301.4C Mini Hydraulic Excavator Caterpillar

Introduction

The main relief valve is located on the left side of the main control valve on the bottom. The main relief valve is accessible from the left side of the machine after removal of the access plate. The main relief valve sets the operating system pressure for the travel hydraulic circuit and the implement hydraulic circuits.

Illustration 1	g02655337
Main relief valve location on main control valve

Required Tools

Illustration 2	g01623868
Tooling group "B" 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 3	g02655376
   Pressure tap for system pressure located on the main pump delivery line (left rear of the machine) (1) Pressure tap for system pressure (2) Delivery line (3) Main pump

3. Attach a 34,450 kPa (5,000 psi) pressure sensor to the pressure tap for the main pump.

Test Procedure

1. Start the engine.

2. Place the engine speed control to the HIGH idle position.

3. Increase the hydraulic oil temperature to 50° ± 10°C (122° ± 18°F).

4. Place the hydraulic activation control lever in the UNLOCKED position.

5. Move the joystick for the bucket to the full bucket CLOSE position (full extension of bucket cylinder) and HOLD in this position.

6. Check the pressure reading for the main relief valve pressure setting. Refer to Table 2.

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

8. If the pressure is not within the specification, refer to "Adjustment Procedure".

Pressure Drop Check

The pressure drop should be checked for each individual circuit. The pressure drop should not exceed 10 percent of the relief valve specification for the circuit being tested.

1. Start the engine.

2. Place the engine speed at high idle.

3. Increase the hydraulic oil temperature to 50° ± 10°C (122° ± 18°F).

4. Move the joystick for a full BUCKET operation and hold.

5. Quickly reduce the engine speed from HIGH idle to LOW idle.

6. Check the pressure reading. Refer to Table 2 for the correct pressure drop range.

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

8. Repeat steps 1 to 7 in order to test each hydraulic circuit.

The pressure drop should not exceed 10 percent of the rated pressure.

Adjustment Procedure

Illustration 4	g02655396
Main relief valve located on the bottom left side of the main control valve (P) Protective cap (A) Adjustment screw (under cap) (L) Locknut

1. Remove the protective cap.

2. Loosen the locknut.

3. Turn the adjustment screw until the pressure reading at the pressure tap is within the specification.

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

   Note: Always make final pressure adjustments on pressure rise.

4. Tighten the locknut.

5. Test the pressure setting again. Refer to "Test Procedure".

6. Replace the protective cap.

Worksheet