What is the blow cock?

Answer 1

A "blowcock", also known as a "blow-off valve" is a cock (valve) in the blow-off pipe of a boiler. Since blow-off valves are installed at low points of the boiler water system, it is obvious that one of their principal uses is to help remove suspended solids or impurities, particularly those that tend toward sedimentation. Secondarily then, it is also obvious that is blowing down, a portion of the boiler water is discharged thereby reducing the water level in the boiler. This function therefore aids as a safety measure, in avoiding carryover of water from the main steam drum in the event of high boiler water-level for whatever reason. A third use of these valves, but far less frequent, is the introduction of boiler cleaning acid to the boiler, and again draining of this acid after the boiler is acid-washed. Many boiler operators choose to pump this fluid through the blow-off valves, since they usually are a handy means of ready access to the boiler.

In the case of a car, the "blow cock", aka blowoff valve(BOV) or dump valve 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. Blowoff valves relieve the damaging effects of compressor "surge loading" by allowing the compressed air to vent to atmosphere, making a distinct hissing sound, or recirculated into the intake upstream of the compressor inlet.