By Dovydas Kersys · Chapter 22 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.
Pressure-control valves can look similar on a manifold but perform very different jobs. A reducing valve controls downstream pressure, a sequence valve starts a later function, and a counterbalance valve controls or holds a load.
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 22. Simplified diagnostic view for 22. Reducing, Sequence and Counterbalance Valves.
What the technician may observe
- secondary circuit pressure too high or low
- functions occur in wrong order
- vertical cylinder creeps or runs away
- actuator hesitates before moving
- valve setting changes with return pressure
Diagnostic sequence
- Identify which port is sensed and which port drains. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Measure inlet, outlet and pilot/drain pressures during the function. Record the result before changing the next variable so the test actually narrows the fault.
- Verify sequence pressure against the actual load requirement. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Check counterbalance pilot ratio and pilot supply. Record the result before changing the next variable so the test actually narrows the fault.
- Inspect for contamination in small pilot passages. Compare the reading with a known-good baseline or the machine specification rather than relying on a generic value.
- Check whether return backpressure is influencing a valve that expects low drain pressure. 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
- Restore correct valve type and cartridge orientation.
- Set values from documented machine data.
- Correct blocked external drains.
- Use load-holding valves appropriate to the safety requirement.
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 22. reducing, sequence and counterbalance valves, 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 |
|---|---|
| Secondary circuit pressure too high or low | Measure pressure at pump and actuator under the actual load. |
| Functions occur in wrong order | Measure the controlled variable before and after the suspected component. |
| Vertical cylinder creeps or runs away | Secure the load, then isolate valve leakage from actuator leakage. |
| Actuator hesitates before moving | 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 Relief Valves: Setting, Instability and Leakage
- Next chapter: Hydraulic Directional Control Valves and Sticking Spools
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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.