What is a blow off valve and how does it work?

A blow-off valve, or BOV, is a pressure relief valve that is used in turbocharged or supercharged internal combustion engines. When the throttle is closed, vacuum is created in the intake manifold, and the BOV is opened to allow excess boost pressure to escape. This prevents the turbo or supercharger from overboosting and potentially causing engine damage.

BOVs work by using a diaphragm or piston to seal off the intake manifold from the turbo or supercharger. When the manifold vacuum is high, the diaphragm or piston is pulled closed, blocking the flow of boost pressure. As the manifold vacuum decreases, the diaphragm or piston is pushed open, allowing boost pressure to escape.

The size and type of BOV used in a particular engine depends on the amount of boost pressure that the engine produces. Small, low-pressure turbocharged engines may use a simple diaphragm-type BOV, while large, high-pressure turbocharged or supercharged engines may use a piston-type BOV or even a combination of both types of valves.

BOVs are an important part of any turbocharged or supercharged engine, and they play a vital role in preventing engine damage.