Dump valve on turbo, explanation of

The compressor draws air in and the compressed air is delivered through the carb, to the inlet manifold. A sensing line from the compressor housing actuates the wastegate diaphragm at a predetermined pressure and opens the dump-valve, thus reducing exhaust gas-flow to the turbine and thereby controlling compressor delivery.

A sensing line from the plenum chamber is connected to the ECU and fuel pressure regulator valve. At high engine revs the boost pressure is increased by an electronically controlled solenoid valve that vents air from the sensing line. This reduces the pressure to the actuator diaphragm and the turbine pressure is allowed to increase to a maximum, controlled by the dump valve. The fuel regulating valve increases the fuel pressure in proportion to the compressor pressure.