Thermal relief valve is required for liquif filled service pipe, and for the blocked in piping fluid of up to 500 l and exposed to hotter fluid operating condition (either to sun or to heat tracing system). Normally people tend to install TRV instead of valve with cavities (check valve also can do the job with drilled check valve). or even small bypass check valve is also acceptable.
unless TRV is not installed i n the system, then small bore bypass valve is acceptable.
We replaced all the reliefs on our WKM power seal and Saf t seal valves with 3/8" tubing and check valves. The termination point was back into the line on a side of the valve that had other relief systems. As a matter of fact we removed all relief valves between block valves and installed the check valves abck to a single point that was protected. We save several thousand dollars per year inspecting the relief valves under DOT regulations and we were applauded by DOT for this move. We worked with Foster valve and modified their valve to include this check valve system with a return point into a tap on the valve flane (like an orifice flang tap).
