GB2403788A - Anti-pumping dispense valve - Google Patents

Abstract

An anti-pumping dispensing valve comprises a fluid transport housing (206) having a fluid inlet passage (222) an intermediate fluid passage (232) a fluid outlet passage (214) and first and second fluid transport chambers (224, 234). The first fluid transport chamber includes a valve seat (230). An actuator housing (208) is attached to the fluid transport housing and includes first and second actuator chambers that are in contact with the fluid transport chambers. A diaphragm/poppet assembly (226) is disposed within the first fluid transport chamber and comprises a poppet (228) positioned downstream of the seat (230) for placement against the seat to stop fluid flow through the first fluid transport chamber. Means are provided to change the volume of the second fluid transport chamber in response to poppet movement. An actuator is disposed within each of the actuator chambers for moving the diaphragm-poppet assembly and means for changing volume. Dispense valves of this invention operate to provide a slight vacuum within the fluid flow passageway in the valve to retain or pull back into the valve any non-dispensed liquid, thereby eliminating and/or greatly reducing the possibility product contamination via unwanted excess liquid dispensing the dispensing of dried residual liquid.

Description

ANTI-PUMPING DISPENSING VALVE

This invention relates to fluid handling valves used for dispensing liquids and, more particularly, to fluid handling valves that are specially designed to repeatably dispense accurate volumes of chemically aggressive and/or chemically pure liquids without degrading or otherwise deleteriously affecting the liquids or the manufactured product.

Fluid handling valves, e.g., fluid dispensing valves, are used in applications where the valve internals are subjected to corrosive acidic or caustic liquids, or where the purity of the liquids which flow through the valve must be maintained. An example of such application is the semiconductor manufacturing industry where the process chemical delivered through such a valve must maintain a high degree of chemical purity to avoid contamination that may occur on the microscopic level, and that is know to cause damage to the manufactured product, e.g., a semiconductor wafer.

It is also desired, during certain process steps, that a precise amount of the process chemical be deposited onto the product. It is, therefore, important that a dispensing valve used to perform such function-be capable of repeatably dispensing an accurate volume of the process liquid without dribbling excess liquid onto the product after the valve has been shut. It is, however, known in the industry that dispensing valves used to perform this function do not always terminate the dispensing of liquid after the valve is closed or shut.

For example, conventional dispensing valves used in this capacity are known to cavitate and/or seep out a small volume of liquid after the valve has been closed. This extra volume of liquid is either dispensed from the valve onto the product, providing an undesired excess of the delivered liquid, or is retained within the outlet port of the valve or the ultimate delivery device, - 2 e.g., a pipe or nozzle. In the case where the excess liquid is retained within the valve, this situation too presents a problem because the liquid can dry near the tip of the ultimate delivery device. The dried portion of liquid can then be dispensed onto a product the next time that a volume of the process liquid is delivered from the dispensing valve. Delivery of such dried portion of the liquid onto the product is known to cause damage to the product and, thus, is not desired.

It is,-therefore, desired that a dispensing valve be designed in such a manner so as to control and/or eliminate the potential for liquid cavitation and/or excess liquid seepage and/or delivery once the valve has been shut or closed. It is also desired that such a dispensing valve be configured to enable its operation with chemically aggressive and/or pure liquids without degrading or otherwise functioning in a manner that could introduce contaminant material into the liquid. It is further desired that such dispensing valve be constructed in a manner so as to reduce the number of liquid leak paths therethrough, thereby reducing the possibility of chemical leakage to the outside environment.

According to the present invention, there is provided a dispensing valve comprising: a fluid transport housing having a fluid inlet passage extending into the housing, a fluid outlet passage extending out of the housing, first and second fluid transport chambers disposed within the housing, the second fluid transport chamber being downstream of the first fluid transport chamber, the first fluid transport chamber including an integral valve seat; an actuator housing attached to the fluid transport housing and including first and second actuator chambers in contact with respective first and second fluid transport chambers; - 3 a diaphragm/poppet assembly disposed within the first fluid transport chamber and comprising a poppet positioned downstream of the seat for placement against the seat to stop fluid flow through the first fluid transport chamber; means disposed within the second fluid transport chamber for changing the volume of the second fluid transport chamber liquid in response to poppet movement; and actuator means disposed within each first and second actuator chambers for moving the respective diaphragm/poppet assembly and means for changing volume.

In this structure, means are disposed within the second fluid transport chamber for changing the volume of the second fluid transport chamber, ...

À e.g., increasing the volume of the second fluid transport chamber. An.: id- -.

: actuator means is disposed within each first and second actuator chambers. : À. for moving the- respective poppet/diaphragm assembly and the means for.

changing volume.

I; 20. L'- ' i'. . : Dispensing valves of this invention are referred to as an "anti-pumping" valves because the combined movement of the poppet and the means for controlling volume do not operate to push or "pump" an additional and.-.; unwanted volume of liquid from the valve after it has been closed. Rather,the.: poppet and/or means for controlling volume each operate to provide a slight vacuum within the fluid flow passageways of the respective valves to retain or pull back into the valve any nondispensed liquid. This operation is desired as it eliminates and/or greatly reduces the possibility for product contamination via unwanted excess liquid dispensing or the dispensing of any dried residual liquid.

The present invention is illustrated by way of example with reference to the - 4 - following detailed description taken with the accompanying drawings, wherein: Figure 1 is a perspective view of a dispensing valve constructed according to the present invention; and Figure 2 is a cross-sectional side view of the dispensing valve of Figure 1 in a closed operating condition for controlling the displacement of fluid therethrough.

Dispense valves constructed in accordance with the practice of this invention comprise a one-piece diaphragm/poppet assembly that is positioned within a valve housing. The diaphragm/poppet assembly is configured having a poppet positioned in a sealing position downstream of a valve seat disposed within a fluid transport chamber through the housing.

Configured in this manner, the diaphragm/poppet assembly serves to control - and/or eliminate the undesired cavitation- and/or seepage of liquid from the valve after it has been placed into a closed or shut position.

Dispensing valves of this invention can include, in addition to the abovedescribed diaphragm/poppet assembly, a second diaphragm disposed within a second fluid transport chamber through the housing, downstream from the diaphragmipoppet assembly. The second diaphragm is actuated in conjunction with the diaphragm/poppet assembly to increase the volume of the second fluid transport chamber to thereby retain any liquid downstream of the diaphragm/poppet assembly within the valve after the valve has been placed into a closed position. Dispensing valves of this invention include wetted parts that are formed from fluoropolymeric materials to resist undesired degradation from exposure to chemically aggressive process liquids.

Figures 1 and 2 illustrate a second embodiment dispensing valve 200 constructed according to principles of this invention, generally comprising a valve body 202 made up of, moving from the bottom of Figure 1 upwardly, a base 204, a fluid transport housing (FTH) 206 disposed on top of the base 204, and an actuator housing 208 disposed on top of the FTH 206. Screws 210, or other suitable attachment means, extend through the actuator housing 208 and the FTH 206, and are threaded into the base 204 to attach the actuator housing 208 and FTH 206 thereto. The FTH 206 includes a fluid inlet port 212 through one of its side walls, and a fluid outlet port 214 through an opposite side wall. In an air- or pneumatically- actuated embodiment of the dispense valve 200, the actuator housing 208 includes an inlet air port 216 and an air outlet port or vent (not shown) extending through its side wall.

The FTH may also be configured having a leak detection port (not shown) extending through one of its side walls to monitor the occurrence of any fluid leakage within the dispense valve.

The FTH and actuator housing are both configured to contain a second fluid transport system 220 that is positioned downstream of a first fluid transport system 218. The first fluid transport system 218 is configured in a fashion described below.

Moving downstream from the fluid inlet port 212, the FTH 206 comprises a i fluid inlet passage 222 that is in fluid flow communication with the fluid inlet port and that empties into a first fluid transport chamber 224. The first fluid transport chamber has a diaphragm/poppet assembly 226 disposed therein that has a poppet 228 positioned to interact with a valve seat 230. The valve seat 230 is interposed between the fluid inlet passage 222 and an intermediate fluid passage 232.

The FTH includes a second fluid transport system 220 downstream from the intermediate fluid passage 232 comprising a second fluid transport chamber 234 that is in fluid flow communication with the intermediate fluid passage - 6 232. The FTH includes a fluid outlet passage 236 that is downstream from the second fluid flow chamber 234 and that is in fluid flow communication with the fluid outlet port 214. The second fluid flow chamber 234 is generally cylindrical in shape and extends axially within the FTH from a closed base 238 to an oppositely oriented open end 240. Unlike the first fluid transport system 218, the second fluid transport system does not include a member that is designed to shut off or close the flow of liquid through the FTH.

- The FTH 206 can be formed from any type of structurally rigid material. In an example embodiment, where the dispense valve is for the purposes of dispensing process chemicals used in the application of semiconductor manufacturing, it is desired that the FTH be formed from a non-metallic material to avoid process liquid contamination. In such application, the FTH can be formed from conventional plastic or polymeric building materials such a polypropylene and the like. If desired, the FTH can be formed from a fluoropolymeric material selected from the group including polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (PEP), perfluoroalkoxy fluorocarbon resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylenetetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF) and the like. In a preferred embodiment, the FTH is moulded from polypropylene. Since the base 204 is not wetted by the process liquid, it can be made from a metallic material and, in a preferred embodiment for application with a semiconductor manufacturing process, is formed from stainless steel.

The actuator housing 208 is attached to the FTH in the manner described above and is configured to accommodate the actuating members for both the first and second fluid transport systems. The actuator housing 208 comprises a first actuator or piston chamber 242 that contains the piston gland 244, the actuator piston assembly 246, the spring 248, and the detent assembly 250 each as described above and illustrated in Figure 2 for the - 7 first embodiment dispense valve. The actuator housing 208 further I comprises a second actuator chamber 252 that is separate and apart from the first actuator chamber 242. The second actuator chamber 252 comprises an open end 254 positioned adjacent the FTH and an axially opposed partially-closed end 256. The actuator housing 208 can be formed from the same types of materials listed above for the FTH. However, since the actuator housing is not wetted by the process liquid routed through the valve it can be fommed from a metallic material. In an example embodiment, the actuator housing is formed from stainless steel. ! Moving upwardly in Figure 1, starting in the second fluid transport chamber 234, the second fluid transport system 220 comprises a diaphragm 258 disposed across an open end of the second fluid transport chamber. The diaphragm 258 is in the form of a one-piece construction comprising a centrally positioned imperforate head 260, and a movable thin-walled section - 260 extending radially outwardly a distance from the head. The diaphragm is defined along its radially outermost peripheral edge by a flange 262 that includes an axially projecting tongue 264 that is placed within a groove that is disposed circumferentially around the open end of the second fluid - 20 transport chamber 234. The tongue is configured having a thickness that is slightly larger than that of the groove width to provide a leaktight - ; interference fit with the FTH. The diaphragm 258 can be formed from the same type of materials discussed above for the FTH. In an example embodiment, for use in the semiconductor manufacturing process with aggressive and high purity chemicals, it is desired that the diaphragm/poppet assembly be moulded from a fluoropolymeric material, such as Teflon PTFE, which is provided for example by DuPont Company of Wilmington, Del.

An actuator assembly 266 is positioned within the actuator housing 208 and in contact with the diaphragm 258. Moving upwardly from the diaphragm 258, the actuator assembly comprises a stem 268 that is disposed axially - 8 within the actuator chamber 252, and that includes a collar 270 at one axial end that is configured to cooperate with the diaphragm. Specifically, the collar is defined by a central opening 272 that is sized to receive an axially extending backside projection of the diaphragm head. The stem 268 comprises a first diameter section that defines an outside surface of the collar 270, and a second diameter section, extending axially away from the collar towards an opposite end of the stem, that is larger than the first diameter section. The stem can be formed from the same type of material disclosed above for the FTH, and in an example embodiment is formed from a metallic material, such as aluminum.

A support 274, in the form of an annular member, is disposed within the actuator chamber 252. The support has a central opening that accommodates placement of the stem collar therethrough, and extends radially between the stem collar and an edge of the FTH adjacent the open end: 240. The support 274 is interposed axially between the diaphragm flange 262 on one side and a spacer 276 on an opposite side; The support I- - can:be formed from the same type of materials listed above for the FTH and - - in a--preferred embodiment is moulded from polypropylene. The spacer 276 20will be described in detail below.

A spring 278 is disposed around the second diameter section of the stem 268, and is interposed axially between the- support 274 at one of its axial ends, and an annular ring 280 at its other axial end. The annular ring 280 is retained within a groove in the stem second diameter section and projects radially outwardly therefrom a sufficient distance to provide a mounting surface for the spring. The spring is sized and configured to impose a desired spring force between the ring and support. Configured and assembled in this manner, the support 274 serves as a guide to the stem collar, a mounting surface for the diaphragm flange, and a mounting surface for the spring. - 9 -

In an example embodiment the spring and the retaining ring are each formed from a metallic material such as stainless steel.

The spacer 276 is a generally cone-shaped annular member that is disposed concentrically within the actuator chamber 252, and that is interposed axially between the FTH and the actuator housing. The spacer 276 includes a shoulder 282 that projects radially outwardly a distance from one axial spacer end, and that is interposed between opposed FTH and actuator housing open ends. The spacer 276 includes neck that extends axially away from the shoulder 282, that has a diameter smaller than the shoulder, and that fits concentrically within the side wall surface defining the actuator chamber 252. The neck includes an axial end that is positioned adjacent the actuator housing partially-closed end 256. Configured in this manner the spacer, when loaded into the actuator chamber 252, the serves to impose a desired an axially-directed loading force onto the support 274 at one axial - - . -end, and onto a mounting portion.of a.second diaphragm, at.an opposite axial end, as will be better described below. The spacer.can be fommed from! - .. . : . .: -the same types of materials used to form the FTH. Neither the support nor - . - .the spacer, while disposed within the actuator.charnber, are considered to be.: ..

: :: 20 parts of the actuator assembly 266 because they. are each static members - within the actuator housing. :

The actuator assembly 266 further comprises a second diaphragm 284 that is positioned within the actuator chamber 252 against an axial end of the stem 268 opposite the collar 270. The second diaphragm 284 includes a centrally located head 286, a thin-walled section 288 extending radially outwardly from the head, and a flange 290 defining a peripheral edge of the thin-walled section. The flange includes a tongue that projects axially outwardly therefrom and that is disposed within a groove disposed circumferentially around a diameter of the actuator housing partiallyclosed end 256. The tongue is sized having a thickness that is slightly greater than the width of the groove to provide a leak-tight interference fit therewith. - 10

The flange 290 is interposed between an axial end of the spacer 276 and the partially-closed end 256.The second diaphragm serves to enable axial movement of the stem 268 within the actuator chamber while at the same time sealing off the remainder of the actuator housing from any potential fluid leaks within the actuator chamber. The second diaphragm can be formed from the same type of material used to form the diaphragm 258.

The actuator assembly 266 further comprises a shaft 292 that projects axially away from a surface of the second diaphragm 284 opposite the stem 268 through an opening 294 through the actuator housing 208. The shaft 292 includes a first axial end that is in contact with the second diaphragm, and a second axial end that projects outwardly from the actuator housing and that includes a knob 296 attached thereto. The shaft 292 includes one or more axially depending grooves 298 disposed therealong that are located adjacent a detent mechanism 300 that is disposed within a side wall section - - of the annular housing. The shaft can be formed from the same types of -- materials used-to form the FTH, and can be formed from metallic materials if so desired.

The detent assembly 300 is configured for purposes of controlling the stroke of the shaft 292 and actuating assembly 266 within the second fluid transport system. The shaft also includes an O- ring seal disposed circumferentially - therearound for purposes of providing a leak-tight seal between the shaft - i and the annular housing, and thereby containing pneumatic actuating pressure within the annular housing. The Oaring seal can be formed from a material having desired property of elasticity. Where chemical resistance is also desired, the O-ring seals may be made from Britons or from other types of commercially available fluoropolymeric materials.

As mentioned briefly above, the annular housing 208 includes an air inlet port 216 for purposes of receiving pressurized actuating air. First and second air ports 302 and 304 are disposed within the annular housing and are in air - 11 flow communication with the air inlet port 216. The first air port 302 directs pressurized air into the piston chamber 242 for purposes of actuating the actuator piston assembly 246, and the second air port 304 directs pressurized air into the opening 298 for purposes of actuating the actuating assembly 266. Configured in this manner, air directed into the actuator housing via the air inlet port operates to actuate each first and second fluid transport system.

The second fluid transport system 266 operates to assist the first fluid transport system in the function of retaining and/or pulling back any volume of liquid remaining in the FTH after the first fluid transfer system has been placed in the closed position. Generally speaking, the second fluid transport system does this by retracting the diaphragm 258 within the second fluid transport chamber 234 shortly after the poppet 228 in the first fluid transport system is sealed against the valve seat 230. This timed retraction of the diaphragm serves to increase the volume of the second fluid transport chamber; after the first fluid-transport system is closed, thereby creating a slight suction that operates to retain or pull any remaining liquid in the fluid outlet passage 236 and fluid outlet port 214 back into the second fluid 2G transport chamber 234. : . - The staged retraction of the diaphragm 258 after closure of the first fluid transport system can be achieved by a number of different methods. One method could be to provide differently timed actuation signals, e.g., pneumatic charges, to the first and second actuation chambers. In a preferred embodiment, the first and second actuation chambers are charged by a common air inlet port. Thus, in such preferred embodiment, the staged retraction is provided via use of different stroke lengths for the first and second actuator assemblies. In a preferred embodiment, the second actuator assembly is designed having a longer stroke than that of the first actuator assembly so that after the first actuator assembly is activated to place the poppet in a closed position against the valve seat, the second - 12 actuator assembly has not yet completed its stroke and still moves within the second fluid transport chamber to cause the desired volume increase.

The ability to control the placement of liquid within the valve of this invention in the above-described manner, downstream of the valve seat, eliminates and/or greatly reduces the possibility of excess unwanted liquid leaving the valve after it has been closed. Thus, eliminating or greatly reducing the possibility of unwanted contamination resulting therefrom.

The above-identified members used to form dispensing valve embodiments of this invention made from polymeric materials can be formed by either mould or machine process, depending on both the specific type of material that is chosen and the project budget.

. . .. ! - 13

Claims (24)

1. A dispensing valve comprising: a fluid transport housing having a fluid inlet passage extending into the housing, a fluid outlet passage extending out of the housing, first and second fluid transport chambers disposed within the housing, the second fluid transport chamber being downstream of the first fluid transport chamber, the first fluid transport chamber including an integral valve seat; an actuator housing attached to the fluid transport housing and including first and second actuator chambers in contact with respective first and second fluid transport chambers; a diaphragm/poppet assembly disposed within the first fluid transport chamber and comprising a poppet positioned downstream of the seat for placement-against the seat to stop fluid flow through the first fluid transport chamber; . . means disposed within the second fluid transport chamber for changing the volume of the second fluid transport chamber liquid in À response to poppet movement; and - . - actuator means disposed within' each first and second actuator chambers for moving the respective diaphragm/poppet assembly and means for changing volume.

2. A valve according to Claim 1 further comprising means for controlling the relative movement of each actuator means within its respective first and second actuator chambers.

3. A valve according to Claim 2 wherein the means for controlling - 14 comprises a pair of detent mechanisms each disposed within the actuator housing, and each configured to make contact with a portion of each respective actuator means to control a stroke length of each actuator means.

4. A valve according to Claim 3 wherein the means for controlling operates to both provide movement of the actuator means used to move the diaphragm/poppet assembly to cause the poppet to seal against the valve seat, and provide movement of the actuator means used to move the means for changing volume to cause an increase in volume in the second fluid transport chamber after the poppet has be sealed against the seat.

5. A valve according to any one of Claims 1 to 4 wherein the actuator means comprises a first actuator assembly and a second actuator assembly, wherein each first and second actuator assembly forms a leak-tight seal within a respective first and second actuator chamber to facilitate actuation : movement by pneumatic means, and wherein each first and second actuator assembly is biased into a nonactuated state by springs that are disposed in each first and second actuator chamber. : . 20-

6. A valve according to any one of Claims 1 to 5 wherein the - - diaphragm/poppet assembly comprises a movable diaphragm disposed at an axial end opposite the poppet, the movable diaphragm including a flange positioned along a peripheral diaphragm edge that forms a leak-tight with the - fluid transport housing.

7. A valve according to Claim 6 wherein the diaphragm/poppet assembly is a one-piece construction, and the poppet is imperforate.

8. A valve according to any one of Claims 1 to 7 wherein the diaphragm/poppet assembly is fixedly attached to a respective actuating means. - 15

9. A valve according to any one of Claims 1 to 8 wherein the volume changing means comprises a movable diaphragm disposed within the second fluid transport chamber and having a flange 5 positioned along a peripheral edge that forms a leak-tight seal with the fluid transport housing.

10. A dispensing valve comprising: a fluid transport housing having first and second fluid transport chambers interposed between a fluid inlet passage into the housing and a fluid outlet passage out of the housing, the second fluid transport chamber being downstream of the first fluid transport chamber and in fluid flow communication therewith, the first fluid transport chamber including a valve seat interposed between the fluid inlet passage and the second fluid transport chamber; À - .. an actuator housing connected with the fluid transport.housing and - :.

À -- . . -: - Including first and second actuator.chambers connected withr.espective first. .r, and second fluid transport chambers;. .: . ... - :. . .20.. a first actuator assembly disposed within the first.actuator chamber: - . and in contact with a:poppet disposed.within the first fluid transport chamber. - - . downstream of the seat and in sealing communication with the seat when. ;- À . the valve is placed in a closed position; . - . - ; a second actuator assembly disposed within the second actuator chamber and in contact with a movable diaphragm positioned within the second fluid transport chamber, the movable diaphragm comprising a flange along a peripheral edge that forms a leak-tight seal with the fluid transport housing; and means for controlling the relative movement of the first and second actuator assemblies within their respective actuator chamber such that there - 16 results an increase in volume in the second fluid transport chamber after the poppet is sealed against the seat.

11. A valve according to Claim 10 wherein the means for controlling the relative movement comprises a pair of detent assemblies that are disposed within the actuator housing, and that register with a portion of a respective actuator assembly.

12. A valve according to Claim 10 or 11 wherein the poppet is positioned at one axial end of a diaphragm/poppet assembly comprising a second movable diaphragm disposed at an opposite axial end, the second diaphragm including a flange along a peripheral edge that farms a leak-tight with the fluid transport housing.

13. A valve according to Claim 12 wherein the diaphragm/poppet assembly is a one-piece construction, and the poppet is imperforate. - - : . . , , ' . , . . , , ; ;T.P., ' . ;, ; : . . 1..

:-

1-4. A valve according to Claim 12 or 13 wherein the diaphragm/poppet: assembly comprises a hollow channel that extends axially partially through ^.r20 the assembly, and wherein the diaphragm/poppet assembly is attached to - ; - the first actuator assembly by use of a common shaft that extends between; . i - the first actuator assembly and the into the channel. - : - . .

15. A valve according to any one of Claims 10 to 14 wherein the first actuator assembly comprises a shaft that extends axially into the first actuator housing, an annular piston and a piston gland that are each positioned within the first annular chamber and disposed around different sections of the shaft, and a spring that is disposed within the first actuator housing and that is interposed axially between the annular piston and piston gland to urge the poppet against the seat.

16. A valve according to any one of Claims 10 to 15 wherein the second 17 actuator asserrbly comprises a shaft that extends axially into the second actuator housing that is in contact at one of its axial ends with a third movable diaphragm disposed within the second actuator chamber, and a stem that is interposed axially between the movable diaphragm and the third movable diaphragm, wherein the stem is biased into a desired non-actuated position by a spring positioned around the stem and disposed within the second actuator chamber.

17. A valve according to any one of Claim 10 to 16 wherein the actuator housing includes an air inlet port for receiving an actuating pressurized stream of air, and air distribution ports directing the actuating air into the first and second actuator chambers in parallel.

18. A valve according to any one of Claim 10 to 17 wherein the first and second fluid transport chambers are connected together by an intermediate fluid port that extends through the fluid transport housing downstream of the seat to the second fluid transport chamber. . ..

-

19. A valve according to any one of.Claims. 1 to 18 wherein. the poppet and. I. 2 the diaphragm are each formed from a fluoropolymeric. material. ; : . By. . :. .; - . .

20. A method for cortrolling liquid.within a dispensing valve comprising the - -.

steps of: providing a supply of liquid into the valve, and into a valve first fluid transport chamber; actuating a poppet within the first fluid transport chamber to initiate dispensing of the liquid across a valve seat, wherein the poppet is positioned downstream of the valve seat; directing the liquid to a second fluid transport chamber disposed A - 18 within the valve downstream of the first fluid transport chamber, and dispensing the liquid from the valve, the second fluid transport chamber comprising a diaphragm disposed therein; actuating the poppet to seal against the valve seat to terminate dispensing of the liquid from the first fluid transport chamber; and actuating the diaphragm to increase the volume of the second fluid transport chamber, thereby retaining any liquid not yet dispensed from the valve after dispensing from the first fluid transport chamber had been temminated.

21. A method according to Claim 20 further comprising the step of controlling the relative speed at which the poppet and diaphragm are actuated to provide a sequenced movement of the diaphragm relative to the poppet.

- . . , . ; .,.

--

22. A method according to Claim 20 wherein the speed of the diaphragm is -;. - i- : controlled so that is actuated at a speed slower than that of the poppet. :" '; - if,- . - i

23. A method according to any one of Claims 20 to 22 wherein the first and :- I:: : second fluid transport c.I,ambers ate disposed within a common fluid - - transport housing, and wherein th& poppet and diaphragm each comprise a flange member that forms a leak-tight seal with the fluid transport housing.

24. A method according to any one of Claim 20 to 23 wherein the steps of actuating the poppet and diaphragm are performed by separate actuator assemblies that are each disposed within a respective actuator chamber in a common actuator housing.