Diaphragm Pump

This invention relates to diaphragm pumps operated by fluid pressure.

Examples of such diaphragm pumps are described in WO91/00417. For reasons of cost and facility of production, it is desirable to reduce the number of components required to assemble a pump. There may be particular advantages in this for pumps intended to be used in clean or sterile conditions, such as pumps used in medical and surgical procedures. In the said WO91/00147 one example of construction has an integrally formed diaphragm and gas outlet valve closure element interconnected by a collapsible stem, which can all be formed in a single moulding, but it is not simple to ensure that the resilient mounting that holds the closure element can close the valve reliably.

According to the present invention, there is provided a pressure-operated pump comprising a pumping chamber for the fluid to be pumped and a fluid pressure driving chamber having a valve-controlled outlet, a flexible diaphragm between said chambers and being displaceable by pressure in the driving chamber to expel fluid from the pumping chamber, said diaphragm being connected to a resiliently deformable member that includes a valve closure element for said driving chamber outlet and to an extensible tension element that urges the closure element to its operative closing position.

It is found that the provision of the tension element can give a more assured closure. In addition, it is possible to form the diaphragm, closure element and tension element as a single integral member. In contrast to the known pump described above, the connection between the diaphragm and the valve closure element need not apply a closing force to the valve closure element and it can be arranged to operate in a non-collapsible manner.

For efficiency of operation, it is desirable to arrange that the driving chamber outlet valve opens relatively quickly, preferably with a snap-action. For this purpose, the member is so formed that it is resiliently deformed during the pumping stroke, while the valve remains closed, the release of energy of deformation aiding the opening of the valve. For instance, a stem portion of the member connecting the diaphragm to the valve closure element can be arranged to be increasingly tensioned during the pumping stroke to urge the closure element away from the outlet while a pressure differential acts on the element restraining the opening of the valve. When said tension force is sufficient to displace the closure element and allow the countervailing pressure differential to drop, the stored tensile energy opens the valve the faster. Additionally or alternatively, resilient flexure of the valve closure itself can similarly store energy which is released to accelerate the opening movement of the valve.

It may be noted here that in the form of pump described above from WO91/00417, such snap-action does not occur because there is no release of stored energy at the instant of valve opening.

Preferably, the tension that holds the valve closed during a return stroke of the diaphragm is exerted by an element of said member acting as a weak spring having a relatively low rate as compared with the spring rate of the element or elements providing said stored energy. This is desirable in order to minimise the opposing force to said snap-action opening.

By way of example, the invention will be described in one particular form with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is an axial section through a pump according to the invention, and

FIG. 2 is a plan view of the pump in FIG. 1.

The illustrated pump comprises a two-part casing 2 comprising upper and lower parts 2a,2b coaxially located by an integral circumferential rib and groove 6 and angularly located by integral spigot and bore connections 8. A diaphragm 10 is engaged sealingly between the two parts which are solvent-bonded together. The diaphragm divides the interior of the casing into a pumping chamber 12 and a driving chamber 14. Liquid to be pumped fills the pumping chamber 12 through an inlet 16 provided with a non-return valve 18 comprising a pair of flexible lips, normally closed together as shown but flexed apart by an inlet pressure greater than the pressure in the chamber 12. The liquid exits the chamber 12 through an outlet 20 which may also be provided with a non-return valve (not shown) preventing back flow.

The pump is driven by a pressure gas source (not shown) which supplies gas under pressure continuously through an inlet 22 to the driving chamber. An outlet passage 24 is provided for gas exiting the chamber 14 but the passage is normally sealed by a valve comprising a seating 26 which is sealed by a closure element 28. The connecting conduits to the inlets and outlets 16,20,22,24 may be solvent bonded in place if the pump is to be used in sterile conditions, but other known forms of connection can of course be provided.

The diaphragm 10 and the valve closure element 28 form integral parts of a rotationally symmetrical member 30 moulded from resiliently flexible material such as natural rubber. The diaphragm is connected to the closure element by a stem 32 of the member 30 which in this example has a smaller diameter necked portion 34 immediately adjacent the closure element. The resiliently deformable member 30 also includes an integral tail 36 extending from the closure element and through a collar 38 fixed coaxially within the outlet passage 24 by lugs 40. The tail 36 has a relatively small cross-section compared with the stem and neck but incorporates an enlarged portion 42 intermediate its length having a significantly larger cross-section than the internal diameter of the collar through which it passes. The upper end 44 of the tail serves as a guide to thread it into the collar and to pull the enlarged portion 42 through. The tapered top face of the enlarged portion 42 assists its passage through the collar on top of which it is locked in place against the tensions applied to the tail in use. The tail 36 is so formed that in the rest position of the member 30 it is held slightly extended by the engagement the portion 42 with the collar 38, in order to retain the closure element 28 against the valve seating 26. Also, although not visible in the drawings in the rest position there is some tension in the stem 32 flexing the diaphragm slightly upwards.

Starting in the illustrated rest position of the pump, when the driving chamber 14 is pressurised by supplying pressure gas through the inlet 22, the diaphragm 10 is flexed downwards to pump liquid from the pumping chamber 12, from where it can escape only through the outlet 20. The gas pressure also acts on the underside of the closure element 28, the area of action being increased by the reduced diameter neck 34 of the member 30, so the closure element 28, is initially held more firmly in the sealing position against the seating 26.

As the diaphragm 10 continues to flex downwards due to the gas pressure, the tension in the stem 32 and neck 34 increases and the annular portion of the closure element 28 between the neck 34 and the valve seating 26 is flexed downwards. The deforming forces in the member 26 continue to increase with the deflection of the diaphragm, storing energy in the member 30 until the downward force on the closure element 28 is sufficient to begin to move it away from the seating 26. Gas can now escape through the outlet passage 24 and the pressure in the driving chamber then falls, although gas continues to be supplied through the inlet 22, because the inlet has a restriction 48 which limits the rate of replenishment of the gas in the chamber.

With the drop of gas pressure, the energy stored in the deformation of the stem, and closure element of the flexible member 30 is released. As a result, the closure element moves sharply away from the outlet passage 24 to release the gas pressure in the chamber 14 completely while the diaphragm begins to return to the illustrated position, so drawing further liquid into the pumping chamber 12. It may be noted that this snap action opening can be used to increase the rate of operation of the pump since the release of pressure from the driving chamber will be less sensitive to the rate at which pressure gas flows into the chamber.

The return of the diaphragm allows the outlet valve to close again, assisted by the tension in the tail 36. The continuing supply of pressure gas to the driving chamber 14 now causes the pressure to build up again in the chamber for the next cycle of operation.

The relatively small cross-section of the tail 36 ensures that the tension force it applies is small in comparison with the release forces acting to open the valve and so the presence of the tail does not impose significant restraint on the opening of the valve. However, the tension in the tail 36 does ensure that the closure element 28 is held centrally with respect to its seating 26 and is always drawn centrally towards that seating when the release forces are dissipated. In this way, each time the gas pressure on the diaphragm 10 is released it is ensured that the valve returns to a fully closed position so that the full driving stroke of the diaphragm is made in the following movement and gas escapes from the driving chamber only when the rapid opening action of the closure element has begun.

The illustrated pump is intended to provide a supply of sterile water under pressure for use in surgical procedures. It is known to provide sterile water in sealed bags which are pierced by a tubular stabbing connecting to give access to the water and the pump may have a suitable connector fixed to the inlet 16 for this purpose. When so used the pump hangs with the inlet uppermost and the position of the outlet 20, close to the top of the pumping chamber then ensures that the pump will be self-priming at start-up.