Thrust Restraint I sometimes see cartoons in advertisements for hubless couplings and the couplings are shown leaking. Does this really happen, and what would cause a coupling to leak?
Properly installed hubless couplings do not leak or fail. Hubless couplings used to join hubless pipe and fittings together utilize a rubber gasket sleeve which is compressed by a stainless steel shield and clamp assembly. On the few occasions in which leaks have occurred, the leaks were caused by movement in the joint and resulting partial separation. These movements are usually caused during tests when installers attempt to test multiple floors without proper thrust restraint. Thrust occurs when a column of water fills a vertical stack. A ten foot column of water (recommended for testing purposes) produces pressure of 4.3 PSI at the base of the column, but thrust increases as the diameter of the column of water increases. A four inch stack with ten feet of hydrostatic head produces 65 pounds of thrust at the base of the stack: a ten inch stack with the same ten feet of hydrostatic head produces 337 pounds of thrust even though the pressure in both stacks is only 4.3 PSI. This thrust
