Method of branching off a tube

Method in branching off a tube (10) wherein an oval aperture (11) is made in the tube wall and a tube element (12) having a flange (13) at one end thereof, is inserted through the oval aperture from the outside of the tube. The flange is pressed against the inside surface of the tube by means of a ring (15) provided on the tube element, which is engaged with the outside surface of the tube and is fixedly secured to the tube element, a sealing ring being located between said flange on the tube element and the inside surface of the tube.

The present invention relates to a method in branching off a tube wherein 
an oval aperture is made in the tube wall and a tube element is inserted 
into the aperture from the outside and is secured to the tube. 
Concrete tubes are branched off in this way by using an insert socket 
comprising an injection moulded tube element of PVC which forms an outside 
abutment collar and is "sanded" on the outside surface thereof. When an 
aperture has been made in the concrete tube, the insert socket is inserted 
from the outside into the aperture until the abutment collar engages the 
outside surface of the concrete tube, the insert socket then being fixedly 
positioned by a heavy concrete bead being moulded around the insert 
socket. 
The method cannot be applied to smooth PVC tubes. In that case there is 
used instead saddle branch tubes (which are used also in connection with 
concrete tubes). The saddle branch tube forms a substantially 
semi-cylindrical flange which is engaged with the outside surface of the 
main tube over the aperture made therein, the saddle branch tube at a 
guiding edge being inserted from the outside into the aperture to seal 
against the outside surface of the main tube by means of a sealing ring 
surrounding the aperture. Then, the saddle branch tube is fixedly 
positioned on the main tube and this can be effected by gluing the flange 
to the main tube. It can also be effected by clamping the flange to the 
main tube either by means of two straps around the main tube and the 
flange or by applying a complementary semi-cylindrical element to the 
outside of the main tube, located on the side opposite to the saddle 
branch tube and engaging by wedge action the flange thereof, said element 
being knocked into position while being axially displaced until the 
saddle branch tube is tight on the main tube. 
The prior art methods are relatively inconvenient, because several 
operational steps are required wherein expensive tube elements and other 
elements are used. Moreover, it may be difficult to obtain the necessary 
sealing at the branching-off. However, above all the prior art methods 
cannot be applied to corrugated double-wall tubes now commonly used. In 
that case it is necessary to join to the main tube prefabricated tube 
elements by using a slide socket. This method is not only expensive but 
also very unsuitable in case a main tube forming part of a surface or 
waste water conduit, is to be branched off when in use, because 
contaminated water and waste and/or faeces entrained therein will flow 
into the trench when the aperture is being made, which is very 
inconvenient for people working in the trench. Another method as far as 
corrugated double-wall tubes are concerned comprises insertion of 
prefabricated branch tube elements through apertures in the main tube, 
said elements being provided with a sealing ring on the edge thereof. This 
method is commonly used in connection with well tubes. Said latter method 
involves the risk of the sealing ring being dislocated or ineffective due 
to displacement of the branch tube element under the influence of ground 
movements. 
The purpose of the invention is to provide a method in branching off a tube 
which can be universally used for tubes of any type, smooth as well as 
corrugated, and which makes possible to provide a permanently leak-proof 
branching-off by simple operations and by using uncomplicated tube 
elements and other elements. Moreover, this method can also be applied 
without inconvenience to a tube conduit when in use, which is not the 
least important aspect in this connection. 
Said purpose is achieved by the method of the type referred to above 
wherein the tube element is inserted at a flange at one end thereof 
through the oval aperture and is pressed against the inside surface of the 
main tube by means of a ring provided on the tube element, which is 
engaged with the outside surface of the main tube and is secured to the 
tube element, a sealing ring being provided between the flange and the 
inside surface of the main tube. It is important that the branching-off is 
sealed on the inside surface of the main tube where sealing always can be 
effected against a smooth surface also in case of corrugated double-wall 
tubes.

In the wall of a conventional tube 10, such as a plastic tube, there is 
made at the location where said tube is to be branched off, an oval 
aperture 11 which is initially marked by using a suitable templet. Then, 
the aperture is made by using a piercing saw. The tube element to be 
connected with the tube 10 to form the branch tube thereof is designated 
12, and for working the method of the invention this tube element forms a 
flange 13 at one end thereof. The shape and size of the aperture 11 have 
to be designed geometrically in relation to the diameter of the tube 10 
and the diameter of the tube element 12, but said aperture must be 
sufficiently large to allow the flange 13 to be inserted through the 
aperture from the outside of the tube 10 and to be engaged with the inside 
surface of the tube along the entire circumference of the aperture. If the 
tube element 12 is made of plastic material such as PVC, as is usually the 
case, it has some inherent elasticity so that it can be compressed 
transversely, and in that case it has been found that the shape and size 
of the aperture can be substantially in agreement with the shape and size 
of the insert end opening of the tube element, said opening being 
positioned in a plane inclined to the axis of said element at an angle 
corresponding to the branching-off angle. Thus, even if the flange 13 
projecting from the edge of said end opening of the tube element, has an 
outer dimension which is larger than the aperture 11, it can be 
manipulated through the aperture without difficulties, possibly by 
compressing the tube element transversely, so as to be brought into said 
position engaging the inside surface of the tube 10. However, before the 
tube element is inserted a sealing ring 14 should be passed onto said tube 
element against the flange 13 so as to seal between the flange and the 
inside surface of the tube as shown in FIG. 2. This sealing ring can be a 
flat sealing ring as shown or an O ring located in a channel or groove in 
the flange 13. The sealing ring should be rather thin, which is true also 
as far as the flange is concerned so as to minimize disturbance of the 
flow through the tube 10 by inwardly projecting portions of the 
branching-off. 
In order to lock the tube element 12 in the intended position thereof an 
annular sleeve 15 is passed onto the tube element 12 and is tightly 
pressed against the outside surface of the tube 10. Possibly, an elastic 
ring 16 may be passed onto the tube element so as to be located between 
the outside surface of the tube and a flange 17 at one end of the sleeve 
15 as shown in FIG. 2. When the flange 17 is pressed against the outside 
surface of the tube, the elastic ring 16 will be compressed. The purpose 
of said ring primarily is not to seal although it can fulfil this function 
on a tube 10 having a smooth outside surface, but to provide a spring 
action between the flange 17 and the outside surface of the tube 10 in 
order to maintain automatically the seal between the flange 13 and the 
inside surface of the tube 10 by adjustment of the flange 13 under the 
spring bias of the ring 16 when the sealing ring 14 ages. 
In order to position fixedly the sleeve 15 on the tube element 12 in the 
intended position thereof pressed against the tube 10, several 
arrangements may be used. E.g. in the inside surface of the sleeve 15 and 
the outside surface of the tube element 12, grooves may be provided which 
register in the intended position of the sleeve 15, a strap member being 
slid through a tangential opening into the annular passage formed by the 
grooves to lock the sleeve 15 and the tube element 12 to each other in the 
axial direction thereof. In order to allow adjustment several grooves may 
be provided, the grooves in the sleeve having another spacing than the 
grooves in the tube element such that different grooves register in 
dependence on the relative displaced position of the sleeve and the tube 
element. 
FIG. 3 discloses a further embodiment wherein a groove 18 is provided in 
the sleeve 15 and a groove 19 is provided in the tube element 12, a strap 
member 20 being slid into the grooves to lock the sleeve and the tube 
element, respectively, against relative displacement in the directions 
indicated by arrows. The pressure then can be adjusted by sliding strap 
members of different widths into the grooves. 
The tube element can be corrugated on the outside thereof and in that case 
the strap member 20 can have T-shaped cross section to engage into the 
groove 18 in the sleeve 15 and in a proper groove in the corrugated tube 
element. 
FIG. 4 discloses a still further embodiment of the locking mechanism, 
wherein the sleeve 15 is dispensed with and a ring 21 only, corresponding 
to flange 17 formed by the sleeve 15, is provided. The tube element 12 has 
two or more shoulder portions 22 which are chamfered at the end thereof 
facing away from the insert end of the tube element as shown at 23, so 
that the ring 21 can be displaced along the tube element 12 and passed 
over the shoulder portions to engage by snap action behind the shoulder 
portions in a position wherein the ring presses tightly the elastic ring 
16 against the outside surface of the tube 10. It is also possible to 
arrange the ring 21 as a clamp ring which is tightened around the tube 
element 12, no shoulder portions being provided in that case. 
It should be mentioned that the method of the invention can be applied also 
to tubes having a relining of polyethylene. Such relining has a tendency 
to fold into the tube when the aperture 11 is made, which is of no 
importance, however, when the tube is branched off as described above.