The invention relates to a pipe coupling having an essentially cylindrical housing with radially inward directed end portions, said housing being provided with a longitudinal dividing slit and being contractible circumferentially by means of clamping bolts, a tubular sealing sleeve of elastomer material being provided which is enclosed by said housing and has inwardly bent end portions to act as sealing lips, said sleeve being further provided with conical end faces slanting towards the centre and towards the axis of the coupling, said end faces supporting correspondingly conically shaped clamping rings, which are circumferentially split and thereby circum¬ ferentially contractible, said clamping rings engaging the housing with their outer circumferential edges at the transitional area between the cylindrical part and the radially inward directed end portions, and are provided at their inner circumference with tooth-shaped projections facing the surface of the pipes to be coupled.

The invention is particularly concerned with clamping rings, which have to provide the required pull tightness of the pipe connection, and which to that end may penetrate with their tooth-shaped projections into the surface of the pipes to be coupled.

Such a coupling, which is designed for use at high pressures (of 80 bar and higher) is known from Dutch Patent Specification 180874. With this known coupling the tooth- shaped projections of the clamping ring are formed by providing J-shaped incisions directed essentially radially outwards from the inner circumferential edge thereof, and bending the edge segments thus obtained out of the plane of the clamping ring.

Although the tooth-shaped projections thus formed may in principle penetrate well into the material of the pipes to be coupled when the coupling housing - and thus the clamping ring - is being contracted, it has been found that a clamping ring designed in this way is not equally

suitable for all pipe materials. In case of plastics material in particular, the tooth-shaped projections are generally found in practice to act as a cutter, i.e. involving removal of chips and/or notchforming, which results in a poor pull tightness.

Furthermore such a clamping ring tends to wrinkle when it is contracted circumferentially around the pipe in question, which results in a non-uniform engagement of the tooth-shaped projections in the pipe material. The invention aims at overcoming these drawbacks of the well-known coupling, by particularly improving the clamping ring in such a way that its functioning will be less dependent on the material of the pipes to be coupled. According to the invention this aim is achieved in that at least one of the clamping rings is extended at its inner circumference in the form of a foot portion that extends in the axial direction, the inner circumferential face of which foot portion being provided with several (series of) projections positioned close to each other in the axial direction.

With the clamping ring according to the invention the axial forces to be exerted by the clamping onto the pipe are distributed over several (series of) projections, while in particular the "dam" of the tubular material confined between adjacent (series of) tooth-shaped projections is secured against undesired shearing (stripping) .

The foot portion of the ring extending essentially in the axial direction also provides a reinforcement of the inner circumferential region of the clamping ring, due to which the foot portion will contract as a ferrule around the pipe.

The invention will be hereinafter explained in greater detail with reference to the drawing of an exemplary embodiment.

Fig. 1 is a side view - partially in longitudinal section - of the pipe coupling according to the invention;

Fig. 2 is an end view of the pipe coupling according to Fig. 1; and

Fig. 3 shows an axial section on a larger scale, in which the engagement between the foot portion of the clamping ring and a pipe to be coupled can be seen. The pipe coupling shown in the drawing has a housing 1 which may e.g. be formed of a stainless steel sheet into the shape of a cylindrical body, that extends over an arc length of less than 360° and is provided with radially inwardly directed end portions or flanges 2. The longitudinal slit or gap 3 between the adjacent longitudinal edges of the cylindrical housing 1 is bridged by a filler plate 4, which may e.g. also be formed of a stainless steel sheet and loosely engages the inner circumferential wall of the cylindrical housing.

A plate element 5 which is bent to form a loop for accommodating a clamping bar 6 is fixed on either side of the gap 3 on the outside of the housing 1. In the exemplary embodiment shown the two clamping bolts 6 which extend parallel to each other in the direction of the axis of the coupling are connected to each other by two clamping bolts 7 that extend tangentially relative to the housing 1. The latter bolts extend at their headed ends through transverse bores in the clamping bar 6 on the right hand side and engage with their threaded ends in correspondingly threaded transverse holes of the clamping bar 6 on the left hand side (see Fig. 2) . Tightening of the clamping bolts 7 causes the two clamping bars 6 to be pulled towards each other, and thereby causes the housing 1 to be contracted to a housing of smaller diameter.

The housing 1 encloses a cylindrical sleeve 9, which has end portions 10 which are turned back inwardly and which may sealingly close as sealing lips around the pipes to be coupled.

Thus far the pipe coupling shown corresponds to the coupling disclosed in Dutch Patent Specification 180874. The end faces 11 of the sleeve 9, which is made of an elastomer, e.g. rubber, are conical in shape. Each of these end faces is covered by a correspondingly formed flat- conically shaped ring 12, which extends over an arc length of at least 360°, and in which the "gap" between the

opposite ends 12a lies angularly offset through 90° relative to the gap 3 of the cylindrical housing 1.

At each end of the coupling a specially shaped clamping ring 13 bears on the flat-conically shaped cover ring 12. Said clamping ring consists of a flat-conically shaped body part 13a, which encloses an angle of approximately 70° with the axis of the coupling, and a foot portion 13b which connects thereto and extends virtually in the axial direction (see also Fig. 3) . In its untensioned state the clamping ring 3 extends over an arc length less than 360°. The "gap" between the ends 13c of the ring lies diametrically opposite the gap 3 of the cylindrical housing 1. The clamping rings 13, which are preferably made of stainless spring steel, have the outer circumferential edge of the respectively body part 13 engaging the inner wall of the housing 1, in the corner between the cylindrical part and the flange 2 at the appropriate end of the pipe coup¬ ling. Adjacent the foot portion 13b the turned-back end portion 10 is provided, at the respective end of the pipe coupling, with a circumferential recess in which the foot portion 13b is accommodated.

The foot portion 13b is provided with five toothed ribs 14 on its inner circumferential surface (see Fig. 3) . To establish a pull resistant coupling between two pipes, for example pipes of plastics material, each of said pipes is inserted into one end of the coupling shown in Fig. 1. The bolts 7 are then tightened, due to which the housing will contract around the sleeve 9 and the latter will become with its sealing lips 10 sealingly clamped around the two pipes.

During contraction of the housing 1, the cover rings 12 and the clamping rings are simultaneously compressed radially and tangentially to a smaller diameter, thereby reducing the gaps between the free ends 12a and 13c respectively of these rings. The toothed ribs case bite into the surface of the respective pipe 15 (see Fig. 3), due to which the pipe cannot slide out of the coupling under the influence of the internal operating pressure. The axial outward force which is exerted by the pipe on the

foot portion under the influence of the operating pressure, will be uniformly distributed over the five toothed rings, so that even at relatively high operating pressures there is no risk of slippage through stripping of pipe material. In view of the fact that contraction of the rings

12 and 13 to a smaller diameter will involve sais rings to become also slightly flatter (less conical) , it is preferable to form the foot portion 13b in such a way that it has a conicity of a few degrees in the untensioned state (with maximal gap) .