GB2060086A - Reciprocating Pump Apparatus and Reversing Mechanism Therefor - Google Patents

Abstract

A reciprocating pneumatically operated pump apparatus 10 for use in a post-mix syrup dispensing operation has a fail-safe pump reversing system which includes a valve actuating member 17 for reversing the valve mechanism 40 which controls the reciprocating pump action. An overcenter, snap-acting mechanism is provided to preclude the valve actuating member 17 from sticking in a central position. The snap-acting mechanism is configured to substantially preclude bearing load in a direction transversely of the direction of movement of the valve actuating member 17. The pump housing 11 is of molded plastic with all fluid passages and pump connections formed therein. The output valves of the pump are positioned at the highest point in the discharge sections 28, 29 of the piston chambers to minimize the accumulation of air bubbles. <IMAGE>

Description

SPECIFICATION Reciprocating Pump Apparatus and Reversing Mechanism Therefor This invention relates to reciprocating pump apparatus, more particularly to a pneumatically operated diaphragm pump utilized in a Post-mix beverage syrup dispensing system and more specifically to a reciprocating pump including a spring actuated reversing means for reversing the direction of a reciprocating pump at the end of its respective strokes.

Diaphragm pumps are widely used particularly for pumping liquid solutions and highly viscous materials and are frequently used under conditions such that the viscosity of the fluid being pumped, the head of the suction side of the pump and the back pressure on the pump discharge may all vary as conditions under which the pump is operating vary. The speed of such pumps has generally been controlled by inserting an adjustable valve in the air line leading to the pump. However, this approach requires that the operation of the pump be kept under continuous observation and the valve adjusted to suit varying conditions, otherwise the speed of the pump will vary substantially depending upon the conditions of operation.For example, if the back pressure on the pump should increase or decrease for any particular reason, or if the viscosity of the liquid being pumped should vary, then the speed of operation and the quantity of liquid being pumped per unit of time will accordingly be affected.

Therefore, it is highly desirable that the pump be controlled such that it operates at a substantially constant speed under varying conditions.

Furthermore, it is essential that the entire pumping cycle be completed so as to ensure continuous delivery of the medium being pumped at a constant consistency or concentration. In order to ensure the latter, means have been suggested such as disclosed in U.S. Patent 4,008,984 wherein opposed coil springs are provided for assisting the respective valve member in the completion of its pumping cycle.

The coil compression springs of identical force under the pressurized gas system assist in completion of the pumping cycle first in one direction, and then by asserting a positive reversing effect when either of the springs becomes fully compressed. Although providing a reversing mechanism for the double acting pump disclosed there are inherent disadvantages with such a system. For example, if for some reason the pressurized system is effected in such a way that a back pressure is created or established so as to inhibit or reverse the pumping cycle before it is completed, there is no means for overcoming the undesirable effect, and the fully compressed state of the spring is not reached.Thus, it is possible that the pumping cycle could be reversed regardless of the presence of the compression springs, before the cycle is completed, thus effecting the efficiency if not the complete purpose of the reciprocating pump.

Viewed from one aspect the present invention provides a reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston members therein dividing each of said chambers into a driving section and a discharge section, said piston members being mounted on a common shaft, manifold means in said housing for connecting said driving sections and discharge sections of said chambers with a fluid inlet and outlet, respectively, valve means in said discharge sections for controlling the flow of liquid to be pumped to and from said discharge sections with respect to said manifold means, and control means for directing driving fluid alternately to a selected one of said driving sections defined by said pistons in said lateral chambers, said control means including control valve means coupled to the source of driving fluid, a valve actuating member for said control valve means, movable on a bearing surface between first and second positions longitudinally of said shaft to alternately direct said driving fluid to the respective driving sections, and snap-acting means for precluding the stopping of said valve actuating member between said first and second positions, said snap-acting means exerting substantially no net force transversely of said shaft against said bearing surface.

Viewed from another aspect the present invention provides a reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston members therein dividing each of said chambers into a driving section and a discharge section, said piston members being mounted on a common shaft, a common passageway in said housing for interconnecting said discharge sections of said chambers with a common dispensing outlet, valve controlled outlets in said discharge sections for releasing under pressure liquid from said discharge sections into said common passageway, and control means for directing pressurised fluid alternately to a selected one of said driving sections defined by said pistons in said lateral chambers, said valve controlled outlets being disposed at the highest possible position in said discharge sections.

Viewed from yet another aspect the present invention provides a reversing mechanism for a fluid control valve which selectively directs a fluid alternately in one of two directions in response to the switching of the control valve between first and second positions comprising; a slidable valve actuating member for engaging said control valve and switching said valve to said first or secdnd positions; a bearing surface disposed on a predetermined axis along which valve actuating member slides; and snap-acting means for precluding the stopping of said valve actuating member between said first and second positions, said snap acting means exerting substantially no net force transversely of said axis against said bearing surface.

Viewed from still another aspect the present invention provides a reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston member therein dividing each of said chambers into a driving section and a discharge section, said piston members being mounted on a common shaft, a common passageway in said housing for interconnecting said discharge sections of said chambers with a common dispensing outlet, valve controlled outlets in said discharge sections for releasing under pressure liquid from said discharge sections into said common passageway, and control means for directing pressurized fluid alternately to a selected one of said driving sections defined by said pistons in said lateral chambers, said piston members including flexible diaphragms supported by respective metal plates, said flexible diaphragms being folded toward said discharged sections around the periphery of said metal plates.

Thus viewed more specifically the present invention provides a pumping device comprising a pair of flexible diaphragms mounted on the respective ends of a common shaft. The outer surface of the diaphragms are in contact with the liquid to be dispensed by the system, more particularly syrup for a Post-mix beverage dispensing system. The chamber within the pump housing contains an inner wall in which passages are provided for directing compressed air, introduced into the reciprocating pump, to the surfaces of the diaphragms. The flow of air is controlled by a reversing valve adapted so as to redirect the flow of compressed air to the respective diaphragm at the completion of each stroke of the pump in a cyclic manner. The valve actuating member or yoke is provided which engages the shaft within the inner chamber of the pump housing the travels with the pumping action of the shaft.The yoke is designed so as to engage the reversing valve during the terminal phase of the pumping stroke thus activating the valve and reversing the piston action of the pump.

To complete the pump reversing system, a snapacting spring actuating means interconnected with the yoke of the shaft, is centered within the inner chamber of the housing of the pump, pivotably mounted beneath the shaft connecting the diaphragms The valve is provided with 0rings positioned within the valve body with respect to the air passages of the valve such that during the first half of the reciprocating cycle pressurized gas is introduced through the respective passage ways and directed to the air chamber of one of the diaphragms. At the same time a passage is provided for exhaust gases to be released from the air chamber of the remaining diaphragm.Upon interaction with the shaft yoke and the spring mounted actuating means the relatidnship of the valve openings to the pressurized gas acting on the surface of the respective diaphragm is changed at the completion of the pumping stroke so as to reverse the action of the pump. The snap-action mechanism provided precludes the sticking of the pneumatic reversing system in an intermediate position.

In operation, pressurized gas is introduced through a passageway into a valve member and is directed via a passageway within the inner wall of the pump housing to the air chamber of one of the diaphragms with the pump. As the piston action of the diaphragm forces syrup from the diaphragm chamber out the appropriate passage to the dispensing outlet, movement of the shaft also moves the remaining diaphragm in a nonpressurizing direction. This same shaft movement also engages the shaft yoke. As the shaft yoke moves it initiates the pivotal action of a pair of snap-acting compression springs which, prior to rotating off center, are pushing against each other. As the springs rotate off-center they uncoil, and push the shaft and yoke along in the direction of the established movement.The action of the spring mechanism ensures that the movement of the diaphragm, initiated by the air pressure, is taken to completion by the snap-action of the compression while at the same time reversing the flow of pressurized air within the valve member.

This procedure is then repeated as long as the dispensing outlet is open and the syrup is being dispensed as a pressurized stream. When the dispensing outlet is closed sufficient back pressure is exerted on the diaphragms to prevent shaft movement.

It had been determined in the course of the present invention that a reciprocating diaphragm pump for syrup in a Post-mix beverage dispensing system can be provided such that the liquid can be delivered under controlled pressure conditions in a reliable manner. A reversing valve is provided which includes a pair of compression springs bearing one on the other so as not to apply pressures of the bearing surfaces on the pump shaft. As the pistons of the diaphragm pump are driven by the pressurized gas there is always the possibility that a back pressure or some other malfunction might occur which could result in a premature reversing of the pump cycle before it is, completed thus interrupting delivery of the necessary syrup at the dispensing outlet. Upon the introduction of the spring actuated means of the instant invention, this premature cycle reversal is eliminated by the snap action resulting from the specific positioning and interrelationship of the compression springs within the valve reversing system.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.

Figure 1 is a cross-sectional view of a pump of the present invention representing the initial position of a pressure stroke in the direction indicated; Figure 1A is a top view of the pump of Figure 1, illustrating the details of the fluid input and output manifolds and the inlet and outlet valves of the pump of the present invention; Figures 2A and 28 are partial side and bottom views respectively, of the pump of Figure 1 illustrating a spring reversing system of the present invention at the snap-over center toward the right; Figures 3A and 38 are partial side and bottom views respectively, of the pump of Figure 1, illustrating a spring reversing mechanism of the present invention immediately after the snap-over position of Figures 2A, 28, which causes the pump shaft to reverse directions and move to the left;; Figure 4 is a cross-sectional view of a reversing valve of the present invention in the position that it occupies when the pump shaft of Figure 1 is driven to the right; Figure 5 is a cross-sectional view of a reversing valve of the present invention in the position that it occupies when the pump shaft of Figure 1 is driven to the left; Figure 6 is an exploded view illustrating the details of how a yoke of the present invention is mounted on the pump shaft; and Figure 7 is a partial view illustrating another embodiment of a pump diaphragm of the present invention.

Referring now to Figures 1 and 1 A, there is seen a cross-sectional side and top view, respectively, of the reciprocating pump of the present invention generally designated 10, comprising a housing 11 having an input manifold 1 2A and an output manifold 1 2B in its top wall for carrying the syrup to be pumped from the inlet SI through the respective chambers discussed below to the pump outlet SO. Within an inner chamber 13 of the pump is positioned a shaft 14 interconnecting diaphragms 1 6A and 1 68. An actuating member or yoke 1 7 with protrusions or arms 1 7A is slidably supported on the shaft 14 by the longitudinal bore 1 78, Figure 6, passing therethrough. A reversing valve 40 is attached to the inner wall 21 of housing 11 within the inner chamber 13 of the pump.The shaft 14 is press-fit with a pin 25, which upon operation of the pump, travels with the movement of the shaft predetermined distance before engaging an end of slot 26 provided in the yoke 17. Shaft 14 is mounted for sliding movement in O-ring seals or at its respective ends. Pivotally mounted beneath the yoke and interconnected therewith is a spring actuating member 27, (Figures 28, 38) within the housing chamber 1 3.The reversing effect of the valve 40 is facilitated as a result of the interrelationship between the actuating yoke member 17 and the spring actuating means 27 and alternately directs pressurized gas introduced through passageway 22 to the respective air chambers 1 SA and 15B, through passsgeways 23 and 24, to apply pressure to the respective diaphragms 1 6A and 16B. The reversing valve 40 comprises a valve body 41 and spool element 42 with O-rings 43. A more complete discussion of the operation of the reversing valve can be found below with respect to Figures 2A, 2B, 3A, 38, 4, and 5. Each diaphragm of the pump is constructed of a flexible material, such as rubber, secured to the inner walls of the pump housing at positions 20.

In a preferred embodiment of the present invention, the diaphragms further include a metal piston on the outer face of the respective diaphragm and a metal retaining cap on the inner surface of the respective diaphragm, as illustrated in Figure 7 to be discussed hereinafter.

The pumping cycle of the pump of the present invention and the flow of fluid therethrough can be best illustrated by reference to Figure 1 A. Fluid to be pumped is introduced through inlet SI to input manifold 1 2A which extends across the top of the pump and communicates with fluid chambers 28 and 29 via normally closed check valves 31 L, 31 R. When the fluid pressure in input manifold 1 2A exceeds the pressure in either chamber 28 or 29, check valves 31L, 31R open.

Since the pump of the present invention is a reciprocating pump, the fluid pressures in chambers 28, 29 are always in the opposite state.

That is, if the pump shaft in Figure 1A is moving to the right chamber 28 has a higher fluid pressure than manifold 12A, and chamber 29 has a lower fluid pressure than manifold 12A. Under these conditions check valve 31 L opens introducing fluid into chamber 29 and check valve 31 R is closed. Thus, as the pump cycles, check valves 31L, 31R alternately open and close.

Outlet check valves 32L, 32P, disposed in an output manifold 128, function in substantially the same manner. This is, when the pressure output manifold 128 is less than the pressure in one of the respective chambers 28,29 the check valve in that chamber opens, discharging fluid therefrom to pump outlet SO. In the above example, with the pump shaft 14 moving to the right, the pressure in chamber 28 is high, thus opening valve 32R and permitting the fluid therein to discharge via manifold 1 2B and pump outlet SO.

The check valves 31 L, 31 P, 32L, 32P are substantially identical except for the respective orientations thereof. Each is formed from rubber and includes a central stem fixedly mounted in the pump wall, and a disc-shaped seat B, which normally seats on fluid ports C. When biased by fluid pressure to open, disc-shaped seat B flexes away from parts C, permiting fluid to pass therethrough.

The above-described check valves are disposed at the highest positions of chambers 28, 29 to preclude the formation of air pockets which could be sucked out through pump outlet SO, resulting in an uneven flow of fluid.

Figure 6 illustrates the details of actuating member or yoke 17, which is mounted for movement on shaft 14. Yoke 17 includes a pair of upstanding arms 1 7A described hereinbefore for engaging the valve 40 and switching the same from one state to another. A longitudinal bore 178 is provided in yoke 17 for receiving pump shaft 14. After pump shaft 14 is inserted in bore 1 78, pin 25, described hereinbefore is press-fit into aperature 1 4A in shaft 14. A bottom plate 1 7C is suitably attached to the bottom of yoke 17, thus supporting a pair of pins 39 therein. As will be discussed hereinafter pins 39 support one pair of ends of spring members of the snap acting mechanism illustrated in Figures 28 and 38.

Referring now to Figure 2A, 28, there is seen in cross-section the pump mechanism set forth in Figure 1 representing a pressure stroke of the pump in the direction indicated at the point of engagement of the pin 25 of shaft 14 with an end of slot 26 in the shaft yoke 1 7. At this instant the yoke is picked up by pin 26 and begins to move with the shaft and the spring actuating member 27, connected to the yoke, begins to pass over center. The diaphragm 16 applies pressure to the liquid present in the chamber 28, which is released via check valve 32R into passageway 12 and directed out through the pump outlet SO to the respective discharge stations. Figures 28, 38 represent the position of the diaphragm, shaft and yoke at the completion of the stroke.As the reversing mechanism, generally indicated 27, moves over center there is produced a snap action effect which thrusts one arm 1 7A of the yoke against the protruding end of the spool 42 thus changing immediately the position of the 0rings of the valve so as to suddenly reverse the flow of pressurized air through the valve 40 at the completion of the stroke, and reverse the piston action of the pump.

Figures 28 and 38 illustrate the details of the spring reversing mechanism 27. The spring reversing mechanism in one embodiment comprises a coil spring 36 wrapped about a pin 37 and pivotally attached by way of pin 38 to the housing and pin 39 to the yoke 17. Upon engagement by the pump shaft, the yoke 17 will move in the direction of the stroke of the pump which in turn rotates pin 38 over center about pins 38 such that the springs 36 take over and push the yoke in the direction of the established movement at a speed faster than the shaft movement, until the yoke hits against the spool 42 of the valve mechanism so as to reverse the direction of the flow of pressurized air within the system and establish the piston action of the pump in the opposite direction. The position of the compression springs and yoke at the ends of the stroke are represented in Figure 38.The presence of the pins 37 within the coil spring 36 prevents the spring member from buckling during the movement of the piston during the operation of the pump. Alternately, torsion springs 36T in phantom may be substituted for the coil springs herein illustrated to provide the snap-acting actuating means of the present invention. The yoke 17 slides or is pushed along by the shaft and spring mechanism 27 of the pump first in one direction then in a reverse direction according to the reversing action of the valve 40.

In Figures 4 and 5 there is illustrated a simplified enlarged cross-sectional view of the reversing valve 40 of the present invention which is represented herein as a spool valve comprising a valve body 41, the spool 42 having three 0rings 43 intermittently positioned thereon within the valve cavity 44. Within the upper area of the valve body are located air passages 45 coupled to passage 22 of Figure 1, for introducing the pressurized gas into the valve cavity 44, and 46 and 47 coupled to passages 23, 24 respectively of Figure 1 , for directing air through the valve to the surface of the respective diaphragms of the pump.The valve 40 herein represented shows air under pressure being introduced to the valve cavity 44 through passageway 45 such that during the first half of the reciprocating cycle the air is directed to the respective air chamber 1 5B, through passageway 46 and passageway 24 (See Figure 1), while at the same time remaining passageway 47 provides for exhaust gases to be released as illustrated from the air chamber of the remaining or opposite diaphragm air chamber 15A.Upon contact by the left protruding end of the spool 42 with the yoke 1 7 as discussed above, the spool 42 is thrust to the right such that at the end of the pumping action the 0-rings 43 shift their position as illustrated in Figure 4, and the pressurized gas is now directed in the opposite direction so as to be introduced into the air chamber 1 5A of the diaphragm 1 6A, thus driving the pump in the opposite direction. In this position, the left end of the spool now projects from the valve cavity 44 and awaits to be engaged by an arm 1 7A of the shaft yoke in the reverse action of the piston.

In operation the valve 40 alternates the air flow through the respective passages 23, 23 to the air chamber 15A,15B of the diaphragms 16A, 1 6B.

The compression springs 36 or 36T interconnected to the yoke continuously urge the shaft of the diaphragm pump first in one direction then the other, responsive to the location of the yoke 1 7 along the shaft. The pressurized air is introduced into the air chambers 15A, 15B behind the respective diaphragms 16A, 16B and drives the diaphragms so as to discharge the liquid from the diaphragm chambers. As stated above, the yoke 1 7 on the shaft 14 initially moves in conjunction with the movement of the shaft upon engagement of an end of slot 26 with the pin 25 in shaft 14.The compression springs 36 or 36T, - which at the time of engagement are pushing against each other, with substantially no net force in a direction transverse to the pump shaft, pivot over center and apply a further driving force to the yoke which is then caused to move quickly by the snap-action of springs 36 to seat the projecting portions or arms 1 7A of the yoke 17 against the protruding spool 42 of the valve 41. This changes the positions of the O-rings within the valve body and reverses the flow of pressurized air therein thus completing the first half of the cycle of the diaphragm pump. The continuous introduction of pressurized air into the valve 40 initiates the pumping action of the shaft mounted piston in the opposite direction, first compressing the springs 36 or 36T and then repeating the action described above in the opposite direction, the compressed springs not pushing in the opposite direction. The spring reversing mechanism ensures that the movement of either of the diaphragms initiated by the air pressure, is completed thus preventing premature reversal of the pumping stroke or sticking of the valve 40 in a central position.

Referring now to Figure 7, there is seen in cross-section a pump construction similar to that discussed above with respect to Figures 1 and 1 A, except with respect to the structure of diaphragms 16A, 1 6B. The diaphragms 1 SA and 1 SB further include cup-shaped metal plates 52 on the outer face of the respective diaphragm surface and cup-shaped retaining cap 54 on the inner surface of the respective diaphragms. This configuration eliminates the formation of crevices in the flexible diaphragms.

Preferably, the pump housing is contructed of a molded plastic, as herein represented in Figure 1, such that the valves are mounted through the pump and all the lines or passageways run inside the plastic housing. This construction eliminates unnecessary joints and external lines which contributes to a more reliable system. As is seen in Figure 1, the inner wall of the housing comprises one continuous member which surrounds the pump reversing system components.The outer walls of the housing 11 are also fabricated of molded plastic which provides for an overall more desirable construction of the diaphragm pump of the present invention, It will thus be seen that the invention, at least in its preferred and illustrated embodiments, provides a reciprocating diaphragm pump for delivering, under: constant pressure, syrup to a Post-mix beverage dispensing system which will overcome the disadvantages noted hereinbefore.

Furthermore the invention provides a double acting reciprocating pump for syrup in a Post-mix beverage dispensing system wherein a reversing means is provided for reversing the direction of the pump at the end of each respective strokes, Furthermore the invention provides a gas operated diaphragm pump including a specializec valve, actuated by a spring-loaded member attached to a common shaft, which alternates the supply of pressurized gas to the respective diaphragm. Furthermore the invention provides a double acting reciprocating pneumatic pump for dispensing syrup to a dispensing outlet wherein the pump cycle reversing system includes a snap acting reversing means which ensures the completion of the pumping cycle. Furthermore the Invention provides a pneumatic double acting reciprocating pump having a reversing system which includes a valve, a valve actuating member, and a snap-acting spring member which reliably directs the supply of pressurized gas to the surface of either one of the two diaphragms in a cyclic manner. Furthermore the invention provides a reciprocating pneumatic diaphragm pump including a reversing means which allows for the dispersing of fluid from either one of two diaphragm chamber at the respective ends of the pump in a systematic, controlled manner.

Claims (19)

Claims

1. A reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston members therein dividing each Of said chambers into a driving section and a discharge section, said piston members being mounted On a common shaft, manifold means in said housing for connecting said driving sections and discharge sections of said chambers with a fluid inlet and outlet, respectively, valve mesns in said discharge sections for controlling the flow of liquid to be pumped to and from said discharge sections with respect to said manifold means, and control means for directing driving fluid alternately to a selected one of said driving sections defined by said lateral chambers, said control means including control valve means coupled to the source of driving fluid; a valve actuating member for said control valve means, movable on a bearing surface between first and second positions longitudinally, of said shaft to alternately direct said driving fluid to the respective driving tions, and snap-acting means for precluding the stopping of said valve actuating member between said first and second positions, said snap-acting means exerting substantially no net force transversely of said shaft against said bearing surface.

2. A pump apparatus according to claim 1, wherein said piston members comprise diaphragms interconnected by said common shaft, said shaft comprising a means for engaging said valve actuating member which in turn actuates said snap-acting means so as to quickly move said valve actuating member thus reversing said control means and redirecting the flow of pressurised fluid to produce the appropriate reciprocating pump action.

3. A pump apparatus according to claim 2, wherein said means for engaging said valve actuating means comprises a pin in said shaft which engages an end of a slot in said valve actuating means at a prodetermined position of movement of said shaft.

4. A pump apparatus according to claim 2 or 3, wherein each of said diaphragme further includes a metal piston on the outer surface of said diaphragm and a metal retainer cap on the inner surface of said diaphragm.

5. A pump apparatus according to any of the preceding claims, wherein said snap-acting means comprises a pair of opposed compression springs disposed in opposite sides of an axis which is parallel to a longitudinal axis of said shaft.

6. A pump apparatus according to claim 5, wherein said compression springs are coil springs.

7. A pump apparatus according to claim 6, wherein said coil springs are disposed about support means which preclude buckling of said coil springs.

8. A pump apparatus according to claim 5, wherein said compression springs are torsion springs.

9. A pump apparatus according to any of the preceding claims, wherein said pump housing is constructed of molded plastic.

10. A pump apparatus according to any of the preceding claims, wherein said valve means are disposed at the highest possible positions in said discharge sections.

11. A reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston member therein dividing each of said chambers into a driving section and a discharge section, said piston members being mounted on a common shaft, a common passageway in said housing for interconnecting said discharge sections of said chambers with a common dispensing outlet, valve controlled outlets in said discharge sections tor releasing under pressure liquid from said discharge sections into said common passageway, and control means for directing pressurised fluid alternately to a c-elected one of said driving sections defined by said pistons in said lateral chambers, said valve controlled outlets being disposed at the highest possible position in said discharge sections.

12. A reversing mechanism for a fluid control valve which selectively directs a fluid alternately in one of two directions in response to the switching of the control valve between first and second positions comprising; a slidable valve actuating member for engaging said control valve and switching said valve to said at or second positions; a bearing surface disposed on a predetermined axis along which valve actuating member slides; and snap-acting means for precluding the stopping of said valve actuating member between said first and second positions, said snap acting means exerting substantially no net force transversely of said axis against said bearing surface.

13. A reversing mechanism according to claim 12, wherein said snap acting means comprises overcenter spring means coupled to said valve actuating member, which causes said valve actuating member to snap to one side or the other of a position substantially equidistant between said first and second positions.

14. A reversing mechanism according to claim 13, wherein said overcenter spring means comprises a pair of opposed compression springs disposed on opposite sides of said axis.

15. A reversing mechanism according to claim 14 wherein said pair of springs are coil springs.

16. A reversing mechanism according to claim 15, wherein said coil springs are disposed about support means which preclude buckling of said coil springs.

17. A reversing mechanism according to claim 11 Z, wherein said compression springs are torsion springs.

18. A reciprocating pump apparatus comprising in combination a housing having laterally spaced chambers with piston members therein dividing each of said chambers into a driving section and a discharge section, said piston members being mounted on a common shaft, a common passageway in said housing for interconnecting said discharge sections of said chamber with a common dispensing outlet, valve controlled outlets in said discharge sections for releasing under pr- ur liquid from said discharge sections into said common passageway, and control means for directing pressurised fluid alternately to a selected one of said drivin g sections defined by said pistons in said lateral chambers, said piston members Including flexible diaphragms supported by respective metal plates, and flexible diaphragms being folded toward said discharge sections around the periphery of said meal plates

19. Pump apparatus substantially as hereinbefore described with reference to the accompanying drawings.