GB2113788A - Pipe couplings - Google Patents

Abstract

The pipe coupling is designed for use with plastics pipes having a large coefficient of thermal expansion and in circumstances where large temperature changes are experienced such as in central heating systems. With existing seal arrangements the seal can be damaged during insertion of a pipe into a socket, and the pipe may be pulled from the socket by thermal contraction forces. The coupling described employs a tubular seal body (25) having an internal flange (24) at its inner end which abuts with the extremity (30) of pipe, and a cap nut (5) is threadedly engaged with external threads (7) on the pipe socket (6). The cap nut has an inwardly directed sleeve portion (12) having frusto-conical internal and external surfaces (15, 16) and provided with pipe gripping projections (27). The sleeve portion (12) cooperates with a frusto-conical bore wall (18) of the socket to provide a wedging action on tightening of the cap nut which also acts to confine the seal body. On insertion of a pipe into the socket, the sleeve portion (12) aligns the pipe end with the socket before the pipe meets the seal body. <IMAGE>

Description

SPECIFICATION Pipe couplings This invention relates to pipe couplings for sealably connecting piping particularly, but not exclusively, plastics piping having a substantial coefficient of thermal expansion.

Various proposals have been made for pipe couplings which avoid the need to mould an internal groove in the coupling socket to receive a resilient seal. In some cases an O-ring is held captive in the socket by the radial flange of a capnut, and in other cases the seal comprises an annular sealing head integral with the radially inner end of a generally radially extending limb, the radially outer end of which is held against the outer end of the socket by a cap nut. Such seals generally provide a sealing area with the pipe of small axial extent which is susceptible to damage during insertion of a pipe end into the socket, particularly when the pipe end is not precisely aligned with the socket. O-rings are susceptible to damage by rolling during insertion of the pipe end.

According to the invention a pipe coupling comprises socket body which is externally threaded for engagement by internal screw threads formed on a skirt portion of a cap nut, the cap-nut comprising a sleeve portion which is received within the axially outer part of the bore of the socket, and a resilient tubular seal body located in the socket axially inwardly of the cap nut sleeve portion, the part of the socket bore in which the sleeve portion is located being tapered slightly so as to have a smaller diameter at its inner end, the arrangement being such that when a a pipe end is inserted through the cap nut sleeve portion and into the seal body, the pipe end being of a diameter to be slidably received, or received with some interference, by the undeformed cap nut sleeve portion, and the cap nut is screwed further onto the socket body, the sleeve portion is compressed radially by interference with the wall of the tapered bore to grip the pipe end.

With such a coupling the sleeve portion may be made sufficiently long to ensure that when a pipe end which is not initially aligned with the socket is forced into the socket, the extremity of the pipe end at least is forced into alignment with the seal body before it enters the seal. The seal is therefore less likely to be damaged by the pipe end.

Since the seal body can be made of substantial length, the possibility of any deterioration of the sealing action may be reduced.

The radial compression of the sleeve portion provides a gripping action on the pipe end to resist withdrawal of the pipe end. Since the compressive force can be arranged to be substantial, any change in the compressive force due to differential thermal expansion of different materials, when the pipe is of a different material from that of the cap nut or socket body, may be arranged to have only a minor effect on the gripping action.

Preferably the sleeve portion is provided internally with one or more radial projections to assist in gripping the pipe end.

Preferably there are a plurality of projections in the form of circumferentially equally spaced projecting pips.

Each projection is preferably located closer to the inner end than to the outer end of the sleeve portion.

The axially inner end of the sleeve portion is preferably engageable with the adjacent end of the tubular seal, and the tubular seal is substantially confined so that on tightening of the cap nut onto the socket body the seal body is subjected to an axial force by the sleeve portion thereby resulting in an increased radial sealing force between the seal and the pipe end.

The seal body is preferably connected at its axially inner end with an internal flange which abuts with the extremity of the pipe end. On tightening of the cap nut with the extremity of the pipe engaged with the seal flange, the pipe end may be urged axially inwardly by the cap nut to increase the sealing force between the pipe extremity and the seal flange, and increase the confinement of the seal body.

The socket body may be integrally provided at one end of a pipe, or at one end, branch or outlet of a fitting. The socket body may, however, act as a coupling sleeve, in which case the inner ends of a pair of oppositely directed tubular seal bodies may be spaced apart by a circumferentially extending radially inwardly directed flange on the body.

A coupling sleeve assembly in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which~ Figure 1 is a longitudinal cross-section of the coupling sleeve in use connecting two pipe ends, the cap nuts being shown fully tightened: and Figure 2 is an enlarged view corresponding to the upper right hand part of Figure 1 to show details of the engagement between the cap nut, sleeve and the socket body.

The coupling sleeve assembly of Figure 1 is symmetrical about a central transverse plane so that only the right hand end will be described in detail. The sleeve assembly 1 is shown in Figure 1 sealably connecting together two identical pipe ends 2 and 3 which initially were perfectly plaincylindrical but have been radially deformed at 4 during tightening of the respective cap nut 5. A tubular socket body 6 is moulded from an engineering plastics, such as NYLON 6, and is provided with external screw threads 7 of buttress form extending axially inwardly from its opposite ends 8, 9.

For convenience, the end 8 will be referred to as the outer end of the socket body.

Cap nut 5 comprises a skirt portion 10 integrally connected to the outer end 1 1 of a sleeve portion 12 by a radial bridging portion 13 so that the cap nut 5 is of generally U-shape in transverse cross-section with one limb of greater length than the other. The skirt portion 10 is formed with internal screw threads 14 complementary to threads 7. Cap nut 5 is also moulded from an engineering plastics, and as moulded the internal and external surfaces 15 and 1 6 respectively, Figure 2, of the skirt portion 10 are both frusto-conical with a cone angle of 20 in each case.

The bore 17 of the body 6 in each half comprises an outer part 18 of length equal to that of the surface 16 and of complementary frustoconical form, with the same cone angle, and an inner part 19 of plain cylindrical shape which meets part 18 smoothly at 20, the point reached by the inner end 21 of the sleeve portion 12 when the cap nut 5 is screwed fully onto the body 6. The body 6 is provided with an integral internal flange 22 which provides opposed annular abutment surfaces 23 engaged by a radial flange 24 at the inner end of a respective elastomeric seal 25 formed of a thermo-plastic rubber such as EPDM.

Seal 25 comprises a tubular seal body 26 which in its free state is of plain cylindrical shape, both externally and internally, the external diameter of the seal body 26 being such as to provide a sliding fit, on assembly of the seal, between the seal 25 and the wall of bore part 1 9.

Seal body 26 is of substantially axial lengths, approximately two thirds times the external radius of the pipe end 2, in order to provide a large sealing area with the pipe end 2. The length of seal body 26 is also chosen such that it substantially fills the length of the plain bore portion 19.

Sleeve portion 12 is provided at a position approximately one third of its length from its inner end with a series of circumferentially equally spaced, radially inwardly projecting pipes 27. In this case each pipe 27 is of generally truncated-pyramidal shape, as defined by four concave sidewalls 29 and a flat end face 28 facing radially inwardly of the sleeve portion 1 2, but any suitable shapes of pips may be employed which will provide a gripping action with the pipe end.

As moulded, the internal diameter of the smaller diameter, inner end 21 of sleeve portion 12 is made equal to the external diameter of the pipes with which it is intended to be used. The radial height of the pips 27 is preferably made such that the sleeve portion 1 2 cannot be pushed over such a pipe without some interference occuring with the pips 27 which necessitates a small amount of radial expansion of the sleeve portion 1 2, and some deformation of the pipe in the case of a soft plastics pipe. Such radial expansion of the sleeve portion 12 can readily take place when the cap nut 5 is not secured on socket body 6, or when the cap nut is threaded on body 6 but in a loose condition.

In order to effect a connection with a pipe end 2, the seal 25 is slid into position in the socket body, and cap nut 5 is partially threaded onto the socket body 6, so that the inner end 21 of the sleeve portion 12 is axially-spaced from seal 25, and the pipe end 2 is push#ed into the bore of sleeve portion 1 2 as far as it will go, to bring the extremity 30 of pipe end 2 into abutment with seal flange 24.In the circumstance that pipe end 2 is not precisely aligned with the coupling 1 prior to insertion, as will often occur in practice, so that pipe end 2 initially enters sleeve portion 12 at an angle to the axis of the coupling 1, it will be guided into alignment during passage through sleeve portion 12 by co-operation with the frusto conical internal wall 1 5 of sleeve portion 1 2, the misalignment of the pipe being accommodated by flexing of that portion of the pipe external to the coupling 1. Since the extremity 30 at least of pipe end 2 is aligned with the bore of seal 25 when the pipe extremity 30 enters the seal 25, any damage to the seal 25 is kept to a minimum.The internal diameter of the seal body 26 of seal 25 is such as to provide an interference fit between body 26 and pipe end 2 during insertion of pipe end 2, so that pipe extremity 30 will readily enter seal body 26 without any cutting of the seal body.

On tightening of the cap nut 5 on threads 7 the co-operation between frusto-conical surface 16 of .sleeve portion 12 and the complementarily inclined wall of socket bore part 18 produces a progressive radially inward compression of sleeve portion 12 to enhance the gripping force exerted by sleeve portion 12 on pipe end 2. In addition, as the cap nut is screwed further onto the socket body 6, the tube end is urged inwardly by the gripping force to urge tube extremity 30 more firmly against flange 24, to provide an enhanced sealing force between the flange 22 and the tube extremity 30.

Furthermore, it is arranged that during tightening of nut 5 the inner end 21 of sleeve portion 12 engages with the outer end of tubular part 26 of seal 25 to compress seal body 26 axially and thereby exert an increased radial sealing force on tube end 12 due to the fact that the seal body 26 is confined between the wall of bore part 1 9, the outer surface of tube end 1 2, by end 21, and by the clamped flange 24. Tubular seal body 26 will therefore exert a sealing force on tube end 12 over its entire length.

In the-fully tightened condition of cap nut 5 shown-in Figure 1, the pipe end 2 is deformed radially inwards in the regions 4 by the pips 27 to provide a strong gripping action which resists any withdrawal force acting on the pipe end 2. The compressive forces exerted by the seal 25 will also provide some resistance to withdrawal, but unlike many known constructions the force exerted by the seal is not relied upon to prevent withdrawql.

Since substantial compressive forces are exerted on the pipe end 2 by the sleeve portion 12 after assembly, any changes in the dimensions of the pipe end 2 and parts of the coupling sleeve 1 due to differential thermal expansions and contractions will not result in complete loss of gripping force on the pipe end 2. The coupling is therefore suitable for use in applications where large changes of temperature are experienced, such as in central heating pipework.

The coupling described is capable of being used to connect polymeric pipes such as pipes of crosslinked high density polyethylene, pipes of relatively soft plastics such as polybutalene, and copper pipes.

In a modification, not shown, the tubular body 26 of seal 25 is of corrugated form.

Claims (10)

1. A pipe coupling comprising a socket body which is externally threaded for engagement by internal screw threads formed on a skirt portion of a cap nut, the cap nut comprising a sleeve portion which is received within the axially outer part of the bore of the socket, and a resilient tubular seal body located in the socket axially inwardly of the cap nut sleeve portion, the part of the socket bore in which the sleeve portion is located being tapered slightly so as to have a smaller diameter at its inner end, the arrangement being such that when a pipe end is inserted through the cap nut sleeve portion and into the seal body, the pipe end being of a diameter to be slidably received, or received with some interference, by the undeformed cap nut sleeve portion, and the cap nut is screwed further onto the socket body, the sleeve portion is compressed radially by interference with the wall of the tapered bore to grip the pipe end.

2. A pipe coupling as claimed in claim 1 in which the sleeve portion is provided internally with at least one radial projection to assist in gripping the pipe end.

3. A pipe coupling as claimed in claim 2 in which there are a plurality of such projections in ,the form of circumferentially equally spaced projecting pips.

4. A pipe coupling as claimed in claim 2 or claim 3 in which each projection is located closer to the inner end than to the outer end of the sleeve portion.

5. A pipe coupling as claimed in any of the preceding claims in which the axially inner end of the sleeve portion is engageable with the adjacent end of the tubular seal, and the tubular seal is substantially confined so that on tightening of the cap nut onto the socket body the seal body is subjected to an axial force by the sleeve portion thereby resulting in an increased radial sealing force between the seal and the pipe end.

6. A pipe coupling as claimed in any of the preceding claims in which the seal body is provided at its axially inner end with an internal flange which abuts with the extremity of the pipe end.

7. A pipe coupling as claimed in any of the preceding claims in which the skirt portion, prior to tightening of the cap nut, has a frusto-conical radially inner surface with its narrower ends towards the seal.

8. A pipe coupling as claimed in claim 7 in which the skirt portion, prior to tightening of the cap nut, has a frusto-conical radially outer surface having substantially the same cone angle as that of its radially inner surface.

9. A pipe coupling substantially as described with reference to the accompanying drawings.

10. A pipe coupling sleeve assembly comprising two pipe couplings each as claimed in any of the preceding claims.