Coupling Movement Under Pressure
Internal pressure may cause pipe movement if there is inadequate restraint. However, it can also cause coupling movement. A Viking Johnson stepped coupling is in effect a reducer, and internal pressure will tend to push it towards the smaller diameter pipe. Under normal circumstances, i.e. modest diameter reduction, buried service, standard water pressures etc., soil and pipe friction are sufficient to prevent coupling movement.
However, for larger diameter and for above ground service, and in particular higher pressures, the pressure thrust acting on the stepped coupling sleeve can be sufficient to cause coupling movement and consequent disengagement. Positive steps must be taken to restrain the coupling to prevent movement along the pipe. This may take the form of harness rods, stops on the pipe or within the coupling or encasement in concrete.
Alternatively, the use of Viking Johnson’s UltraGrip restrained fittings offer a cost-effective solution that prevents the coupling / stepped coupling from sliding along the smaller pipe.
