A highly versatile pipe coupling is especially useful in connecting or repairing two ends of pipe that is not coaxially aligned. Bushings allow the same coupling components to connect pipe of different material and wall thickness. When repairing a broken pipe it is common practice to cut away the section of the pipe which is cracked or leaks and connect the resulting two pipe ends by an appropriate pipe coupling. Generally a pipe coupling will comprise a sleeve, two deformable gaskets, two pressure plates and means to connect the two pressure plates.Typically, to install a pipe coupling a deformable gasket and a pressure plate are placed around one pipe end. A sleeve is then mounted on that pipe end and a pressure plate and gasket are mounted on the other pipe end. The sleeve is then moved to overlay both pipe ends. Connectors, usually bolts, are utilized to draw the two pressure plates together and fix them in place; the pressure plates squeezing the deformable gasket between the inner wall of the sleeve and the outer wall of the pipe thereby forming a fluid tight connection between the sleeve and the pipe. When the coupling has achieved a fluid tight connection on both ends of the sleeve, the repair is completed. Such a coupling is most effective if the pipe ends are coaxially aligned. If the pipe ends are not aligned the tension drawing the two pressure plates together will not be acting uniformly about at least one of the pipe ends. Thus the deformable gasket may become skewed on one of the pipe ends making a fluid tight seal very hard to achieve. The pressure plates should fit closely about each pipe section and squeeze the deformable gasket between the sleeve and the pipe surface without extruding the gasket out between the pressure plate and the pipe; thus the pressure plates should have an inner diameter approximating the pipe outer diameter. Generally the inner diameter of the pipe is known, i.E., it will be known that a 4-inch pipe is to be repaired. However, the outer diameter of the pipe to be repaired is not always known, and this is the critical dimension for a pipe coupling.
Various makes and compositions of pipes, although they all have the appropriate specified inner diameter, may have significantly varying outer diameters. For example, an asbestos cement 4-inch pipe will have a significantly greater outer diameter than a cast iron 4-inch pipe. The situation where the pipe outer diameter is unknown often occurs when the repairman must dig into the ground to find and repair the broken pipe. In such a situation, the exact length of the defective portion of the pipe cannot be ascertained beforehand, and this further complicates the pipe coupling work.
