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Handbook of Turbomachinery Second Edition Revised - Ventech!

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mounted on or near the exhaust manifold or turbine housing. The wastegate<br />

provides a flow path through which exhaust gases can bypass the turbine,<br />

going directly to the discharge exhaust pipe. A common form <strong>of</strong> wastegate<br />

uses a poppet valve connected to a diaphragm (Fig. 20). The chamber in<br />

front <strong>of</strong> the diaphragm is connected by a pressure feed line that senses boost<br />

pressure downstream <strong>of</strong> the compressor housing in the intake manifold.<br />

When the boost pressure exceeds a threshold value, the pressure on the<br />

diaphragm begans to overcome the pressure exerted by the spring on the<br />

otherside <strong>of</strong> the diaphragm, thus compressing the spring and opening the<br />

poppet valve. This lets an increasing percentage <strong>of</strong> the exhaust gas travel to<br />

the turbine exhaust pipe without passing through the turbine, halting the<br />

acceleration <strong>of</strong> the turbine and the subsequent increase in boost pressure.<br />

The amount <strong>of</strong> boost pressure is determined by the strength <strong>of</strong> the spring,<br />

sometimes referred to as the cracking pressure. Springs can be changed to<br />

vary boost pressure. Some more expensive wastegates have the capability to<br />

Figure 20 Turbocharger fitted with an integral boost pressure control valve. Boost<br />

pressure sensed in the discharge outlet from the compressor is transmitted via the<br />

tubing to the diaphragm side <strong>of</strong> the control valve. When boost pressure exceeds the<br />

spring force, the poppet valve is opened so a portion <strong>of</strong> the exhaust gas bypasses the<br />

turbine. (Courtesy Kuhnle, Kopp & Kausch AG.)<br />

Copyright © 2003 Marcel Dekker, Inc.

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