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 1 and 28.1 W.C. (2.5 and 70 mbar). The valve will reseal when the tank returns to a safe pressure.
Unlike the conventional PVRV, the Model 102 discharges vapour and takes in air through the same vent, consequently a single end-of-line flame arrestor provides protection from the potential ingress of flames emanating from an external fire.
The integral deflagration flame arrestor is designed to minimise pressure loss and with an element constructed with a <0.65mm Maximum Experimental Safe Gap is suitable for gas groups IIB and IIA.
Several features are inherent in the valve design to ensure a smooth, positive and effective operation. The body is self-draining and drip design prevents condensate from settling on seating surfaces. A diaphragm and seal manufactured from Teflon reduce the possibility of ice formation and sticky residues hindering the valve opening, while the pallet assembly moves freely on its guide post.