By Dovydas Kersys · Chapter 32 of 40 in Hydraulic Troubleshooting.
Before you begin: Hydraulic equipment can contain lethal stored energy. Only trained and authorized personnel should perform hydraulic work. Isolate energy, support loads, verify the pressure state, use pressure-rated instruments and follow site-specific lockout/tagout procedures. The diagrams are simplified training illustrations; use the actual machine schematic and manufacturer instructions.
Accumulators store hydraulic energy and can smooth pulsation, supply peak flow, maintain pressure or absorb shock. Because they store energy, troubleshooting requires strict isolation and verified depressurization before gas-side service.
In practice, the fastest diagnosis comes from deciding what the component is supposed to control and then measuring the variable on both sides of that component. Pressure tells you about load and restriction; flow tells you about speed; temperature tells you where power is being lost; leakage tells you whether clearances or seals are allowing oil to bypass the intended path.
Figure 32. Simplified diagnostic view for 32. Accumulators and Precharge Problems.
What the technician may observe
- rapid pressure drop after pump stops
- pump cycles excessively
- pressure spikes worsen
- accumulator seems “empty”
- bladder failure contaminates system
Diagnostic sequence
- Identify accumulator type and intended function. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Isolate and depressurize the hydraulic side using the approved procedure. Record the result before changing the next variable so the test actually narrows the fault.
- Check nitrogen precharge with correct charging equipment. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Compare precharge with system design and temperature conditions. Record the result before changing the next variable so the test actually narrows the fault.
- Inspect for gas valve leakage or bladder damage. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Check whether an isolation or dump valve is malfunctioning. Record the result before changing the next variable so the test actually narrows the fault.
How to interpret the measurements
Begin by asking whether the symptom affects the whole machine or only this function. If other functions sharing the same supply remain normal, a common pump or reservoir fault becomes less likely and the local valve, actuator, plumbing and mechanical load deserve more attention.
Next, compare pressure upstream and downstream while oil is actually flowing. A large pressure difference across a component means that component or passage is consuming hydraulic energy. If flow is low everywhere, investigate pump delivery, inlet conditions, speed and major internal leakage before blaming a local valve.
Finally, repeat the test at the condition that creates the complaint: hot oil, full load, a particular direction, low speed or rapid cycling. Hydraulic clearances, viscosity, pilot pressures and valve forces change with operating condition, so a static test may look normal while the production fault remains.
Corrective actions after the cause is proven
- Use dry nitrogen only; never oxygen or shop air.
- Restore correct precharge.
- Replace damaged bladder or accumulator components.
- Verify automatic dump function where safety requires it.
Common mistakes
- Adjusting the relief or compensator before recording the original setting and proving that the setting is wrong.
- Replacing a component because it is hot, even though the heat may be arriving from an upstream restriction or continuous bypass flow.
- Calling a problem “low pressure” when the actual complaint is low flow or excessive mechanical load.
- Testing only with cold oil when the production fault appears after the system reaches operating temperature.
Field rule: For 32. accumulators and precharge problems, do not replace a component until one measurement or isolation test shows how it fails to perform its intended function.
Symptom-to-next-test table
| Observed condition | First useful test |
|---|---|
| Rapid pressure drop after pump stops | Measure pressure at pump and actuator under the actual load. |
| Pump cycles excessively | Measure the controlled variable before and after the suspected component. |
| Pressure spikes worsen | Measure pressure at pump and actuator under the actual load. |
| Accumulator seems “empty” | Measure the controlled variable before and after the suspected component. |
Field practice
Before leaving the machine, write down three numbers that would let another technician judge whether the repair truly restored normal operation. Good choices are usually operating temperature, a pressure at a defined machine state, and either flow or cycle time. This creates the baseline that makes the next fault faster to diagnose.
Continue the series
- Previous chapter: Hydraulic Hoses, Tubes, Fittings and Hidden Restrictions
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Adapted from Hydraulic Troubleshooting for Maintenance Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.