GB2150243A

GB2150243A - Couplings for tubes

Info

Publication number: GB2150243A
Application number: GB08331191A
Authority: GB
Inventors: John Derek Guest
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-11-23
Filing date: 1983-11-23
Publication date: 1985-06-26
Also published as: GB8331191D0; GB2150243B

Abstract

A tube coupling having a collet 13 with resilient arms 16 co-operating with a cam surface 20 on a body member 10 surrounding the collet whereby the collet arms are forced inwardly radially by movement of the collet in the axial direction when a tube gripped at 12 is pulled outwardly from the body member 10. Two resilient annular members 29, 30 are provided in the body member between the inner ends of the arms 16 of the collet and a shoulder 28 in the body member. Each of the members 29, 30 seals around the tube 12 and each sealingly engages the surrounding wall of the body member. <IMAGE>

Description

SPECIFICATION Couplings for tubes This invention relates to couplings for tubes and is more particularly concerned with a tube coupling of the kind having a collet with resilient arms arranged to co-operate with a cam surface on a member surrounding the collet, which member has an internal surface tapering in one direction and engaging the arms of the collet so that the arms are forced radially inwardly by axial movement of the collet in said one direction.

With such a tube coupling, the collet is arranged so that said one direction is the direction of withdrawal of the tube from the member. The end of the tube is pushed into the tube in the opposite direction through the collet. Any outward pull on the tube with respect to said member tends, by the engagement between the collet and the tube, to pull the collet in said one direction thereby causing the arms, by engagement with the cam surface, to grip the tube more tightly. Such a tube coupling thus serves to hold a tube in said member; the end of the tube can be inserted directly into the coupling and is engaged thereby in a manner which prevents withdrawal of the tube merely by a pull thereon. The tube can be released however by pushing of the collet inwardly into said member whilst pulling the tube outwardly.This release can only be effected by a deliberate action and not by an accidental pull on the tube. It is known moreover to provide additional means for preventing any accidental pushing of the collet inwardly in a manner which might release the tube.

It is commonly required to seal the tube in said coupling and it is the usual practice to provide an Oring within the bore in said member inwardly of the collet, the O-ring fitting tightly around the end of the tube. If there is any leakage of fluid between the end of the tube and said member, the fluid pressure tends to force the O-ring back against the collet and thus serves not only to apply pressure to the collet in a direction tightening the grip of the collet arms in the tube but also serves to deform the O-ring to hold it more tightly against the tube in the surrounding surface of said member.

British Specification No 1520742 shows examples of such quick release couplings employing an 0-ring inwardly of the collet.

The sealing of such a coupling against leakage of fluid relies upon the O-ring seal. This must be in tight engagement with the outer periphery of the tube and with the surrounding wall of the body member. Pressure on the O-ring, pressing it in the axial direction, causes radial expansion inwardly and outwardly so as to improve the sealing against the tube and body member. It is therefore the practice, in couplings of this kind, to design the collet, body member and O-ring in relation to the tube diameter so that the O-ring is initially a tight fit against the tube and body member in the radial direction and preferably also is compressed against a shoulder in the body member by the end of the collet so that the O-ring is confined also in the axial direction.This further tends to minimise leakage and ensures that any fluid pressure due to fluid escaping around the end of the tube into the region of the seal, applies a pressure axially onto the 0 ring.

It has been found however that, with O-rings of rubber or other polymeric material, even from the most reputable manufacturers, a very small proportion, possibly 0.001% have flaws or splits which may result in an imperfect seal of the coupling. In some circumstances, such an imperfect seal may have very serious consequences.

Couplings of this kind may be used for example in pipelines conveying inflammable liquid fuel or may be used in brake fluid lines on vehicles.

It is an object of the present invention to provide an improved coupling of the kind described in which effective sealing can be obtained despite a faulty 0ring seal.

According to this invention in a tube coupling of the kind having a collet with resilient arms arranged to co-operate with a cam surface on a body member surrounding the collet, which cam surface is tapered to a smaller diameter in the axial direction and engages the arms of the collet so that the collet arms are forced radially inwardly by movement of the collet in said axial direction to grip a tube in the coupling, the collet arms being releasable to move radially outwardly by movement of the collet in the opposite axial direction, two resilient annular members are provided in said body member between the inner end of the arms of the collet and a shoulder in the body member each of said resilient annular members sealing around a tube inserted in the coupling and each annular member sealingly engaging the surrounding wall of said body member.Preferably the two annular members are in contact with one another.

With this construction if either of the annular members should be faulty in a way which permits of leakage of fluid, such fluid will apply pressure in the axial direction onto the other of the annular members and will improve the sealing effected by said other member.

The following is a description of one embodiment of the invention, reference being made to the accompanying drawing which is a longitudinal section through part of a tube coupling.

Referring to the drawing there is shown a tube coupling comprising a body member 10 having a bore 11 therethrough. Atube 12, 12,shown in chain lines, is insertable into the coupling from the righthand end thereof as seen in the drawing to be gripped by a collet 13. This collet has a cylindrical portion 14 terminated at its outer end by a flange 15 and has resilient arms 16 extending axially inwardly into the body member 10 from the cylindrical portion 14. Each of the arms has a projection 19 in its inner surface, the projections 19 lying in a plane normal to the axis of the collet and serving to grip the tube 12. The collet may be made of metal or of plastics material; in the latter case the projections 19 may be constituted by metal inserts.On their outer face, the collet arms 16 have a portion 21 the diameter of which increases in the axial direction into the coupling body member to form a tapered surface co-operating with a tapered cam surface 20 on the body member 10 such that, if the collet is moved axially outwardly, that is to say to the right in the drawing, the collet arms 16 are forced radially inwardly to grip the tube 12.

The tube 12 is inserted through the outer end of the collet, the right-hand end in the drawing, to extend through the collet and to abut against a shoulder 25 formed in the coupling member 10. This shoulder forms a stop for the tube and is constituted by the end of an enlarged diameter portion 26 of the bore 11. The internal diameter of this portion of the body member is made just sufficient to accommodate the tube 12. The collet fits in a still larger diameter part 27 of the member 10, which part is terminated by a second shoulder 28. The collet and body member are dimensioned to permit of two resilient O-rings 29,30 being provided in the body member around the tube 12 between the shoulder 28 and the end of the collet.Each O-ring is of an elastomeric material, e.g. rubber or a polymeric material and is made of a size such that it fits closely over the tube 12 and also fits closely within the bore in the body member. Conveniently the two O-rings 29, 30 are of the same dimension, The O-ring 29 preferably bears against the shoulder 28. Any leakage of fluid around the end of the tube 12 will reach the O-ring 29 and will cause axial compression thereof. This axial compression causes the O-ring to expand radially inwardly and outwardly and serves to force the O-ring into any irregularities in the tube 12 and thereby to effect good sealing between the O-ring and the tube. It also serves to force the O-ring outwardly to seal in the body member. If the O-ring 29 should have a flaw or in any way be faulty such that leakage occurs through or past it, then the fluid pressure is exerted on the O-ring 30 so improving the sealing effected by the O-ring 30 against the tube and against the body member. This arrangement thus gives effective and satisfactory sealing despite any failure in one of the O-rings. It therefore provides a substantial improvement in safety in any circumstances in which the coupling is used for conveyance of inflammable or other dangerous fluid or in circumstances, where the coupling is used, e.g. in a brake fluid line in a vehicle where failure of the coupling may cause an accident.

Claims

1. A tube coupling of the kind having a collet with resilient arms arranged to co-operate with a cam surface on a body member surrounding the collet, which cam surface is tapered to a smaller diameter in the axial direction and engages the arms of the collet so that the collet arms are forced radially inwardly by movement of the collet in said axial direction to grip a tube in the coupling, the collet arms being releasable to move radially outwardly by movement of the collet in the opposite axial direction wherein two resilient annular members are provided in said body member between the inner end of the arms of the collet and a shoulder in the body member each of said resilient annular members sealing around a tube inserted in the coupling and each annular member sealingly engaging the surrounding wall of said body member.

2. Atube coupling as claimed in claim 1 wherein the two annular members are in contact with one another.

3. A tube coupling as claimed in either of the preceding claims wherein said two resilient annular members are of the same dimensions.

4. A tube coupling as claimed in any of the preceding claims wherein said two resilient annular members are of the same material.

5. A tube coupling as claimed in any of the preceding claims wherein the resilient annular members are O-rings formed of elastomeric material.

6. Atube coupling as claimed in any of the preceding claims wherein one of said resilient annular members bears against a shoulder in said body member.

7. A tube coupling substantially as hereinbefore described with reference to the accompanying drawing.