Imagine your turbocharger spinning at 80,000 rpm. It's pumping a truckload of air through your inlet pipes at nearly 90 metres per second ... and then you close the throttle to change gears. That air suddenly has nowhere to go and it is the job of the dump valve (sometimes known as a Blow-Off Valve) to then open and vent the excess pressure. If your valve is not up to the task, a large pressure spike can occur in the inlet piping and the air will try to force its way back out through the turbo compressor wheel. This slows the compressor wheel rapidly and creates huge torsional, thrust and impact loads on the turbo's rotating and bearing assembly (a condition commonly known as "compressor surge"). A dump valve protects your turbo from compressor surge by venting sufficient air.

The majority of factory installed dump valves (also referred to as bypass or diverter valves) are designed to leak pressure at elevated boost levels as preventative measure against boost spikes. However, if you are intentionally raising the boost level in your car for more power, a dump valve will aid you in this task by ensuring that all of the pressurised air makes it to the engine.