Fire sprinkler system comprising a network of CPVC pipe lengths in which at least some of the pipe lengths are interconnected with mechanical devices having resilient sealing members that are chemically compatible with the CPVC composition. Repairs and system modifications can be made without the use of solvent cement. In-line joints are formed with a coupling device including a pair of arcuate coupling segments having a first end, a second end, and an interior concave surface extending between the first end and the second end. A longitudinal channel extends along the concave surface. At least one mechanical fastener is operative to detachably connect the pair of coupling segments. A resilient annular seal is located within the longitudinal channel of each segment. A branching device connects a branch pipe to a main pipe through an orifice in the main pipe utilizing a saddle-like sealing member. The pipe assemblies are able to pass UL testing protocols for wet fire sprinkler systems.