Marine PV valve(pressure/vacuum valve for cargo oil tank)is also called as high-velocity relief valve, high velocity P/V valve, generally used in the relief system of the oil tanker and chemical tanker, according to the current regulations IMO and IBC.The purpose of the high velocity valve is to provide automatic control of pressure differentials during liquid cargo ship loading, voyage,ballasting and de-ballasting without any manual operation, also, it provides auto-protection against fire and explosions on deck. Additionally in the event that the inert gas system can not supply gas promptly, the vacuum valve can auto open to protect the tank against excessive vacuum when de-ballasting on dock. Normal, when the pressure risen in tank because of temperature or loading, the pressure valve open automatically and vent gas. When the pressure of tank come to pressure differentials, the vacuum valve or pressure valve all can be automatic resetted. If an ignition occurs outside the tank space, the flames will be quenched in the flame trap.
A gas freeing cover is necessary while doing other works fo the tank such as cleaing, removing the gas. Becaues such works needs ventilation and the pressure can not work when the pressure is not low or without pressure.
The pressure valve can not be opened manually, and it works with the velocity oof not smaller than 30m/s.