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
