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Personal injury can result from hydraulic oil pressure and hot oil.
Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system.
Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.
Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine.
To prevent personal injury or death, perform the following:
Park the machine on a smooth, level surface.
Lower the work tool to the ground and engage the parking brake.
Stop the engine and remove the key.
Block the wheels and install the steering frame lock.
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.
Refer to Special Publication, PERJ1017, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat® products.
Dispose of all fluids according to local regulations and mandates.
- Release the pressure from the hydraulic system.
Reference: Refer to Systems Operation, Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
Illustration 1 g00912763 Location of the main relief valve pressure tap
(1) Pressure tap
- Attach the 177-7861 Hose As and 8T-0859 Pressure Gauge to pressure tap (1).
- Start the engine and increase the temperature of the oil to normal operating temperature.
- Raise the lift arms to the maximum height.
- Increase the engine speed to high idle rpm. Move the joystick control lever to the RAISE position.
- Observe the pressure gauge. The pressure setting of main relief valve (2) should be
19995 ± 345 kPa (2900 ± 50 psi).
Note: Do not keep the joystick control lever in the RAISE position, at the relief valve setting, more than 5 seconds.
Note: If the pressure setting of the main relief valve is not at the specification, it will be necessary to adjust the main relief valve.
- Lower the bucket to the ground. Stop the engine.
Illustration 2 g00819732 Main control valve
(2) Main relief valve
Illustration 3 g00912765 Main control valve with auxiliary control valve
(2) Main relief valve
Note: The location of Main relief valve (2) changes if the machine is fitted with the auxiliary control valve
Illustration 4 g00912767 (2) Main relief valve
(4) Adjusting screw
- Loosen locknut (3) on main relief valve (2). Turn adjusting screw (4) clockwise for an increase in pressure. Turn adjusting screw (4) counterclockwise for a decrease in pressure.
- Tighten locknut (3) to
50 ± 7 N·m (37 ± 5 lb ft). Repeat Steps 3 through 6.
- When the pressure setting of main relief valve (2) is correct, lower the bucket to the ground.
- Stop the engine. Remove the test equipment from pressure tap (1).