This invention concerns pipe couplings of the type stated in the introductory portion of claim 1 as well as a method of fixing a pipe end by using such a pipe coupling.

These pipe couplings are used for many purposes, e.g. in connection with plumbing installations where one or more pipes are to be pieced together in a manner so as to form a distribution network for water.

Pipes for such purposes frequently consist entirely of metal or plastics, but, in addition to these, use is in¬ creasingly made of pipes which are composed in a strati- fied manner of metal and plastics as well as of different plastics materials, utilizing the mechanical properties and good oxygen diffusion tightness of the metal as well as the corrosion preventing properties of the plastics, and a good oxygen diffusion tightness with respect to some plastics materials. These types of pipes are produced in large amounts and are cut to suitable lengths for the application concerned.

Known pipe couplings for joining such pipes must therefore necessarily be provided with parts for fixing the pipe ends. These fixing parts are adapted to be deformed so as to provide either a frictional connection between the pipe end and the pipe coupling or a geometric locking of the pipe end in the pipe coupling. In the latter situation, the actual pipe end will inevitably be deformed.

All of these known pipe couplings require the use of either an expensive special tool or at least two ordinary hand tools.

In addition, in the use of known pipe couplings, the walls of the pipe end are subjected to inexpedient torsional forces or columnar forces seen in relation to the longitu¬ dinal axis of the pipe, which, in particular in connection with plastics pipes and stratified pipes, may cause unin¬ tentional crack formation in the pipe and delamination in the stratified pipes, resulting in leakages.

A pipe coupling is moreover known from FR-A1-2 622 272, comprising an element having an interior, annular chamber. When the chamber is filled with a fluid under pressure, the element is pressed against the internal or external surface of a pipe to ensure a tight connection. However, this coupling requires that the fluid under pressure is supplied from an external source. If a pipe end which has just been cut from a pipe length without other subsequent treatment is used in this coupling, the pipe end will only be retained in the pipe coupling by friction. This is ob¬ viated in FR-A1-2 622 272 by using a pipe end having a bead. Thus, this as well as the said external source of pressure requires the use of special tools which are nor¬ mally not available at e.g. a building site, or when the installation is made by private persons.

The object of this invention is therefore to provide a pipe coupling which does not require the use of special tools or several hand tools, and which does not subject the pipe end to the above-mentioned inexpedient torsional or columnar forces.

This is obtained by the pipe coupling according to claim 1 and by the method according to claim 7. It is ensured in this manner that the pressure of the membrane against the wall of the pipe end substantially affects it by a radial force, thereby retaining the pipe end without subjecting the wall of the pipe to torsional or columnar forces.

Further, the joint thus achieved can resist very great water pressures, which may e.g. occur by the so-called water hammer effect, since the pipe end is deformed plas¬ tically and is retained in a profiled means. In addition, it is possible, by simple means, to establish the neces¬ sary hydrostatic pressure, which renders the use of seve¬ ral hand tools or special tools superfluous.

When the second cavity is provided as stated in claim 3, the necessary fluid pressure may be established solely by means of a pair of tongs, a screwdriver, a small adjust¬ able spanner, a hexagon spanner or the like.

The subject-matter defined in claim 4 makes it possible to ensure maximum deformation of the diaphragm and to protect the thread of the screw against stripping, and also makes it possible always to tighten the diaphragm with a well- defined pressure.

The use of a hardening fluid in the pipe coupling, as stated in claim 5, ensures that the fixing of the pipe coupling will be permanent, which results in improved protection against leakage.

Claim 6 defines a special method of obtaining the neces¬ sary fluid pressure, viz. by chemical expansion in a closed space. This makes it possible to control the pres¬ sure impact on the diaphragm in a simple manner by simple dosing of the chemical substances which take active part in the expansion process.

The method of claim 8 ensures that the pipe is retained, even if the fluid pressure on the diaphragm should drop. It is additionally ensured that the pipe joint is diffi- cult to disassemble following assembly.

The method defined in claim 9 makes it possible to use the pipe coupling again following removal of a pipe joint.

Embodiments of the invention will be described more fully below with reference to the drawings, in which:

fig. 1 is a sectional view of the fixing parts to receive a single pipe end in a pipe coupling,

fig. 2 is a sectional view similar to fig. 1, but with an inserted pipe end,

fig. 3 is a sectional view similar to fig. 2, but with a deformed diaphragm,

fig. 4 is a sectional view of a straight-through joint according to the invention adapted to fix two pipe ends,

fig. 5 shows a T-member according to the invention adapted to fix three pipe ends, and

fig. 6 is a sectional view of an embodiment according to the invention in which the diaphragm is positioned on the stub at the inner side of the pipe.

A pipe coupling may be provided with a number, at least one, of attachments for the coupling of pipes which are fixed in the pipe end by fixing means which are integrated in the pipe coupling. Fig. 1 thus shows a section of a single attachment in a pipe coupling according to the in¬ vention to fix a circular pipe. The fixing means are formed by a circular stub 1 extending around the line of symmetry 11 and having a through hole 4, said stub 1 being provided on its outer side with one or more recesses 3 which can optionally accommodate a sealing ring 2.

In addition, the fixing means are formed by a sleeve 5 whose inner side is provided with a diaphragm 7, which, in combination, define a cavity 6 communicating with a second cavity 8 via ducts 10. The cavity 8 is formed by a threaded hole, which is closed by means of a screw 9. The cavities 6, 8 and the ducts 10 are filled with a liquid.

The fixing parts hereby define a circular depression 13 in which the wall 12 of a pipe end can be located, as shown in fig. 2. In this situation, the seal 2 serves to retain the pipe end temporarily.

Fig. 3 then shows the joint of the pipe coupling and the pipe end 12 following tightening of the fixing parts. Tightening of the screw 9 reduces the volume of the second cavity 8 so that the contained liquid is pressed at a high pressure into the cavity 6 via the ducts 10, causing the diaphragm to be deformed to firmly engage the wall 12 of the pipe end. The engagement pressure exerted by the dia- phragm on the wall 12 of the pipe end may e.g. be so great, as shown in the drawing, that the wall 12 of the pipe end is deformed into the recesses 3, resulting in geometric locking, or the pressure may be so small that the wall of the pipe end is not deformed, but sufficient for the friction between the coupling parts and the pipe end to ensure that the pipe is fixed in use.

This may be ensured e.g. in that the threads of the threaded hole have a predetermined depth, which means that the diaphragm can just be deformed to a predetermined level. It moreover means that the diaphragm can be tight¬ ened with a well-defined pressure.

As will be seen from the foregoing, the fixing process just requires tightening of the screw 9 after the pipe end 12 has been positioned in the depression 13, so that just

a simple hand tool is necessary for the entire fixing pro¬ cess, e.g. a hexagon spanner. It will moreover be seen that the fixing solely involves a radial pressure on the wall 12 of the pipe end, thereby obviating application of inexpedient torsional and columnar forces to it, which would e.g. result in unintentional mechanical deformation.

It is clear that the necessary hydraulic pressure to pro¬ vide the deformation of the diaphragm 7 may be established by other means than the threaded hole with the screw shown in figs. 1, 2 and 3. The screw may e.g. be replaced by a spray nipple for a grease gun, which establishes the ne¬ cessary pressure. The threaded hole may e.g. also be re¬ placed by a smooth hole which accommodates a frictional piston instead of a screw, said frictional piston being pushed in by means of a simple pair of tongs.

The hydraulic pressure may also be established utilizing chemical expansion, said cavity 8 being provided with a substance that can be activated to expand chemically. This expansion may be activated outside the pipe coupling. The chemical expansion may e.g. be obtained by means of a small explosive charge positioned in the cavity 8, and the activation of this explosive charge may e.g. be made in a known manner via an ignition pin positioned in the screw

9. It is hereby possible in practice to dimension the size of the explosive charge for the purpose concerned.

Alternatively, the screw 9 may be replaced by a nozzle, to which the mouth of e.g. a nail gun may be positioned. The necessary pressure is hereby supplied in a simple manner by firing the explosive charge of the nail gun into the nozzle.

Fig. 4 and fig. 5 show pipe couplings according to the invention, a straight-through joint for joining two pipes

in extension of each other and a T-member for joining three pipes at a mutual angle of 90°, respectively. As will be seen from these figures, the cavities 6 behind the diaphragms 7 are in communication with each other, making it possible to fix all the pipes in the pipe couplings simultaneously by tightening the screw 9. This can be done in principle with any embodiment of the pipe coupling.

Fig. 6 shows an embodiment of the invention in which the diaphragm is positioned on the outer side of the stub fac¬ ing the wall of the pipe end, the recesses 3 being located on the inner side of the sleeve 5 in this situation.

As will appear from the above, various media may be used for establishing the hydrostatic pressure. In certain cases requiring a specially safe joint, it may be expe¬ dient, however, to utilize a liquid as a pressure medium that can be activated to harden following tightening of the pipe coupling. Such a liquid may e.g. be formed by a liquid epoxy which has been filled with small glass beads containing a hardener, said glass beads being caused to burst by tightening of the coupling and the consequent pressure increase, whereby the epoxy hardens.