GB2030237A - Sealing ring assemblies - Google Patents

Abstract

A rod or piston sealing assembly of the V-ring pack type comprises at least two sealing rings 1, 2 made of a thermoplastic plastics material, and an energising ring 3 made of a synthetic rubber which is softer than the plastics of the sealing rings. The rings 1, 2 and 3 fit coaxially together with the energising ring 3 at one end of the assembly. The rings are not bonded to each other but preferably snap fit one into the other, each sealing ring 1, 2 having a concave end face 4 into which the adjacent ring fits. The sealing rings have inner and outer peripheral sealing lips 5 and 6, and the energising ring has an inner peripheral sealing lip 14 having a diameter which is less than the diameters of the inner lips 5 of the sealing rings. In addition, the energising ring 3 has on its end face 11 remote from the sealing rings 1 and 2 a series of circumferentially spaced, axially projecting, circular bosses 12 having flat end faces 13. <IMAGE>

Description

SPECIFICATION Improvements relating to sealing ring assemblies This invention relates to sealing ring assemblies for forming a sliding seal between two relatively recip rocable members, one of which has a cylindrical surface. The invention may be applied to piston sealing assemblies in which the assembly moves with the piston and its outer periphery forms a sliding seal against the cylinder in which the piston is reciprocated, but primarily the invention is concerned with sealing ring assemblies which are intended to form a seal between a rod, such as a piston rod, and a surrounding housing through which the rod is reciprocated. In this case the assembly is mounted in the housing and the inner periphery of the assembly forms a sliding seal against the cylindrical surface of the rod.

In particular, the invention relates to sealing ring assemblies of the "V-ring pack" type. An assembly of this type comprises a number of sealing rings (at least two) and an energising ring which fit together, but are not bonded to each other, coaxially end to end so that the energising ring is located at one end of the assembly, each of the sealing rings having radially inner and outer circumferentially extending peripheral sealing lips and a concave face which is towards the energising ring and into which the adjacent ring fits so that, in use, when the assembly is subjected to axial compression the peripheral sealing lips of the sealing rings are caused to expand radially to seal against the two relatively reciprocable members.In at least one known assembly of this type, the energising ring also has a circumferen- tially extending peripheral sealing lip, for engaging the member having the cylindrical surface.

While a sealing ring assembly of the V-ring pack type may be used as a piston sealing assembly, it is much more commonly used as a rod sealing assembly. In this case the assembly is usually located in a housing surrounding the rod in what is sometimes referred to as a stuffing box, that is, an annular groove in which one of the axial facing end walls is removed to allow the sealing ring assembly to be fitted in position and is then replaced so that the assembly is axially compressed between the two end walls of the stuffing box. The assembly is single acting in that it is intended to resist pressure applied to it in an axial direction from only one of its ends, that is from the end at which the energising ring is located, and the assembly is fitted in the stuffing box accordingly.Usually, the arrangement is such that the energising ring of the assembly abuts the fixed end wall of the stuffing box.

The degree of axial compression which is imposed on the sealing ring assembly when fitted in the stuffing box is important to the operating efficiency of the assembly, and consequently the relationship of the axial dimensions of the sealing assembly (when unstrained) and the stuffing box is important, particularly when the removable end wall of the stuffing box is not axially adjustable and the box has a fixed axial length. However, it is very difficult to achieve the correct relationship since the adjustment of the length of the sealing assembly, by varying the number of its sealing rings, is very rough, and there are often large differences in the actual length of stuffing boxes of the same nominal size.Known seal ing ring assemblies of the V-ring pack type, due to their construction and the nature of the materials from which their rings are made, are not able to accommodate very well large differences in stuffing box dimensions, and often premature failure to the sealing assembly occurs due to incorrect compres sion of the assembly in the stuffing box.

With the aim of providing a sealing ring assembly of the V-ring pack type which does not suffer so much from the above disadvantage, according to the present invention a sealing ring assembly of the V-ring pack type for forming a sliding seal between two relatively reciprocable members and in which the energising ring has a circumferentially extending peripheral sealing lip for engaging the member hav ing the cylindrical surface, is characterized in that the energising ring is made of a synthetic rubber and the sealing rings are made of a thermoplastic plastics material which is harder than the rubber, and in that the energising ring has a series of circumferentially spaced, axially extending, protuberances on its end face remote from the sealing rings.

With this arrangement the relative softness of the rubber from which the energising ring is made, together with the protuberances which, in use, abut the fixed end face of the stuffing box, enable the assembly to accommodate much greatertolerances in the stuffing box length without adversely affecting the axial compressive force which is placed on the sealing rings. Furthermore, in operation, the protuberances allow the fluid under pressure to enter the stuffing box and to act axially on the end face of the energising ring around the protuberances. This assists the operation of the sealing assembly. Particularly suitable materials for the rings of the assembly in accordance with this invention are nitrile rubber for the energising ring, and a thermoplastic polyester elastomer, preferably having a hardness between 50 and 65 Shore D, for the sealing rings.

The protuberances, which preferably should all extend the same djstance as each other from the end face of the energising ring and are preferably evenly spaced circumferentially around the ring, may take any suitable form. Preferably, however, each protuberance is in the form of a circular boss having a flat end face for engaging the stuffing box wall.

In the case of a rod sealing assembly, the peripheral sealing lip on the energising ring is, of course, on the inside of the ring, and preferably projects radially inwards further than the inner peripheral sealing lips of the sealing rings when the assembly is not in use. Also, the outer periphery of the energising ring is preferably cylindrical and has the same diameter as the outer peripheral sealing lips of the sealing rings, when the assembly is not in use.

Preferably the profiles of the concave face of each sealing ring and the opoosite end face of the adjacent ring are such that the two rings interlock as a snap fit. In the case of a rod sealing assembly, this is preferably achieved by means of a radially inwardly projecting bead on the outer wall of the concave face of each sealing ring, and a radially outwardly project ing bead on the opposite end face of the adjacent ring. The axial end face of the assembly remote from the energising ring is preferably flat.

An example of a rod sealing assembly in accor dance with the invention is illustrated in the accom panying drawings, in which: Figure 1 is a radial section through the assembly but showing the individual rings of the assembly spaced axially apart from one another; and, Figure 2 is an axial end view of the assembly look ing in the direction of the arrow in Figure 1.

The assembly comprises two sealing rings 1 and 2 made of a thermoplastic polyester elastomer, and an energising ring 3 made of a nitrile rubber which is softer than the polyester elastomer of the sealing rings 1 and 2. The rings 1,2 and 3 are arranged to fit coaxially together end to end with the energising ring 3 at one end of the assembly. Each of the two sealing rings 1,2 has an identical concave end face 4 at its end towards the ring 3, and inner and outer circumferentially extending peripheral sealing lips 5 and 6 at the inner and outer edges of the face 4. The end faces 7 of the rings 2 and 3 directly opposite the concave faces 4 of the sealing rings 1 and 2 respectively have identical profiles which are complementary to the profiles of the concave faces 4 so that the rings can fit axially together.The profiles of the complementary faces 4 and 7 are provided with beads 8 and 9 respectively which snap past each other to interlock the rings when the rings are fitted together.

The end face 10 of the sealing ring 1 remote from the concave face 4 is flat, and the end face 11 of the energising ring 3 remote from the sealing rings 1 and 2 is also flat apart from a series of circular bosses 12 which project axially from the face 11 and which are evenly spaced circumferentially around the ring 3. Each boss 12 projects the same distance from the face 11 and has a flat end face 13.

The inner periphery of the energising ring 3 has an inwardly projecting circumferentially extending sealing lip 14 having a slightly smaller diameter than the inner sealing lips 5 of the sealing rings 1 and 2. The outer periphery of the energising ring 3 is cylindrical and has the same diameter as the outer sealing lips 6 of the rings 1 and 2.

The axial length of the assembly may be increased by adding one or more further intermediate sealing rings which are identical to the ring 2.

Claims (12)

1. A sealing ring assemblyforforming a sliding seal between two relatively reciprocal members, one of which has a cylindrical surface, the assembly comprising a number of sealing rings and an energising ring which fit together, but are not bonded to each other, coaxially end to end so that the energising ring is located at one end of the assembly, each of the sealing rings having radially inner and outer circumferentially extending peripheral sealing lips and a concave face which is towards the energis ing ring and into which the adjacent ring fits so that, in use, when the assembly is subjected to axial compression the peripheral sealing lips of the sealing rings are caused to expand radially to seal against the two members, and the energising ring also having a circumferentially extending peripheral sealing lip for engaging the member having the cylindrical surface, characterized in that the energising ring is made of a synthetic rubber and the sealing rings are made of a thermoplastic plastics material which is harder than the rubber, and in that the energising ring has a series of circumferentially spaced, axially extending, protuberances on its end face remote from the sealing rings.

2. A sealing ring assembly according to claim 1, in which the energising ring is made of nitrile rubber.

3. A sealing ring assembly according to claim 1 or claim 2, in which each of the sealing rings is made of a thermoplastic polyester elastomer.

4. A sealing ring assembly according to claim 3, in which the hardness of the polyester elastomer is between 50 and 65 Shore D.

5. A sealing ring assembly according to any one of the preceding claims, in which the protuberances are evenly spaced circumferentially around the end face of the energising ring and all extend the same distance as each other from the end face.

6. A sealing ring assembly according to any one of the preceding claims, in which each protuberance is in the form of a circular boss having a flat end face.

7. A sealing ring assembly according to any one of the preceding claims, in which the profiles of the concave face of each sealing ring and the opposite end face of the adjacent ring are such that the two rings interlock as a snap-fit.

8. A sealing ring assembly according'to any one of the preceding claims, which is intended to be used as a rod seal, the peripheral sealing lip on the energising ring being on the inner periphery of the ring.

9. A sealing ring assembly according to claim 8, when dependent upon claim 7, in which the snap-fit is achieved by means of a radially inwardly projecting bead on the outer wall of the concave face of each sealing ring, and a radially outwardly projecting bead on the opposite end face of the adjacent ring.

10. A sealing ring assembly according to claim 8 or claim 9, in which the peripheral sealing lip on the energising ring projects radially inwards further than the inner peripheral sealing lips of the sealing rings when the assembly is not in use.

11. A sealing ring assembly according to any one of claims 8 to 10, in which the outer periphery of the energising ring is cylindrical and has the same diameter as the outer peripheral sealing lips of the sealing rings when the assembly is not in use.

12. A sealing ring assembly according to claim 1 substantially as described with reference to the accompanying drawings.