Because HDPE pipe is different from ductile iron pipe, steel pipe, PVC pipe etc common pipe, HDPE pipe is easy to be deformed, so for PE pipe, judberd designed restrained type flange adaptor, why it is called restrained flange adaptor?  

Because we designed extra brass grip ring (Figure NO.1 as below) based on normal rubber ring sealing,   the role of the brass grip ring is to grip HDPE pipe tightly and prevent the pipe from moving because of deformation.You know deformation may cause sealing failure.

Judberd has designed a bevelled design on the gland of the restrained flange adaptor (Figure No.2 as below) to match with the brass grip ring, so that when we tighten the bolt (Figure No.3 as below) with a spanner, the gland (Figure No.2 as below) is squeezed with the brass grip ring under the pressure of the bolt. Then the brass grip ring will move toward outside the flange adaptor ,and the grip brass ring will be squeezed more and more when it move toward outside because the gland is more and more narrow, which will shrink the grip brass ring to make the inner diameter of brass grip ring smaller and smaller ,then it can grip the HDPE pipe more and more tightly.

 The gasket behind the grip ring (Figure No.5 as below) move towards the outside of the flange adaptor under water pressure, and you can see that our restrained flange adaptor body has a sloped contact surface with the gasket as the gasket move outwards, and the further the gasket move outwards, the less space there is, thus forming a compression of the gasket and then sealing is achieved.

Judberd designed this restrained flange adaptor and coupling with a short bolt design, which allows the two sides of the coupling to be tightened independently from each other, and at the same time can be tightened with a small torque (from 25N.m to 30N.m).