Having a spare as a technical diver is routine. This Over Pressure Relief Valve can get you out of a jam if you find a problem with the one attached to your BCD. Many technical divers custom build their own BCD Hollis supplies all the required parts to do just that. The O.P.R. comes with a pull knob for easy venting of air when trimming buoyancy, is made from durable impact resistant polycarbonate plastic, makes a great safe-a-dive kit item.