blowoff valve
dump valve

Blowoff valve - An element of modern turbocharged vehicles.

A blowoff valve is connected by a vacuum hose to the intake manifold after the throttle plate.

A blowoff valve (BOV) or dump valve is a pressure release system present in most turbocharged engines.

When the throttle is closed, the relative manifold pressure drops below atmospheric pressure and the resulting pressure differential operates the blowoff valve's piston.

One notable aspect of the turbo versions was that they were not intercooled and there was no form of blowoff valve, only an emergency pressure release valve.

It is also possible to actually release large amounts of already compressed air similar to a blowoff valve but on a constant basis to maintain desired boost at the intake manifold.

By using a blow-through method, the MAF won't be affected by the blowoff valve opening as the pressure is vented before the air reaches the MAF.

An alternative method for utilizing both a MAF and a blowoff valve is to have the MAF located down stream between the intercooler and the throttle plate.

Some military diving rebreathers have a diffuser over the blowoff valve, which helps to conceal the diver's presence by masking the release of bubbles, by breaking them up to sizes which are less easily detected.

Mr. McGrath said that the foreman at the site had failed to open a drain on the bottom of the underground pipe known as a "blowoff valve," apparently because an extension rod that controls it was jammed.

Blowoff valves relieve the damaging effects of compressor "surge loading" by allowing the compressed air to vent to the atmosphere, making a distinct hissing sound, or recirculate into the intake upstream of the compressor inlet.

In the case where a mass airflow sensor (MAF) is used and is located upstream from the blowoff valve, the engine control unit (ECU) will inject excess fuel because the atmospherically vented air is not subtracted from the intake charge measurements.