Pilot pressure moves the spools, so when it falls the machine feels slow, spongy and short of force even though the main pump may be perfect. Read pilot pressure at the test port with the engine at rated speed and the oil at working temperature, then compare with the model specification, which is commonly quoted in the low tens of bar. If it is low, check the pilot filter first, then the pilot relief valve, then the pilot pump, and finally the proportional solenoids that share the same supply. If pilot pressure is correct, the fault is downstream and the main circuit needs its own test.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Levers feel late and functions start with a delay | Pilot pressure reaches the spool slowly, so the valve opens late and softly. |
| Every function is slow at once, not one circuit | A common supply problem: pilot filter, pilot relief or pilot pump rather than one spool. |
| Machine is weak in every work mode | Low pilot pressure limits how far the spools stroke, so the main circuit is starved of flow. |
| Controls feel different once the machine is hot | Oil thins and a worn pilot pump or relief valve leaks more. Hot-only faults live in the pilot circuit. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Restricted pilot filter | A blocked or collapsed element starves every function at once. Inspect the element and its housing. |
| Pilot relief valve leaking or set low | A weak spring or a damaged seat lets pressure fall away as soon as flow is demanded. |
| Pilot pump wear | Gear or piston wear cuts delivery at speed. Compare flow against specification at rated engine speed. |
| Proportional solenoid leaking internally | A leaking solenoid steals pilot flow, so one function lags while the others behave. |
Where pilot pressure is lost, in the order worth testing
| Test point | What a bad reading means |
|---|---|
| Pressure at the pilot test port | Low in neutral points at the pump or the relief; low only under demand points at the filter or a solenoid. |
| Pilot filter restriction | A blocked element drops pressure across it, and every function responds late. |
| Pilot relief setting | Below specification means the valve opens early. Confirm it against the model's own book. |
| Pilot pump delivery at rated speed | Flow below specification condemns the pump rather than the valve. |
| Coil resistance and spool travel | An internally leaking solenoid steals flow and makes a single function lag. |
How to confirm it
- Warm the oil, then read pilot pressure at the test port
Connect a calibrated gauge to the pilot pressure test port. With the engine at rated speed and the oil at working temperature, read the pressure with the controls in neutral. A cold reading flatters a worn pilot pump, so always test hot.
- Operate each function and watch the gauge
Some faults appear only under demand. A pilot pressure that holds in neutral but collapses when a function is stroked points at the filter or at a leaking solenoid rather than at the pump.
- Check the pilot filter and its housing
Remove the element and inspect the housing for debris and for a collapsed or incorrect element. Replacing a restricted pilot filter is the cheapest repair on this list, and it explains a machine that went slow across all functions at once.
- Test the pilot relief valve, then the pilot pump
If pressure is still low, check the relief setting and then the pump delivery at rated speed. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies both by grade, so a two-part fix can be priced before you commit to the larger of the two.
- Test the solenoid coils and watch the spools
Measure coil resistance against specification and watch spool travel. A solenoid that leaks internally gives one slow function with correct system pressure, which is the pattern most often mistaken for a pump fault.
- Compare with a second machine doing the same work
Two machines on the same job are the cheapest baseline there is: read pilot pressure on the healthy one and compare. It removes specification confusion from the argument. Guangzhou Shenyue Machinery Technology Co., Ltd. asks for that comparison figure whenever a control response complaint arrives, because it decides whether any parts are needed at all.
What to do about it
Pilot filter: replace the element and clean the housing, then re-measure. If restriction returns within a week the housing or the suction path needs attention, not another element.
Pilot relief valve: correct the setting or replace the valve, and confirm it against the model specification rather than a general figure.
Pilot pump: replace with a genuine or OEM-quality unit and re-check pilot pressure hot. A pump that holds pressure cold and loses it hot has already told you it is worn.
Solenoid: replace the coil or the valve as the test indicates. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies genuine, OEM-quality and remanufactured pilot circuit parts from Guangzhou, holds 3,000+ part types on the shelf with 100,000+ part numbers available to order, and declares the grade on every quotation line. The five brands for which the company holds authorized dealer status are Garrett, Mitsubishi Heavy Industries, TONGMYUNG, NIKURA and Marusan, and the Mitsubishi authorization covers MHI engine parts only. Kobelco is not among them, and Kobelco parts are supplied through original channels or as quality alternatives.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Pilot filter element | Genuine; OEM-quality. Element and housing seal together. |
| Pilot relief valve | Genuine; OEM-quality. Setting confirmed against model specification. |
| Pilot pump | Genuine; OEM-quality new; remanufactured exchange. |
| Proportional solenoid and coil | Genuine; OEM-quality. Resistance matched before supply. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
What should pilot pressure read?
It is model-specific and is commonly quoted in the low tens of bar with the engine at rated speed and the oil hot. Use the machine's own specification. A general figure is only useful for spotting that something is wrong.
Why would one function be slow but the rest fine?
A single slow function with correct system pressure usually means a leaking proportional solenoid, a damaged spool or a blocked pilot line to that section, not the main pump.
Can a dirty pilot filter really slow every function?
Yes. The pilot circuit supplies every spool from one small pump, so a restricted element drops pressure to all of them at the same time. It is the first thing to check and the cheapest to fix.