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

Answer 1

The blow-off valve should not be confused with a waste-gate. The waste-gate is a device that by-passes the turbine wheel of the turbocharger, limiting the shaft-speed of the turbocharger. Therefore, limiting the boost (pressure) that the compressor generates and keeping the turbocharger from over-speeding. A blow-off valve is mounted in the intake Plumbing between the turbocharger compressor and the throttle plate. The blow-off valve is a second safety measure against the turbocharger over-boosting and damaging the engine. The blow-off valve is more commonly used to keep the turbocharger spinning when the throttle plate is suddenly closed. When the turbocharger is generating maximum boost pressure at full throttle and then the throttle is suddenly closed, compressed air coming from the compressor slams against the throttle, generating extremely high pressures that travel backwards to the compressor stopping the compressor from spinning. When the throttle plate is again opened, the engine must spool the turbocharger shaft again. The effects of this high pressure can also be very damaging to the turbocharger.