GB2097490A - Ring seals - Google Patents

Abstract

A ring seal is provided with a pressure balancing arrangement which offsets the loads normally applied to the ring and which tend to cause it to jam. The seal comprises a housing 15 within which the ring (21) operates, the ring dividing the interior volume of the housing into at least two chambers (24, 25, 26). The exterior pressures are fed to the chambers so that the higher pressure enters the inner chambers (25, 26) to tend to lift the ring off its co-operating surface, while the other chamber (24) is supplied with the lower pressure and provides a relatively low load which tends to force the ring into contact with the surface. The inner chambers (25, 26) differ in height to provide a desired side load. <IMAGE>

Description

SPECIFICATION Piston ring seals This invention relates to piston ring seals.

Piston ring seals have been widely used to seal between pairs of members which do not move relative to one another or which move in a reciprocatory fashion. The seals normally comprise an annular housing formed in or attached to one of the members and a piston ring mounted within the housing and resiliently urged into contact with an annular surface of the other member. The ring abuts against the inner face of the housing and the annular surface to provide the necessary sealing.

When the seals are of relatively small diameter, this basic form of seal is quite satisfactory.

However, when a large diameter seal is required there is a greater tendency for the ring to jam against the annular surface and the seal becomes less satisfactory.

The present invention provides a piston ring seal which is arranged to reduce the chance of jamming or sticking of the ring.

According to the present invention a piston ring seal adapted in operation to seal against an annular surface between regions of higher and lower pressure comprises a housing within which is mounted a piston ring resiliently urged toward said surface, the piston ring dividing the housing into at least two chambers a first of which is defined by the housing and a face of the ring which faces away from the annular surface and a second of which is defined by the housing and a face of the ring which faces towards the annular surface, and duct means which allow, in operation, said lower pressure to communicate with said first space and said higher pressure to communicate with said second space.

The piston ring seal may seal against a coaxial cylindrical surface.

In a preferred embodiment there are three said chambers defined between a piston ring of substantially T-section and a substantially rectangular housing, the extremity of the stem of the T-section sealing against the annular surface while the two chambers under the head of the T are arranged to be at the higher pressure and the one chamber over the head of the T is arranged to be at the lower pressure.

In this case the sizes of the chambers either side of the stem of the T may be arranged to provide a desired degree of side load on the piston ring.

The invention will now be particularly described, merely by way of example, with reference to the accompanying drawing which is a radial section through a piston ring seal in accordance with the present invention.

In the drawing are shown parts of a static member 10 and a movable member 11 which has a cylindrical outer surface 12. To effect a seal between the members 10 and 11 a piston ring seal generally indicated at 1 3 is provided. The seal 13 comprises a housing 14 made up of two co-operating annular portions 1 5 and 1 6 which are bolted together by bolts 1 7 which also fasten the housing to the member 10.

It will be seen that the housing 14 encloses a volume whose shape is substantially that of a rectangular toroid, and that its inner annular surface is provided with an annular slot defined between a pair of inwardly extending lips 18 and 1 9. Through the slot projects the stem portion 20 of a piston ring 21 of substantially T-shaped cross section. The head portion 22 of its T-section slidingly engages with the inner walls of the housing 14 so that the ring can move radially inwards and outwards in relation to the housing.

The ring 21 is made of a springy material and is of such a size as to cause its inner face 23 of the stem 20 to engage resiliently against the annular surface 12. In this way a seal is made between these two components. In order to ensure that the inward load on the ring is not such as to cause the ring to jam against the surface 12, the pressure balance on the ring is arranged to provide a predetermined load which does not force the ring against the surface 12 to an excessive degree.

Thus the head portion 22 and the stem portion 20 of the T-section ring divide the toroidal chamber formed within the housing 14 into three different chambers. One chamber 24 is defined between the upper face of the head 22 (the face which faces away from the surface 12) and the inside of the housing 14, while two more chambers 25 and 26 are formed between the lower face of the head 22 (the face which faces towards the surface 12) and the inside of the housing 14.

Ducts 27 through the annular portion 15 allows the higher pressure from the left-hand side of the seal 13 to communicate with the chamber 25, while ducts 28 through the stem portion 20 of the piston ring transmit this pressure to the chamber 26. The pressure acting on the underside of the head 22 is thus the higher of the two pressures available.

In a similar manner ducts 29 in the annular portion 1 6 allow the lower pressure to the righthand side of the seal to communicate with the chamber 24. Thus the pressure acting on the upper side of the head 22 is the lower of the two available pressures.

Therefore the overall inward force on the ring comprises the lower pressure times the area of the upper surface of the head 22 minus the high pressure times the area of the lower surface of the head of the ring section together with a contribution from the face 23. Obviously, the area of the upper surface of the head 22 is greater than that of the lower surface since the lower surface has the stem portion 20 taken out of it. The use of the lower pressure acting on the upper surface of the head provides a relatively low inward force and the total inward force can thus be reduced.

It will be noted that the chambers 25 and 26 differ in height, and therefore the side loads on the piston ring due to the pressure in these chambers will differ. The sideways force will be the high pressure times the difference in side area of the chambers, minus the low pressure times this difference in area, and a contribution from the remaining side facing areas of the ring. It will be seen that this can again be predetermined to be a particular value, but in general the difference in areas may be used to counteract the usual force on the ring which acts from the higher pressure region towards the lower pressure region.

This embodiment therefore provides a piston ring seal in which the normal pressures on the piston ring are offset to provide reduced forces acting on the ring to cause it to jam or stick.

Clearly it would be possible to devise alternative shapes of ring and housing which would allow the pressure offset to be achieved, and it is also evident that the radial load offset could easily be used on its own without use of the axial offset of load.

Claims (9)

Claims

1. A piston ring seal adapted in operation to seal against an annular surface between regions of higher and lower pressure, the seal comprising a housing within which is mounted a piston ring resiliently urged towards said surface, the piston ring dividing the housing into at least two chambers, a first of which is defined by the housing and a face of the ring which faces away from the annular surface and a second of which is defined by the housing and a face of the ring which faces towards the annular surface, and duct means which allow in operation, said lower pressure to communicate with said first space and said higher pressure to communicate with said second space.

2. A piston ring seal as claimed in claim 1 and in which said annular surface comprises a cylindrical surface.

3. A piston ring seal as claimed in claim 1 or claim 2 and in which said piston ring is substantially T-shaped in cross section, the extremity of the stem of the T-section sealing with said annular surface.

4. A piston ring seal as claimed in claim 3 and in which said first chamber is formed between the upper face of the head of said T-section and the housing and said second chamber comprises one of a pair formed between the lower face of the head, the side face of the stem, and the housing.

5. A piston ring seal as claimed in claim 4 and comprising duct means through the stem of the piston ring by which the pressures in said pair of chambers are equalised.

6. A piston ring seal as claimed in any one of the preceding claims and comprising duct means extending through the wall of said housing to allow said higher and lower pressures access to the respective chambers.

7. A piston ring seal as claimed in any one of claims 4-6 and in which said pair of chambers are of different depths so that the sideways forces on the ring due to said chambers are unequal.

8. A piston ring seal as claimed in claim 7 and in which said chamber are arranged to provide an overall sideways load on the ring which opposes the load on the ring from the high to the low pressure region.

9. A piston ring seal substantially as hereinbefore described with reference to the accompanying drawings.