Background Art A sealing ring of this kind is particularly intended for use in plastic tubes, for instance tubes of ethylene plastic. Prior-art sealing rings of this kind are often difficult to mount in the groove in the inner tube. It can also be difficult to slide the outer tube onto the inner tube provided with the sealing ring while main- taining the sealing ring in its correct position in the groove. When sliding on the tube, it can also be diffi- cult to achieve the compression of the sealing ring re- quired to obtain a satisfactory seal of the gap between the tubes.

One particular problem in connection with corrugated plastic tubes is the relaxation of the tube material, i. e. that the form of the material changes over time, which in prior-art sealing rings leads to a reduced sealing effect or even a complete loss of sealing effect. Another problem is that it can be difficult, when using prior-art sealing rings, to achieve a uniform stretching of the sealing ring as this is mounted in the groove in the inner tube, which

may result in a reduced tightness in the more stretched parts of the sealing ring.

Summary of the invention Therefore, the object of the invention is to provide a sealing ring which can be easily mounted in the groove in the inner tube while being uniformly stretched, allows the outer tube to be slid on in a relatively easy manner and yet provides a reliable seal and which has the abil- ity to adjust to any changes in dimension of the groove and gap as a result of the relaxation or deformation of the tube material.

This object is achieved by means of a sealing ring of the kind described by way of introduction and char- acterised in that the lateral sealing portions consist of projecting, elastically flexible tongues, which extend obliquely axially-radially outward from the first sealing portion on both sides of the second sealing portion, that the axial distance between the free ends of the two tongues is larger than the width of the groove, that the tongues are adapted to engage the side walls of the groove adjacent to the mouth of the groove, and that a circumfer- ential recess is formed between the second sealing portion and each lateral sealing portion to allow the second seal- ing portion and each lateral sealing portion to be moved towards each other in case of deformation of the sealing ring.

A sealing ring thus formed can be easily mounted in the groove in the inner tube while being uniformly stretched, and it is also easy to slide the outer tube onto the inner tube, since the circumferential recesses between the second sealing portion and the lateral seal- ing portions make it easy to compress the sealing ring in the groove. Notwithstanding this, the sealing ring will provide a reliable seal even if relaxation or deformation of the tube material should occur, inter alia owing to the fact that the pressure of the fluid transported in the conduit formed by the two tubes influences the second

sealing portion and the lateral sealing portions, via the circumferential recesses, and forces them to abut sealingly against the inner surface of the outer tube and the side walls of the groove, respectively.

In a preferred embodiment, each of the recesses between the second sealing portion and the lateral sealing portions tapers towards its bottom.

The tongues'end portions, which are adapted to engage the side walls of the groove, preferably taper outwards.

In addition, a circumferential recess is suitably formed also between the first sealing portion and each lateral sealing portion to form a cavity between the sealing ring and the side walls of the groove when the sealing ring is located in the groove.

The first sealing portion is preferably smaller in width than the bottom of the groove.

The width of the second sealing portion preferably increases radially outwards.

The second sealing portion advantageously has a circumferential, radially projecting central portion.

The sealing ring is preferably symmetrical relative to a plane which is perpendicular to the centre axis of the sealing ring.

Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1 is a sectional view of a sealing ring accord- ing to the invention in axial section along a diameter.

Fig. 2 is a sectional view of the sealing ring as mounted in an exterior, circumferential groove in an inner tube.

Fig. 3 is a sectional view of the sealing ring in a position where it seals an annular gap between the inner tube and an outer tube.

Fig. 4 shows a portion of Fig. 3 on an enlarged scale.

Fig. 5 corresponds to Fig. 4 but shows the sealing ring as exposed to an increased pressure at one side.

Description of a Preferred Embodiment The sealing ring 1 shown in Fig. 1 is adapted to seal an annular gap 2 (see Fig. 3) between an inner tube 3 and an outer tube 4. In the example shown in the draw- ings, the sealing ring 1 is used to seal a gap 2 between a corrugated spigot end portion 5 of the inner tube 3 and a socket end portion 6 of the outer tube 4, said socket end portion 6 being slid onto the spigot end portion 5 in the way illustrated in Fig. 3. In this example, the tubes 3 and 4 are corrugated tubes of ethylene plastic. The corrugations of the inner tube 3 form circumferential, exterior grooves in the spigot end portion 5. The sealing ring 1 is to be arranged in the groove 7 closest to the free end of the spigot end portion 5.

The sealing ring 1 shown in Fig. 1 is made of rubber and has a radially inner first sealing portion 8, which is adapted to abut with an inner peripheral surface 9 against the bottom of the groove 7 formed in the spigot end portion 5 of the inner tube 3. The width of the first sealing portion 8 increases radially inwards.

The sealing ring 1 also has a radially outer second sealing portion 10, which is adapted to abut with an outer peripheral surface 11 against the inside of the socket end portion 6 of the outer tube 4. The outer peri- pheral surface 11 has a central, circumferential, pro- jecting portion 12. The width of the second sealing portion 10 increases radially outwards.

The sealing ring 1 further has two lateral sealing portions 13 and 14, which consist of two projecting, elastically flexible tongues, which extend obliquely axially-radially outward from the first sealing portion 8 on both sides of the second sealing portion 10 and which are adapted to abut against either side wall of the groove 7. The tongues 13 and 14 are adapted to abut against the side walls of the groove 7 with a surface 15

and 16, respectively, facing radially inwards and being formed on the free end portion of the respective tongues.

These end portions have an outwardly tapering shape. The axial distance between the free ends of the two tongues 13 and 14 is larger than the width of the groove 7.

Circumferential recesses 17 and 18, tapering towards their bottom, are formed between the second sealing por- tion 10 and the lateral sealing portions 13 and 14, re- spectively. Circumferential recesses 19 and 20 of a wide and shallow shape are formed between the first sealing portion 8 and the lateral sealing portions 13 and 14, respectively.

As shown in Fig. 1, the sealing ring 1 is symmet- rical relative to a plane which is perpendicular to the centre axis of the sealing ring.

The sealing ring 1 is easy to mount in the groove 7 in the spigot end portion 5 of the inner tube 3 and will, owing to its design, be uniformly stretched in the groove. During mounting, the sealing ring's 1 lateral sealing portions or tongues 13 and 14 with their surfaces 15 and 16 first make contact with the side walls of the groove 7 adjacent to the mouth of the groove, and are then slightly bent radially outwards. This means that the recesses 17 and 18 will be slightly narrower when the sealing ring 1 is in its mounted position compared with its non-assembled position (see Fig. 2 and Fig. 1, re- spectively).

The socket end portion 6 of the outer tube 4 can be easily slid onto the spigot end portion 5 of the inner tube 3, since the sealing ring 1, owing to the recesses 17 and 18, is relatively easy to compress. When sliding on the outer tube 4, the sealing ring 1 is pressed ra- dially inwards by the socket end portion 6, which causes the lateral sealing portions or tongues 13 and 14 to bend slightly more radially outwards (see Fig. 3 and Fig. which means that, once the socket end portion 6 has been slid on, the recesses 17 and 18 will be narrower than

they are when the sealing ring 1 is mounted in the groove 7 and the socket end portion 6 has not yet been slid on (Fig. 2).

As shown in Fig. 3 and Fig. 4, the first sealing portion 8 abuts with its surface 9 against the bottom of the groove 7, whereas the lateral sealing portions 13 and 14 with their surfaces 15 and 16 abut against the walls of the groove 7 adjacent to the mouth of the groove. The corrugations of the inner tube 3 have their weak sections in the region between the crests and valleys of the cor- rugations, i. e. as far as the groove 7 is concerned in the walls of the groove. As shown, the sealing ring 1 does not engage these weaker sections but only the stronger sections of the inner tube 3, i. e. the bottom of the groove 7 and the wall portions thereof located adjacent to the mouth of the groove. As further shown in Figs 3 and 4, the second sealing portion 10 abuts with its surface 11 and its compressed projection 12 against the inside of the socket end portion 6 of the outer tube 4 opposite the groove 7.

Because the lateral sealing portions or tongues 13 and 14 have been elastically bent in the direction of the second sealing portion 10 in the way described above during the mounting of the sealing ring 1 in the groove 7 and the sliding-on of the socket end portion 6 onto the spigot end portion 5, they will maintain their engagement with the walls of the groove 7 even if these would be slightly moved away from each other as a result of re- laxation or deformation of the tube material. The fact that the pressure of the fluid transported in the conduit formed by the two tubes 3 and 4 may influence both the second sealing portion 10 and the lateral sealing por- tions 13 and 14, via the recesses 17 and 18, and force them to abut sealingly against the inner surface of the outer tube 4 and the side walls of the groove 7, respec- tively, contributes to ensuring a proper seal both before and after a possible relaxation.

Fig. 5 illustrates the function of the sealing ring 1 when the pressure of the fluid acting on the sealing ring is higher at one side thereof. In Fig. 5, the seal- ing ring 1 is subjected to a higher pressure at its left side, which causes the second sealing portion 10 to be displaced to the right. However, this displacement does not result in a complete loss of sealing effect, since the second sealing portion 10 rests on the lateral seal- ing portion 13 and the lateral sealing portion 14 main- tains its engagement with the side wall of the groove 7.

As is evident from the above description, the seal- ing ring according to the invention has a large number of advantages. It can be easily assembled in the groove while being uniformly stretched and it will maintain the seal of the gap even if a relaxation of the tubes should occur or the fluid pressure at one side of the sealing ring should be higher than at its other side.

The invention can be modified within the scope of the appended claims.