High velocity Pressure Vaccum valve (also known as P/V valve). The international name is: High velocity Pressure / Vacuum valve (PV valve).
Application of High velocity Pressure Vaccum valve:
When down / return: If the cargo cellar is closed, the steam pressure will deform the cargo cellar. The Pressure head helps the valve exhale and the Vacuum head helps the valve to inhale. Balance the vapor pressure in the cargo cellar with the atmosphere.
When the temperature changes, rows and vapors expand as well. Valves do the same task as above.
Why need High velocity Pressure Vaccum valve, high-speed breathing?
Ensure safety: When discharged at a speed of >30m / s, the fire will not be able to penetrate the cargo tunnel.
To ensure down-line and return speeds. Fast breathing valves, large flow will help to get off the line faster.
High-velocity vent: A device intended to prevent the passage of flame and composed of a mechanic valve which could adjust the airflow opening based on the inlet pressure to ensure jet velocity ≥ 30 m/s (98 ft/s) so as to prevent the passage of flame.