Detroit Diesel MBE 4000 Service Manual page 27

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EGR Cooler
The EGR Cooler is equipped with a single-pass cooler. Part of the exhaust gasses from the first
three cylinders are directed through the EGR shutoff valve and through the cooler and reed valves,
past the EGR modulated control valve and the mixer and then back to the cylinder.
EGR Control Valves
There are two EGR valves on the MBE 4000 EGR engine — the EGR shutoff valve and the EGR
modulated control valve. The EGR shutoff valve is a pneumatically driven butterfly valve,
located at the inlet of the EGR cooler. It closes when the exhaust flap or turbo-brake actuates,
avoiding exhaust gas flow and excessive pressure in the EGR cooler and reed valves. The EGR
modulated control valve is an electronically actuated butterfly valve located after the EGR cooler
and reed valves, controlled by the DDEC-ECU (formerly PLD-MR). This valve controls the
exhaust gas flow for the intake manifold.
Reed Valves
The reed valves work like a check valve, allowing flow of gas only in one direction, avoiding gas
back flow when the intake pressure is higher than exhaust gas pressure. As the average exhaust
pressure is lower than the intake pressure, the gas flow through the reed valves is possible due to
exhaust gas pressure peaks — peaks slightly higher than the intake air pressure, which occur as
the engine exhaust valves open. During this peak of pressure, the reed valves open and allow gas
flow to the EGR modulated valve and mixer.
EGR Mixer
The purpose of the mixer is to ensure good mixing of the cooled EGR gasses with filtered charge
air. Once the exhaust gasses are cooled and have completed their cycle through the EGR system,
they are released into the EGR mixer. The recycled exhaust gasses are combined with the charged
air and directed to the cylinders.
All information subject to change without notice.
6SE412 0403 Copyright © 2004 DETROIT DIESEL CORPORATION
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MBE 4000 SERVICE MANUAL
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