The main relief valve sets the maximum pressure the hydraulic system is allowed to reach. Every digging force, every lifting capacity and every stall load is limited by it, so a relief that opens early — through misadjustment, a weak spring or a damaged seat — makes the entire machine weak in every function at once. That signature is what separates a relief problem from a pump or cylinder problem: one circuit weak is a component; everything weak is a limit. The check itself is straightforward: fit a gauge of adequate rating to the pressure test port specified in the service manual, bring the oil to operating temperature, and load the circuit against the relief exactly as the manual directs, because the function used for the test and the engine speed during it are specified per model. Compare the reading against the specification for that serial number, not against a remembered figure from a similar machine. Only after a low reading is measured and recorded is adjustment justified, and then in small steps with the locknut secured afterward.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Every function is weak under load, not just one | Boom, stick, bucket and travel all feeling feeble together is the signature of a system-level limit: relief pressure, pump output or engine power. The relief is the cheapest of the three to check. |
| The machine stalls functions well before it used to | A relief opening early caps the force available. Work that used to finish now stops halfway, with no noise and no smoke. |
| Pressure rises during the test, then falls back suddenly | A relief that lifts and then cannot reseat cleanly gives a falling or fluttering gauge instead of a stable ceiling. That is a seat or contamination problem, not a setting problem. |
| The weakness came on suddenly, not gradually | Springs break and seats pick up debris in a single event. A machine that was strong yesterday and weak today has not worn out overnight; something has changed state. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Misadjustment | A relief screw that has been turned without a gauge — often by a previous attempt to buy back power — leaves the setting low, high or unstable. Adjustment without measurement is the most common cause of a wrong setting. |
| A weak or broken spring | Springs lose rate with age and heat, and a broken spring coil drops the ceiling abruptly. No adjustment range fixes a spring that has failed. |
| Seat damage or contamination | A particle trapped on the seat, or a seat scored by previous contamination, lets the valve leak below its setting. The gauge reads low and the valve may buzz or run hot. |
| The wrong cartridge fitted previously | Relief cartridges for different pressure ranges look identical. A cartridge from the wrong range fitted during an earlier repair produces a ceiling that adjustment cannot correct. |
What the gauge tells you, and what to do next
| Gauge behavior | What it means and the next step |
|---|---|
| Stable reading below specification | Adjustment, weak spring or wrong cartridge; adjust toward spec in small steps and watch whether the ceiling follows. |
| Stable reading at specification | The relief is innocent; move the investigation to pump output and engine speed under load. |
| Reading rises then falls or flutters | Seat leakage or contamination; remove and inspect the cartridge before any adjustment. |
| No pressure rise at all | Wrong test port, a circuit not actually loaded, or a gauge fault; verify the setup before condemning the valve. |
| Reading above specification | Someone has been here before with the same idea; return the setting to spec and find the real fault they were masking. |
How to confirm it
- Get the specification for the exact machine
Relief settings differ between models, serial ranges and even individual circuits. Take the figure from the service manual for the serial number in front of you, and note the engine speed and oil temperature the specification assumes, because both change the reading.
- Fit a gauge rated comfortably above the expected pressure
Use the test port named in the manual, a gauge with a safety margin above the specification, and fittings that match the port thread exactly. Keep the gauge and hose out of pinch points and moving linkages before the engine starts.
- Warm the oil to operating temperature
Cold oil reads differently from working oil, and the specification assumes a warm machine. Run the hydraulics through their range until the tank is at normal working temperature before any number is written down.
- Load the circuit against the relief as the manual directs
Each model specifies which function is held at stall for the test. Hold it, read the gauge at the specified engine speed, and record the number with the conditions. Release the load between readings rather than holding the system on relief.
- Adjust only against the gauge, in small steps
Where the reading is low and the cartridge is confirmed correct and clean, adjust in small increments, re-testing after each, and secure the locknut afterward. If the ceiling will not follow the adjustment, the spring or the cartridge is the fault and adjustment time is over.
- Verify the repair under real work
After the setting is confirmed on the gauge, put the machine through the work that exposed the weakness. A number on a gauge and a function under load together close the job; either one alone leaves it open.
What to do about it
Adjustment to specification: where the cartridge is sound, bring the setting to the manual's figure, secure the locknut and mark it. An unmarked adjustment invites the next undocumented turn of the screw.
Cartridge replacement: a damaged seat, a weak spring or a wrong-range cartridge means a replacement matched to the valve model and pressure range, fitted into a clean cavity with new seals where the kit provides them.
System cleaning: contamination found on a relief seat did not arrive alone. Change the return and pilot filtration and inspect the tank before the new cartridge is asked to survive in the old oil.
Parts for any of these repairs — relief cartridges, valve seal kits, pressure gauges and test hoses, and filtration elements — are supplied by Guangzhou Shenyue Machinery Technology Co., Ltd. from Guangzhou, with 3,000+ part types on the shelf and 100,000+ part numbers available to order, and the grade of every line declared as genuine, OEM-quality or aftermarket. 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 |
|---|---|
| Relief cartridges | Genuine; OEM-quality matched to valve model and pressure range. |
| Valve seal kits | Genuine; OEM-quality kit by valve section number. |
| Pressure gauges and test hoses | Rated above system pressure, with the correct port fittings. |
| Filtration elements | Genuine; OEM-quality; aftermarket element to the same rating. |
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
Can I just turn the relief up to get the power back?
No, and this is the single most expensive habit in the field. The relief protects the pump, the hoses and the structure. Turning it up to mask a worn pump or a mechanical fault converts a repair into a failure, and the components downstream were never rated for the new ceiling.
How often do relief settings drift on their own?
Slowly, if the machine is healthy. Spring relaxation and seat wear move a setting over thousands of hours, not weeks. A machine that repeatedly needs relief attention has a contamination problem or a cartridge problem, and the relief is the messenger.
Do I need a flow meter as well as a pressure gauge?
For the relief check itself, no. Pressure at stall against the manual's figure answers the relief question. Flow measurement becomes necessary when the relief is proved innocent and the investigation moves to pump output, which is a different test at a different port.