ince the introduction of PVC in the U.S. during the 1940's, thermoplastic valves, pipe and fittings have gained wide acceptance. They are often the material of choice for systems that were traditionally designed in metal. Unlike metal, however, plastic valves and components have a high resistance to corrosion, will not scale or rust, and will not contaminate sensitive fluids. Further, as non-conductors, they are immune to electrolytic and galvanic corrosion. Equally important, they contain nothing to leach out and contaminate sensitive fluids