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| Illustration 1 | g01374819 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (left side brakes) (10) Brake accumulator port (right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve | |
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| Illustration 2 | g01333114 |
(15) Shuttle valve (16) Load sensing port (17) Check valve | |
Service Brake Operation
Brake Operation Below Cut-In Pressure
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| Illustration 3 | g01374532 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (left side brakes) (10) Brake accumulator port (right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve (15) Shuttle valve (16) Load sensing port (17) Check valve (18) Rod | |
The cut in valve (2) controls the minimum pressure of the braking system. When the service brake pressure is below the cut in pressure, the cut in valve (2) allows pressurized oil to flow to shuttle valve (15). Shuttle valve (15) shifts to the left and shuttle valve (15) allows the pressurized oil to exit the load sensing port (16) in order to upstroke the pump. Pressurized oil and spring pressure hold the priority valve (1) closed. Maximum pump flow is directed to the brake section of the control manifold in order to satisfy the demand of the brake system. The excess flow that is not used by the brakes is diverted to the fan motor.
Pump flow enters the control manifold through the pump supply port (12). Pump flow goes through the following components: screen (11), check valve (17) and orifice (7). Pump flow goes to the inverse shuttle valve (8). The inverse shuttle valve (8) senses the brake accumulator port (9) or (10) that has the highest pressure. The accumulator port with the highest pressure seats the check valve. Rod (18) 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 (6) senses pressure in the brake accumulators. When the pressure is low, the sensor activates a warning lamp on the monitoring system.
Brake Operation at Cut Out Pressure
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| Illustration 4 | g01374548 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (left side brakes) (10) Brake accumulator port (right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve (15) Shuttle valve (16) Load sensing port (17) Check valve (18) Rod | |
When brake system pressure reaches the cut out pressure, cut out valve (14) opens. Cut out valve (14) drains the spring side of cut in valve (2) to the tank return port (5). System pressure overcomes the spring pressure on the cut in valve (2). The cut in valve (2) shifts to the right. When the cut in valve (2) shifts to the right, pressurized oil from the right side of shuttle valve (15) and the spring side of the priority valve (1) is metered to the tank return port (5). System pressure overcomes the spring pressure on priority valve (1). Priority valve (1) opens and the priority valve allows pump flow to the fan system. At the same time, shuttle valve (15) 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 Brake Cut In Pressure
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| Illustration 5 | g01374544 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (left side brakes) (10) Brake accumulator port (right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve (15) Shuttle valve (16) Load sensing port (17) Check valve (18) Rod | |
When the brake system pressure is below cut in pressure, the brake system receives a higher priority than the fan system. Priority valve (1) is closed. Pump flow to the fan motor is blocked when the priority valve is closed.
Operation with the Fan Speed Solenoid De-Energized
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| Illustration 6 | g01374554 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (left side brakes) (10) Brake accumulator port (right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve (15) Shuttle valve (16) Load sensing port (17) Check valve (18) Rod | |
The fan system has priority when the brake system pressure is at the cut out pressure. Fan speed solenoid (3) controls the load sensing pressure for the pump when the brake system is fully charged. Fan speed solenoid (3) is a proportional solenoid. As current to the fan speed solenoid increases, the output pressure decreases. When fan speed solenoid (3) 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 (12). Oil flow from the pump flows through the priority valve (1). The oil flow exits the supply port for the fan motor (13). A small amount of pressurized oil flows through fan speed solenoid (3). Fan speed solenoid (3) 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 (3), then fan speed solenoid (3) shifts in order to meter output pressure to the tank return port (5). The output pressure of the fan speed solenoid is then reduced. Oil that is at a reduced pressure flows to shuttle valve (15). Shuttle valve (15) shifts to the right. Pressurized oil exits through the load sensing port (16) in order to upstroke the pump.
Operation with the Fan Speed Solenoid Energized
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| Illustration 7 | g01374556 |
(1) Priority valve (2) Cut in valve (3) Fan speed solenoid (4) Main relief valve (5) Tank return port (6) Brake pressure sensor (7) Orifice (8) Inverse shuttle valve (9) Brake accumulator port (Left side brakes) (10) Brake accumulator port (Right side brakes) (11) Screen (12) Pump supply port (13) Supply port for fan motor (14) Cut out valve (15) Shuttle valve (16) Load sensing port (17) Check valve (18) Rod | |
The fan system has priority when the brake system pressure is at the cut out pressure. The fan speed solenoid (3) controls the load sensing pressure for the pump when the brake system is fully charged. The fan speed solenoid (3) is a proportional solenoid. As current to the fan speed solenoid increases, the output pressure decreases. When the fan speed solenoid (3) 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 Electronic Control Module (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 (3). 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 the fan speed solenoid (3). 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 (12). Oil flows through priority valve (1) to the fan motor. A small amount of pressurized oil flows through fan speed solenoid (3). Fan speed solenoid (3) 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 (3), then fan speed solenoid (3) shifts in order to meter output pressure to the tank return port (5). The engine ECM sends current to the fan speed solenoid (3) 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 (15). Shuttle valve (15) shifts to the right. Pressurized oil exits through the load sensing port (16). The pressurized oil changes the output of the pump in order to meet system demands.