Third Edition

Vacuum Relief Valve — a spring-loaded valve
mounted at the top of some nonpressure tank cars,
designed to open and allow air into the tank if an
excessive vacuum is formed that may cause the tank to
collapse. A vacuum relief valve should not be depressed
to determine if there is pressure in the tank. Doing so
may dislodge the sealing component causing the device
to leak vapor or liquid.
Valves — A device attached to a tank car tank designed
to control the flow of lading into and out of the tank.
Purposes include, but are not limited to: measure fluid
pressure and temperature, sample fluids in the tank,
detect or determine liquid levels, or relieve overpressures
for the purposes of emergency relief or
temperature control.
Vapor Line — a pipe equipped with a valve, cap, or
blind flange closure that extends to the top of the tank
through which vapor is introduced or removed during
loading or unloading. On a nonpressure tank car, this
device is usually called an air line and is used to introduce
compressed air or vapor, or an inert gas to unload the
car.
Vapor Space — the space in a tank above the liquid;
may also be referred to as outage.
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