PIN 1506308 - Caterpillar

The exhaust bypass valve controls the flow of exhaust gas to the turbine wheel in order to maintain the desired boost pressure.
Illustration 1 g00820098
Right side view and rear view (1) Tube from the turbocharger compressor outlet (2) Exhaust bypass valve (3) Breather
Illustration 2 g00812973
Section view of an exhaust bypass valve (4) Opening for sensing of the boost pressure (5) Diaphragm (6) Springs (7) Adjusting screw (8) Valve (9) Exhaust gas to the turbocharger (10) Exhaust gas to the exhaust elbow (11) Opening for the breatherValve (8) is activated directly by a pressure differential.Atmospheric pressure is exerted through opening (11) for breather (3) on one side of diaphragm (5). Force from springs (6) is on the same side of the diaphragm. The force of the springs are adjusted with adjusting screw (7) .Boost pressure is exerted on the other side of the diaphragm through opening (4) for tube (1) from the compressor outlet. On the same side of the diaphragm, exhaust gas exerts pressure on valve (8) .When the force of the springs plus the atmospheric pressure is overcome by boost pressure, valve (8) opens in order to divert some exhaust gas (9) from the turbocharger to the exhaust elbow (10). This prevents the turbocharger from providing too much boost pressure.Excessive boost pressure can cause engine overload, overheating, detonation, and instability. The amount of exhaust gas to the turbine wheel is maintained in order to provide the correct boost pressure. This limits the horsepower of an engine that has the correct air/fuel ratio. The boost pressure determines the throttle angle at full load operation.When the air/fuel ratio is correct, a throttle angle of approximately 70 degrees is recommended for full load operation.Under constant load conditions, the exhaust bypass valve maintains a stable position.The exhaust bypass valve is cooled by engine coolant.