Sometimes referred to as a compressor relief valve, the compressor bypass valve is a mechanical device that makes use of vacuum action to release pressure from the intake system on various types of motors. Found in the design for many turbocharged and supercharged automobile engines, bypass valves are also found in the engines of various types of planes and in some train engine designs as well. Developed in the early 20th century, the efficiency and use of the compressor bypass valve has continued to be refined over the years.
Designed to function as a vacuum actuated valve, the compressor bypass valve helps to route the pressure generated within a turbo or supercharged engine back into the non-pressurized end of the intake system. At the same time, the pressure is not reintroduced into the mass airflow sensor, so the action of the valve does not inhibit overall efficiency of the use of air in the creation of power and motion. However, the bypass valve does make it possible for the intake system to avoid the generation of compressor surges that could result in spikes of pressure that would weaken the overall intake process.
The main function of the compressor bypass valve is to allow the escape of pressure during the segment of operation when the throttle plate is closed. Without the presence of the valve to allow the pressure to be rerouted, the pressurized air would simply crash into the plate, build up, and eventually be repelled back into the turbo. This strong wave of pressurized air would not only create additional wear on the turbo proper, but also slow and possible stop the action of the turbo altogether.
One of the first designs for the compressor bypass valve was included in the AEM, a design for an electric vehicle developed in France and released in 1924. Since that time, the compressor bypass valve has continued to be enhanced, allowing the basic function of the valve to easily adapt to larger and more powerful engines.