Hydraulic System Won’t Hold Pressure: What to Check and How to Fix It

If your hydraulic system loses pressure under load, won’t maintain cylinder position, or shows sluggish performance, you’re likely dealing with internal leakage or component failure. A system that won’t hold pressure wastes energy, reduces force output, and often leads to sudden breakdowns.

What Does “Not Holding Pressure” Really Mean?

When a hydraulic system fails to maintain pressure, fluid is escaping internally through a bypass, worn seal, or faulty valve. The pump may still run and build pressure, but the system can’t hold that pressure where it’s needed — usually in cylinders, motors, or valve sections.

Top Causes of Pressure Loss in Hydraulic Systems

  • Worn pump: An old or damaged pump slips internally, losing flow and pressure output.
  • Leaky relief valve: A stuck or misadjusted relief valve constantly dumps fluid back to tank.
  • Cylinder bypass: Worn piston seals allow fluid to pass internally, reducing holding force.
  • Directional control valve leakage: Internal spool wear or damaged seals allow pressure to bleed off.
  • Contaminated or incorrect fluid: Poor lubrication or incorrect viscosity leads to internal wear and slippage.

How to Diagnose Pressure Loss

  1. Use a pressure gauge to measure system pressure at the pump outlet, control valve, and cylinder ports.
  2. Compare pressure readings under idle, operating, and holding conditions.
  3. Isolate suspected components by blocking off circuits and observing pressure decay.
  4. Listen for bypassing (hissing) at the relief valve or directional valves.

Effective Repairs Based on Cause

  • Relief valve replacement or adjustment: Set to manufacturer’s pressure spec and test performance.
  • Pump rebuild or replacement: If the pump can’t maintain pressure under load, it’s time for overhaul.
  • Cylinder resealing: Install new piston seals to prevent internal bypass and restore holding force.
  • Valve service: Replace worn spools and o-rings in leaking valve sections.

Preventing Future Pressure Issues

  • Flush hydraulic system regularly and use OEM-spec oil
  • Replace filters before restriction indicators trigger
  • Check and document pressure readings during routine service
  • Install test ports at key locations for fast future diagnostics

Conclusion

A hydraulic system that won’t hold pressure under load is unreliable, inefficient, and at risk of failure. With the right diagnostic tools and repair strategy, most pressure problems can be corrected quickly — restoring full power, control, and productivity to your equipment.

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