Kobelco Excavator Slow Overall Movement: Troubleshooting & Main Relief Valve Adjustment Guide

When operating a Kobelco excavator, encountering a sudden or gradual slow overall movement can severely impact work efficiency.  In today’s blog post, we’ll shares a professional diagnostic and adjustment guide focusing on the main relief valve and hydraulic system data.

Step 1: Check Monitor Data (Main Pressure & Pilot Pressure)

First, enter the excavator cab to check system pressures through the monitor display:

• Turn on the key and navigate to Service Diag 2 (around page 30+).

• Locate items C-1 and C-2, which represent the main system pressure.

• Start the engine and perform boom or arm movements to observe the pressure change. Normal main pressure should reach between 31.2 and 33.0 MPa (310–330).

• If the main pressure is insufficient, check the pilot pressure. If the pilot pressure fails to reach 3.0, it can directly cause insufficient main pressure.

Step 2: Locate and Inspect the Main Relief Valve

If the monitor data indicates abnormal pressure, the issue often points to the main relief valve located on the control valve. Do not rush to replace it immediately, as the main relief valve can be adjusted and serviced.

Step 3: How to Adjust the Main Relief Valve Pressure

Over time, internal valve needles wear out or O-rings age, leading to pressure drops. Follow these steps to adjust the pressure:

1. Loosen the outer lock nut of the relief valve.

2. Use an internal hex wrench to turn the inner small screw. Turning it inward increases the pressure; turning it outward decreases it.

3. For machines with multi-stage adjustments, the second section can also be adjusted by loosening its retaining position and moving the overall body inward.

Step 4: Replacing O-Rings and Maintenance

If adjusting the screw or replacing aged O-rings (which cause internal oil leakage) does not restore the ideal pressure, consider replacing the entire main relief valve component.