MIL-HDBK-1027/1B
in height and should discharge vertically upward. The discharge
vents should be equipped with a loose rain cap so that it will
not restrict the flow of propane vapor through such vent. The
rain cap or end of the vent should be installed to direct the
discharge vertically upward only. It is preferable to install
the pressure relief valves on a multiport manifold so that one
valve at a time can be shut off for repair or replacement while
the tank is properly protected by the remaining valve or valves
which are still in service and cannot be shut off, thus,
ensuring full required relieving capacity. The vertical
discharge of propane vapor 2150 mm above the top of the
container assists in dispersing propane in a general safe
manner.
f) Storage tank liquid and vapor operating
connections are to be equipped with internal valves. These
internal valves function as a primary shutoff valve and have
built-in excess flow protection. The valves are to be operated
manually at the installed location, or from a remote location
via pneumatic actuator. Provide a fusible plug at the valve
location to close the valve in the event of fire.
g) The water drain discharge opening of the pressure
relief valves must be equipped with a diverter to deflect any
product flow when the valve operates away from impingement on
the tank or an adjoining tank. This is necessary to prevent a
hot spot and a possible tank shell failure if such discharge
would become ignited.
h) Each connection to the storage tank should be
equipped
with an excess flow valve or a backflow check valve as
required
in NFPA 58 except for the pressure relief valve and
openings
of 1 mm or smaller. The container should also be
equipped
with a pressure gauge.
i) Liquid piping between shutoff points should be
equipped with a hydrostatic pressure relief valve to relieve the
pressure caused by an increase in the liquid temperature
resulting in an increase in pressure when the shutoff valves are
in a closed position.
j) Accuracy in filling the tanks is important because
of the expansion of the liquid as its temperature rises. The
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