By Dovydas Kersys · Chapter 3 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.
A simple force calculation prevents many bad diagnoses. If the load requires more pressure than the system is designed to provide, adjusting valves will not make the machine healthy. Conversely, a system that reaches the required pressure but still cannot move may have a mechanical problem.
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 3. Simplified diagnostic view for 3. Cylinder Area, Force and Load Calculations.
What the technician may observe
- cylinder will not lift rated load
- machine works at low load only
- extension and retraction forces differ
- pressure spikes near end of stroke
- unexpectedly high pressure after tooling change
Diagnostic sequence
- Confirm bore and rod diameter from drawings or nameplate. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Calculate cap-end and rod-end effective area. Record the result before changing the next variable so the test actually narrows the fault.
- Convert required load force into theoretical pressure. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Add a practical margin for friction and dynamics rather than assuming ideal efficiency. Record the result before changing the next variable so the test actually narrows the fault.
- Compare theoretical pressure with actual gauge readings. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Check for mechanical binding if pressure is adequate yet motion is poor. 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
- Return relief and counterbalance settings to engineered values.
- Correct overloaded or mechanically jammed tooling.
- Verify cylinder size after replacement; “same mounting” does not guarantee same area.
- Update maintenance notes when machine loading is changed.
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 3. cylinder area, force and load calculations, 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 |
|---|---|
| Cylinder will not lift rated load | Measure the controlled variable before and after the suspected component. |
| Machine works at low load only | Measure the controlled variable before and after the suspected component. |
| Extension and retraction forces differ | Measure the controlled variable before and after the suspected component. |
| Pressure spikes near end of stroke | Measure pressure at pump and actuator under the actual load. |
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 Pressure, Flow, Force and Speed
- Next chapter: Reading Hydraulic Schematics Without Guessing
- Browse all Hydraulic Troubleshooting chapters
Adapted from Hydraulic Troubleshooting for Maintenance Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.