How to Diagnose and Fix Low Hydraulic Pressure in Diesel Equipment

Hydraulic systems are essential to operating heavy-duty diesel equipment, providing the power needed for lifting, pushing, and maneuvering massive loads. When hydraulic pressure drops, machinery performance suffers, leading to sluggish operation, overheating, and potential system failure. Addressing low hydraulic pressure quickly is critical to avoiding costly repairs and extended downtime.

This guide will cover the common causes of low hydraulic pressure, step-by-step troubleshooting techniques, and proven repair methods for restoring your equipment to full functionality.

Understanding Hydraulic Pressure in Diesel Equipment

Hydraulic systems rely on the controlled movement of pressurized hydraulic fluid to transfer force and power to key components. These systems are widely used in construction, agriculture, and transportation, making them indispensable for heavy-duty operations.

Key components of a hydraulic system include:

• Hydraulic Pump – Converts mechanical energy into hydraulic energy by pressurizing fluid.
• Control Valves – Direct hydraulic fluid to specific components such as cylinders or motors.
• Hydraulic Hoses and Fittings – Transport fluid throughout the system.
• Actuators (Cylinders and Motors) – Convert hydraulic energy into mechanical movement.
• Reservoir and Filters – Stores and filters hydraulic fluid to prevent contamination.

A properly functioning hydraulic system maintains steady pressure to ensure efficient performance. When the pressure drops, it indicates that one or more of these components is malfunctioning.

Common Causes of Low Hydraulic Pressure

Identifying the root cause of pressure loss is the first step toward effective repair. Below are the most common reasons for low hydraulic pressure in diesel equipment.

1. Low or Contaminated Hydraulic Fluid

• Insufficient fluid levels lead to poor system performance and cavitation.
• Contaminants such as dirt, metal shavings, and moisture cause blockages and wear.
• Fluid degradation over time results in reduced viscosity, making it less effective.

2. Air in the Hydraulic System

• Air bubbles in the fluid create spongy operation and erratic pressure readings.
• Entrapped air can lead to cavitation, causing damage to the pump and valves.
• Loose fittings, improper fluid refilling, or leaks often introduce air.

3. Worn or Malfunctioning Hydraulic Pump

• A failing pump cannot generate adequate pressure, leading to weak operation.
• Pump failure signs include whining noises, excessive heat, and slow performance.
• Cavitation and contamination accelerate pump wear, requiring early replacement.

4. Clogged Hydraulic Filters

• Filters are designed to trap debris, but when clogged, they restrict fluid flow.
• Severe blockages force the pump to work harder, leading to overheating and pressure loss.
• Using the wrong filter type or skipping maintenance can contribute to this issue.

5. Leaky Hoses, Fittings, or Seals

• External leaks cause visible fluid loss, leading to gradual pressure reduction.
• Internal leaks allow fluid to bypass critical components, reducing system efficiency.
• Worn-out seals on cylinders and valves create hidden pressure losses that are harder to detect.

6. Faulty Pressure Relief Valve

• If stuck open, the system will struggle to build adequate pressure.
• If stuck closed, pressure spikes may damage hoses, seals, or even the pump.
• Misadjusted relief valves can cause erratic system performance.

7. Cylinder or Motor Wear

• Hydraulic cylinders and motors wear down over time, allowing fluid to bypass seals.
• Symptoms include slow movement, loss of lifting power, and excessive heat buildup.
• Cylinder drift (unintended movement when holding a load) strongly indicates internal leakage.

Step-by-Step Guide to Diagnosing Low Hydraulic Pressure

When low hydraulic pressure symptoms arise, follow this structured diagnostic process to pinpoint the root cause efficiently.

Step 1: Check Hydraulic Fluid Condition and Levels

• Inspect the fluid level in the reservoir. If it is low, refill it to the recommended level.
• Check for contaminated fluid. A milky or foamy fluid indicates air or water contamination.
• Smell the fluid—a burnt odor suggests overheating or breakdown.

Step 2: Inspect for Leaks

• Look for visible leaks around hoses, fittings, and hydraulic cylinders.
• If no external leaks are found, check for internal leaks by monitoring for excessive heat or weak cylinder operation.
• Examine connections to ensure they are appropriately tightened without over-torquing.

Step 3: Test the Hydraulic Pump

• Listen for whining, grinding, or cavitation noises indicating a failing pump.
• Use a flow meter to measure gallons per minute (GPM) and compare it to specifications.
• If the pressure is low despite no leaks, the pump may need to be replaced or rebuilt.

Step 4: Check Filters and Screens

• Remove and inspect the hydraulic filter for blockages, excessive dirt, or metal shavings.
• If contaminants are present, flush the system before replacing the filter.
• Ensure the correct filter type and micron rating are used to prevent premature clogging.

Step 5: Inspect the Pressure Relief Valve

• Use a pressure gauge to verify if the valve is regulating pressure correctly.
• The valve may be stuck open or improperly adjusted if the pressure is too low.
• If the pressure is erratic, consider replacing or cleaning the valve.

Step 6: Evaluate Cylinders and Actuators

• Observe the operation of hydraulic cylinders and motors for signs of weak performance.
• Internal seals may be damaged if a cylinder drifts or loses load-holding ability.
• Perform a leakage test to determine if fluid is bypassing internal seals.

How to Fix Low Hydraulic Pressure Issues

Once the root cause is identified, the appropriate fix is applied to restore the hydraulic system's performance.

1. Refill or Replace Hydraulic Fluid

• Use the correct fluid type and viscosity recommended by the equipment manufacturer.
• If contamination is detected, drain and flush the system before refilling.
• Monitor fluid regularly to prevent future issues.

2. Remove Air from the System

• Cycle the hydraulic system multiple times to purge trapped air.
• If air contamination persists, inspect for loose fittings or suction leaks.

3. Repair or Replace the Hydraulic Pump

• If the pump is worn, rebuilding or replacing it may be necessary.
• Address cavitation issues by ensuring adequate fluid levels and clean filters.

4. Replace Clogged Filters

• Change primary and secondary filters at manufacturer-recommended intervals.
• Install a higher-capacity filter if contamination is a frequent problem.

5. Fix or Replace Leaking Hoses and Fittings

• Tighten loose connections, but avoid overtightening, which can damage fittings.
• Replace hoses and seals that are showing signs of wear or cracking.

6. Adjust or Replace the Pressure Relief Valve

• If stuck open, clean or replace it.
• If it is over-pressurizing, adjust it to the manufacturer’s recommended setting.

7. Rebuild or Replace Worn Cylinders and Actuators

• If hydraulic cylinders leak internally, reseal or replace them.
• Address scored cylinder walls before reassembling.

Preventative Maintenance to Avoid Future Pressure Loss

To prevent low hydraulic pressure issues from recurring, follow these maintenance best practices:

• Regularly check fluid levels and condition.
• Inspect hoses and fittings for leaks or wear.
• Replace hydraulic filters at recommended service intervals.
• Bleed air from the system after repairs or fluid changes.
• Monitor pump performance and address wear early.

Conclusion

Low hydraulic pressure in diesel equipment can significantly reduce productivity and lead to costly repairs if left unchecked. Following a structured troubleshooting process, you can quickly diagnose the issue and implement the right fix to restore full hydraulic function. Contact a trusted diesel repair shop today for professional hydraulic repairs in Fredericksburg, VA.