17-400 series pressure only relief valves are engineered to protect against excessive pressure buildup due to thermal expansion in hot water supply systems. Both models are CSA certified to ANSI Z21.22 Relief Valves for Hot Water Supply Systems. In addition the 17-402 is design certified to ASME Section IV for hot water relief. Connection Sizes 1/2 (Model 17-401) and 3/4 (Model 17-402) CSA Verified to ANSI Z21.22 Pressure Settings 75 thru 150 psi @ 250 F max. ASME Section IV Hot Water, Model 17-402 Only