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Pump diaphragm

Pump diaphragm description/claims

The present application claims the benefit of and priority to Great Britain (GB) Application Serial No. 0716294.4, filed on Aug. 21, 2007, the entire content of which is incorporated herein by reference.

1. Technical Field

The present invention relates to a diaphragm for use in a fluid pump, and more particularly, to a diaphragm configured to be coated with a protective layer such that the protective layer would avoid fracturing in use.

2. Background of Related Art

Diaphragm-type fluid pumps and, in particular liquid pumps, have a flexible pumping diaphragm which is driven to effect the pumping action of the pump. In such pumps, the diaphragm comprises a flexible circular or oval disc which has its outer peripheral edge clamped and sealed within the body of the pump. The diaphragm may have a central aperture which is secured to a moveable actuator such as a piston, which reciprocates back and forth causing the diaphragm to flex between a concave and a convex configuration. In an alternative pump configuration, however, the diaphragm does not have a central aperture and forms a partition with a driving fluid chamber in which the hydraulic pressure of the driving fluid is repeatedly alternated between high and low pressures, thereby causing the diaphragm to flex between a concave and a convex configuration. In both pump types, the repeated flexing of the pump diaphragm causes fluid displacement in a pumping chamber which results in the pumping action.

When such pumps are used to pump inert or un-reactive fluids, such as water, the diaphragm can be constructed from plain rubber material, since there is no problem with the fluid reacting with or corroding the diaphragm material. However, if the pump is intended for use with fluids having a more chemically reactive nature, an elastomeric diaphragm, such a natural rubber, alone is unsuitable as it is rapidly corroded, leading quickly to pump failure.

In order to solve this problem, it is desirable to provide the elastomeric diaphragm with a protective coating to prevent the pump fluid from reacting with or corroding the elastomer. However, the materials which would be most desirable to use for such a protective layer due to their excellent chemical resistance properties, such at PTFE, have plastic material properties, meaning they are unable to stretch and recover their original shape. However, when conventional pump diaphragms are in use, the repeated flexing between convex and concave positions causes the rubber of the diaphragm to repeatedly stretch and deform. Therefore, if a conventional diaphragm is coated with a protective layer, such as PTFE, it results in the protective coating cracking and splitting when the pump is in use, since the protective layer cannot cope with the repeated elastic deformation which the diaphragm experiences.

It is therefore an object of the present invention to provide a pump diaphragm that substantially alleviates or overcome the problems mentioned above.

Accordingly, the present invention provides a diaphragm for use in a fluid pump comprising a disc of resilient material having a substantially dished shape, the curvature of the disc being formed from a plurality of steps.

Preferably, the diaphragm is circular, but may also be oval.

The plurality of steps are preferably formed from a series of flat annular rings of increasing diameter axially displaced from one another and joined at their adjacent edges by shoulder portions extending in an axial direction.

In a preferred embodiment, the diaphragm has a substantially inelastic chemically resistant coating on at least one side thereof. The chemically resistant coating may be formed on the concave side of the diaphragm or may be formed on the convex side, or may be formed on both/all sides of the diaphragm.

Preferably, the chemically resilient material is PTFE.

The resilient material may be rubber. However, if the diaphragm is for use in a hydraulic pressure type pump in which the diaphragm deflection is achieved by alternating hydraulic pressure of a driving fluid, then the resilient material will need to be compatible with the hydraulic media (e.g. oil). In such cases, the resilient material may be nitrile or a low-temperature resistant rubber material.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of a prior art diaphragm pump;

• Provisional Patent
• Utility Patent

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