Breather Valve, also known as direct acting Pressure/Vacuum Relief Valves, are special types of Relief Valves which are specifically designed for tank protection.
Pressure/Vacuum Relief Valves are used extensively on bulk storage tanks, including fixed roof tanks with floating covers, to minimize evaporation loss. The Valves prevent the build-up of excessive pressure or vacuum which can unbalance the system or damage the storage vessel.
Pressure and vacuum protection levels are controlled with weighted pallets or springs and can be combined to provide the required Pressure/Vacuum settings.
It is common to combine pallet and spring systems in one unit i.e. pressure settings require a spring section, whilst the vacuum settings use the pallet method.