A vacuum pressure relief valve is a special piece of chemical process equipment that provides overpressure relief as well as internal vacuum relief for low-pressure storage tanks. Certain scenarios could cause the pressure in the storage tank to rise above the pressure rating of the tank and can include a fire around the tank. A fire could cause the liquid to vaporize, increasing the pressure. A vacuum could also form if the liquid contents of the storage tank are pumped out too fast. This could crumple the tank, causing a hazardous situation. Properly sizing a vacuum pressure relief valves is critical to plant safety.
Determine the maximum amount of vapor that could be generated if there is a fire near the storage tank. This is done using the formulas found in the resource listed below and represents the minimum flow rate capacity of the pressure side of the relief valve. The value is typically calculated in volumetric units of Standard Cubic Feet per Hour (SCFH) and represents what the valve must release to relieve the pressure.
Determine the maximum amount of vapor that is needed to break the vacuum formed if the storage tank liquid contents are pumped out too quickly. This is typically caused when certain controls fail to operate the pump correctly and the liquid volume leaves the tank creating a void vacuum. The resource listed below is also used and the flow-rate capacity of the vacuum side of the relief valve. The value is typically calculated in volumetric units of SCFH and represents what the valve must flow to break the vacuum.
Select a pressure vacuum relief valve that has the capacity specifications to flow the minimum volume of vapor generated from a fire and the minimum volume of void volume created from pump out.