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You seem to understand most of it.
At the lowest level of control, the wastegate acutator would be connected to the pressure side of the turbo somewhere, typically at the compressor scroll housing's hose barb. The pressure wants to open the wastegate but has to fight the spring in the wastegate actuator capsile. The wastegate will open prematurely which will create boost delay, but the pressure will balance to a fixed amount. The pressure can be adjusted with differenct springs or capsules and adjusting the actuator arm will provide some limited adjustment range as well. This is a negative feedback system as the output pressure will try to reduce the pressure.
The engine/turbo system wants to be a positive feedback system. And without a controller, the pressure will build exponentially.
Now almost all boost conrollers increase pressure above what the wastegate capsule would produce, by limiting the amount of the pressure that the capsule sees. The basic pressure divider or bleeder valve does this, but again you get the boost delays. The adjustable valve in the bleeder does the pressure reduction, but again the wastegate spring is providing the feedback control to regulate the pressure.
The ball-spring units are simpler, but are not linear devices. The act the same, but don't start flowing any gas until the pressure reaches a certain threashold. Then the pressure is able to get some flow past the spring loaded ball. The resistance of the spring/ball coupled with the bleed orifice creates the pressure reduction. Tightening the spring does two things. First it increased the pressure at which flow will begin, and second, once flow does commence a tigher setting increases the flow resistance past the spring loaded ball. That higher reistance and its higher pressure drop coupled with the bleed orifice creates a greater pressure drop, so the boost gets higher. Note that whatever setting or controller, the pressure to the wastegate acutator will not be changing very much as differenct boost levels are set, a curious thing at first thought.
posted by 207.43.195...
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