What is the purpose of pressure-vacuum relief valves?

Pressure-vacuum relief valves play a crucial role in maintaining the integrity of storage tanks by allowing them to operate safely at atmospheric pressure. Their primary function is to prevent the tank from becoming either over-pressurized or under-pressurized due to temperature changes or liquid loading and unloading operations.

When a tank is filled, the liquid displaces the air, which can lead to an increase in internal pressure. The pressure relief mechanism of the valve opens to release excess pressure when it exceeds a certain threshold. Conversely, if the liquid is withdrawn from the tank, the reduction in the internal volume can create a vacuum. The vacuum relief function allows air to enter the tank, preventing the risk of collapse due to external atmospheric pressure.

In this way, pressure-vacuum relief valves maintain a balanced and stable pressure environment within the tank, ensuring both safety and operational efficiency. This maintenance of atmospheric pressure is essential for the longevity and safe handling of materials stored within the tank, particularly hazardous cargo.