DRIVE GP-FAN 1125997 - Caterpillar

Illustration 1 g00874967
Left side view (1) Aftercooler (2) Bypass valve (3) Tube (4) Actuator (5) Exhaust manifold (6) Monitor panel (7) Air lines (8) Main supply of pressurized airDuring engine acceleration and deceleration in the middle range of speed (rpm), the turbocharger can produce boost pressures that are greater than the requirement for efficient engine operation.Turbocharger surge - In response to the excess pressure in the air inlet manifold (boost pressure), the flow of air across the turbocharger compressor wheel is reversed. This reversal of the air flow is called turbocharger surge. During a turbocharger surge, the turbocharger overspeeds temporarily. This places a greater axial load on the thrust bearing and higher than normal torque on the shaft. The turbocharger surge can result in severe damage to the turbocharger.The compressor bypass group reduces the opportunity for a turbocharger surge. The compressor bypass group is located at the rear of the engine.Note: Specific setpoints are dependent on the engine arrangement. The setpoints (rpm) that follow are used as a general guideline for purposes of explanation only.A speed sensor measures the speed of the flywheel. The speed sensor sends a signal to the engine speed switch. The speed switch is programmed to activate a relay for the compressor bypass group at 630 rpm. The relay is deactivated at 950 rpm. To ensure smooth operation of the compressor bypass group during acceleration and deceleration, time delays have been programmed into the speed switch.At speeds below 630 rpm, the bypass valve remains closed. When the engine speed is greater than 630 rpm, the relay energizes a solenoid in monitor panel (6). The solenoid opens a valve in order to provide pressurized air from main supply (8) to the bypass valve's actuator (4) via air lines (7).
Illustration 2 g00874971
Front view of the actuator's shaft (2) Bypass valve (4) ActuatorThe air pressure causes actuator (4) to move a shaft that is connected to a plate inside bypass valve (2). The force of the shaft overcomes the spring force that holds the plate closed and the bypass valve opens.When bypass valve (2) opens, noncooled compressed air from the upper housing of aftercooler (1) passes through tube (3). The air flows through bellows and tubes into exhaust manifolds (5) on each side of the engine. The air mixes with the exhaust gases and the mixture flows through the turbine sides of the turbochargers.When the inlet air from the turbocharger compressor is diverted from the air inlet manifold, the boost pressure is prevented from becoming excessive in the air inlet manifold. This reduces the opportunity for a turbocharger surge. Also, exhaust manifold temperatures are reduced.The bypass valve remains open for the middle range of speeds (630 rpm to 950 rpm).When the engine speed is greater than 950 rpm, the speed switch de-energizes the relay for the solenoid in monitor panel (6). The solenoid's valve closes and the pressurized air is shut off from actuator (4). The spring-loaded bypass valve (2) closes. The residual pressurized air is purged from actuator