Need a spare Over Pressure Valve (OPV) for your Lift Bag or BCD? XS Scuba's OPV comes in both 1" and 2" (2.5 and 5.1 cm) Diameters. OPV is made from Durable Noncorrosive Plastic with a Durable Corrosion Resistant Spring. Valve has a Pull Cord with Plastic Knob for Easy use. If your Lift Bag or BCD is Over-Inflated the Valve will automatically Compress the Valve Spring and Relive Pressure to avoid rupture of the Bag or BCD. OPV makes a great Save-a-Dive Kit item.