MIL-HDBK-1027/1B
liquid has been off-loaded from the transport to the storage,
there will be some residual propane vapor in the transport. The
vapor is recovered by switching the compressor valving so that
it will then draw vapor from the transport and discharge it into
the storage tank. This vapor piping to the storage tank should
discharge into the liquid of the tank and not into the vapor
space. This assists in condensing the vapor to liquid and thus
speeds up the transfer. The recovery of the vapor results in an
economic benefit.
l) Propane or water may be delivered to the storage
by tank cars. In such cases, a proper tank car unloading
facility must be installed. The facility should be a platform
facility adjacent to the tank car unloading location. The
facility should be equipped with liquid and vapor pipe lines and
a hose connection at the platform. The hose connection should
be of proper length to properly reach the tank car valve dome.
There will be two liquid hoses so that a connection can be made
to both liquid eduction valves on the tank car. These will be
connected to the platform liquid piping at a three-way fitting.
At the hose connection to this fitting, a backflow check valve
should be installed at each hose connection to prevent backflow
into the tank car. The tank car liquid education and the vapor
openings on the manhole cover plate are equipped with excess
flow valves on the underside of the manhole cover. Hose
connections are also equipped with shutoff valves in the
protective dome. A pressure relief valve is installed in the
center of the protective dome with an opening in the dome cover
above the relief valve. The tank car is equipped with a
sampling tube extending down from the manhole cover to the sump
at the tank bottom so that a sample of the propane or water may
be drawn off. There is also a thermometer well extending into
the car tank. The thermometer well have an antifreeze solution
in it to a height of about 310 mm to provide conductivity of
propane liquid temperature to the thermometer when it is
inserted in the well.
m) The transport trucks or tank cars should always
have the wheels blocked by chock blocks to prevent movement
while parked and especially while unloading. The transport
truck or tank car unloading point must be equipped with an
emergency shutoff valve to prevent a discharge from the storage
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