Home / Gadgets / Blow-Off Valves: Working Principle and Functions

Blow-Off Valves: Working Principle and Functions

Power and speed enthusiasts depend heavily on the turbo kids to increase power out put from the engines. More and more people are seeking better ways to increase the power output, protect the engine also increase efficiency. Blow-off valves provide one of the most effective ways to achieve this.

Working Principle

The blow-off valve(BOV) is actually an enhancement, rather than an integral part of the turbo kit. It is normally attached to the intake manifold, between the turbo air pump and the throttle valve. When the driver wants to switch gears, they usually release the throttle pedal, which closes the throttle valve. At this point, the turbo is still spinning, thus delivering more boost to the intake manifold. To maintain this rev, there is need to release some pressure from the inlet manifold. This means that when the driver presses the throttle pedal again, the turbo will still be turning, allowing for smooth transitions, and continuous power output.

When the throttle plate is open, for example when revving, or accelerating, the air pressure is equal on both sides of the blow valve. However, when the throttle is closed, like when shifting gears or decelerating, there is a vacuum formed in the inlet manifold. When this is combined with the compressed air from the turbo kit, it forces the BOV valve open, thus allowing for pressure relief.


The primary function of the blow-off valve is to release pressure form the intake manifold section of the turbo kit. A regular turbo kit is prone to lag due to the high turbine rev speeds. This lag leads to loss of power and general inefficiency. The blow-off valve aids in maintaining the rev for a longer period. This allows the driver to easily maintain the momentum and reduce lag when changing shifts.
The second function is to reduce wear on the turbo kit. As earlier mentioned, the turbo shaft spins at high speeds (around 150,000rpm). Such high speeds are associated with high temperatures and increased wear on the components, especially the shaft. By reducing the pressure and the lag on the system, the valve does reduce the wear.
Thirdly, the valve adds on some tuning perks. There is a noted hissing sound when the driver changes shifts, due to the released pressure. Most racing and car fanatics find this hiss quite a gist. Some people actually install this component for this function, rather than the primary function of efficiency.
The BOV prevents the detrimental effects associated with a compression surge; that is, releases the compressed air into the atmosphere, or recirculates, when it is not required. When the throttle valve is open, there is the continuous surge of air compressed air into the system. However, when the throttle is suddenly closed, the incoming boost bounces back into the turbo. This can damage the air pump wheel, shaft and bearings.

Not all turbocharged engines require the BOV valve though. Others integrate a diverter valve, which serves the same purpose albeit on a different working system. The blow-off valve is not recommended for MAF- type systems, as the sudden release of the air into the atmosphere results to stalling, engine hesitation and sometimes flooding. They instead use a bypass valve to divert the pressure back into the turbo system.

Leave a Reply

Your email address will not be published. Required fields are marked *