Compression sealing provides greater stability minimising lateral movements. It also compensates for irregularities and blemishes on the surface of the spigot.The sealing function is dependent on initial compression and residual stress at long term. Stress relaxation tests indicate the suitability of the material for long-term use and help predict the service life of the coupling. As an indication compression for sealing is less than 20% for a 60 IRHD element that is often preferred as an optimum for most applications.Higher compression values may result in increased push-in force to assemble the joint and may even damage the rubber element.
The lip seal adds flexibility and the sealing function is not purely dependent on the residual stress. Compression/deflection shall be to the magnitude of greater than 50% without appreciable increase in push-in force. This flexibility in lips will accommodate lateral movements and deflection in service life due to ground movements and still ensure effective sealing.
Deflection and Flexibility
During their life, all pipelines are subject to lateral movements and deflections. The couplings are designed so as to guarantee sealing under these conditions. The couplings are tested to EN295-3 for shear and flex resistance.
Packing rings in Jacking Couplings are compressed progressively during jacking. The ground area of the spigot should accommodate the effect of this compression and consequent reduction in effective length so as not to damage the housing of the coupling.
AS PER PIPE TYPE AND DIAMETER RECESS DIMENSIONS GL AND GD ARE TO BE DISCUSSED
Dimension gl
This will be calculated to allow full compression of the packer ring and to allow an agreed deflection having lip seal 1 and compression seal 2 in full function.
Dimension gd
Ideally, this will be minimum to give maximum pressure surface for jacking force transfer. A recess of 10 mm is achievable in most cases by optimising the rubber and housing profile.
