GB2214991A - Improved double-acting pump - Google Patents

Abstract

An improved double-acting pump includes two fluid passages (17, 18) extending between an inlet (1) and opposite ends of the pumping cylinder (5), two fluid passages (27, 28) extending from the cylinder ends to an outlet (2), two inlet valves (11, 12) to control the flow of fluid material into the respective fluid passages (17, 18), two outlet valves (20, 21) to control the flow of fluid material from the respective fluid passages to the outlet (2), and piston means (4) for increasing and reducing the fluid pressure in the fluid passages alternately. The outlet valves (20, 21) comprise two outlet valve members urged apart by a spring (26) to engage respective axially-aligned annular valve seats (22, 23). <IMAGE>

Description

Improved Double-acting Pump The present invention is a double-acting pump having improved properties in terns of the accuracy of the volume of fluid material delivered by it.

Double-acting pumps are well known in which fluid material from a cation inlet is fed by two alternative routes to a common outlet, the pressures in the respective streams being alternately raised and lowered by means of a reciprocating piston. Control of the fluid flaw i5. achieved by means of an inlet valve and an outlet valve in each stream, so disposed that a reduction of pressure in a given fluid stream causes the respective inlet valve to open to admit fluid and simliltaneously causes or allows the outlet valve to close.

Thus the alternating increases and reductions in pressure in the two streams effect a flow of fluid from inlet to outlet by the two routes alternately.

Pumps of this type can be used to deliver accurate quantities of fluid material on a repetitive basis, the quantities of material in successive deliveries being accurately maintained. Hbwever inaccuracies can arise at the point between deliveries where one of the outlet valves closes and the other one opens. If, transiently, both outlet valves are open sinLltaneously, then the quantity of product delivered may be inaccurate.

DoLle-acting putts of the foregoing type may be adopted when it is desired to deliver material to a filling machine, wherein a succession of containers, for example paint tins or food cans, are to be filled. In this contest, the need for the delivery of accurately-metered quantities of material may arise fran not only commercial but also legal considerations. Thus there is a need for an improved form of double-acting pump in the the above-described inaccuracies are reduced or eliminated.

It is an object of the present invention to provide such an improved pump.

The double-acting pump according to the present invention is characterised by a double outlet valve, wherein back-to-back valve members are resiliently urged apart to engage opposed valve seats.

Thus the invention is a double-acting pump comprising a fluid inlet, two fluid passages within the pump, two inlet valves located to control the flaw of fluid material into the respective fluid passages, a fluid outlet fran said pump, two generally annular valve seats in axial alignment at the outlet ends of the respective fluid passages, two outlet valve members resiliently urged apart to engage the respective generally annular valve seats and thereby to control the flow of fluid material fran the respective fluid passages to the fluid outlet, and piston means for increasing and reducing the fluid pressure in the fluid passages alternately.

The two generally annular valve seats at the outlet ends of the fluid passages are axially aligned and the fluid passages may therefore conveniently include final lengths which are also in axial alignment. A particularly compact pump design is achievable if the inlet ends of the fluid passages are also aligned and the two inlet valves are disposed with their valve numbers and valve seats similarly axially aligned. Thus, for example, the inlet valves may conveniently be incorporated in a three-way fitting, comprising the fluid inlet and the two aligned inlet valves.

As stated, the outlet valve comprises two generally annular valve seats in axial alignment and two valve members resiliently urged apart to engage the valve seats. In a preferred form of the pump according to the present invention, the valve members are mounted on telescopically overlapping shafts, whereby the alignment of the valve members is assisted.

The valve members may be urged apart by any convenient resilient means but it is particularly preferred to locate a helical compression spring between the two member. For example, when the valve members are mounted on telescopically overlapping shafts, such a helical spring may encircle one or both of the shafts.

In a copending patent application filed on the sme date as this present application, a valve incorporating a novel form of valve member is described. It is particularly advantageous to adopt that valve as a feature of the doubleacting pump according to the present invention, especially as the pump outlet valve but also for the inlet valves.

The invention will now be further described with reference to the accompanying drawing, which illustrates in vertical section one preferred embodiment of the double-acting pump according to the present invention.

The illustrated pump comprises a fluid inlet 1, a fluid outlet 2 and a reciprocating piston 3 by nreans of which fluid is pumped fran the inlet to the outlet. The piston 3 is mounted upon a shaft 4 for reciprocation within a cylinder 5 and ocoprises two PIFE cups 6, 7 supported by PmE rings 8, 9.

The piston 3 is driven by an air cylinder (not shown) linked to the shaft 4.

The inlet 1 is constructed as part of a three-way inlet fitting 10 which also incorporates two inlet valves in the form of valve members 11, 12 urged by springs 13 and 14 respectively to engage annular valve seats 15 and 16 respectively.

The inlet valve 11, 15 is linked by a tubular conduit 17 to the end of the cylinder 5 remote fram the shaft 4 and the inlet valve 12, 16 is linked by a tubular conduit 18 to the shaft end of the cylinder 5.

The outlet 2 is a part of a three-way fitting 19 which incorporates a double outlet valve comprising valve mEmbers 20 and 21 acting against valve seats 22 and 23 respectively. The valve member 21 is supported by a shaft 24 which fits within a hollow shaft 25 supporting valve member 20.

The valve members 20 and 21 are urged apart towards the respective valve seats 22 and 23 by a helical compression spring 26 located between the shafts 24 and 25. The outlet valve 20, 22 is linked by a tubular conduit 27 to the end of the cylinder 5 remote fran the shaft 4 and the outlet valve 21, 23 is linked by a tubular conduit 28 to the other end of the cylinder 5.

The orientation of the pump is not critical but it is preferred to mount the pump with the shaft 4 in a generally horizontal position with the outlet 2 above the inlet 1, as this assists priming of the pump. The pump operates as follows.

From the position illustrated in which the shaft 4 is within the cylinder 5 to its maximum extent, the;-shaft and piston 3 are initially withdrawn. This increases The pressure on the fluid on the shaft side of the piston and in the conduits 18 and 28, thus retaining the inlet valve member 12 in its closed position and opening the outlet valve mEmber 21 and discharging fluid through the outlet 2. Opening of the outlet valve member 21 assists the helical spring 26 in holding the other outlet valve mmber 20 in its closed position.At the same time, the movement of the piston 3 also reduces the pressure on the fluid in the conduits 17 and 27 and in the adjacent end of the cylinder 5. This further assists in holding closed the outlet valve member 20 and also opens the valve member 11 and permits fluid to enter the pump via the inlet 1.

At the end of the stroke of: the shaft 4 and piston 3, the valve members 11 and 21 return to their closed positions under pressure of the springsl3 and 26 respectively. The piston is nsw driven in the opposite direction by the air cylinder and fluid is taken in by valve 12, 16 and discharged via valve 20, 22.

Delivery of one dose of the fluid product may entail a complete cycle of the piston as described or alternatively that cycle may deliver tWD doses. The quantity of material delivered on each stroke may be varied by varying the length of each stroke, while variations in the fluid viscosity and specific gravity and in the desired speed of delivery may be acclrmodated by adjusting the air pressure to the drive cylinder.

By means of the pump according to the present invention, and in particular with the aid of the double outlet valve described, it has proved possible to deliver volumes of paint for example, varying fran 100ml to 5 litres with an accuracy of 0.5 per cent by volume.

Claims (8)

1. An improved double-acting pump comprising a fluid inlet, two fluid passages within the pump, two inlet valves located to control the flow of fluid material into the respective fluid passages, a fluid outlet fran said pump, two generally annular valve seats in axial alignment at the outlet ends of the respective fluid passages, two outlet valve members urged apart to engage the respective generally annular valve seats and thereby to control the flow of fluid material frgn the respective valve passage to the fluid outlet, and piston means for increasing and reducing the fluid pressure in the fluid passages alternately.

2. A pump as claimed in claim 1, wherein the two fluid passages include terminal lengths thereof which are in axial alignment.

3. A pump as claimed in claim 2, wherein the inlet ends of the two fluid passages are also in axial alignment and the two inlet valves are disposed with their valve mergers and valve seats axially aligned.

4. A pump as claimed in claim 3, including a three-way fitting comprising the fluid inlet and the two inlet valves.

5. A pump as claimed in any of the preceding claims, wherein the two outlet valve members are mounted on telescopically overlapping shafts.

6. A pump as claimed in any of the preceding claims, wherein the two outlet valve members are urged apart by a helical compression spring between the tWD members.

7. A pump as claimed in any of the preceding claims, wherein the piston means canprises a piston mounted for reciprocation within a cylinder extending between the two fluid passages.

8. An improved double-acting pump, substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawing.