GB1566844A - Couplings for tubing - Google Patents

Description

(54) IMPROVEMENTS IN QR RELATING TO COUPLINGS FOR TUBING (71) We, KAY & COMPANY (EN GINEERS) LIMITED, a British Company of Acresfield House, 15, Exchange Street, Bolton BL1 lRS, Lancashire, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow mg statement: This invention relates to an improved fitting for connection of tubing and is primarily directed to a fitting for polyethylene or other synthetic plastics tub mg such as is used in the distribution of natural gas.

Plastics tubing for the distribution of gas has considerable advantages from the point of view of laying the pipes which can be rolled off a drum, and furthermore the tubing is able to accommodate terrestial movement. The higher pressures used in conveying natural gas has led to the adoption of smaller bore piping with attendant savings in cost. Jointing devices used in such tubing must have the capability of sealing at higher pressures than hltherto, and in addition the mechanical strength and resistance to mechanical stresses from exterior sources must be high. It is a requirement that the joint used for plastics tubing must be of greater strength than the tensile pull failure point of the tubing itself so that if mechanical disturbance of the pipe takes place then the point of failure will be the tubing at the zone of disturbance and not the coupling which could be some considerable distance away and remain unnoticed. The tensile strength of plastic piping used is high and for this reason any jointing device must also be of considerable strength.

It is an object of this invention to provide a coupling for a plastics pipe, principally one used for distribution of natural gas, which affords a strength greater than the tubing itself, which is easy to assemble and joint correctly and which is able to absorb tolerances in the wall thickness of the piping which are an inherent part of che manufacturing process.

According to this invention there is provided a fitting for connection of a tube of plastics material, the fitting comprising a cylindrical barrel with the internal surface thereof relieved from one end to define an abutment surface, a support liner with a body for insertion into the bore of a tube to be connected and a laterally extending flange at one end of the body defining a shoulder against which a resilient sealing ring bears, the arrangement being such that the tube and liner may be inserted within the barrel with the sealing ring lying between the flange of the liner and abutment surface of the barrel, the fitting further including a compression ring for location around the periphery of the tube and a securing nut engageable with the barrel serving to move the ring into the one end of the barrel whereby compression against the tube outer surface secures same to the fitting.

The support liner preferably includes angled ridges on the outer surface of the body to grip the tube and form a gas-tight seal therewith.

The compression ring or olive will preferably have a tapered noise to coact with an internally flared end of the barrel whereby radially inward compression onto the tube occurs with longitudinal movement produced by the nut. The surface of the ring bearing against the tube may include annular ridges to bite into the tube material.

Preferably the support liner has the outer surface of the body tapering outwardly towards the end having the flange.

The fitting of the invention provides a double seal with the compression of the tube forming a first seal and the sealing ring forming a second seal. Furthermore the tapering arrangement of the support liner body provides good resistance to tensile loads.

In an embodiment the position of the compression ring is part way along the tapering body part of the liner whereby any movement of the tube produce a wedging action against the nose of the compression ring.

One embodiment according to the invention is shown by way of example in the accompanying drawings. In the drawings: Figure 1 shows a fitting in part section with a polyethylene tube connected therewith, Figure 2 shows a part in detail of the support liner body and compression ring, and Figure 3 shows a detail as in Figure 2 but with the nut tightened to effect coupling and sealing of the tube.

Referring to Figure 1 the fitting has a cylindrical barrel 1 with the internal surface of one end relieved at 2 whereby an abutment surface 3 is formed. A support liner 4 has a body portion 5 which is of a dimension suitable to enter the internal bore of a tube 6 of polyethylene or the like synthetics plastics material. An end of the body 5 of the support liner is provided with a laterally extending flange 7 which defines a shoulder 8 in which a resilient rubber sealing ring 9 lies. The ring 9 is arranged to be between the flange 7 and abutment surface 3 whereby with longitudinal force applied between the support liner and barrel a gas-tight seal is formed. The support liner body 5 includes ridges 10 on the outer surface thereof and the surface of the body tapers outwardly towards the end having the flange 7. The internal surface of the barrel is flared at 11 and a compression ring or olive 12 is arranged to locate around the outside of the tube 6 with the nose 13 thereof tapered to coact with the flared end 11.

A nut 14 engages the barrel 1 and contacts the back surface of the ring 12 to produce longitudinal movement of the ring and compression thereof around the tube 6 by virtue of the coacting surfaces 11 and 13.

The function is similar to customary compression type fittings.

The internal surface of the ring 12 has ridges 15 which serve to grip the surface of the tube 6.

Referring now to Figures 2 and 3 in which the reference numerals are omitted for clarity; in Figure 2 the fitting is shown in part with the various components assembled but with the nut hand tight only, and Figure 3 shows the nut fully tightened and the compression of the ring ensures that the tube is fully bedded on to the liner body to provide a gas-tight seal and that the ridges on the body and ring together with the nose and back of the ring provide a means for firmly securing the tube against tensile forces, thus preventing its withdrawal from the fitting.

The two ridges C shown on the liner body in Figures 2 and 3 effectively prevent any leakage path between the tube and liner body and are made of sufficient height to penetrate any longitudinal withdraw mark or imperfection on the inside wall surface of the tube. The shape of these ridges is also arranged to have a shallow angle leading edge in order to allow the liner to readily enter the bore of the tube. The compression ring is arranged so that on initial tightening the leading edge and serrations E penetrate the tube surface before the rear ridges F and G and trailing edge of the ring commence to distort. When the front edge of the ring is fully compressed down the flared end of the barrel further tightening causes the back end of the ring to distort downwards onto the tube and the rear ridges F and G are then forced into the pipe surface producing a further gripping effect and also causing the tube to compress onto the ridges H of the support liner body.

The purpose of the ridges H is to penetrate the inner surface of the tube by a controlled amount to ensure that the liner firmly grips the tube so that a good tensile strength at the joint is produced. The arrangement provided is capable of compensating for tolerances in the tube wall thickness without any substantial loss of sealing qualities or strength.

The tapering of the liner also produces a locking arrangement whereby if any movement occurs under tensile forces the resistance at the joint will at least remain the same or possibly increase due to movement of the tube along the taper, which produces increasing resistance by virtue of the tube being pulled into and against the nose of the compression ring forming a wedging action.

If the joint is less than fully tight then this wedging effect will occur after a relatively considerably movement of the tube, but in all cases the liner will necessarily move with the tube and the support and wedging effect is maintained.

The worst conditions of joint will occur when the tolerance of the tube tends to maximum in bore and minimum in wall thickness. This condition will allow the greatest gaps to occur between the components in the fitting and the tube whereby a substantial part of the compression ring movement is taken up in removing the tolerances before effective gripping occurs.

The fitting of the invention using the tapered support liner avoids certain disadvantages under these conditions in so far as the size of the liner may be arranged so that contact will be established with the taper on the liner at some point so that the effect of worst conditions tolerances can be to a large extent compensated without substantial reduction in the efficiency of the joint.

The embodiment of the invention thus provides a fitting which is simple to assemble and in which the joint is made by tightening of a single nut. The fitting includes two characteristic features being the method of double sealing against gas leaks effected through the seal onto the support liner and by the resilient sealing ring at the head of the liner, both in conjunction with the compression ring seal, and the arrangement whereby increasing tensile loads applied to the tube produce a wedging action in front of the compression ring to ensure that the tube would fail along its length prior to extraction from the fitting body.

WHAT WE CLAIM IS: 1. A fitting for connection of a tube of plastics material, the fitting comprising a cylindrical barrel with the internal surface thereof relieved from one end to define an abutment surface, a support liner with a body for insertion into the bore of a tube to be connected and a laterally extending flange at one end of the body defining a shoulder against which a resilient sealing ring bears, the arrangement being such that the tube and liner may be inserted within the barrel with the sealing ring lying between the flange of the liner and abutment surface of the barrel, the fitting further including a compression ring for location around the periphery of the tube and a securing nut engageable with the barrel serving to move the ring into the one end of the barrel whereby compression against the tube outer surface secures same to the fitting.

2. A fitting according to Claim 1, wherein the support liner includes angled ridges on the outer surface of the body to grip the tube and form a gas-tight seal therewith.

3. A fitting according to Claim 1 or 2, wherein the compression ring has a tapered nose to coact with an internally flared end of the barrel whereby radially inward compression onto the tube occurs with longitudinal movement produced by the nut.

4. A fitting according to any preceding claim, wherein the surface of the compression ring bearing against the tube has annular ridges to bite into the tube material.

5. A fitting according to any preceding claim, wherein the support liner has the outer surface of the body tapering outwardly from the end towards the flange.

6. A fitting according to Claim 5, wherein the position of the compression ring is part way along the tapering part of the liner, whereby movement of the tube produces a wedging action against the end of the compression ring lying within the barrel.

7. A fitting for connection of a tube of a plastics material constructed and arranged to function substantially as herein described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. the liner at some point so that the effect of worst conditions tolerances can be to a large extent compensated without substantial reduction in the efficiency of the joint. The embodiment of the invention thus provides a fitting which is simple to assemble and in which the joint is made by tightening of a single nut. The fitting includes two characteristic features being the method of double sealing against gas leaks effected through the seal onto the support liner and by the resilient sealing ring at the head of the liner, both in conjunction with the compression ring seal, and the arrangement whereby increasing tensile loads applied to the tube produce a wedging action in front of the compression ring to ensure that the tube would fail along its length prior to extraction from the fitting body. WHAT WE CLAIM IS:

1. A fitting for connection of a tube of plastics material, the fitting comprising a cylindrical barrel with the internal surface thereof relieved from one end to define an abutment surface, a support liner with a body for insertion into the bore of a tube to be connected and a laterally extending flange at one end of the body defining a shoulder against which a resilient sealing ring bears, the arrangement being such that the tube and liner may be inserted within the barrel with the sealing ring lying between the flange of the liner and abutment surface of the barrel, the fitting further including a compression ring for location around the periphery of the tube and a securing nut engageable with the barrel serving to move the ring into the one end of the barrel whereby compression against the tube outer surface secures same to the fitting.

2. A fitting according to Claim 1, wherein the support liner includes angled ridges on the outer surface of the body to grip the tube and form a gas-tight seal therewith.

3. A fitting according to Claim 1 or 2, wherein the compression ring has a tapered nose to coact with an internally flared end of the barrel whereby radially inward compression onto the tube occurs with longitudinal movement produced by the nut.

4. A fitting according to any preceding claim, wherein the surface of the compression ring bearing against the tube has annular ridges to bite into the tube material.

5. A fitting according to any preceding claim, wherein the support liner has the outer surface of the body tapering outwardly from the end towards the flange.

6. A fitting according to Claim 5, wherein the position of the compression ring is part way along the tapering part of the liner, whereby movement of the tube produces a wedging action against the end of the compression ring lying within the barrel.

7. A fitting for connection of a tube of a plastics material constructed and arranged to function substantially as herein described with reference to and as shown in the accompanying drawings.