Model No: 121

Storagetech™’s Model 121 Pressure-Vacuum Relief Valve provides protection to bulk storage tanks and vessels from over and under pressurisation. The valves are mounted on the tank roof flange or a vent pipe from the vapour space.

In the closed position the pressure relief pallet and diaphragm assembly is held tightly against a seal to prevent the loss of vapour to atmosphere. As the internal pressure in the tank increases, due to product filling and vapour development, the pressure in tank increases and in the event that the set pressure of the unit is reached, the diaphragm will open and discharge the gas to atmosphere. The opening set-point is selectable from a range between +61 mbar and +1000 mbar (+24 inch W.C. and 400 inch W.C.), and the valve will reseal when the tank returns to a safe pressure.

The vacuum pallet and diaphragm assembly is similarly maintained in the closed position. As the internal pressure in the tank reduces, due to emptying, the balance between the tank pressure and the external atmospheric pressure changes, and when the set pressure of the unit is reached, the diaphragm opens to admit air and rebalance the internal pressure. The vacuum set-point is selectable from a range between +61 mbar and +1000 mbar (+24 inch W.C. and 400 inch W.C.). The valve will reseal when the tank returns to a safe pressure.

The integrity of the seal is tested for leakage in accordance with API Standard 2521 – Use of Pressure-Vacuum Vent Valves for Atmospheric Loss.

The size of the vent should be calculated in accordance with API Standard 2000 (ISO 28300) – Venting Atmospheric and Low-Pressure Storage Tanks or other international standards.