Mechanical couplings for joining pipe elements together end-to-end comprise interconnectable segments that are positionable circumferentially surrounding the end portions of pipe elements. The term “pipe element” is used herein to describe any pipe-like item or component having a pipe like form. Pipe elements include pipe stock, pipe fittings such as elbows, caps and tees as well as fluid control components such as valves, reducers, strainers, restrictors, pressure regulators and the like.
Each mechanical coupling segment comprises a housing having arcuate surfaces which project radially inwardly from the housing and engage plain end pipe elements, shoulder end pipe elements, or circumferential grooves that extend around each of the pipe elements to be joined. Engagement between the arcuate surfaces and the pipe elements provides mechanical restraint to the joint and ensures that the pipe elements remain coupled even under high internal pressure and external forces. The housings define an annular channel that receives a gasket or seal, typically an elastomeric ring which engages the ends of each pipe element and cooperates with the segments to provide a fluid tight joint. The segments have connection members, typically in the form of lugs which project outwardly from the housings. The lugs are adapted to receive fasteners, such as nuts and bolts, which are adjustably tightenable to draw the segments toward one another.
For installation ready couplings of the type disclosed in U.S. Pat. No. 7,086,131 to Gibb et al., the coupling segments are preassembled at the factory, i.e., bolted together, but supported on the seal in spaced apart relation, one of the features which allow the pipe elements to be inserted into the coupling without first disassembling it. To facilitate positioning of the pipe elements within the coupling so that their arcuate surfaces align with circumferential grooves in the pipe elements the seal will have a stop comprising a circumferential ring. The stop ring is positioned concentric with the seal between the sealing surfaces which engage the pipe elements. The stop ring projects radially inwardly toward the center of the seal. Pipe elements are inserted into the seal between the segments until they contact the stop ring. The bolts holding the segments together are then tightened, drawing the segments toward one another to compress the seal against the pipe elements and engage the arcuate surfaces with the grooves to effect a fluid tight mechanical joint.
Typically, the stop ring is made of the same flexible, resilient material as the seal. One disadvantage to such a construction is that a stop ring made of a soft, flexible material such as an elastomer can be damaged when pinched between the ends of the pipe elements, for example, during a bending test of the pipe joint or a major seismic event, where the pipe elements held by the coupling are substantially angularly displaced relative to the coupling. The pinched portion of the stop may become deformed, which is considered unacceptable for some applications. There is clearly a need for a stop ring which does not suffer the disadvantages described above to promote safety in critical fire protection systems while allowing for the economic advantages permitted by the use of installation ready couplings.