What is blow off valve?

A blow off valve (BOV) is a mechanical valve used in turbocharged or supercharged engines to relieve the pressure built up in the intake manifold when the throttle is suddenly closed. This pressure, known as boost pressure, needs to be released to prevent damage to the turbocharger and other components of the engine.

When the throttle is closed, the boost pressure that has built up in the intake manifold can cause a surge of air to flow back into the turbocharger, causing it to slow down rapidly. This sudden deceleration can cause damage to the turbocharger blades and shaft.

The blow off valve releases this excess pressure by venting it to the atmosphere, creating the distinctive "pssh" or "whoosh" sound that is often associated with turbocharged engines. This helps to protect the turbocharger and prevent compressor surge, which can reduce the performance and longevity of the engine.

Blow off valves come in various types, including atmospheric, recirculating, and hybrid designs. Atmospheric blow off valves vent the excess pressure directly to the atmosphere, while recirculating blow off valves route it back into the intake system. Hybrid blow off valves combine the features of both types for optimal performance.

Overall, a blow off valve is an important component in turbocharged engines, helping to maintain performance and protect the engine from potential damage.