Bypass (valve)

In rebreather breathing sets, a bypass is a hand-operated valve that can be used to let more oxygen (or other breathing gas) into the breathing system, by-passing the cylinder's flow rate control valve.

A blowoff valve (BOV), dump valve or compressor bypass valve (CBV) is a pressure release system present in most turbocharged engines. Its purpose is to prevent compressor surge, and reduce wear on the turbocharger and engine. These valves relieve the damaging effects of compressor "surge loading" by allowing the compressed air to vent to the atmosphere (BOV case), making a distinct hissing sound, or recirculate into the intake upstream of the compressor inlet (CBV case).