How a Dump Valve Works

A dump valve--also commonly referred to as a blow-off valve, diverter valve or compressor bypass--is a pressure release valve that allows air to escape from the equipment that connects the turbocharger on a vehicle to the throttle.

The purpose of installing a dump valve can be one, or a few, of many things. The primary functions that dump valves accomplish are making an often desired noise--unique to turbocharged vehicles as air releases, allowing air to escape without backtracking through the airflow chambers, eliminating rattling in the turbocharger caused by backward airflow, increased fuel economy and lowered emissions.

Research has not been conclusive as to whether dump valves increase the life of a turbocharger, but many believe that the elimination of rattling caused by backward airflow can prolong the life of equipment.

Dump valves are actuated piston valves that rely on vacuum and pressure signals to open and close. When an engine is idling or cruising, there is equal pressure on both sides of the valve, meaning there is no need for pressure to be released. To ensure the piston keeps the valve closed at idle, a spring applies pressure to the mechanism.

The amount of pressure necessary can vary slightly with elevation and the specifications of the dump valve, so it is important that it is calibrated so just enough pressure is applied to keep the valve closed at idle. If the valve is open unnecessarily, the car will be subject to stalling and flooding.

When the throttle is opened to accelerate, boost pressure is created, which flows over both sides of the valve. When the throttle is once again closed, however, a vacuum is created, which opens the valve and rapidly releases the pressure before it closes again.

A common question asked by prospective dump valve users is whether or not dirt or debris can get into the engine from the atmosphere when the dump valve is open. The answer is no; dump valves are one-way valves, meaning it is only possible to exit the air chamber when open.

Another common question is whether or not the spring must be calibrated to accommodate different levels of boost; again the answer is no. Since more boost will flow over both sides, there is no need for adjustment. As long as there is enough pressure to keep the valve closed at idle, the car will take care of the rest.