CG938H Wheel Loader. Manual - part 15

 

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positioning is installed on pilot-controlled valve at lifting, retracting and floating positions. 

Note: in case of long-time shutdown, slight steering may be necessary after restarting to provide adequate supply 

pressure for pilot system before operating pilot handle to do lifting, retracting, tipping, lowering, etc. 

4. Selector valve 7130-B 

 

The selector valve adopted for the loader is pilot-controlled hydraulic multi-path change valve, 

mainly consisting of tipping couplet, are moving couplet, main overflow valve, overload valves, 

inlet check valve, oil filling valve for movable arm chamber, etc. System pressure is adjusted via 

overflow cock at the inlet. Tipping couplet is equipped with two overload valves to protect tipping 

cylinder and pipelines. 

When the selector valve plug is in neutral position, oil inlet and outlet are connected, so there is 

no operation of working unit. 

Turn the tipping handle, pressure oil in proportion to travel is output by pilot-controlled valve 

to apply a force on one end of selector valve plug to slowing reverse the plug. As pressure gradually 

accumulates at oil inlet of selector valve, oil inlet check valve is opened, and pressure oil enters 

working port to activate working unit. 

5. Driving control block RSM16           

 

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Lift the oil cylinder (7) to place the pressure on the piston side, the pressure also will be placed 

on the one-way valve of the valve element (2) and accumulator (6). 

Lift the oil cylinder (7) to the oil circuit of the accumulator (6), and close by the valve element 

(2) (switch to the position 2). In the valve element (2), an internal accumulator (6) has the function 

of pressure reduction (switch to the position 3). The opening pressure is higher than the shutoff 

pressure about 30bar (switch to the position 2). 

The two-position three-way reversal valve may be switched to the position 2 according to the 

driving speed of the vehicle (>8km/h). The valve element (2) is switched to the position 4 to collect 

the piston side of oil cylinder (7) with the accumulator (6), and rod side of lifting oil cylinder (7) 

with the oil tank. 

Overflow valve (4) is designed to prevent impermissible pressure in the accumulator (the 

opening pressure <allowed pressure of accumulator). This overflow valve is selective upon the 

user’s willing. 

Pressure relief of this module: 

Prior to maintenance of this system, the pressure of this module shall be relieved. In pressure 

relief, the loader shall be parked at a safe place, and the protective device of lifting oil cylinder shall 

be installed well (see the chapter on safety). And then relieve the pressure of the accumulator 

through the emergency oil discharging screw (5). The position of the oil discharging screen is the 

position the serial number 1 indicates in the right figure. In the schematic diagram, it is a 

two-position two-way mechanical solenoid valve. 

 

 

 

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V. Troubleshooting of working hydraulic system 

 

No. Symptoms 

Causes 

Solutions 

A Insufficient 

lifting force of 

movable arms 

or insufficient 

bucket turning 

force  

1．Cylinder oils seal is damaged 

2．Clearance between selector 

valve rod and valve body 

exceeds limits due to 

overwearing 

3．Oil leakage in piping system 

4．Severe internal leakage of 

working pump 

5．Low pressure at safety valve 

6．Oil intake line or oil filter is 

jammed 

7．Low pilot pressure causes 

insufficient reversing of selector 

valve 

8．Severe internal leakage of the 

pump delivering oil to 

pilot-controlled valve 

1．Replace oil seal 

2．Replace selector valve or 

check and repair valve plug 

3．Check for cause of leakage 

and eliminate it 

4．Replace working pump 

5．Adjust system to nominal 

value 

6．Replace oil and clean oil filter

7．Adjust pilot pressure to 

nominal value 

B Slow  bucket 

turning or slow 

lifting of movable 

arms at high rpm 

1． See causes in A 

2． Overload valve is blocked 

1． See solutions in A 

2． Replace or check and repair 

overload valve 

1.3.2 Brake system 

The loader adopts original pedal brake valve (06-466-240) and refill valve (06-463-230) 

manufactured by MICO USA. Refer to Installation and Service Manual of MICO Products – 

Two-way Refill Valve and Installation and Service Manual of MICO Products – Two-way Serial 

Pedal Valve for details. 

Accumulator manufactured by HYDAC is adopted. 

 

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1.3.3 Description of steering hydraulic system 

I. Principle: 

 

II. System description 

Steering system adopts a load-sensing hydraulic steering mechanism mainly consisting of pump, 

load-sensing steering gear, priority steering control valve, steering cylinder, emergency steering 

power unit, check valves and pipelines. LS pipeline transfers internal pressure signal from steering 

gear to priority valve to achieve balance of the valve plug, thus 

ensuring the flow rate required by port CF. When the pressure at the 

outlet of the steering pump is less than 8 bars, the pressure switch 

installed at the outlet will close to drive the emergency steering power 

unit to realize the function of emergent steering. 

III. Description of Components 

1. Pump: Denison 3520VQS21A12-297DD20R position is shown 

in the figure below: 

Denison vane pump meets SAE and IOS standards. Hydrocushion 

design ensures long service lives of shaft and bearing with extremely 

small noise and high volumetric efficiency. The main internal structure is as shown in the right 

figure.