Die vinnig draaiende kompressor turbine trek 'n groot hoeveelheid lug in en forseer dit deur die enjin. As die turbo-aanjaer se uitsetvloei die enjin se volumetriese vermoë oorskry sal die inlaatverdeelpyp se druk te hoog word. Die rotasiesnelheid van die turbine kan ook te hoog word en daarom moet die uitlaatgas wat dit aandryf beheer word. Vir die doeleinde is die gebruik van 'n afvoersluis die mees algemene meganiese manier om die spoed te beheer. Die stelsel word dikwels deur 'n bykomstige elektroniese beheerstelsel bygestaan. Die hoofdoel van die afvoersluis is dus om van die uitlaatgas rondom die turbine te lei wanneer die verlangde inlaatdruk verkry is. Die meeste passasiersvoertuie se afvoersluise word by die turbo-aanjaer ingebou.
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===Anti-Surge/Dump/Blow Off Valves===
Turbo charged engines operating at wide open throttle and high rpm require a large volume of air to flow between the turbo and the inlet of the engine. When the throttle is closed compressed air will flow to the throttle valve without an exit (i.e. the air has nowhere to go).
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This causes a surge which can raise the pressure of the air to a level which can be destructive to the engine e.g. damage may occur to the throttle plate, induction pipes may burst. The surge will also decompress back across the turbo, as this is the only path with the air can take.
The reverse flow back across the turbo acts on the compressor wheel and causes the turbine shaft to reduce in speed quicker than it would naturally. When the throttle is opened again, the turbo will have to spin-up for longer to the required speed, as turbo speed is proportional to boost/volume flow. In order to prevent this happening, a valve is fitted between the turbo and inlet which vents off the excess volume of air. These are known as anti-surge, dump or blow-off valves. They are normally operated by engine vacuum or by electronic control.
The primary use of this valve is to prevent damage to the engine by a surge of compressed air and to maintain the turbo spinning at a high speed. They can also be used as a bypass valve to control boost in a similar fashion as a waste gate, but this is rarely seen as it is impractical. The air is usually vented to atmosphere, or can be recycled back into the turbo inlet. Recycling back into the turbo causes the venting sound to be reduced but as the excess volume of air is not removed problems may arise.