HUB ASSEM. 5K4408 - 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 g00812962
Typical example (top view)
(1) Tube from the aftercooler
(2) Exhaust bypass valve
(3) Breather
Illustration 2 g00812973
Section view of an exhaust bypass valve
(4) Opening for the tube from the aftercooler
(5) Diaphragm
(6) Spring
(7) Adjustment screw
(8) Valve
(9) Exhaust gas to the turbocharger
(10) Exhaust gas to the exhaust elbow
(11) Opening for the breather Valve (8) is activated directly by boost pressure.Atmospheric pressure is exerted through opening (11) for breather (3) on one side of diaphragm (5). Force from spring (6) is on the same side of the diaphragm. The force of the spring is adjusted with adjusting screw (7).Boost pressure is exerted on the other side of the diaphragm through opening (4) for tube (1) from the aftercooler. On the same side of the diaphragm, exhaust gas exerts pressure on valve (8).When the force of the spring plus the atmospheric pressure is overcome by boost pressure, valve (8) opens in order to bypass some exhaust gas (9) from the turbocharger to the exhaust elbow. This prevents the turbocharger from providing too much boost pressure.Excessive boost pressure can result in overloading of the engine, overheating, detonation, and turbocharger surge. The amount of exhaust gas to the turbine wheel is maintained in order to provide the correct boost pressure.Under constant load conditions, the exhaust bypass valve maintains a stable position.At full load, the position of the exhaust bypass valve will be open by 20 percent.