990K Wheel Loader Machine Systems Caterpillar

Pilot Pressure (Pressure Reducing Valve) - Test and Adjust

Usage:

990K A9P

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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 attachments have been lowered, 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.

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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.

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NOTICE

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, NENG2500, "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.

Specifications

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Table 1
Test Specification
Test Conditions	Engine speed set at High Idle (2010 RPM ± 25 RPM)	Operating Temperature Range - 50° C to 88° C (122° F to 190.° F)
Implement Pilot Pressure	Desired	Actual
Implement Pilot Pressure	3500 ± 345 kPa (500 ± 50 psi)

Required Tools

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Illustration 1	g03676396

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Table 2
Required Tools (B)
Item	Qty	Part Number	Description
B1	1	8T-0855	Pressure Gauge⁽¹⁾
B2	1	6V-3989	Fitting
B3	2	6V-4143	Quick Connect Coupler
B4	1	177-7860⁽²⁾	Hose As
B4	1	177-7861⁽²⁾	Hose As
B4	1	177-7862⁽²⁾	Hose As

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⁽¹⁾	The 198-4240 Digital Pressure Indicator is also available.
⁽²⁾	Optional Tooling

Test Preparation

Park the machine on a smooth, level surface. Move the machine away from other operating machines and away from personnel.
Permit only one operator on the machine. Keep all other personnel away from the machine or in sight of the operator.
Position the work tool on the ground.
Engage the parking brake.
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Illustration 2 g03676672
Place the steering frame lock in the LOCKED position.
Relieve the pressure in the hydraulic system.
Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

Test Procedure

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Illustration 3	g03676416
(6) Implement pilot pressure reducing valve (T3) Implement pilot pressure tap

Ensure that the engine start switch is in the OFF position. Open the center platform access door to the pilot pressure reducing valve.
Install a 8T-0855 Pressure Gauge or a 198-4240 Digital Pressure Indicator to pressure tap (T3) on the pilot pressure line to the main control valve.
Start the engine and warm the hydraulic oil to a normal operating temperature of 50° C to 88° C (122° F to 190.° F).
Run the engine at high idle. Raise the work tool until the lift cylinders are fully extended.
Observe the pressure gauge while the lift cylinders are fully extended.
The pressure reading should be 3500 ± 300 kPa (508 ± 44 psi).
If the pilot oil pressure is not correct, proceed to the "Required Tools" section below.
If the pressure is correct, return the work tool to the ground and turn the engine start switch to the OFF position.
1. Release the hydraulic pressure. Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release".
2. Remove the test equipment from the machine.

Adjustment Procedure

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Illustration 4	g03676613
(6) Pilot pressure reducing valve (6A) Locknut (6B) Adjustment screw (T3) Pilot pressure tap

Release the hydraulic system pressure. Refer to Testing and Adjusting, "System Pressure - Release".
Ensure that the work tool is on the ground. Turn the engine start switch to the OFF position.
Note: Always, turn adjustment screw (6B) clockwise in order to adjust the pressure. Clockwise movement will compensate for any internal friction inside the valve that would oppose the setting of the bias spring. For example, if the adjustment screw needs to be turned counterclockwise by 1/2 turn, turn the adjustment screw counterclockwise by one full turn. Then, turn the adjustment screw clockwise by 1/2 turn.
Loosen locknut (6A). Turn adjustment screw (6B) clockwise in order to increase the pressure setting. One turn will increase the relief valve setting by 515 kPa (75 psi). Turn adjustment screw (6B) counterclockwise in order to decrease the pressure setting of the relief valve. One turn will decrease the relief valve setting by 515 kPa (75 psi).
After adjustment screw (6B) is turned for an adjustment, hold adjustment screw in place and tighten locknut (6A) to a torque of 8.1 ± 1.3 N·m (72 ± 12 lb in).
Repeat Test Procedure Steps 4 through 8.
If pressure setting is not correct, repeat Adjustment Procedure Steps 1 through 4.
If the Pressure Reducing Valve (6) requires replacement, release the hydraulic system pressure. Refer to Testing and Adjusting, "System Pressure - Release". When a new reducing valve is installed, tighten the valve to a torque of 35 ± 1 N·m (26 ± 1 lb ft). Torque for the locking nut on the reducing valve is approximately 8.1 ± 1.3 N·m (72 ± 12 lb in).