GB2077368A - Packing assembly - Google Patents

Abstract

A seal member 16 is disposed in an annular groove 12 in a piston 10 and has lips 17 which seal respectively against a base wall of the groove 12 and the side wall of a cylinder (not shown) when the seal member 16 is subjected to fluid pressure from an active end of the cylinder. A pair of support rings 18 and 19 disposed respectively at opposite ends of the seal member 16 and confined by the axial end walls of the groove 12 have holes 23 therethrough which extend between opposite axial end faces of the support rings so as to allow fluid under pressure to leak from a zone defined between the support rings. This prevents excess fluid pressure from buildings up within this zone and distorting the seal member 16 to such an extent that a mechanical lock is created which prevents the piston 10 from being moved within the cylinder. <IMAGE>

Description

SPECIFICATION Packing assembly This invention relates to a packing assembly intended to be located within a groove in one of a pair of members which are movable relatively to each other, and to a piston and cylinder combination including such a packing assembly.

In our British Patent 1,492,539 there is described and claimed a packing assembly of the above described type which includes a deformable seal member having sealing lips on opposite sides for fluid sealing engagement with the base wall of said groove and the surface of the other of the pair of members, and a pair of support members at the opposite ends respectively of the seal member, the support members being confined by the end walls of the groove, the seal member and support members extending substantially at right angles to the direction of relative movement between said pair of members.In order to avoid the accumulation of fluid at high pressure in a zone bounded at its opposite ends by the support members, which it is thought can cause distortion of the support members to such an extent that a mechanical lock is created which renders it impossible to move the two members relative to each other, one of the side faces of each support member is provided with leakage grooves whereby fluid under pressure can leak from the aforementioned zone. This arrangement does, however, have the disadvantage that once a mould has been produced for manufacturing the support members, it is not possible to effect modification to the support members by modifying the mould, and instead a completely new mould must be produced, which of course is very expensive.

It is an objector the present invention to obviate or mitigate this disadvantage.

According to the present invention, there is provided a packing assembly adapted to be located within a groove in one of a pair of members which are movable relatively to each other in one direction, the assembly including a deformable seal member having sealing lips on opposite sides for fluid sealing engagement with the base wall of the groove and the surface of the other of the pair of members, and a pair of support members at the opposite ends respectively of the seal member, said support members being confined by the end walls of the groove, the seal member and the support member extending substantially at right angles to the direction of relative movement, characterised in that each of the support members has at least one hole therethrough extending between the opposite end faces thereof, whereby fluid under pressure can leak from a zone bounded at its opposite ends by the support members.

In this way, the sealing members can be produced by conventional means, and the or each hole can subsequently be drilled out. The holes could, of course, be formed by techniques other than drilling.

Also according to the present invention, there is provided a piston and cylinder combination comprising a piston member and a cylinder member between which is provided a fluid seal, an annular groove formed in one of said members, an annular packing assembly located in said groove, said assembly including a deformable annular seal member having sealing lips on radially inner and outer sides thereof for fluid sealing engagement with the base wall of the groove and the surface of the other member, and a pair of support rings at opposite axial ends respectively of the seal member, said support rings being confined by axial end walls of the groove, characterised in that each of the support rings has at least one hole therethrough extending between opposite axial end faces thereof, whereby fluid under pressure can leak from a zone bounded at its opposite ends by the support rings.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a sectional side view of part of a piston and cylinder combination including a packing assembly according to the present invention; and Figure 2 is an end view of a support ring which forms part of the packing assembly shown in Figure 1.

Referring first to Figure 1, a piston 10 is slidably located within a cylinder (not shown) and has a groove 12 formed in a side wall thereof. The groove 12 is stepped and its deeper portion accommodates a packing assembly 13 whilst the shallower portions of the groove (disposed on opposite axial sides of the deeper portion and forming respective extensions thereof) accommodate respective rings 1 4 and 1 5. These rings serve to prevent extrusion of the packing assembly 13, but also serve as bearing rings to accommodate side thrust developed during use of the piston and cylinder combination. It should be pointed out that, as shown in the drawing, the piston is of solid construction: however, in practice it may be necessary to split the piston in order to allow assembly of the packing assembly 13 and the rings 14 and 15.The rings 14 and 15 are formed from synthetic resin material, such as nylon.

The packing assembly 13 comprises a deformable annular seal member 1 6 which is formed from elastomeric material (conveniently a rubber) and which is provided on its radially inner and outer faces with sealing lips 17. These lips cooperate with the base wall of the groove 12 and with the side wall of the cylinder to define a fluid seal.

At opposite axial ends of the seal member 1 6 there are disposed support rings 18 and 1 9 respectively. The support rings engage the axial end walls of the deeper portion of the groove 12, and are also recessed to accommodate the rings 14 and 1 5 respectively. The support rings 1 8 and 1 9 are formed from a synthetic resin material and are recessed on their faces which are presented to the seal member 16 in order to provide proper support therefor.Most conveniently, the support rings 18, 1 9 are of the anti-roll type as disclosed in British Patent No. 1,512,181,the recesses therein being of substantially triangular section: the apical edge 20 of each recess is offset from the centre line of the respective face of the support ring, preferably in a direction towards an edge of the face which engages the base wall of the groove 12. The walls of each recess which meet at the apical edge 20 are of unequal length.

The axial end faces of the seal member 16 are of a complementary shape to the recesses, and the seal member 1 6 can be regarded as a six-sided body whose radially outer surface is of smaller axial length than its radially inner surface.

The rings 14 and 1 5 are preferably provided with longitudinal grooves 21 and transverse drillings 22 to ensure that the fluid under pressure at the active end of the cylinder is transmitted to the adjacent end of the packing assembly 1 3 to ensure fluid pressure actuation thereof. When this occurs, the sealing lips 1 7 are pressed into firm engagement with the base wall of the groove 12 and the side wall of the cylinder to ensure a positive fluid seal.

It has been discovered that fluid under pressure can be trapped in a zone defined between the support members 1 8 and 1 9, and that this fluid pressure can increase due, it is thought, to a pumping action created by the support members to the extent that distortion of the packing assembly occurs sufficient to create a mechanical lock, thereby preventing relative movement of the piston and cylinder In order to overcome this difficulty, each of the support member 18, 1 9 is provided with a hole 33 therethrough extending between opposite axial end faces thereof. These holes allow any pressure accumulating in the aforementioned zone to be dissipated and thereby minimise the risk of formation of the locking action described above. As can be seen to advantage in Figure 2, it has been found that a single hole in each support ring is sufficient to alleviate the locking action: however, more than one such hole can be provided in each support ring if desired. The hole or holes are preferably formed by drilling after the support member has been moulded.

Whilst in the above-described embodiment the packing assembly 1 3 is located in a groove defined in the piston, it wili be appreciated that other situations exist where the packing assembly is located in a groove defined in the cylinder.

Claims (9)

1. A packing assembly intended to be located within a groove in one of a pair of members which are movable relatively to each other in one direction, the assembly including a deformable seal member having sealing lips on opposite sides for fluid sealing engagement with the base wall of the groove and the surface of the other of the pair of members, and a pair of support members at the opposite ends respectively of the seal member, said support members being confined by the end walls of the groove, the seal member and the support member extending substantially at right angles to the direction of relative movement, characterised in that each of the support members has at least one hole therethrough extending between opposite end faces thereof, whereby fluid under pressure can leak from a zone bounded at its opposite ends by the support members.

2. A packing assembly as claimed in Claim 1, wherein the or each said hole is formed by drilling after production of the support member.

3. A packing assembly as claimed in Claim 1 or 2, wherein the end faces of the support members which are presented to the seal member each have therein a recess of substantially triangular section, the apex of the triangle being offset from a centre line of the respective end face.

4. A piston and cylinder combination comprising a piston member and a cylinder member between which is provided a fluid seal, an annular groove formed in one of said members, an annular packing assembly located in said groove, said assembly including a deformable annular seal member having sealing lips on radially inner and outer sides thereof for fluid sealing engagement with the base wall of the groove and the surface of the other member, and a pair of support rings at opposite axial ends respectively of the seal member, said support rings being confined by axial end walls of the groove, characterised in that each of the support rings has at least one hole therethrough extending between opposite axial end faces thereof, whereby fluid under pressure can leak from a zone bounded at its opposite ends by the support rings.

5. A piston and cylinder combination as claimed in Claim 4, wherein the or each said hole is formed by drilling after production of the support ring.

6. A piston and cylinder combination as claimed in Claim 4 or 5 wherein a pair of rings are disposed at opposite axial ends of the packing assembly and are accommodated within grooves defined in said one member and forming extensions of the first-mentioned groove, the support rings being recessed to accommodate said rings respectively, said rings defining passage, means to allow pressure actuation of the packing assembly.

7. A piston and cylinder combination as claimed in Claim 4, 5 or 6, wherein the axial end faces of the support rings which are presented to the seal member each have therein a recess of substantially triangular section, the apex of the triangle being offset from a centre line of the respective axial end face.

8. A packing assembly substantially as hereinbefore described with reference to the accompanying drawing.

9. A piston and cylinder combination substantially as hereinbefore described with reference to the accompanying drawing.