349D2 MHPU Mobile Hydraulic Power Unit Hydraulic System Relief Valve (Main) - Test and Adjust Caterpillar

Specification

Note: Certain machines will default to "Economy Mode" at machine startup. Change to "High Hydraulic Power Mode" before performing the test procedure.

Introduction

The main relief valve limits the maximum operating pressure of the travel hydraulic circuit and the implement hydraulic circuits when the machine is at a load condition. Machines that are equipped with heavy lift have a high-pressure setting and a low-pressure setting for the main relief valve.

Required Tools

Illustration 1	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

Machine Preparation

1. Position the machine on level ground and stop the engine.

2. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".
   Show/hide table

   Illustration 2	g03408587
   Pump compartment (1) Pressure tap (pressure for drive pump)

3. Attach a 41368 kPa (6000 psi) pressure sensor to pressure tap (1).

Test Procedure

Standard

1. Start the engine.

2. Place the machine controls at the following settings: engine speed dial "10" and AEC switch OFF. Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.

3. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).

4. Move the joystick for the bucket until the bucket is at the full BUCKET CLOSE position (full extension of the bucket cylinder).

5. Check the pressure reading for the main relief valve pressure setting. Refer to Table 1.

6. Return the joystick for the bucket to the NEUTRAL position.

Adjustment Procedure

Standard

Show/hide table

Illustration 3	g02102305
Main relief valve (A) Adjustment screw (L) Locknut

1. Loosen the locknut and turn the adjustment screw until the pressure reading at the pressure tap for the drive pump is within the specification. Refer to Table 1.

   Note: Turn the adjustment screw clockwise to increase the pressure. Turn the adjustment screw counterclockwise to decrease the pressure.

   Note: Always make final pressure adjustments on pressure rise.

2. Tighten the locknut.