Once it's determined that ALL of the application parameters are OK for the plastic component, it is impotrant to look at how the plastic component is installed. Stress on the plastic valve or strainer is the single most important installation factor to consider. Stress can cause immediate damage or it can build up over time and cause damage later on. One is improper alignment of the plastic component in the metal piping system. If either one has to be forced into position, it s sure to cause problems.
Thermal expansion can be a problem is some applications.
Expansion joints can help compensate for this. Another solution is to install plastic pipe on the inlet and outlet of the valve or strainer to isolate it from the metal pipe. Plastic valves and pipeline strainers can be used successfully in many metal piping systems. You just have to be aware of all of the application parameters and how they relate to the plastic component. Not all applications are the same and the recommendations that have been made here may not apply in all cases.