Abstract:
Dispensers with replaceable actuators and related methods. A representative dispenser includes a sealed fluid chamber with a fluid inlet and a valve seat, a valve member configured to be reciprocally moveable relative to the valve seat, and an actuator interface. The dispenser includes first and second actuators configured to be coupled with the actuator interface for reciprocally moving the valve member. The first actuator is configured to operate by a different motive force than the second actuator. The first actuator can be removed and replaced with the second actuator. The methods involve the ability to replace the first actuator with a second actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 10/907,514, filed Apr. 4, 2005 (pending), which claims the benefit of U.S. Provisional Application 60/565,161, filed Apr. 23, 2004, and which is a continuation-in-part of U.S. application Ser. No. 10/975,227, filed Oct. 28, 2004 (abandoned), the entire disclosures of all of which are hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to liquid dispensing devices used for a variety of purposes, but particularly useful for viscous liquids such as hot melt adhesives, sealing compounds, paints, etc. Such devices are referred to as fluid control valves or dispensing guns or modules. 
     BACKGROUND OF THE INVENTION 
     A typical dispensing device for supplying liquid, such as hot melt adhesive, generally includes a body having a valve stem that opens and closes a dispensing orifice. The valve stem is usually actuated in at least one direction by pressurized air to dispense discrete amounts of pressurized liquid. Either a spring mechanism or pressurized air is used to move the valve stem in an opposite direction against a valve seat. This stops the flow of liquid from the dispensing orifice. 
     More specifically, devices generally related to the present invention include a liquid passage adjacent the dispensing orifice and an actuator cavity or chamber at an opposite end of the device. The actuator cavity contains a portion of the valve stem which is connected with a piston member and which is also connected with a spring return mechanism, as discussed above. Under sufficient air pressure applied on one side of the piston member, the valve stem is moved in a direction away from the valve seat to discharge liquid. When the air pressure is relieved, the spring mechanism will automatically return the valve stem to a normally closed position against the valve seat. Such spring mechanisms generally include an adjustment to vary the spring compression and thereby vary the amount of air pressure required to open the valve. Adjustment of the spring compression will also adjust the biasing force used to close the valve. These devices also include a stroke adjustment, or the spring compression adjustment also varies the stroke of the valve stem to adjust the flow rate. 
     Despite the wide success of devices as described above, improvement is desired. For example, a dynamic seal placed generally between the dispenser body and the moving valve stem typically prevents liquid from leaking into the actuator cavity. Dynamic seals are conventionally understood to be seals between two surfaces that move relative to one another. These dynamic seals may press tightly against the valve stem and cause friction and seal wear. The higher friction may place greater demands on the requirements for pressurized air to move the valve stem. On the other hand, selecting a looser dynamic seal could result in inadequate sealing, thus allowing the liquid to bind the piston and pressurized air to enter into the liquid passage, causing undesired dispensing discontinuities. Even with reduced friction, the dynamic seal will wear over time and lose its ability to seal properly. 
     It would therefore be desirable to provide a dispenser that eliminates or reduces the need for dynamic seals in contact with the pressurized liquid, thus eliminating or reducing problems such as those mentioned above. 
     SUMMARY OF THE INVENTION 
     Accordingly, certain embodiments of the present invention relate to a dispenser including an actuating section having a first moveable member and a hydraulic section coupled with the actuating section in a side-by-side configuration and having a second moveable member. The hydraulic section includes an outlet and is adapted to dispense liquid therefrom and the actuating section is adapted to control dispensing of the liquid. The dispenser further includes an actuator assembly operatively coupling the first moveable member with the second moveable member, wherein the first moveable member is operative to move the second moveable member between open and closed positions for respectively starting and stopping flow of liquid from the outlet. 
     In one exemplary embodiment of the invention, the actuating section is a pneumatic section wherein the first moveable member is configured as a piston that is adapted to move in response to pressurized fluid. The dispenser may further include a solenoid for delivering pressurized fluid to the piston. A biasing member, such as a spring, may be coupled with the piston to bias the piston in a preferred direction. In the exemplary embodiment, the hydraulic section has a second moveable member configured as a needle capable of reciprocating movement within the hydraulic section. The hydraulic section includes an inlet for coupling the hydraulic section with a source of pressurized liquid and an outlet through which the liquid is dispensed. The hydraulic section may also include a biasing element, such as a spring, that biases the needle in a preferred direction. 
     The actuator assembly includes a pivoting lever arm having a first end coupled with the piston and a second end coupled with the needle. In one aspect of the invention, the second end of the pivoting lever arm couples with the needle at a point located between the inlet and outlet. Coupling the end of the pivoting lever arm with the second moveable member, such as the needle, between the inlet and outlet advantageously reduces or eliminates stagnation points and consequently reduces or eliminates the formation of char and other material buildup within the hydraulic section. The actuator assembly further includes a flexible seal coupled with the pivoting lever arm and adapted to be positioned between the actuating section and the hydraulic section to prevent liquid from leaking into the actuating section. The seal can be a non-diaphragm seal wherein the periphery of the seal is unrestrained and is capable of flexing to accommodate the movement of the pivoting lever arm while retaining a fluid-tight seal. The seal may be further adapted to withstand large hydraulic operating pressures, such as from approximately 80 psi to at least 1,500 psi and other pressure ranges. A bushing support may be provided that couples with the pivoting lever arm and supports the seal. The bushing support is positioned radially inward of the seal&#39;s periphery. Furthermore, the actuator assembly may also include a pivoting member, such as a pivoting pin, coupled with the pivoting lever arm and adapted to define a fixed pivot point around which the pivoting lever arm pivots. 
     Variations of the above-described dispenser are contemplated to be within the scope of the present invention. For instance, in some embodiments of the invention, the actuating section is an electrical section wherein the first moveable member is configured as an armature that is adapted to move in response to an electrical current. The first end of the pivoting lever arm is then coupled with the armature such that movement of the armature moves the second moveable member, such as a needle, between the open and closed positions. In other embodiments of the invention, the second moveable member within the hydraulic section is configured as one or more pads. The pads are adapted for reciprocating movement within the hydraulic section between open and closed positions for respectively starting and stopping flow of liquid from the outlet. Yet other embodiments of the invention include a hydraulic section configured to operate in a snuff-back mode, a three way mode or both. 
     In another embodiment, a dispenser includes a sealed fluid chamber with a fluid inlet and a valve seat, a valve member configured to be reciprocally moveable relative to the valve seat, and an actuator interface. The dispenser includes first and second actuators configured to be coupled with the actuator interface for reciprocally moving the valve member. The first actuator is configured to operate by a different motive force than the second actuator. The first actuator can be removed and replaced with the second actuator. 
     In yet another embodiment, a method includes operating a first actuator to reciprocally move a valve member relative to a valve seat, removing the first actuator from an actuator interface of the dispenser, coupling a second actuator with the actuator interface of the dispenser to replace the first actuator, and operating the second actuator to reciprocally move the valve member relative to the valve seat. The first actuator is configured to operate by a different motive force than the second actuator. 
     These and other objects, advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
         FIG. 1  illustrates a schematic perspective view of a dispenser in which a hydraulic section and an actuating section are arranged side-by-side in accordance with the invention; 
         FIG. 1A  illustrates a partial sectional view of the dispenser of  FIG. 1  generally taken along the line  1 A- 1 A; 
         FIG. 2  illustrates a sectional view of an exemplary dispenser having an actuator assembly in accordance with the invention; 
         FIG. 3  illustrates a partial cutaway view of an exemplary actuator assembly in accordance with the invention; 
         FIG. 3A  illustrates a sectional view of the exemplary actuator assembly of  FIG. 3 ; 
         FIG. 4  illustrates a sectional view of an exemplary dispenser in accordance with the invention in which the actuator assembly operatively couples with a liquid dispensing passageway; 
         FIG. 5  illustrates a sectional view of an exemplary dispenser in accordance with the invention that includes a recirculating port; 
         FIG. 6  illustrates a sectional view of an exemplary dispenser in accordance with the invention that includes snuff-back operation; 
         FIG. 7  illustrates a sectional view of an exemplary dispenser in accordance with the invention that includes a self-aligning needle; 
         FIG. 8  illustrates a sectional view of an exemplary dispenser in accordance with the invention that includes snuff-back operation and a recirculating port; 
         FIG. 9  illustrates a sectional view of an exemplary dispenser in accordance with the invention that utilizes a pad in the hydraulic section in accordance with the invention; 
         FIGS. 10 and 11  illustrate alternative pivoting lever arms in accordance with the invention useful with the exemplary dispenser of  FIG. 9 ; 
         FIG. 12  illustrates a perspective view of a dispenser in accordance with the invention wherein the solenoid and actuating section are formed as an integral assembly; 
         FIG. 12A  illustrates a sectional view of the dispenser of  FIG. 12  generally taken along line  12 A- 12 A; 
         FIG. 13  illustrates a sectional view of an exemplary dispenser in accordance with the invention that includes a pressure balanced hydraulic section; and 
         FIG. 14  illustrates a sectional view of an exemplary dispenser in accordance with the invention wherein the actuating section is configured as an electrical section. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic depiction of an exemplary dispenser in accordance with the invention. Unlike previous dispensers, the dispenser of the invention includes a hydraulic section  102  and an actuating section  104  arranged in a side-by-side manner instead of in a vertical manner. As the hydraulic section  102  is often coupled with a heated manifold or other heater block, the present side-by-side arrangement allows the actuating section  104  to be thermally isolated from such a heater block. As a result, O-rings and other seals within the actuating section  104  should not be exposed to the same high temperatures as experienced in conventional dispensers. Additionally, other electrical components, such as, for example, solenoids, will not be exposed to high temperatures as well. This permits closer coupling of the solenoid with the actuating section, which improves response time. Overall, the side-by-side arrangement will provide increased reliability and performance over the conventional, vertically-arranged dispensers. 
     As shown in  FIG. 1A , an exemplary dispenser in accordance with the invention generally includes a hydraulic section  102 , an actuating section  104 , and an actuator assembly  106 . The hydraulic section  102  receives a pressurized liquid, for example, liquid hot melt adhesive, from an inlet  103  and dispenses the liquid through an outlet, such as nozzle  107 . The actuating section  104  includes a first moveable member  108  and the hydraulic section includes a second moveable member  110 . The actuator assembly  106  operatively couples the first moveable member  108  with the second moveable member  110  such that the first moveable member  108  is operable to move the second moveable member  110  between open and closed positions for respectively starting and stopping dispensing of the liquid. The first moveable member  108  is coupled with an actuator  112  that is capable of moving the first moveable member  108 . A biasing force  114  may be applied to first moveable member  108  to bias the first moveable member in a preferred direction. The actuating section is adapted to control the dispensing of liquid through the hydraulic section  102  by controlling the movement of the first moveable member  108 . 
     The hydraulic section  102  and the actuating section  104  can be coupled together by any variety of methods. For example, in  FIG. 1 , four bolts  116  are used to connect the actuating section  104  and the hydraulic section  102  together. Furthermore, the hydraulic section  102  includes a face  118  that is coupled with a dispensing manifold (not shown) of a liquid dispensing system. For example, through bolt holes  120  may be used to couple the hydraulic section  102  to the manifold (not shown). When coupled, the orifice  122  cooperates with an outlet port of the manifold so that pressurized liquid (e.g., 500 psi) is received within the hydraulic section  102 . As explained in more detail below, this pressurized liquid is dispensed from the nozzle  107  in a precise and accurate manner. In advantageous embodiments, the hydraulic section  102  is constructed from a heat transferable material, including non-interactive metals such as aluminum, brass, or stainless steel while the actuating section  104  may be constructed from a metal or a temperature resistant plastic, including a fluoroplastic. 
     The following figures and description thereof provide various embodiments of the invention showing different configurations of the hydraulic section  102 , actuating section  104  and actuator assembly  106 . For instance, as described below, the actuating section  104  may be configured as a pneumatic section, wherein a pressurized fluid controls the movement of a piston or an electrical section, wherein electrical current controls the movement of an armature. Additionally, the hydraulic section  102  may have many different configurations, such as including a needle, ball or one or more pads capable of reciprocating movement within the hydraulic section that cooperates with a valve seat for starting and stopping the dispensing of liquid through the nozzle  107 . The hydraulic section  102  may also be configured with a snuff-back feature, a three-way feature or both. Thus although several embodiments of the invention are shown and described herein, the invention is not so limited as those of ordinary skill in the art will recognize other configurations that may be used with the invention. 
       FIG. 2  depicts a sectional view of an exemplary dispenser according to an embodiment of the invention. The solenoid  206  and the manifold  217  are shown as simple blocks as their operation is well understood by one of ordinary skill in this field. In particular, the solenoid  206  performs so as to deliver pressurized air  208  in a controlled manner to a piston  212  of the pneumatic section  204 . The manifold  217  performs so as to deliver pressurized liquid  216  to the hydraulic section  202 . This sectional view does not depict the bolts or other connectors that may be used to secure the hydraulic section  202  with the pneumatic section  204 . Neither does it depict the valve guides and stoke adjust mechanisms that are often included within the hydraulic section of a dispenser. 
     The hydraulic section  202  includes a chamber  218  that receives the pressurized liquid  216 . Within the chamber  218  is a needle  220  that is configured to engage a valve seat  221 . When the needle  220  engages the valve seat  221 , no pressurized liquid travels from the chamber  218  through the passageway  223  and out the orifice  224  of the nozzle  222 . However, when the needle  220  is positioned so as not to engage the valve seat  221 , then pressurized liquid exits the chamber  218  via the passageway  223 . Thus, by controlling the position of the needle  220 , the dispensing of pressurized liquid from the orifice  224  can be accurately and precisely controlled. In addition to a needle valve as shown in  FIG. 2 , a ball and seat may also be used to control dispensing of pressurized liquid. 
     One of ordinary skill will recognize that a number of alternative hydraulic sections are contemplated in addition to the specific exemplary hydraulic section  202  of  FIG. 2 . For example, alternative hydraulic sections contemplated within the scope of the present invention may include integrally formed heater blocks or heater elements. Additionally, the exemplary hydraulic sections may be integrally formed with a manifold, or other similar assembly. In addition, the term “needle” is used in a generic sense and is intended to encompass a wide range of movable members having a variety of shapes and contours. 
     The pneumatic section  204  includes a piston  212  that is biased upwards via a spring  214 . In operation, pressurized air  208  is delivered to the piston  212  with sufficient force to overcome the spring  214  and move the piston  212  downward. 
     The piston  212  of the pneumatic section  204  and the needle  220  of the hydraulic section  202  are operatively coupled together via a pivoting lever arm  230 . The arm  230  includes one end  236  that couples to the piston shaft  213 . For example, the end  236  may be ball shaped and fit within a through-bore  237  machined into the shaft  213 . As an alternative to the through-bore  237 , a blind hole may be machined into the shaft to receive the end  236  in a manner in which the end  236  is free to rotate within the blind hole. Similarly, the other end  238  of the arm  230  may couple with the needle  220 . The arm  230  pivots around a pivoting point  234  so that downward motion of the piston  212  results in upward motion of the needle  220 . Conversely, upward motion of the piston  212  results in downward motion of the needle  220 . The pivoting point  234  may be accomplished by a variety of functionally equivalent methods but may, for example, include a pin that passes through the center of the arm  230 . The ends of the pin may be supported in a recess or cavity formed in the hydraulic section  202  such that the pin is free to rotate and therefore allow the arm  230  to pivot. 
     The seal  232  is located between the hydraulic section  202  and the pneumatic section  204  to prevent pressurized liquid  216  from leaking into the pneumatic section  204 . Unlike previous dispensers, the seal  232  is not a dynamic seal around a reciprocating shaft. Instead, the seal  232  is a flexible seal around the pivoting lever arm  230  that is able to flex or “rock” as the pivoting lever arm  230  moves. Accordingly, the flexible seal  232  performs better and lasts longer than earlier dynamic seals. Additionally, the seal  232  is not a diaphragm seal that is supported along its outer periphery and restrained from moving along its outer periphery. Instead, the seal  232  is preferably substantially annular with its inside edge surrounding the arm  230  and its outside edge unrestrained yet sealingly engaging the exterior of the hydraulic section  202 . In this way, the seal  232  is able to flex along its periphery so as to accommodate pivotal movement of pivoting lever arm  230 . Furthermore, as explained in more detail below, seal  232  is supported from the inside of the seal  232  as opposed to being support along the periphery, as is typical in diaphragm seals. In addition to an annular shape, alternative shapes for the seal  232  may be used such as, for example, square or rectangular. As depicted in  FIG. 2 , the hydraulic section  202  is shaped so as to create a cavity for the seal  232  to sit in. As those of ordinary skill in the art will recognize, however, a cavity may alternately be formed in the actuating section  204 . The seal  232  is preferably made from a resilient or flexible material such as, for example, an elastomeric material that is deformable so that when the pneumatic section  204  and the hydraulic section  202  are coupled together, the seal  232  is slightly compressed in the cavity area and provides a seal between the two sections  202  and  204 . 
     Although not explicitly depicted in  FIG. 2 , the chamber  218  may include an adjustment mechanism for the needle  220  as is known in the art. A needle stroke adjust mechanism typically includes a physical stop within the chamber  218  that limits the amount of travel of the needle  220 . Embodiments of the present invention are capable of operating with the wide variety of needle stroke adjust mechanisms that are known in this field. 
       FIGS. 3 and 3A  depict an exemplary actuator assembly comprising flexible seal portion  304  and a bushing support  312 , such as a washer, formed around a pivoting lever arm  306 . As described above, the seal  304  sits within an appropriately shaped cavity formed by the mating surfaces of an actuating section and a hydraulic section of a liquid dispenser. 
     A pivot pin  302  extends through the pivoting lever arm  306  and may be coupled thereto, such as through a press fit, and also extends through the flexible seal  304  such that the pivoting lever arm  306  pivots about a pivot point defined by pin  302 . The material from which the flexible seal  304  is constructed can be any of a variety of available elastomers or plastics, such as, for example, the fluoroelastomer marketed as Viton®. The bushing support  312  radially supports the seal  304  from the center, unlike a diaphragm seal which is supported along its periphery. The bushing support  312  also provides support for the flexible seal  304  to withstand hydraulic pressure generally operating along the major axis of the pivoting lever arm  306 . In this way, the seal  304  may be configured to withstand relatively large hydraulic pressures, such as from approximately 80 psi to at least 1,500 psi. The seal  304  may also be configured for other hydraulic pressure ranges. For example, the seal  304  may be configured to withstand hydraulic pressure from approximately 100 psi to approximately 1,500 psi. Preferably, the seal  304  may be configured to withstand hydraulic pressures from approximately 200 psi to approximately 1,500 psi. More preferably, the seal  304  may be configured to withstand hydraulic pressure from approximately 300 psi to approximately 900 psi. Still more preferably, the seal  304  may be configured to withstand hydraulic pressures from approximately 400 psi to approximately 800 psi. 
     Accordingly, in an advantageous embodiment, the bushing support  312  is made of a rigid material such as brass, or other metal, and coupled with the pivoting lever arm  306  and the flexible seal  304 . The bushing support  312  may include a semi-circular cavity  320  adapted to receive pin  302  therein. The bushing support  312  may not be rigidly coupled with the pin  302  so that the bushing support  312  and pin  302  may move relative to each other. The flexible seal  304  may be molded over the pivoting lever arm  306 . In addition, the pivoting lever arm  306  may advantageously include a profile that provides more surface area on the pivoting lever arm  306  for the flexible portion  304  to grip. This profile, for example, may include ridges  314  or grooves. Alternatively, or in addition, the flexible seal  304  may be adhered to the pivoting lever arm  306 . In the exemplary embodiment of  FIG. 3 , the flexible seal  304  includes a recessed portion  305 . However, this shape is exemplary in nature and other shapes are contemplated as well. 
     As shown in  FIG. 3A , the bushing support  312  includes a hydraulic face  322  and an actuating face  324 . The hydraulic face  322  abuts seal  304  and lies in a plane going through a pivot point defined by the intersection of the pin  302  and the pivoting lever arm  306 . The bushing support  312  also includes a bore  326  adapted to receive the pivoting lever arm  306  therethrough. The bore  326  has a hydraulic end  328  having a diameter substantially equal to the diameter of the pivoting lever arm  306 . In this way, the hydraulic face  322  may fully support the seal  304  and further prevent extrusion of the seal  304  into the bore  326 . The bore  326  is further configured to increase in diameter in a direction toward actuating end  330 . For instance, the bore  326  may be generally cone-shaped. The increase in diameter of bore  326  from hydraulic end  328  to actuating end  330  provides a clearance space  332  that allows the pivoting lever arm  306  to pivot, as illustrated by the phantom lines in  FIG. 3A . 
     The pivoting lever arm  306  includes an end  308  that couples with the second moveable member in the hydraulic section, such as needle  220  in  FIG. 2 , and another end  310  that couples with the first moveable member in the actuating section, such as piston  212  in  FIG. 2 . When coupled in this manner, the pivoting lever arm  306  pivots about a point where the arm  306  is intersected by the pin  302  and, thus, the up or down motion of the end  310  translates into an oppositely-directed motion of the end  308 . The pivoting lever arm  306  and the pin  302  are advantageously made from high strength steel. However, other materials such as brass, aluminum or a high-strength non-metallic or composite material may be used as well. 
     When the pivoting lever arm  306  moves, the flexible seal  304  flexes but maintains a seal along its outside periphery and also between itself and the pivoting lever arm  306 . Such a small amount of flexure will not disturb the sealing arrangement provided by the seal  304 . Constructing the flexible seal  304  from Viton® or similar material will permit angular deflection of around 4.5 degrees without compromising the seal between a hydraulic section and an actuating section. Thus, even though the flexible portion  304  may flex as the pivoting arm  306  moves, it still acts as a flexible seal that will last longer and be more reliable than earlier dynamic seals for reciprocating shafts. Different materials and different size seals may be used if angular deflection of greater than around 4 to 5 degrees is desired. 
     Additionally, in a prior-art vertical arrangement of hydraulic and actuating sections, there is substantial hydraulic pressure pushing the second moveable member back out of the hydraulic section towards the actuating section. The hydraulic pressure from the pressurized liquid within the hydraulic section acted to push the second moveable member in a direction opposite to the force supplied by the actuating section. Thus, the actuating section was required to be sized to overcome this additional hydraulic force. In the present embodiments having a side-by-side arrangement, such as for example, that shown in  FIG. 2 , the pressurized liquid  216  within the hydraulic section  202  still exerts a force against the pivoting lever arm  230  but this force is transverse to the direction of motion of the piston  212 . This transversely directed force is transferred to the bearing surfaces of the support  312 , not to the piston  212 . In the embodiment of  FIG. 3  for example, the force is transferred by pivot pin  302 , although alternate load bearing means are contemplated. Bushing support  312  transfers the load to the pneumatic body  204  while the ball end  308  of the pivoting lever arm  306  is designed to fit into opening  237  (see  FIG. 2 ) with clearance so that no transverse load is transferred to the piston  212 . 
       FIG. 4  illustrates one alternative embodiment of a dispenser in which the hydraulic section does not include a needle. The dispenser of  FIG. 4 , includes a hydraulic portion  402 , a pneumatic portion  404 , and a solenoid portion  403 . As described earlier, the solenoid portion  403  delivers a pressurized air  406  in a controlled manner to the piston  412 . In response, the piston  412  is either displaced downward by the pressurized air  406  or urged upward by a spring  416 . 
     According to this embodiment, a pivoting lever arm  414  extends from the pneumatic section  404 , through a seal  418 , into a chamber  410  of the hydraulic section  402 . The pivoting lever arm  414  engages the spring  416  on one end  413  and a passageway  422  at the other end  415 . The spring  416  operates to push the pivoting lever arm  414  upward against the piston  412 . In response to sufficient pressurized air  406  to overcome the spring  416 , the piston  412  operates to push downward on the pivoting lever arm  414 . The up and down motion of the pivoting lever arm  414  causes it to pivot around a pivot point  419 , such as a pin. The pivoting of the pivoting lever arm  414  causes the opposite end  415  to move in a direction (up or down) opposite to that of the end  413 . 
     The hydraulic section  402  includes an inlet  408  for receiving pressurized liquid, such as, for example, hot melt liquid adhesive. This liquid is received into a chamber  410  and exits through a passageway  422  out an orifice  424 . On the end  415  of the pivoting lever arm  414  within the chamber  410 , there is a pad  420  attached that fits over the passageway  422 . When the end  415  is lowered, the pad  420  covers an opening to passageway  422  such that the passageway  422  is blocked and no liquid is dispensed from the orifice  424 . However, when the end  415  is raised so that the passageway  422  is no longer blocked by the pad  420 , then liquid leaves the chamber  410  through the orifice  424 . The pad  420  may be bonded to the arm  414  in a variety of ways and may be constructed from a material that can advantageously seal the passageway  422  such as, for example, plastic, elastomer, rubber or a high performance fluorocarbon material. Additionally, instead of a flat rectangular shape, the pad  420  may have alternative shapes such as, for example, a ball. 
     When the arm  414  is positioned so that liquid is being dispensed from the orifice  424 , the portion of the arm  414  within the chamber  410  is hydraulically balanced. Even though the liquid within the chamber  410  is under pressure, the pressure on the top and the bottom of the arm  414  balances out. A hydraulically balanced arm permits faster movement of the end  415  and its closing action with the passageway  422 . Additionally, the force needed to move the arm  414  is reduced as well. For example, pressurized air  406  at between 20-40 psi and in quantities of 0.1 cc to 0.5 cc is sufficient to operate the piston  412 . As a result, a smaller piston may be utilized resulting in a smaller dispensing module. In previously-described embodiments (and later-described embodiments), the end  415  of the pivoting lever arm  414  is sometimes replaced with a needle. In these embodiments, as well, the side-by-side arrangement of the hydraulic section and the pneumatic section create a hydraulically balanced needle such that when the valve is open, hydraulic forces on the needle cancel each other out and the needle “floats” in liquid. As a result, resistance to closing the needle is reduced, or eliminated, making the needle easier to close. 
     Another embodiment of the invention is illustrated in  FIG. 5 . Similar to previous drawings, the general components of the dispenser are the same. A manifold  505  is coupled with a hydraulic section  502  that is coupled, in a side-by-side manner, with a pneumatic section  504 . A flexible seal  520  is located between the two sections and prevents liquid from the hydraulic section  502  from leaking into the pneumatic section  504 . A pivoting lever arm  518  operatively couples a piston  512  of the pneumatic section  504  with a needle  510  of the hydraulic section  502 . A solenoid section  503  delivers pressurized air  514  in a controlled manner to the piston  512  so that it may push downward against the spring  516  in order to control the movement of the needle  510 . 
     The dispenser of  FIG. 5  differs from earlier dispensers in that it includes an inlet port  508  for receiving a pressurized liquid, such as hot melt liquid adhesive, as well as a recirculating port  506  for diverting pressurized liquid back into the manifold section  505 . Such a dispenser is commonly referred to as a three-way dispenser. As depicted in  FIG. 5 , the end  522  of the needle  510  is seated within a seat  523  in order to prevent liquid from leaving the chamber  530  via the dispensing orifice  526 . Instead, liquid within the chamber  530  travels upward to the recirculating port  506  where it returns to the manifold section  505 . If the needle  510  is moved upward, such as by moving the piston  512  downward, then the end  524  of the needle  510  will block the seat  525  of the recirculating port  506 . In this configuration, the end  522  will no longer sealingly engage the seat  523  and liquid from the chamber  530  will be dispensed via the orifice  526 . 
     One alternative embodiment, to those already described, is depicted in  FIG. 6 . According to this embodiment, a hydraulic section  602  is coupled with a pneumatic section  604  in a side-by-side manner. Between the two sections a cavity is formed by their mating faces to securely hold a flexible seal  616  having a pivoting lever arm  612  extending therethrough. The pivoting lever arm  612  operatively connects the piston  608  of the pneumatic section  604  with the needle  618  of the hydraulic section  602  such that movement of the piston  608  is translated into movement of the needle  618 . 
     In contrast to previously described embodiments, the piston  608  of  FIG. 6 , moves upward in response to the solenoid  603  providing pressurized air  606  while the spring  610  pushes the piston  608  downward when no pressurized air  606  is being applied. Upward motion of the piston  608  causes the needle  618  to descend so that the end  624  no longer engages the valve seat  626 . With the needle  618  in this position, liquid within the chamber  619  (received via an inlet port  620 ) is dispensed out via the orifice  622 . When the piston  608  moves downward, the needle  618  moves upward and causes the end  624  to engage the valve set  626  thereby cutting off the dispensing of any liquid within the chamber  619 . This type of motion of the needle  618  is known as “snuff-back” and provides the benefit that the needle  618  tends to draw liquid up from the orifice  622  when the end  624  engages the seat  626  instead of forcing the liquid out the orifice  622 . 
       FIG. 7  depicts another three-way liquid dispenser having a recirculating flow for the liquid. Liquid enters the chamber  711  of the hydraulic section  702  via an inlet port  710  and can exit from either the dispensing orifice  712  or a recirculating port  708 . Depending on the position of the needle  715 , either the end  718  will sealingly engage the seat  719  or the other end  716  will sealingly engage the seat  717 . The position of the needle  715  is controlled by the pivoting lever arm  714  that extends from the hydraulic section  702  to the pneumatic section  704 . The pivoting lever arm  714  passes through a flexible seal  720  and pivots about a pivoting point  721 , such as that defined by a pin. One end  722  of the arm  714  engages the piston  724  and the other end  723  engages the needle  715 . The spring  726  acts to force the piston  724  downward and the solenoid section  703  delivers pressurized air  728  to urge the piston  724  upward. 
     In particular, the end  723  may be spherical in nature and interact with a through-hole  730  bored into the needle  715  without being rigidly fixed to one another. As the end  723  moves up and down, a tangential point on its spherical surface contacts the inside surface of the through-hole  730 . Additionally, the seats  717  and  719  are shaped to complement the ends  716  and  718  of the needle  715 . Thus, as an end  716 ,  718  moves towards a seat  717 ,  719 , respectively, the needle  715  is urged into alignment with the seat  717 ,  719  because the needle  715  is free to wobble around its connection with the end  723  of the pivoting lever arm  714 . In this way, the needle  715  is self-aligning. 
     In contrast, standard vertical arrangements of the pneumatic and hydraulic sections in dispensing guns create a situation in which the needle in the pneumatic section is not self-aligning. The rigid connection of the needle to the actuating piston as well as the dynamic seal below the piston restrict the movement of the needle so that it does not automatically align itself with the valve seat while being moved into the closed position. 
       FIG. 8  illustrates an embodiment of the present invention that incorporates both a three-way dispenser and snuff-back operation. The hydraulic section  802  includes a needle  806  that closes at the dispensing end  810  via upward motion, thereby providing the snuff-back operation. Additionally, the end  808  interfaces with a recirculating port  809  in order to provide a liquid return path to the manifold  805 . The pneumatic section  804  and solenoid section  803  operate as described earlier to cause the piston  811  to move the pivoting lever arm  812  in a way so as to control the movement of the needle  806 . 
       FIGS. 9 and 10  illustrate two different embodiments of the invention that provide a three-way implementation without the presence of a needle within the hydraulic section. In particular, the hydraulic section  902  includes a recirculating port  934  and an inlet port  932 . Pressurized liquid, such as hot melt liquid adhesive is received from a manifold (not shown) via the inlet port  932  and may return to the manifold via the recirculating port  934 . These ports  932 ,  934  may include a respective O-ring  918 ,  916  or similar device to provide a liquid seal when the hydraulic section is coupled with the manifold (not shown). 
     A solenoid  903  provides pressurized air  905 , or other fluid, to operate the piston  906  of the pneumatic section  904 . In particular, the pressurized air  905  operates to push the piston  906  downward against the force of the spring  908  which urges the piston  906  upward. A pivoting lever arm  910  extends from within the pneumatic section  904  to the hydraulic section  902 . This pivoting lever arm  910  pivots about a pivot point  914 , such as, for example, a pin. The pivot arm  910  also passes through a flexible seal  912 , the seal  912  preventing pressurized liquid within the hydraulic section  902  from leaking into the pneumatic section  904 . 
     One end  909  of the pivoting lever arm  910  engages the piston  906  so that movement of the piston  906  results in movement of the end  909 . When the end  909  moves, it causes the pivoting lever arm  910  to rotate or pivot thereby causing the end  911  to move. The end  911  of the pivoting lever arm  910  is located within the hydraulic section  902  and moves opposite to that of the other end  909 . Furthermore, this end  911  includes two pads  922 ,  924  that are bonded thereto. When the end  911  moves upward, the pad  922  engages the seat  928  and closes off the recirculating port  934 . Concurrently, the pad  924  disengages the seat  926  thereby allowing liquid to enter the passageway  930  and be dispensed through the orifice  920 . When the end  911  moves downward, the pad  924  and seat  926  close off the passageway  930  and the pad  922  and seat  928  disengage so as to allow liquid to exit via the recirculating port  934 . These pads are similar in construction to the pad  420  described in relation to  FIG. 4 . 
     The embodiment of  FIG. 10  is substantially similar to that of  FIG. 9  except for the end of the pivoting lever arm within the hydraulic section. In particular, the pivoting lever arm  1010  includes an end  1009  that engages the piston  906  as before. However, the end  1011  does not include the use of additional pads. Instead, the end  1011  is shaped to effectively engage the seats  926  and  928 . Thus, the end  1011  of the pivot arm  1010  opens and closes liquid passageways to the recirculating port  934  and the dispensing orifice  920 . 
       FIG. 11  illustrates an alternative embodiment for the pivoting lever arm  1010  of  FIG. 10 . In this particular embodiment, the flexible seal  1102  is formed similar to before but has a portion  1104  that substantially encloses the end  1011  of the pivoting lever arm  1010 . The portion  1104  provides a resilient surface that advantageously cooperates with valve seats  926  and  928  to provide fluid-tight seals and further blocks travel of any liquid between the seal  1102  and the pivoting lever arm  1010 . 
       FIGS. 12 and 12A  show an alternate embodiment of a dispenser having a pneumatic section with a double acting piston coupled with a solenoid for supplying pressurized fluid, such as air, to both sides of the piston. The alternative embodiment of  FIG. 12  includes a solenoid  1202  and a housing  1203 . The solenoid  1202  includes a coil  1204  and an armature comprised of body  1209  and shaft  1208 . Through the electric current supplied to the coil  1204 , via an electrical connector  1206 , an electrical field is created that moves the armature ( 1208 ,  1209 ) up and down. The housing  1203  includes a number of passageways and a spool or poppet  1217 . The poppet  1217  is pushed down by the shaft  1208  of the armature and a spring  1219  urges the poppet  1217  upwards against the force of the shaft  1208 . Included within the housing  1203  is a first exhaust port  1210 , a second exhaust port  1214  and an air inlet port  1212 . There is also a first passageway  1218  and a second passageway  1216  that are in fluid communication, respectively, with passages  1222  and  1220  of the pneumatic section  1207 . 
     The exemplary housing  1203  and solenoid  1202  are distributed by MAC Valves as Model Number 44B-L00-GFDA-1KV. As this is a commercially available product, the operation of the seals of the poppet  1217  and the cavity in which it moves are not described in minute detail. However, its general operation is described herein. A constant source of pressurized air is received at the inlet port  1212  and is directed to one of the passageways  1216  or  1218 . The vertical position of the poppet  1217  determines if passageway  1216  or  1218  is in communication with the inlet port  1212 . 
     For example, if the poppet  1217  is positioned so that air is directed from the inlet port  1212  through the passageway  1216 , then it flows into passage  1220  and into the cavity  1226  below the piston  1230 . This air flow will force the piston  1230  to move upward. As the piston  1230  moves upward, air is forced from the cavity  1224  through the passage  1222 . With the poppet  1217  in this position, the air is able to exit the passage  1222  into the passageway  1218  and out the first exhaust port  1210 . 
     Conversely, if the air is directed from the inlet port  1212  through the passageway  1218 , then it flows into passage  1222  and into the cavity  1224  above the piston  1230 . This air flow will force the piston  1230  to move downward. Accordingly, air exits the cavity  1226  via the passage  1220  and enters the passageway  1216 . Because of the poppet position, the air is able to escape from passageway  1216  out the second exhaust port  1214 . 
     In this manner, the solenoid  1202  and poppet  1217  can be used to move the piston  1230  up and down within the pneumatic section  1207 . The piston  1230  may include one or more O-rings  1232  as depicted in  FIG. 12 . The pneumatic section  1207  typically includes an open bottom that permits the piston  1230  to be inserted therein. This bottom can be closed off with a plug  1228  that may be threaded or otherwise connected to the pneumatic section  1207 . By using pressurized air to move the piston  1230  both up and down, the pneumatic section  1207  eliminates the spring depicted in other embodiments described herein. Thus, movement of the piston  1230  does not have to overcome the spring force and, therefore, less force (i.e., volume or pressure of air) is needed to move the piston  1230 . Furthermore, when air pressure changes, the opening and closing forces remain balanced. 
     According to one embodiment, the solenoid section ( 1202  and  1203 ) are integrally formed with the pneumatic section  1207 . Because of the side-by-side arrangement of the integral solenoid and pneumatic housing with the hydraulic section  1205 , the solenoid  1202  and housing  1203  are thermally separated from the high temperatures usually associated with the hydraulic section  1205 . For example, in the exemplary arrangement of  FIG. 12 , the temperature at or near the hydraulic section  1205  was found, during testing, to be approximately 350° F. while the temperature of the coil  1204  was approximately 150° F. A number of benefits result from this thermal separation. The solenoid  1202  will require less insulation than with conventional dispensing modules and the solenoid  1202  will likely be more reliable. Within the housing  1203 , the various seals and O-rings may now be constructed of a lower temperature material than conventional hot melt dispensers. Such material would include rubber, such as, for example, case hardened nitrile material which has better friction and wear characteristics than high temperature rubbers such as Viton®. 
     The piston  1230  advantageously includes a groove  1235  extending around the center of its periphery in which one end  1234  of the pivoting lever arm  1236  will engage. The pivoting lever arm  1236  extends through the flexible seal  1239  into a chamber  1252  of the hydraulic section  1205 . The pivoting lever arm  1236  pivots around a pivot point  1238 , such as that defined by a pin, so that when one end  1234  moves downward the other end  1240  moves upward, and vice-versa. The end  1240  is operatively coupled with a needle  1242  within the hydraulic section  1205 . Thus, when the end  1240  moves up or down, the needle  1242  moves up or down as well. 
     In the hydraulic section  1205 , a pressurized liquid is received at the inlet port  1250  and enters the chamber  1252 . If the end  1256  of the needle  1242  is sealingly engaged with the seat  1254 , then the liquid remains within the chamber  1252 . If, however, the needle  1242  is raised so as to disengage its end  1256 , then liquid is dispensed from the chamber  1252  via the dispensing orifice  1243 . The needle  1242  may extend through the orifice (i.e., zero-cavity) or partially through it (i.e., reduced cavity). In this embodiment, a biasing member, such as a spring  1244 , biases the needle  1242  downward and, therefore, the movement of the piston  1230  is sufficient to overcome the force of the spring  1244  in order to dispense liquid from the orifice  1243 . Those of ordinary skill in the art will recognize that the biasing member may be configured as a piston having pressurized air on one or both sides of the piston. 
     The embodiment of  FIG. 12A  explicitly includes a stroke adjust mechanism  1246 . The mechanism  1246  is a threaded rod that passes through a cap  1248  and can be rotated clockwise or counterclockwise to adjust its distance from the top of the needle  1242 . The position of the mechanism  1246  controls the amount that the needle  1242  may travel upward. 
       FIG. 13  illustrates another exemplary dispenser that is similar in many respects to embodiments described earlier. These similar aspects will be briefly described but without great detail. A hydraulic section  1302  is arranged in a side-by-side manner with a pneumatic section  1304  that is coupled with a solenoid  1303 . The solenoid  1303  controls the delivery of pressurized air  1306  to a piston  1307  to overcome a spring  1308 . Movement of the piston  1307  results in movement of the pivoting lever arm  1310  that pivots around a pivot point  1312  and that passes through a flexible seal  1308 . The movement of the pivoting lever arm  1310  is translated into movement of a needle  1327  within the hydraulic section  1302 . Movement of the needle  1327  results in dispensing of liquid or recirculating of liquid within the hydraulic section  1302 . The needle  1327  of this embodiment includes a large diameter portion  1326  and a small diameter portion  1330 . Liquid enters the hydraulic section  1302  through an inlet port  1328  and is either dispensed from the orifice  1324 , or enters the recirculating port  1325 , depending on the position of the needle  1327 . 
     The piston  1307  must overcome a number of forces to hold the needle  1327  in a closed position. Thus, the exemplary hydraulic section  1302  includes a number of beneficial features to help balance the pressures on the needle  1327 . The large diameter poppet  1314  provides a long flow engagement on the recirculating side that results in an increased pressure drop. The small diameter poppet  1322  provides a short flow engagement on the delivery side that results in increased flow capability. The tapering of the poppet  1322  and the seat  1323  also reduces flow resistance when liquid is dispensed. 
     Additional features within this embodiment include the different diameters of the seats  1316  and  1323 . The seat  1316  with which the poppet  1314  seals is larger in diameter than that of the seat  1323  with which the poppet  1322  seals. Because of the relationship between force, pressure and area, the large diameter at the seat  1316  provides a relatively large force even if under a smaller pressure. Conversely, the small diameter at the seat  1323  provides a relatively smaller force even under a larger pressure. For example, if the seats are the same diameter and the delivery pressure is 500 psi, then a 50 psi drop across the recirculation seat  1316  will reduce the force required to seal the delivery side by 10%. However, if the recirculation seat  1316  is sized to be twice the area of the delivery seat  1323 , then the same 50 psi drop will reduce the force required to seal the delivery side by 20%. 
     Elastomer members  1320  and  1318  also provide additional benefits. These members are compressible and may be constructed from an elastomer or similar material that can withstand the heat experienced within the hydraulic section  1302 . When the needle  1327  moves upward, the compressible member  1318  expands and, thereby, reduces the effective stroke length of the needle  1327  on the recirculating side. The result is that there is effectively an increase in the pressure drop at the recirculating side. Independently, the compressible member  1320  compresses when the needle is moved so as to seal the poppet  1322  and the seat  1323 . The additional travel provided by the compressible member  1320  improves the snuff-back operation of the hydraulic section  1302 . 
     By way of example, the delivery side seat  1323  may be designed so as to close against 500 psi. If the seat exit diameter is 1/16 inch, the area is 0.003 square inches, and the force acting down is 1.5 pounds. If there is a 50 psi drop across the recirculation seat  1316  and it is the same size (i.e., 0.003 square inches), then the force acting upward is 0.015 pounds. To close the delivery seat  1323 , the piston  1307  must deliver 1.485 pounds of force. If, however, the 50 psi drop is seen across a recirculation seat  1316  that is ⅛ inch in diameter, then the force acting up is 0.6 pounds (i.e., 50 psi×0.012 square inches). In this second case, the piston  1307  must overcome 0.9 pounds to close the delivery seat  1323 . As a result, the net force the piston  1307  would need to provide to close the delivery seat  1323  has been reduced, as compared to if the seat diameters were the same size, by roughly 40%. 
     In one advantageous embodiment, a piezoelectric actuator element (not shown) is substituted for the pneumatic actuator element. The poppets  1314 ,  1322  and the seats  1316  and  1322  are sized so that the needle  1327  is closed (i.e., in recirculating mode) when the actuator element is in its neutral, or de-energized state, or, in other words, the hydraulic section  1302  has a normally-closed delivery valve. 
     The exemplary embodiments described above included a pneumatic section and a solenoid section that work together to move a piston within the pneumatic section via pressurized air. The present invention is not limited in its use and application to only such pneumatic sections. By way of example,  FIG. 14  depicts a sectional view of an exemplary dispenser having a hydraulic section  1402  in a side-by-side manner with an electrical section  1404 . The hydraulic section  1402  includes a chamber  1418  that receives pressurized liquid  1416  from manifold  1417 . Within the chamber  1418  is a needle  1420  configured to engage valve seat  1421 . When the needle  1420  engages the valve seat  1421 , no pressurized liquid travels from the chamber  1418  through the passageway  1423  and out of the orifice  1424  of the nozzle  1422 . However, when the needle  1420  is positioned so as not to engage the valve seat  1421 , then pressurized liquid exits the chamber  1418  via passageway  1423 . 
     The electrical section  1404  includes an electromagnetic coil  1406  disposed about an armature  1408  that is biased downward by a compression spring  1409 . In operation, electrical current is supplied to coil  1406  by a power source (not shown) through electrical connector  1411 , which generates an electromagnetic field between the armature  1408  and a pole  1410  so as to attract the armature  1408  to pole  1410 . Since pole  1410  cannot move, the armature  1408  will move against the force of the spring  1409  until it hits the pole  1410 . 
     The armature  1408  of the electrical section  1404  and the needle  1420  of the hydraulic section  1402  are operatively coupled together via pivoting lever arm  1430 . The arm  1430  includes one end  1436  that couples to the armature  1408 . For example, the end  1436  may be ball shaped and fit within a through-bore  1437  machined into the armature  1408 . Similarly, the other end  1438  of the arm  1430  may couple with the needle  1420 . The seal  1432  is located between the hydraulic section  1402  and the electrical section  1404  to prevent pressurized liquid  1416  from leaking into the electrical section  1404 . The arm  1430  pivots around a pivoting point  1434 , such as that defined by a pin, in this way, the downward motion of the armature  1408 , such as when electrical current is shut off to coil  1406  and spring  1409  biases armature  1408  downward, results in upward motion of the needle  1420 . Conversely, upward motion of the armature  1408 , such as when electric current is supplied to coil  1406  and armature  1408  is attracted to pole  1410 , results in downward motion of the needle  1420 . 
     Those of ordinary skill in the art will appreciate that different configurations of the electrical section  1404  may be used in the invention. For instance, the electrical section  1404  may be modified such that the needle  1420  is normally closed when no electric current flows to coil  1406 . Additionally, those of ordinary skill in the art will recognize that an electric actuator, such as electrical section  1404 , may be used with the various embodiments of the hydraulic sections shown and described herein. 
     Alternatively, piezoelectric actuators (not shown) may be used as well that resemble the up-and-down motion of a piston. Such electrically actuatable pistons may be coupled with a pivoting lever arm similar to that described herein without departing from the scope of the present invention. As such, the electrical section (which replaces the pneumatic section) may be arranged in a side-to-side manner with the hydraulic section in order to provide the benefits and advantages described herein. The present invention also contemplates using hydraulic sections that include additional air inlets commonly labeled “process air”. Such air is separate from that of the pneumatic section and can be used, as one of ordinary skill would appreciate, to adjust the manner in which liquid is dispensed from the dispensing orifice. 
     While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known.