Double diaphragm pump

Abstract: Provision is made for an air control valve to bypass the ice forming exhaust of a reciprocating pressure activation chamber (18,26) in a reciprocating double diaphragm pump utilising the supply pressure to close a check valve (5a,5b) in line between the valve and the chamber which is then opened to exhaust by exhaust fluid flow from the chamber(18,26).

Description: This invention relates to reciprocating double diaphragm pumps. Current diaphragm pumps, as well as other pneumatic devices, experience two problems: (1) icing which results in reduced/erratic performance of the pump, and (2) inefficiency resulting from oversized valve porting to overcome icing provided in current design. The air motor valving used to control reciprocating motion in current designs handles both the feed air to the driving piston or diaphragm and exhaust air through the same porting. In order to obtain fast switch over and high average output pressure it is important the piston/diaphragm chambers are exhausted as quickly as possible. In order for this to occur the porting through the valve is made as large as possible. The large port area allows the air to exhaust rapidly; however, in doing so large temperature drops are generated in the valve. Any water in the air will drop out and freeze. As with most valves the geometry of the flow path through the valve may contain areas where the flow may be choked followed by large expansions and stagnation areas. These are the areas where water collects and freezes. The valving itself may also become extremely cold since exhaust air is continually flowing through the valve and may cause water in the incoming air to freeze. The large port area required to dump the exhaust is also used to feed the air chamber. During the fill cycle the large porting allows the chamber to fill rapidly and reach a high mean effective pressure in the chamber at high cycle rates. The head pressures developed at high flow rates are relatively low which requires a finite chamber pressure and volume to move the fluid at the required flow rate and head. By sizing the inlet porting to meet flow requirements the volume of air required is reduced as well as the amount to exhaust. US-A-4 406 596 (equivalent to EP-A-0 061 706) discloses a double diaphragm pump in accordance with the preamble of claim 1. According to the present invention, there is provided a double diaphragm pump having a reduced icing air valve comprising a shiftable valve having a pilot piston for shifting said valve for alternately supplying compressed air through first and second supply ports to opposed first and second actuating chambers respectively and for effecting alternating exhaust of said chambers; characterised in that said valve is provided with bypass means intermediate said valve and each of said actuating chambers for bypassing said valve by exhausting air from said actuating chambers, said bypass means being actuable by air supplied to said chambers. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a cross-section of a diaphragm pump showing an air motor major valve; Figure 2 is a cross-section of a reduced icing air valve showing a pilot valve; Figure 3 is a cross-section detail of the pilot valve in an extreme left-hand position; Figure 4 is a cross-section detail showing the air motor major valve spool in an extreme left-hand position; Figure 5 is a cross-section detail showing the pilot valve in an extreme right-hand position; and Figure 6 is a cross-section detail showing the major valve in an extreme right-hand position. In order to exhaust the air chambers rapidly without increasing the fill cycle porting, an alternative flow path is required. Figure 1 is a cross-sectional view of the air motor major valve. Figure 2 is a view of the pilot valve. Both valves are shown in their dead centre positions. In Figure 1, the major valve consists of a spool 1, valve block 2, valve plate 3, power piston 4, quick dump check valves 5a and 5b, and housing 6. Figure 2 shows the pilot valve consisting of a pilot piston 7, push rod 8 and actuator pins 9a and 9b. Both valves are located in the same cavity 12 which is pressurised with supply air. The power piston 4 and pilot piston 7 are differential pistons. Air pressure acting on the small diameters of the pistons will force the pistons to the left when a pilot signal is not present in chambers 10 and 11. The area ratio from the large diameter to the small diameter is approximately 2:1. When the pilot signal is present in the chambers 10 and 11 the pistons are forced to the right as shown in Figures 5 and 6. In Figure 4 the spool 1 is shown in its extreme left position as is the pilot piston 7 in Figure 3. Air in the cavity 12 flows through an orifice 13 created between the spool 1 and valve block 2 through a port 14 in the valve plate 3. The air impinging on the upper surface of the check valve 5a forces it to seat and seal off the exhaust port 15. The air flow deforms the lips of the elastomeric check valve as shown in Figure 4. Air flows around the valve into a port 17 and into a diaphragm chamber 18. Air pressure acting on the diaphragm 19 forces it to the right expelling fluid from a fluid chamber 20 through an outlet check valve. Operation of the fluid check valves controls movement of fluid in and out of the fluid chambers causing them to function as single acting pumps. By connecting the two chambers through external manifolds output flow from the pump becomes relatively constant. At the same time as the chamber 18 is filling, the air above the check valve 5b has been exhausted through an orifice 21, a port 22 and into an exhaust cavity 23. This action causes a pressure differential to occur between chambers 24 and 25. The lips of the check valve 5b relax against the wall of the chamber 25. As air begins to flow from an air chamber 26 through a port 27, it forces the check valve 5b to move upward and seats against the valve plate 3 and seal off a port 28 and opens the port 16. Exhaust air is dumped into the cavity 23. The diaphragm 19 is connected to the diaphragm 29 through a shaft 30 which causes them to reciprocate together. As the diaphragm 19 traverses to the right the diaphragm 29 creates a suction on a fluid chamber 31 which causes fluid to flow into the fluid chamber 31 through an inlet check. As the diaphragm assembly approaches the end of the stroke, diaphragm washer 33 pushes the actuator pin 9a (Figure 5) to the right. The pin in turn pushes the pilot piston 7 to the right to the position shown in Figure 5. O-ring 35 is engaged in bore of sleeve 34 and O-ring 36 exits the bore to allow air to flow from the air cavity 12 through the port 37 in the pilot piston 7 and into the cavity 10. Air pressure acting on the large diameter of the pilot piston 7 causes the piston to shift to the right. The air that flows into the chamber 10 also flows into the chamber 11 through a passage 38 which connects the two bores. When the pressure reaches approximately 50% of the supply pressure, the power piston 4 shifts the spool 1 to the position shown in Figure 6. Air being supplied to the chamber 18 is shut off and the chamber 38 is exhausted through an orifice 41. This causes the check valve 5a to shift connecting air chamber 18 to exhaust port 15. At the same time the air chamber 26 is connected to supply air through the orifice 40 and port 28 and 27. The air pressure acting on the diaphragm 29 causes the diaphragms to reverse direction expelling fluid from the fluid chamber 31 through an outlet check while the diaphragm 19 evacuates the fluid chamber 20 to draw fluid into the fluid chamber 20. As the diaphragm 19 approaches the end of its stroke, the diaphragm washer 39 pushes the actuator pin 9b. The motion is transmitted through the push rod 8 to the pilot piston 7, moving it to the trip point shown in Figure 2. The O-ring 36 re-enters the bore in the sleeve 34 and seals off the air supply to the chambers 10 and 11. The O-ring 35 exits the bore to connect the chambers 10 and 11 to the port 37 in the pilot piston 7. The air from the two chambers flows through the port 42 into exhaust cavity 23. The air in air cavity 12 acting on the small diameters of pistons 4 and 7 forces both to the left as shown in Figures 3 and 4. The power piston 4 will pull the spool 1 to the left to begin a new cycle. Different arrangements to actuate the quick dump valves can be used which include poppet valves, "D" valves and other mechanical or pneumatically actuated valves.

Claims: A reciprocating double diaphragm pump having a reduced icing air valve comprising a shiftable valve having a pilot piston for shifting said valve for alternately supplying compressed air through first and second supply ports (17, 27) to opposed first and second actuating chambers (18, 26) respectively and for effecting alternating exhaust of said chambers; characterised in that said valve is provided with bypass means (15, 16) intermediate said valve and each of said actuating chambers (18, 26) for bypassing said valve by exhausting air from said actuating chambers, said bypass means being actuable by air supplied to said chambers. A pump according to claim 1, comprising mechanically connected diaphragms (19, 29), wherein pressurising one of said opposed first and second actuating chambers (18, 26) effects exhaust of the other of said opposed first and second actuating chambers. A pump according to claim 1 or 2, wherein said shiftable valve is a pneumatically operated spool valve (1, 2). A pump according to any one of the preceding claims, wherein said shiftable valve has a pilot piston (7). A pump according to any one of the preceding claims, wherein said bypass means comprises a pressure operated check valve (5a, 5b) closed to exhaust by the supply of compressed air to its associated actuating chamber and open to exhaust, upon ceasing the supply of compressed air, by return flow of exhaust air. A pump according to claim 5, wherein said pressure operated check valve further comprises a deformable elastomeric check co-acting with an exhaust port (15) to close it off upon supply of compressed air and co-acting with said supply port to close off said supply port to said valve upon exhaust of said actuating chamber. A pump according to claim 6, wherein said exhaust port exits to atmosphere. A pump according to claim 5, 6 or 7, wherein said pressure operated check valve (5a, 5b) further coacts with the respective supply port to prevent return flow of exhaust air to said shiftable valve. A pump according to any one of the preceding claims, and comprising a power piston (4) that is a differential piston.

Inventors: ELFERS ROBERT C, KOZUMPLIK NICHOLAS JR, ELFERS, ROBERT C., KOZUMPLIK, NICHOLAS, JR.
Applicants: INGERSOLL RAND CO, INGERSOLL-RAND COMPANY
Application year: 1995
Main classification: F04B43
IPC codes: F04B53, F04B9, F04B43