Each valve installed in plastic pipe must be designed so as to protect the plastic material against excessive torsional or shearing loads when the valve or shutoff is operated, and from any other secondary stresses that might be exerted through the valve or its enclosure.
Compiled from the Electronic Code of Federal Regulations (eCFR), an editorial compilation and not an official legal edition of the CFR. The official text is the Federal Register and the annual CFR edition. §192.193 on eCFR.