A valve which keeps the tank over pressure or under pressure within
approved, limits. P/V valve provides for the flow of the small volumes
of vapour, air or inert gas mixtures caused by thermal variations in a
cargo tank. The vacuum valve opens if the pressure in the tank falls
below a pre-set level – to draw air into the tank through a flame trap.
In the event of over-pressure, two release valves open to ensure that
venting is upwards and at high velocity, to avoid concentrations of gas
on deck.
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| under pressure |
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| over pressure |
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