By Dovydas Kersys · Chapter 24 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.
Check valves seem simple, but they can create difficult faults when debris prevents seating or when a pilot signal is missing. Load-holding versions also demand special caution because they may be supporting stored energy.
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 24. Simplified diagnostic view for 24. Check Valves and Load-Holding Faults.
What the technician may observe
- cylinder drifts down
- actuator locks and will not retract
- pressure remains trapped unexpectedly
- one direction has excessive resistance
- load drops slightly when valve shifts
Diagnostic sequence
- Support and secure the load before testing. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Measure pressure on both sides of the check. Record the result before changing the next variable so the test actually narrows the fault.
- Verify pilot pressure reaches a pilot-operated check. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Check pilot ratio and required release pressure. Record the result before changing the next variable so the test actually narrows the fault.
- Inspect seat/poppet for contamination or damage. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Confirm orientation and cracking pressure of replacement cartridges. 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
- Replace damaged seats or cartridges.
- Correct missing pilot plumbing.
- Use proper load-holding components rather than relying on directional spool leakage.
- Document trapped-pressure release procedures.
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 24. check valves and load-holding faults, 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 drifts down | Secure the load, then isolate valve leakage from actuator leakage. |
| Actuator locks and will not retract | Measure the controlled variable before and after the suspected component. |
| Pressure remains trapped unexpectedly | Measure pressure at pump and actuator under the actual load. |
| One direction has excessive resistance | 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 Directional Control Valves and Sticking Spools
- Next chapter: Hydraulic Flow Controls and Unexpected Speed Changes
- 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.