Pressure-vacuum (breather) valve

ISO 10628-2 (group 23, safety valves and fittings) / PIP PIC001 / API 520 / API 2000

Drawn as

A housing on a tank nozzle with two arrows inside: one pointing up (pressure relief out) and one pointing down (vacuum relief in), each over a weighted pallet.

Meaning

Tank breather valve on atmospheric tanks (API 650/2000). It vents vapour when the tank fills or heats and lets air in when it empties. No dedicated component; note it on the storage-tank.

Variants

Vacuum breakers alone show only the down arrow
Often combined with a flame arrester below it
Some legends draw a PSV symbol with "P/V" beside it