Hydraulic Pressure Adjustment Explained with Field Cases and Practical Insights

In construction machinery, hydraulic pressure is the lifeblood of movement, control, and lifting power. Whether it’s an excavator, loader, or dozer, the pressure settings directly influence how fast, strong, and safely the machine performs. Low pressure results in sluggish response and weak lifting; excessive pressure can damage seals, hoses, or even the pump itself.

Adjusting hydraulic pressure isn’t just about turning a screw—it’s a system-level task involving pumps, valves, actuators, and control logic. Especially after replacing a hydraulic pump or main control valve, recalibrating pressure is essential to restore proper function and avoid erratic behavior.

Key Pressure Points and Terminology

Hydraulic systems often include multiple pressure settings. Common ones include:

• Main relief pressure: Limits the system’s maximum pressure to prevent overload
• Auxiliary circuit pressure: Controls attachments like breakers or augers
• Pilot pressure: Low-pressure control signals that activate main valves
• Cold-start pressure: Temporarily reduced pressure during warm-up
• Shock relief pressure: Absorbs sudden spikes caused by abrupt load changes

Glossary:

• PSI (pounds per square inch): Common pressure unit in North America
• MPa (megapascal): Metric pressure unit; 1 MPa ≈ 145 PSI
• Relief valve: A safety valve that limits pressure
• Pilot line: A low-pressure line that sends control signals
• Load sense: A system that adjusts pressure based on demand

Adjustment Procedure and Safety Tips

To adjust hydraulic pressure correctly:

• Connect a calibrated pressure gauge to the test port
• Start the engine and let it idle until oil reaches operating temperature
• Slowly turn the relief valve screw—clockwise to increase, counterclockwise to decrease
• Observe system response, including speed, sound, and smoothness
• Check for leaks, overheating, or vibration after adjustment
• Record final pressure settings for future reference

Precautions:

• Never exceed the manufacturer’s recommended pressure limits
• Avoid adjusting pressure when oil is cold or machine is under load
• Replace damaged seals or hoses before increasing pressure
• Always wear eye protection and gloves when working near pressurized lines

Case Study: Restoring Power to an Aging Excavator

A technician in Shandong was called to repair an aging Hitachi EX200 that had lost digging power. The owner had replaced the main pump but skipped pressure calibration. When tested, the main relief pressure was only 18 MPa—well below the factory spec of 30 MPa.

After adjusting the relief valve and confirming pilot pressure at 3.5 MPa, the machine regained full digging force. The operator said it felt “like a new machine,” and the technician emphasized that “replacing a pump without adjusting pressure is like changing shoes without tying the laces.”

Industry Incident: Pressure Overshoot Leads to Injury

In 2023, a newly delivered loader in Jiangsu suffered a hydraulic hose rupture during its first week of operation. The blast of oil caused minor burns to a nearby operator. Investigation revealed that the relief valve had been set 20% above spec during pre-delivery inspection. The incident led to stricter pressure checks and mandatory operator training at several rental companies.

Recommendations for Operators and Technicians

To maintain hydraulic system health:

• Check pressure settings after any major component replacement
• Keep a log of pressure readings and adjustments
• Use manufacturer-approved fluids and filters
• Learn basic hydraulic principles to understand system behavior
• Adjust pressure seasonally if operating in extreme temperatures

For machines working in cold climates, consider using synthetic hydraulic oil and reducing pressure during startup to protect seals and pumps.

Conclusion

Hydraulic pressure adjustment is both a technical skill and a practical art. It affects not just performance, but safety, longevity, and operator confidence. In the world of steel and oil, pressure is the pulse—and knowing how to set it right keeps the heart of the machine beating strong.