Pump

Abstract

A reciprocating fluid operated diaphragm-type pump has a control valve automatically movable at each end of the reciprocating stroke of the pump between two alternate positions to reverse fluid flow to the pump, and thereby cause the pump to reciprocate. A connecting member between the diaphragms of the pump passes through a passage in the control valve and has sealing members located to alternately seal and exhaust the opposite ends of the control valve to pressurized fluid flowing out of the valve passage to the ends of the valve, so that control valve movement at the ends of the pump stroke is positive and rapid.

Description

This invention relates to pumps.

Conventional fluid operated reciprocating pumps usually contain self-acting control valves, which are actuated by the moving pumping means (e.g., a piston or a diaphragm) of the pump, or some structure responsive to movement of the pumping means, at each end of the pump stroke, to reverse the flow of motive fluid (as air or hydraulic fluid) to the pumping means. The movement of the pumping means to one end of its stroke, e.g., causes some fluid passage in communication with the control valve to be opened or closed so as to direct or exhaust fluid through a part of the control valve, and thus causes the control valve to shift positions so as thereby to change the direction of fluid flow to the pumping means. However, once this valve is moved sufficiently to reverse the flow of fluid, it often happens that this reversal causes the fluid passage to be again closed or opened before the control valve has gone entirely to its opposite position. Thus, part of the movement of the control valve is due to the momentum of its initial movement. If the pump malfunctions, or if it is simply shut off during the period of time when the control valve is moving under momentum, it is possible that the control valve can stop intermediate of its two positions. Thus, when the pump is to be started again, it will be necessary to somehow gain access to the control valve or to employ some auxiliary start-up means so as to move the control valve to one of its two positions so that the self-acting pumping may occur and reciprocation can be initiated.

It is an object of this invention to provide a pump in which the control valve is positively impelled between its two reciprocating positions, so that the pump cannot stall.

Another object is to provide an improved reciprocating diaphragm type pump which is compact, light-weight non corrodible, easy to assemble and maintain, and of simple, reliable construction.

The invention features a pump comprising an inlet for a motive fluid supply, such as a source of compressed air, a housing divided into two separate compartments, and a pumping member such as a flexible diaphragm spanning and dividing each of these compartments into inner and outer chambers. The material to be pumped enters and exits the outer chambers through appropriate material inlet means and outlet means. A connecting member secures the two pumping members together for simultaneous movement in like direction, each pumping member being so located in its compartment that it alternately increases and decreases the size of the outer chamber in relation to the inner chamber, by virtue of the introduction of motive fluid to the inner chambers, expelling fluid from the outer chambers while decreasing the size of that chamber, and taking fluid into the outer chamber when travelling in the opposite direction so as to increase the size of the outer chamber. A valve assembly is located between the two compartments and comprises a valve chamber which has a port in communication with each of the inner chambers, a motive fluid inlet port in communication with the motive fluid supply, at least one exhaust port, a control valve, and a pair of spaced apart valve seats. The control valve has opposed actuating ends located opposite the respective valve seats, an internal fluid passage between its ends, and a motive fluid inlet to this internal fluid passage. The valve is disposed to be movable in the valve chamber between two positions, in which one or the other of the actuating ends rests on the respective one or the other of the valve seats, the valve being constructed to connect one of the inner compartments to the fluid inlet port of the valve chamber and the other of the inner compartments to an exhaust in accordance with its position.

To produce automatic movement of the control valve between its positions at each extreme of the reciprocating stroke of the connecting member and its associated pumping members, the connecting member is arranged to extend through the aforesaid internal valve passage between the actuating ends of the valve. Two spaced apart sealing members, mounted for movement with the connecting member, are sized to form sliding seals in the internal valve passage, one member being disposed on each side of the motive fluid inlet to the valve passage to prevent motive fluid from passing out of the valve passage to the respective end of the valve. However, when the connecting member reaches the alternate extreme of its stroke, alternate ones of sealing members are carried out of the internal valve passage, to admit motive fluid out of the internal valve passage past one or the other of the actuating ends of the valve, between that end and its seat. Additional sealing means, also moving with the connecting member, seal that end from exhaust while opening the opposite end to exhaust. The valve thus is moved to its other position. Positive, as well as rapid movement of the control valve between these two positions is assured because as soon as the sealing member moves out of the valve passage to admit fluid, the valve immediately moves in the opposite direction, thus increasing the available area for further motive fluid flow from the valve passage to the actuating end. Since there is increasingly more room for motive fluid to be admitted, the valve movement is continuously accelerated. Moreover, this rapid movement means that the fluid flow area will remain open to the motive fluid from the internal valve passage until the valve has reached its other position, since the sealing member, the movement of which has also been reversed, will be unable to catch up to the valve. Thus, the valve cannot stop between the opposite ends of its cycle, and the pump will be always ready for immediate start-up.

In a preferred valve construction, the internal valve passage of the valve is of cylindrical shape, the sealing members are secured to the connecting member, and the connecting member has a portion between the sealing members of smaller cross-sectional area than that of the internal valve passage so as to provide an annular pressure region therebetween, to which the ends of the valve are alternately exposed.

To provide exhaust from the two actuating ends of the valve, a preferred pump includes a partition between each compartment and the valve assembly, an exhaust passage in each partition, concentric with the internal valve passage so as to allow the connecting member to extend through the partitions, and an exhaust port in each passage. The surface at the interior end of each passage defines one of the valve seats. The connecting member is sized to allow fluid flow between the actuating ends of the valve and the respective exhaust passage, and the aforesaid sealing means are located to prevent such flow. Preferred sealing means comprise two additional spaced apart sealing members secured to the connecting member for movement with it, and sized to form sliding seals in the exhaust passages. The sealing members are so located that one of them is disposed in the respective one of the exhaust passages, sealing the actuating end of the valve from the exhaust port at certain intervals during the stroke at the connecting member, such as when the member is at the extremes of its stroke so that motive fluid is being introduced into the opposite actuating end. The operation of this embodiment is further facilitated by locating these exhaust sealing members in such a manner that even before motive fluid is admitted from the internal valve passage to one end of the valve, the opposite end of the valve is already opened to exhaust and thus, in a sense, the valve is primed for movement between its positions. In addition, the preferred pump construction has baffle means, constructed, e.g., of a synthetic cellular or foam material, located between the exhaust outlet and atmosphere to reduce noise caused by the very rapid reciprocation of the control valve.

In a preferred valve assembly, the valve chamber has two exhaust ports, one for each of the inner chambers. The control valve has an outer surface comprising axially spaced peripheral seals which define therebetween three axially spaced annular fluid flow spaces. The two opposite end spaces are continually in communication with the exhaust ports whereas the intermediate space is continually in communication with the motive fluid inlet port. Then, at each alternate position of the control valve, one of its end spaces is closed to one of the inner chambers, the intermediate space is open to that inner chamber to admit motive fluid to it, and the other end space is open to the other inner chamber so as to exhaust it.

A preferred pumping member is a flexible diaphragm, which spans its compartment, and which may be reinforced by rigid plates located on each side of the diaphragm and connected to each end by a rigid connecting rod. The diaphragm compartments are preferably in the form of opposed outer and inner frustro-conical shapes joined at a common base. The material inlet means to such a compartment is preferably through an inlet conduit disposed radially into the outer frustro-conical shape along its truncated apical end wall and the material outlet means from said compartment is of similar construction. The material inlet means (or outlet means) also includes a single tubular material passage which has an inlet (or outlet) intermediate of its ends, and each of its ends arranged to communicate, past a one-way valve means, with one of the inlet (or outlet) conduits to the diaphragm compartments, so that a single inlet simultaneously feeds fluid under a unitary pressure to both compartments.

Other objects, features, and advantages will be apparent to one skilled in the art from the following description of a preferred embodiment of this invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a sectional view of a preferred embodiment of a diaphragm pump taken along the line 1--1 of FIG. 2;

FIG. 2 is another sectional view of this pump, substantially perpendicular to that of FIG. 1 and along the line 2--2 of FIG. 1;

FIG. 3 is another sectional view of this pump, along the line 3--3 of FIG. 1, showing in particular the interior construction of a diaphragm compartment; and,

FIGS. 4 and 5 are enlarged views of the valve assembly of FIG. 1, with the control valve and connecting rod shown in different positions from that of FIG. 1.

The figures show a diaphragm pump 10 including a pump housing 12 substantially enclosing a first diaphragm compartment 18, a second diaphragm compartment 20, and a valve compartment 22. Pump housing 12 comprises a pair of spaced apart identical cylindrical end plates 24, 26, a pair of identical opposed inner plates 32, 34, and an annular spacing ring 35. All of the plates and rings are secured together by six spaced studs 37, extending through appropriate aligned openings in the plates 24, 32, 34, 26 and in spacing ring 35, and held at one end by nuts 40 and washers 41, and at the other end by acorn nuts 44 and retainers 45.

Referring to FIGS. 1 and 3, the first diaphragm compartment 18 is formed between a first frustro-conical shape 48 formed in cylindrical plate 24, joined at a common base to an opposed frustro-conical shape 50, formed in inner plate 32. Two tubular counterbores 52 extend radially into the truncated apical end wall of shape 48, are sealed at their two ends by appropriate plugs 54, and define, with perpendicularly disposed passages 57, 58, a material inlet conduit 59 to diaphragm compartment 18 and a material outlet conduit 60 from that compartment. A cylindrical counterbore 62, centrally located in the shape 48 of inner plate 24, is sized to receive a nut 64 and the protruding threaded end 65 of connecting rod 67.

A flexible diaphragm 68 is secured between the opposed faces of plates 24 and 32 around its entire periphery, to divide the compartment 18 into an outer or pumping chamber 70 in communication with inlet conduit 59 and outlet conduit 60, and an inner or motive chamber 72, sealed from those passages by the diaphragm 68, and in communication, through a tubular inlet 74 formed in plate 32, with the valve compartment 22. Diaphragm 68 may be formed of, e.g., various reinforced elastomers such as nylon-inserted Buna N, silicon rubber, or fluorocarbons such as those sold under the trade names "VITON," "Kel-F" and the like, or other flexible materials such as thin, convoluted stainless steel sheet. Diaphragm 68 has a central aperture, through which extends one end of connecting rod 67, and disc-shaped diaphragm reinforcing plates 75 are secured on each side of diaphragm 68 between the shoulder 76 of rod 67 and the nut 64, with a gasket 78 arranged to provide a fluid-tight seal between the pumping chamber 70 and the motive chamber 72.

A material inlet 80 communicates with the opening 81 into the tubular passage 82. A spring-biased ball valve 84 is arranged in the ball valve chamber 83 with the shoulder 85 provided at the end of passage 82 forming a valve seat for ball valve 84. This ball valve is arranged to pass material from inlet 80 and passage 82 to diaphragm pumping chamber 70. A gasket 88 seals the interface of inner plate 32 and spacing ring 35 at valve chamber 83. A material outlet 90 communicates with the tubular passage 92. A spring biased ball valve 94 is arranged in the ball valve chamber 93, with the shoulder 95 provided at the end of tubular passage 58 forming a valve seat for ball valve 94. This ball valve 94 is arranged to pass material from diaphragm pumping chamber 70 to outlet 90. A gasket 98 seals the interface of inner plate 32 and spacing ring 35 at valve chamber 93. The diaphragm 68 has an opening adjacent and concentric with each valve chamber 83, 93.

The second diaphragm compartment 20 is formed of frustro-conical shapes 148 and 150, identical to the shapes 48, 50 of first diaphragm compartment 18, and includes two tubular counterbores 152 extending radially into shape 148, sealed at their two ends by plugs 154, and defining, with perpendicularly disposed passages 157, 158, a material inlet conduit 159 to compartment 20, and a material outlet conduit 160 from the compartment 20. Cylindrical counterbore 162, identical to counterbore 62, is for receiving a nut 164 and opposite threaded end 165 of connecting rod 67. A flexible diaphragm 168 (formed of materials such as previously described for diaphragm 68) is secured between the opposed faces of plates 26 and 34, around its entire periphery, to divide the compartment 20 into an outer or pumping chamber 170 in communication with inlet conduit 159 and outlet conduit 160, and an inner or motive chamber 172, sealed from those passages by diaphragm 168, and in communication, through tubular inlet 174, with the valve compartment 22. Disc-shaped diaphragm reinforcing plates 175, which are secured between rod shoulder 176 and nut 164, and gaskets 178 are arranged as previously described for plates 75 and O-rings 78. A cylindrical ball valve chamber 183 is formed in inner plate 34 adjacent the tubular passage 82. A spring-biased ball valve 184 is arranged in chamber 183, with the shoulder 185 provided at the end of passage 82 forming a valve seat for ball valve 184. Ball valve 184, like valve 84, passes material from inlet 80 to diaphragm pumping chamber 170. A gasket 188 seals the interface of inner plate 34 with spacing ring 35 at valve chamber 183. A spring-biased ball valve 194 is arranged in the ball valve chamber 193, with the shoulder 195 provided at the inner end of tubular passage 158, forming a valve seat for ball valve 194. This ball valve 194 passes material from diaphragm pumping chamber 170 to outlet 90. A gasket 198 seals the interface of inner plate 34 with spacing ring 35 at valve chamber 193. The diaphragm 168 has an opening adjacent and concentric with each valve chamber 183, 193.

Referring now to FIGS. 1 and 4, valve assembly 200 includes a stationary annular valve housing 202, secured by fasteners 203 between opposed shallow cylindrical detents 205, 206, formed in the opposing surfaces of inner plates 32, 34. Spool valve 208 has four annular lands 209 each having an annular rubbery O-ring seal 210 at its outer surface, slidingly engaging the inner cylindrical valve chamber 211 of housing 202, the seals 210 being located so as to maintain, by friction with chamber 211, the spool valve 208 in position, in the absence of other forces acting on the spool valve. The seals 210 are fluid-tight and define therebetween three annular fluid flow spaces 212, 213, 214 with chamber 211. The entire spool valve, exclusive of seals 210 may be formed of a rigid plastic, such as acetal. Spool valve 208 also has opposed actuating faces 216, 217 at its opposite ends, disposed opposite the valve seats 218, 219 formed in inner plates 32, 34, respectively. Spool valve 208 has a central bore defining an internal valve passage 220 within which is slidingly received the rubbery O-ring sealing members 222, 223, 224, 225 located on connecting rod 67. These sealing members provide fluid-tight sliding seals around the connecting rod 67, which has, disposed within the valve passage 220, upper and lower portions 228, 230 and a reduced diameter central portion 232. The connecting rod 67 also extends slidingly through exhaust passages 233, 234 in inner plates 32, 34, respectively, and is sealed from the diaphragm compartments 18, 20, by gaskets 236, 237, respectively.

Referring also to FIG. 2, valve housing 202 has an inlet passage 240 in communication with valve space 213 and also with a compressed air line 242, providing a motive fluid supply to operate the pump, and which in turn extends through an opening 244 in spacing ring 35. An annular exhaust port 246 is located between the opening 244 and air line 242, and in communication with the exhaust space 247 in valve compartment 22. An annular air-permeable foam packing ring 248 is arranged as a baffle interior of and adjacent opening 244, to reduce any noise caused by operation of the spool valve 208.

Two outer exhaust passages 250, 251 extend between valve chamber 211 and exhaust space 247, are in communication with valve spaces 212, 214, respectively, and also communicate with valve exhaust passages 252, 253, respectively, which in turn communicate, through diagonal passages 254, 255, respectively, formed in inner plates 32, 34, respectively, with exhaust passages 233, 234, respectively. The diagonal passages 254, 255 are sealed from motive chambers 72, 172, respectively, by connecting rod portion 228 and gasket 236, and connecting rod portion 230 and gasket 237, respectively. Inner chamber fluid passages 258, 259, sealed to have a right-angle configuration by sealing fasteners 260, 261, respectively, communicate through passages 74, 174, respectively, with motive fluid diaphragm chambers 72, 172, respectively.

Inlet 240 is also in communication, through the valve space 213, with one of the inner chamber passages 258, 259, depending on the position of the spool valve 208. The other inner chamber inlet passage is in communication, through valve space 212 or 214, with outer exhaust passage 250 or 251, respectively, Inlet 240 is also in communication, through narrow radial inlet passages 272, 273 through spool valve 208, with the annular pressure region 274 between the central portion 232 of connecting rod 67 and the internal valve passage 220 of spool valve 208.

In operation, a motive fluid, such as compressed air, is introduced through inlet line 242 and passage 240 to valve space 213. In the position of spool valve 218 shown in FIG. 1, this valve space is open, through passages 259, 174 to second diaphragm inner chamber 172. Although both valve spaces 212, 214 are open to atmosphere through passages 250, 251, respectively, only valve space 212 is open to inner diaphragm chamber 72 through passages 258 and 74. Valve space 214 is closed to inner chamber 172. In this spool valve position, therefore, air under pressure is being introduced into motive chamber 172 and air is being exhausted from chamber 72, causing the diaphragms 68, 168 to travel, in unison by virtue of connecting rod 67, in the downward direction in FIG. 1, tending to decrease the size of the inner chamber 72 of the first diaphragm compartment 18, and increase the size of the inner chamber 172 of the second diaphragm compartment 20.

The material being pumped, in the meanwhile, is introduced, under pressure, through inlet 80 into passage 82. So long as the fluid pressure in expanding pumping chamber 70 of the first diaphragm compartment 18 is insufficient, together with the biasing spring of ball valve 84, to overcome the pressure of incoming material in passage 82, ball valve 84 will be unseated, allowing material to pass into pumping chamber 70. However, since pumping chamber 170 of the second diaphragm compartment 20 is decreasing in size with the movement of the diaphragms indicated in FIG. 1, the combined pressure in chamber 170 and the force of the biasing spring of ball valve 184, will be sufficient to retain ball valve 184 seated, and hence no material will enter chamber 170. The increasing pressure in contracting pumping chamber 170 will also unseat ball valve 194, so that material may exit through passage 92 and outlet 90, whereas the pressure in expanding pumping chamber 70 will be insufficient to unseat ball valve 94. The one-way orientation of valve seats for the ball valves 84, 184, 94 and 194 prevents backflow of material through the pump.

In the position shown in FIG. 1, the diaphragms 68, 168 and connecting rod 67 have nearly reached one extreme of the stroke, with pumping chamber 70 almost filled and pumping chamber 170 almost emptied. The outer diaphragm pad 174 is close to the apical wall of shape 148, and the nut 164 and rod end 165 have begun to enter the counterbore 162. The motive fluid main flow around and within flow spool valve 208 is as follows. Compressed air from passage 240 is being led continuously through passages 272, 273 to the pressure region 274, but sealing members 222, 223 are still preventing air from passing to the actuating faces 216 or 217 of valve 208. Diagonal passage 254 is open, however, through the narrow annular space between the upper portion 228 of connecting rod 67 and the exhaust passage 233, to the valve chamber space adjacent actuating face 216, allowing air in that space to exhaust through passages 254, 252 and 250. Diagonal passage 255, however, is sealed from the valve chamber space adjacent actuating face 217 and hence from the valve spool itself by sealing member 224, which is disposed within exhaust passage 234.

With slight further movement of the diaphragms and connecting rod in the downward direction, the sealing member 224 will be moved all the way out of internal valve passage 220, to open the valve chamber adjacent valve actuating face 217 to compressed air from pressure region 274. The valve chamber adjacent opposite actuating face 216 being open to atmosphere, the sudden onrush of compressed air adjacent valve face 217 will lift the spool valve 208 off valve seat 219. As the spool valve 208 is lifted, the annular area for air flow from space 274 between the valve 208 and the sealing member 224 rapidly increases in size, accelerating spool valve movement until the spool valve 208 has travelled to the opposite end of the valve chamber 214, actuating face 216 resting on valve seat 218, in the position shown in FIG. 4. The valve space 213 has now been shifted so as to be between air inlet passage 240 and diaphragm compartment passage 258 to direct compressed air to motive chamber 72, whereas valve space 214 is located to exhaust air from motive chamber 172 through passage 259, space 214, and passage 251. Thus, the rod 67, and hence diaphragms 68, 168 connected thereto, will begin to move in the upward direction, material being expelled from pumping chamber 70 past ball valve 94 and through outlet 90, and material being introduced into expanding pumping chamber 170 through inlet 80, past ball valve 184. Long before rod 67 moves sufficiently for sealing member 224 to reseal pressure region 274 from the actuating face 217, the spool valve 208 has gone completely to the position shown in FIG. 4. Thus, the entire spool valve movement is under the constant force of compressed air from the source 242, causing a rapid and positive movement of the valve, and making it impossible for the spool valve to stop in any position intermediate of those shown in FIGS. 1 and 4. The pump is always, therefore, ready for use. Even when compressed air is exhausted from below the valve face 217, frictional forces between the sealing members and the wall of valve chamber 211 maintain the valve on one or the other of its valve seats.

As the connecting rod 67, with movement of the diaphragms under compressed air, moves to the position shown in FIG. 5, first sealing member 224 seals pressure region 274 from valve face 217. Next sealing member 225 moves out of exhaust passage 234, opening the valve chamber adjacent actuating face 217 to atmosphere through passages 255, 253, and 251, as sealing member 222 moves into exhaust passage 232, to close communication between the valve chamber adjacent actuating face 216 and atmosphere through passages 254, 252 and 250. In this position, as shown in FIG. 5, both actuating faces 216, 217 are closed to the compressed air in space 274, and face 217 is already exposed to atmosphere. Finally, as rod 67 is moved to and past essentially the reverse of the position of FIG. 1, sealing member 223 will move out of internal valve space 220, exposing valve face 216 to compressed air from pressure region 274, rapidly returning the spool valve 208 to the FIG. 1 position, to commence another stroke. With air now being introduced into motive chamber 172 and exhausted from chamber 72, the diaphragms 68, 168 will travel back in the direction indicated in FIG. 1, and material being expelled from pumping chamber 170 and filling pumping chamber 70, the diaphragms 68, 168 and rod 67 will complete the cycle back to the position shown in FIG. 1.

Substantially all parts of the pump may be formed of metal, such as stainless steel, or of light-weight, noncorrodible rigid plastic materials, such as acrylics and the like. The diaphragm pads 74, 174, and connecting rod 67, for greater rigidity, are preferably formed of a metal such as stainless steel, which may be coated, if desired, with a noncorrodible coating such as a thin fluorocarbon film.

Other embodiments will occur to those skilled in the art and are within the following claims.

Claims

What is claimed is:

1. A pump comprising

a housing having two separate compartments,

a pumping member spanning and dividing each of said compartments into inner and outer chambers,

material inlet means and outlet means for each said outer chamber,

a valve assembly for controlling movement of said pumping members, said valve assembly being located between said compartments and comprising

a valve chamber including a port in communication with each said inner chamber, a fluid inlet port for a motive fluid supply, at least one exhaust port, and a pair of spaced apart valve seats, and

a control valve in said valve chamber having opposed actuating ends, an internal passage between said ends, and a motive fluid inlet to said internal passage, said valve being movable in said valve chamber between two positions in which either one or the other of said actuating ends rests on the respective one or the other of said valve seats, said control valve being constructed to connect one of said inner compartments to said fluid inlet port and the other of said inner compartments to said exhaust port through said valve chamber in accordance with its position,

a connecting member between said pumping members, joining said pumping members together for simultaneous movement in said compartments in like directions in a reciprocating stroke, said connecting member extending through said internal valve passage,

at least two spaced apart sealing members, responsive to movement of said connecting member, sized to form sliding seals in said internal valve passage, one of said members being disposed on each side of the said motive fluid inlet to said internal valve passage, and so located that alternate ones of said sealing members are carried out of said internal valve passage when said connecting member reaches the alternate extremes of its said stroke so as to admit motive fluid out of said internal valve passage, past the respective end of said open valve, between that end and its seat, and

sealing means responsive to movement of said connecting member to alternate extremes of its stroke to seal that end of said control valve from exhaust while opening the opposite end of said control valve to exhaust, to allow movement of said control valve between its positions in response to said admitted motive fluid.

2. The pump of claim 1 wherein said sealing members and said sealing means are secured to said connecting member for movement therewith.

3. The pump of claim 2 wherein said internal valve passage is of cylindrical shape, said connecting member has a portion between said sealing members of smaller cross-sectional area than the cross-sectional area of said internal valve passage, defining with said valve passage an annular region continually under fluid pressure from said motive fluid inlet, and said sealing members are located to expose the ends of said control valve to said pressure region.

4. The pump of claim 1 including a partition between each said compartment and said valve assembly, each said partition including

an exhaust passage having an exhaust port, each said exhaust passage being arranged concentric with said internal valve passage, with said connecting member extending through said exhaust passage, and

a surface at the interior end of each said passage defining one of said valve seats,

said connecting member and said exhaust passages being sized to allow fluid flow between the said actuating ends of the valve and the respective passage, and said sealing means arranged to prevent said fluid flow.

5. The pump of claim 4 wherein said sealing means comprises two additional spaced apart sealing members, secured to said connecting member for movement therewith, sized to form sliding seal in said exhaust passages, and so located that one of said sealing members is disposed in the respective one of said exhaust passages between said exhaust port and the said actuating end of said valve at each extreme of the said stroke of said connecting member.

6. The pump of claim 1 wherein said control valve chamber has two exhaust ports for said inner chambers, and valve has an outer surface comprising axially spaced peripheral seals defining therebetween three axially spaced annular fluid flow spaces, the opposite end spaces are in communication with said exhaust ports, the intermediate space is in communication with the fluid inlet port from said motive fluid supply, and said spaces are mutually arranged with the valve chamber ports to said inner chambers so that, at each alternate position of said control valve, one of said end spaces is closed to one said inner chamber, the intermediate space is open to that said inner chamber to admit motive fluid to said chamber, and the other of said end spaces is open to the other said inner chamber to exhaust motive fluid from that chamber.

7. The pump of claim 1 including baffle means between said exhaust port and atmosphere.

8. The pump of claim 1 wherein each said pumping member comprises a flexible diaphragm spanning its respective said compartment, and centrally secured to said connecting member.

9. The pump of claim 8 including rigid reinforcing plates secured to each side of said diaphragm, and wherein said connecting member comprises a rigid rod extending through said plates.

10. The pump of claim 9 wherein each said compartment is constructed in the form of opposed outer and inner frustro-conical shapes joined at a common base.

11. The pump of claim 10 wherein said material inlet means comprises an inlet conduit radially into the outer frustro-conical shape along its truncated apical end wall, and said material outlet means comprises an outlet conduit radially out of said outer frustro-conical shape along its truncated apical end wall.

12. The pump of claim 11 wherein said material inlet means includes a single tubular material inlet passage having an inlet opening intermediate of its ends, and with each end arranged to communicate, past a one-way valve means, with one of said inlet conduits, and a single tubular material outlet passage, having an outlet opening intermediate of its ends, and with each end arranged in communication, past a one-way valve means, with one of said outlet conduits.