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| Illustration 1 | g01513582 |
(1) Port for brake pressure sensor (2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (11) Test port (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice | |
Service Brake Operation
Brake Operation below Cut-In Pressure
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| Illustration 2 | g01855474 |
(2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice (20) Brake pressure sensor (21) Rod | |
Cut-in valve (2) controls the minimum pressure of the braking system. When the service brake pressure is below the cut-in pressure, Cut-in valve (2) allows pressurized oil to flow to shuttle valve (7) . Shuttle valve (7) shifts to the left and shuttle valve (7) allows the pressurized oil to exit load sensing port (15) in order to upstroke the pump. Pressurized oil and spring pressure hold priority valve (10) partially closed. Most flow is directed to the brake section of the control manifold in order to satisfy the demand of the brake system.
Pump flow enters the control manifold through the pump supply port (9) . Pump flow goes through the following components: screen (18) , check valve (17) and orifice (19) . Pump flow goes to the inverse shuttle valve (13) . The inverse shuttle valve (13) senses the brake accumulator port (12) or (8) that has the highest pressure. The accumulator port with the highest pressure seats the check valve. Rod (21) opens the check valve that has the lowest accumulator pressure. The brake accumulator can be charged with the check valve in the open position. Brake pressure sensor (20) senses pressure in the brake accumulators. When the pressure is low, the sensor activates a warning lamp on the monitoring system.
Brake Operation at Cutout Pressure
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| Illustration 3 | g01855515 |
(2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice (20) Brake pressure sensor (21) Rod | |
When brake system pressure reaches the cutout pressure, cutout valve (5) opens. Cutout valve (5) drains the spring side of cut-in valve (2) to the tank return port (6) . System pressure overcomes the spring pressure on cut-in valve (2) . Cut-in valve (2) shifts to the right. When cut-in valve (2) shifts to the right, pressurized oil from the right side of shuttle valve (7) and the spring side of priority valve (10) is metered to tank return port (6) . System pressure overcomes the spring pressure on priority valve (10) . Priority valve (10) opens and the priority valve allows all pump flow to the fan system. At the same time, shuttle valve (7) shifts to the right. This allows the pump to sense the pressure requirements of the fan system. Check valve (17) closes and the check valve maintains brake system pressure.
Operation of the Hydraulic Fan System
Operation at the Cut-In Pressure for the Brake
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| Illustration 4 | g01855474 |
(2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice (20) Brake pressure sensor (21) Rod | |
When the brake system pressure is below cut-in pressure, the brake system receives a higher priority than the fan system. Priority valve (10) restricts flow to the fan motor. When the brake system is charging diverter valve (16) restricts oil flow to the fan in order to prevent the fan from overspeeding.
Operation with the Fan Speed Solenoid De-Energized
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| Illustration 5 | g01855555 |
(2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice (20) Brake pressure sensor (21) Rod | |
The fan system has priority when the brake system pressure is at the cutout pressure. Fan speed solenoid (4) controls the load sensing pressure for the pump when the brake system is fully charged. Fan speed solenoid (4) is a proportional solenoid. As current to the fan speed solenoid increases, the output pressure decreases. When fan speed solenoid (4) is de-energized, the output pressure to the load sensing port is maximum. The pump will be fully stroked and the pump will send maximum flow to the fan motor. Thus, the fan motor is turning at maximum speed.
Pump flow enters the control manifold through port (15) . Oil flow from the pump flows through priority valve (10) . The oil flow exits the supply port for the fan motor. A small amount of pressurized oil flows through fan speed solenoid (4) . Fan speed solenoid (4) is a pressure reducing valve. The solenoid assists in the pressure reducing function. If the fan system pressure is above the pressure reducing pressure of fan speed solenoid (4) , then the fan speed solenoid (4) shifts in order to meter output pressure to tank return port (6) . The output pressure of the fan speed solenoid is then reduced. Oil that is at a reduced pressure flows to shuttle valve (7) . Shuttle valve (7) shifts to the right. Pressurized oil exits through load sensing port (15) in order to upstroke the pump.
Operation with the Fan Speed Solenoid Energized
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| Illustration 6 | g01855576 |
(2) Cut-in valve (3) Backup relief valve (4) Fan speed solenoid (5) Cutout valve (6) Tank return port (7) Shuttle valve (8) Brake accumulator port (Front brakes) (9) Pump supply port (10) Priority valve (12) Brake accumulator port (Rear brakes) (13) Inverse shuttle valve (14) Supply port for fan motor (15) Load sensing port (16) Diverter valve (17) Check valve (18) Screen (19) Orifice (20) Brake pressure sensor (21) Rod | |
The fan system has priority when the brake system pressure is at the cutout pressure. Fan speed solenoid (4) controls the load sensing pressure for the pump when the brake system is fully charged. Fan speed solenoid (4) is a proportional solenoid. As current to the fan speed solenoid increases, the output pressure decreases. When fan speed solenoid (4) is energized, the output pressure to the load sensing port on the pump is reduced. Thus, the fan motor is turning below maximum speed.
The amount of current that is applied to the fan speed solenoid is controlled by the engine ECM. The engine ECM receives three inputs. The ECM receives the following inputs: hydraulic oil temperature sensor, temperature sensor for the inlet air manifold and engine coolant temperature sensor. If the engine ECM determines that the fan speed should be minimum, then the maximum current is sent to the fan speed solenoid (4) . If one of the three sensors shows that there is a demand for more cooling, then the engine ECM will reduce the amount of current to fan speed solenoid (4) . By decreasing the current to the fan speed solenoid, the pump will upstroke in order to provide more cooling capacity.
Pump flow enters the control manifold through port (15) . Oil flows through priority valve (10) to the fan motor. A small amount of pressurized oil flows through fan speed solenoid (4) . Fan speed solenoid (4) is a pressure reducing valve. The solenoid assists in the pressure reducing function. If the fan system pressure is above the pressure reducing pressure of the fan speed solenoid (4) , then the fan speed solenoid (4) shifts in order to meter output pressure to tank return port (6) . The engine ECM sends current to fan speed solenoid (4) in order to reduce the output pressure further. The output pressure of the fan speed solenoid is then reduced. Oil that is at a reduced pressure flows to shuttle valve (7) . Shuttle valve (7) shifts to the right. Pressurized oil exits through load sensing port (15) . The pressurized oil changes the output of the pump in order to meet system demands.