Australian Pipeline Valve - Installation, Operation and Maintenance Manual 23 API6D THROUGH CONDUIT EXPANDING GATE VALVE - AP400-405 SERIES 8.7 PRESSURE RELIEF VALVE OPTION Since an expanding gate valve seals against both the upstream and downstream seats, fluid trapped in the body cavity can cause excessive pressure. This may be due to a temperature change which can cause thermal expansion of the fluid, or the body may be full of liquid and over-pressured when lubricating the seats. Pressure relief valves can be fitted to the valve body cavity on request. A typical installation is shown in Figure 4. As an alternate, the valve can be provided with the upstream relief piping which relieves excess body pressure to the upstream side of the valve (Figure 5). Important: Needle valves must remain open except during testing. Any pressure relief valve must be tested periodically to ensure reliable functioning. The proper pressure relief settings are shown in this table below. NEVER remove the pressure relief valve. NEVER plug the pressure relief valve. REPLACE the pressure relief valve if it is leaking, fails to relieve at the proper set pressure, or fails to reseat after test. A pressure relief valve is an emergency safety device; it is not a substitute for draining the valve body or for taking other common sense safety precautions. The correct relief valves are available through APV service or sales representatives. Figure 5 Figure 4 PRESSURE CLASS OPERATING PRESSURE (psig) SHELL TEST (psig) RELIEF VALVE SETTING (psig) 150 275 425 375 300 720 1100 820 400 960 1450 1060 600 1440 2175 1540 900 2160 3250 2260