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| Illustration 1 | g00277464 |
938G Wheel Loader and IT38G Integrated Toolcarrier Steering System Hydraulic Schematic (1) Steering metering pump. (2) Selector valve. (3) Steering crossover relief valve. (4) Left side steering cylinder. (5) Right side steering cylinder. (6) Spool valve. (7) Steering control valve. (8) Steering backup relief valve. (9) Pressure Tap. (10) Secondary steering pressure switch. (11) Secondary steering pump and electric motor. (12) Secondary steering valve. (13) Primary steering pressure switch. (14) Hydraulic oil tank. (15) Hydraulic oil filter. (16) Steering/pilot pump. (17) Pressure tap. (A) From the main control valve. (B) To pilot selector and pressure control valve. (C) To main control valve. | |
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| Illustration 2 | g00277225 |
938G Wheel Loader and IT38G Integrated Toolcarrier Component Location ( 938G shown) (1) Steering metering pump. (2) Selector valve. (3) Steering crossover relief valve. (4) Left side steering cylinder. (5) Right side steering cylinder. (6) Spool valve. (7) Steering control valve. (8) Steering backup relief valve. (9) Pressure Tap. (10) Secondary steering pressure switch. (11) Secondary steering pump and electric motor. (12) Secondary steering valve. (13) Primary steering pressure switch. (14) Hydraulic oil tank. (15) Hydraulic oil filter. (16) Steering/pilot pump. (17) Pressure tap. | |
The steering hydraulic system is made up of two basic circuits:
- Pilot circuit
- High pressure circuit
When a machine is equipped with the secondary steering attachment, the secondary steering system is an additional circuit.
Pilot Circuit
The pilot system controls the movement of spool valve (6) in steering control valve (7) . The components of the pilot system are steering/pilot pump (16) , steering metering pump (1) , and hydraulic oil tank (14) .
Pump oil from steering/pilot pump (16) flows to steering control valve (7) . The oil then flows to steering metering pump (1) .
Steering metering pump (1) is a small hydraulic hand pump that is used as a metering valve and as a directional valve. The pilot oil flows through steering metering pump (1) to one side of selector valve (2) when the steering valve is turned.
Hydraulic oil tank (14) is located behind the operator's cab. Hydraulic oil filters (15) are located in the top of the hydraulic oil tank.
Steering control valve (7) is located in the middle of the right side of the machine. Steering/pilot pump (16) is located under the operator's compartment.
Steering metering pump (1) is mounted on the bottom of the steering column. The steering metering pump is located under the floor of the operator's compartment.
High Pressure Circuit
The following components are the components of the high pressure circuit: Steering/pilot pump (16), steering control valve (7), left side steering cylinder (4), right side steering cylinder (5) and hydraulic oil tank (14) with hydraulic oil filters (15) .
Steering/pilot pump (16) is a piston pump with variable flow. The steering/pilot pump provides pressure oil for the pilot circuit and for the high pressure circuit.
The oil for the steering system flows from steering/pilot pump (16) to steering control valve (7) . If the pilot oil from steering metering pump (1) moves spool valve (6) to the left turn position or to the right turn position, oil from the pump flows to the steering cylinders. The pressure of this oil moves the steering cylinder rods. This causes the machine to turn.
Secondary Steering
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| Illustration 3 | g00283224 |
Secondary steering pump and electric motor | |
Secondary steering pump and electric motor (11) is mounted on the right side of the machine below the operator's compartment. Secondary steering valve (12) is mounted on the inside of the rear frame on the right side of the machine.
If steering/pilot pump (16) or the engine fails, primary steering pressure switch (13) closes. Primary steering pressure switch (13) closes due to low oil pressure in the steering system. Primary steering pressure switch (13) activates an action alarm and primary steering indicator (20) in the cab.
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| Illustration 4 | g00280052 |
Indicators (18) Secondary steering switch. (19) Secondary steering indicator. (20) Primary steering indicator. | |
After a one second delay, the control box activates the relay for secondary steering pump and electric motor (11) . Secondary steering pump and electric motor (11) pumps steering oil to the steering system. The steering oil flows through secondary steering valve (12) to steering control valve (7) .
The steering oil pumped from secondary steering pump and electric motor (11) causes secondary steering pressure switch (10) to close. Secondary steering pressure switch (10) activates secondary steering indicator (19) in the cab.
The condition of the secondary steering is tested during engine start-up. During the three second test, secondary steering indicator (19) comes on to verify the system is pressurized.
The secondary steering system can be manually tested. Push the secondary steering switch (18) in order to determine if the secondary steering and secondary steering indicator (19) are functional. When the secondary steering switch (18) is pushed, the secondary steering pump and electric motor (11) will run and second steering indicator (19) will light.