Bypass valve

[1] (BPV) A valve that can open and allow fluid or gas to pass through in other than its normal channel.
[2] A switching device (silicon-controlled rectifier or, in the past, mercury arc valve), connected across the converter switching devices of a high-voltage dc transmission system, normally not conducting but able to maintain flow of current whenever the main conducting devices have to be interrupted.
[3] A valve by which the flow of fluid in a system may be directed past some part of the system through which it normally flows, e.g., an oil-filter in a lubrication system.
See also air bypass valve, oil cooler bypass valve, oil filter bypass valve