The most common way to control boost pressure using an actuator is with a bleed-off system controlled by an electronic valve, usually in conjunction with the engine ECU.
The actuator will always control to it’s pre-set value and to increase the boost pressure we need to give the actuator a false pressure signal. This is done by taking the pressure signal from the compressor outlet, passing it through a restrictor before it’s connected to the actuator, and bleeding off some of the pressure via the electronic valve.
For example, if the actuator is set to 1.0 bar and we want the compressor to give 1.5 bar then we must drop 0.5 bar through the restrictor so that the actuator sees only 1.0 bar. We do this by bleeding air through the restrictor, controlled by the electronic valve. The size of the restrictor will depend on the amount of bleed required and the flow capability of the bleed valve, but a 1.0 mm hole would be typical.
