a hopper to an outlet includes a primary pumping unit having a primary material cylinder with a first interior volume for receiving the fluid material from the hopper, a primary hydraulic cylinder fed by a source of hydraulic fluid, and a primary piston unit movable back and forth over a stroke length within the primary material cylinder and the primary hydraulic cylinder. A secondary pumping unit has a secondary material cylinder having a second interior volume less than the first interior volume for receiving the fluid material from the primary material cylinder, a secondary hydraulic cylinder sized smaller than the primary hydraulic cylinder and fed by the source of hydraulic fluid, and a secondary piston unit movable back and forth over a stroke length within the secondary material cylinder and the secondary hydraulic cylinder. The stroke length of the secondary piston unit is less than the stroke length of the primary piston unit. A first ball and seat combination functioning as a check valve is located between the hopper and the primary material cylinder. A second ball and seat combination functioning as a check valve is located between the primary material cylinder and the secondary material cylinder. The primary and secondary piston units are hydraulically controlled and alternately reciprocated over their respective unequal stroke lengths to fill the first interior volume with fluid material from the hopper, pump a portion of the first interior volume of fluid material into the second interior volume and the remainder to the outlet, and pump the second interior volume of fluid material to the outlet while the fluid material is being pulled into the first interior volume in a simultaneous and sequential manner which will produce substantially continuous delivery of fluid material to the outlet. 
         [0015]    The lengths of the primary and secondary material cylinders are unequal, and the lengths of the primary and secondary hydraulic cylinders are unequal. Each of the primary and secondary piston units include a material piston adapter and a hydraulic cylinder rod having pistons on opposite ends thereof. The primary and secondary piston units have unequal hydraulic cylinder rod diameters. The hydraulic cylinder rod of the primary piston unit has a diameter that is greater than the diameter of the hydraulic cylinder rod of the secondary piston unit. The primary and secondary material cylinders have outlet pressures that are equalized by appropriately sizing the primary and second material cylinders with equal bore diameters, sizing the primary and second hydraulic cylinders with equal piston diameters and driving the primary and secondary piston units alternately by the same hydraulic pump. Sensors are included within the primary and secondary pumping units for detecting the position of the primary and secondary piston units. The primary and secondary hydraulic cylinders are hydraulically connected to each other and to a source of secondary hydraulic pump pressure. A material output rate is infinitely variable by controlling the hydraulic fluid supply to the primary and secondary hydraulic cylinders. The primary and secondary piston units have equal extension speed, but have unequal retraction speed. The volume of the primary material cylinder is substantially twice the volume of the secondary material cylinder. 
         [0016]    The invention also contemplates a method of delivering a substantially constant flow of fluid material from a hopper to an outlet using a hydraulic pumping system. The method comprises the step of 
         [0017]    (a) providing a primary hydraulically driven pumping unit having a first interior volume for receiving the fluid material from the hopper; 
         [0018]    (b) providing a secondary hydraulically driven pumping unit interconnected with the primary hydraulically driven pumping unit and having a second interior volume less than the first interior volume for receiving fluid material from the primary hydraulically driven pumping unit; 
         [0019]    (c) providing the primary and secondary hydraulically driven pumping units with hydraulically driven reciprocating piston units with unequal stroke lengths; and 
         [0020]    (d) alternately reciprocating the piston units to fill the first interior volume with fluid material from the hopper, pump a portion of the first interior volume of fluid material into the second interior volume and the remainder of the first interior volume to the outlet, and pump the second interior volume of fluid material to the outlet while fluid material is being pulled into the first interior volume in a sequential and simultaneous manner which will produce a substantially continuous delivery of fluid material to the outlet. 
         [0021]    Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The drawings illustrate the best mode presently contemplated for carrying out the invention. 
           [0023]    In the drawings: 
           [0024]      FIGS. 1 and 2  are schematic illustrations of an unequal length hydraulic cylinder drive system embodying the present invention and showing alternating phases of operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring to the drawings, a hydraulic cylinder drive system  10  forms a constant delivery pump used to provide a pressurized supply of abrasive, compressible fluid material, typically cement, plaster, mortar or the like, from a reservoir or hopper  12  to an outlet  14 . Material delivered to the outlet  14  is normally directed to a spray nozzle for distribution to a desired surface, such as a building wall. 
         [0026]    The system  10  includes a primary hydraulically driven pumping unit defined by a primary material cylinder  16  have a feed line  18  in communication within hopper  12  and an interior volume A at a head of the cylinder  16 . A first one-way check valve  20  is positioned in feed line  18  between hopper  12  and primary material cylinder  16 . The check valve  20  is a conventional mechanical design having a ball  22  movable between a stop  24  and a seat  26 . The check valve  20  allows flow of material from hopper  12  into material cylinder  16  through the line  18 , but blocks flow in the reverse direction. 
         [0027]    A primary piston unit  28  has a material piston adapter  30  with a material piston  32  movable within the interior of primary material cylinder  16 , and a hydraulic cylinder rod  34  with a second piston  36  opposite material piston  32  that is movable within an interior of primary hydraulic cylinder  38 . As will be appreciated, piston adapter  30 , hydraulic cylinder rod  34 , and pistons  32 ,  36  move back and forth in sealed relationship within primary material cylinder  16  and primary hydraulic cylinder  38 . Primary piston unit  28  has a particular stroke length as determined by the lengths of primary material cylinder  16  and primary hydraulic cylinder  38 . One end of primary hydraulic cylinder  38  is provided with a hydraulic line  40  connected to a primary hydraulic pump for supplying and returning hydraulic fluid relative to a source. Flow of hydraulic fluid through feed line  40  is separately controlled. 
         [0028]    The system  10  further includes a secondary hydraulically driven pumping unit defined by a secondary material cylinder  42  having a feed line  44  in communication with an interior volume B at a head of cylinder  42 . The feed line  44  is further in communication with the line  18  extending from the primary material cylinder  16 . A second one-way check valve  46  is positioned in line  44  between primary material cylinder  16  and the secondary material cylinder  42 . The check valve  46  is a conventional design like check valve  20  having a ball  48  movable between a stop  50  and a seat  52 . The check valve  46  allows flow from line  18  into line  44 , the secondary material cylinder  42  and outlet  14 , but prevents flow back into line  18 . 
         [0029]    It is important to note that secondary material cylinder  42  has a length that is shorter than the length of primary material cylinder  16 , and that interior volume B of secondary material cylinder  42  is less than interior volume A of primary material cylinder  16 . Interior diameters of the material cylinders  16  and  42  are substantially equal. 
         [0030]    A secondary piston unit  54  has a material piston adapter  56  with a material piston  58  movable within the interior of secondary material cylinder  42 , and a hydraulic cylinder rod  60  with a hydraulic cylinder piston  62  opposite material piston  58  that is movable within an interior of a secondary hydraulic cylinder  64 . Piston adapter  56 , hydraulic cylinder rod  60  and pistons  58 ,  62  move back and forth in sealed relationship within secondary material cylinder  42  and secondary hydraulic cylinder  64 . Secondary piston unit  54  has a particular stroke length as determined by the length of secondary hydraulic cylinder  64 . It is a key feature of the invention that the stroke length of secondary piston unit  54  is less than the stroke length of primary piston unit  28 . 
         [0031]    Secondary hydraulic cylinder  64  has a length which is shorter than the length of primary hydraulic cylinder  38 , and an interior volume which is less than the interior volume of primary hydraulic cylinder  38 . Diameters of the hydraulic cylinder pistons  36 ,  62  are substantially equal. 
         [0032]    One end of secondary hydraulic cylinder  64  is provided with a hydraulic line  66  connected to a primary hydraulic pump for supplying and returning hydraulic fluid relative to the source. A rod side of secondary hydraulic cylinder  64  is hydraulically connected with a rod side end of primary hydraulic cylinder  38  by means of a common line  68 . A further hydraulic line  70  is connected to line  68  and to a secondary hydraulic pump for supplying and returning hydraulic fluid relative to the rod side of hydraulic cylinders  38 ,  64 . Proximity sensors  72   a ,  74   a  are positioned adjacent the material cylinders  16 ,  42  to detect the fully extended position of piston units  28 ,  54  therein and signal a change in direction for both piston units. Alternatively, proximity sensors  72   b ,  74   b  are positioned adjacent the hydraulic cylinders  38 ,  64  to detect the fully extended position of piston units  28 , 54  therein and signal a change in direction for both piston units. Detection of piston location and signaling direction change may be done by a means other than a proximity sensor, whether electrical, mechanical or hydraulic in nature. 
         [0033]    It is another key feature of the present invention that the diameter of the hydraulic cylinder rod  34  in primary hydraulic cylinder  38  is greater than the diameter of the hydraulic cylinder rod  60  of the secondary hydraulic cylinder  64  as will be fully appreciated below. 
         [0034]    Operation of the system  10  as described above is as follows referring first to  FIG. 1 . Material to be pumped is placed in the hopper  12 . A primary hydraulic pump is connected to the piston side of hydraulic cylinder  64  via line  66  causing secondary piston unit  54  to extend. The hydraulic connection  68  from the rod side of hydraulic cylinder  64  to the rod side of hydraulic cylinder  38  causes primary piston unit  28  to retract. The retraction of piston unit  28  causes material to be drawn into primary material cylinder  16  from the hopper  12  past ball  22  and seat  26  and through line  18 . At the full extension of piston unit  54 , the proximity sensor  74   a  or  74   b  signals a change in direction for stroking the piston units  28 ,  54 . 
         [0035]    Referring now to  FIG. 2 , the primary hydraulic pump flow changes from being directed to the piston side of hydraulic cylinder  64  to the piston side of hydraulic cylinder  38 . Piston unit  28  extends causing approximately half the material within material cylinder  16  to be pumped out of the outlet  14 , while the other half is pumped into material cylinder  42  as piston unit  54  is retracted. Retraction is caused due to the common line  68  from the rod side of hydraulic cylinder  38  to the rod side of hydraulic cylinder  64 . Retraction is further assisted by the action of pumping material from material cylinder  16  to material cylinder  42 . The retraction of piston unit  54  causes material to be drawn into material cylinder  42  from material cylinder  16  past the ball  48  and seat  52  and through line  44 . At the full extension of piston unit  28 , the proximity sensor  72   a  or  72   b  signals the change in direction for the piston units  28 ,  54 . The primary hydraulic pump flow changes from being directed to the piston side of hydraulic cylinder  38  to the piston side of hydraulic cylinder  64 . Piston unit  54  extends causing its full volume of material in material cylinder  42  to be pumped out the outlet  14 . Material is prevented from back flowing into line  18  by check valve  46 . The piston unit  28  is simultaneously retracted. The above steps are repeated to provide a substantially continuous flow of material to the outlet  14 . 
         [0036]    During operation, piston units  28 ,  54  fully extend and retract on each alternating stroke with piston unit  28  having a longer stroke length than the piston unit  54 . The common line  68  establishes a master-slave relationship and allows for transfer of fluid between the hydraulic cylinders  38 ,  64  upon reciprocation of piston units  28 ,  54 . When pumping from material cylinder  16 , approximately one-half the volume is pumped into material cylinder  42  and the other half is pumped out to outlet  14 . When pumping from material cylinder  42 , its full volume is pumped out the outlet  14 . 
         [0037]    Piston units  28 ,  54  have an equal extension speed. Hydraulic cylinders  38 ,  64  have equal diameter pistons  36 ,  62 . The piston units  28 ,  54  are alternately driven by the same primary hydraulic pump. However, piston units  28 ,  54  have an unequal retraction speed. Each piston unit  28  or  54  must reach the fully retracted position at approximately the same time or before the other piston unit  28  or  54  is fully extended. The longer stroke piston unit  28  retracts at a faster speed than the piston unit  54  extends. Piston unit  54  retracts at a slower speed than piston unit  28  extends. This is accomplished by the rods  34 ,  60  having unequal rod diameters such that that the diameter of rod  34  is greater than the diameter of rod  60 . This is further accomplished by making the hydraulic cylinders  38 ,  64  with equal rod-side volumes. Retraction speed of the secondary piston unit  54  may be increased with the addition of material pressure being pumped from the primary piston unit  28 . 
         [0038]    The piston units  28 ,  54  fully extend and fully retract on each alternate stroke due to the proximity sensors  72   a ,  72   b ,  74   a ,  74   b  which signal the change of direction of the stroking for piston units  28 ,  54  upon their full extension. The secondary hydraulic pump supplies additional hydraulic oil between hydraulic cylinders  38 ,  64  via lines  68 ,  70  to ensure full retraction of piston units  28 ,  54  occurs before the change of signal is actuated. 
         [0039]    Material output rate is infinitely variable by controlling the primary pump flow delivered to hydraulic cylinders  38 ,  64 . Material is pumped at equal material pressure from both material cylinders  16 ,  42  due to the fact that material cylinders  16 ,  42  have equal bore diameters, hydraulic cylinders  38 ,  64  have equal diameter pistons  36 ,  62  and the hydraulic cylinders  38 ,  64  are driven at the piston side by the same primary hydraulic pump. Maximum material pressure is accurately limited by a corresponding maximum hydraulic pressure setting at the primary hydraulic pump. 
         [0040]    The present invention thus provides a positive displacement hydraulic cylinder drive system wherein a partial volume A and volume B of material are pumped on each alternating, unequal length stroke of coordinating piston units  28 ,  54  to continuously pump material to the outlet  14 . In contrast with the prior art, the system  10  reduces the number of components required (minimizing the number of check valves), eliminates the need for complex drive systems and separate mechanical pressure limiting devices as encountered in mechanical systems, and allows a greater control of the maximum pressure of the material cylinders. 
         [0041]    It should be understood that the hydraulic system  10  can be either an open loop or a closed loop system. For the purpose of detecting and signaling change of direction of the piston units, the type, the amount and/or location of the proximity sensor may vary. Also, the change in direction could be detected alternately using hydraulic pressure signals and correspondingly piloted valves. 
         [0042]    Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.