Hydraulics
Why does the boom or arm drift down?
If the boom, arm or another hydraulic cylinder moves with the joystick in neutral, oil is escaping from the loaded chamber. The cause may be the cylinder, control valve, load-holding or overcenter valve, relief valve or an external leak. First distinguish visible leakage from internal leakage.
Rule out external leakage first
Inspect hoses, pipes, connections, cylinder and control valve. If oil escapes externally, the leakage point is visible.
Cylinder internal leakage
Worn piston seals can allow oil between cylinder chambers. The function drifts slowly, more when hot, without an obvious external leak. Isolate the cylinder or lines only using the specific machine’s test procedure.
Control valve
A worn spool or section body may leak internally. Contamination, incomplete return to neutral, internal cracks or a faulty check valve are also possible.
Load-holding valves
Booms and other hazardous functions may have a load holding, counterbalance, overcenter or hose rupture valve. If it does not hold, the cylinder can lower even with neutral controls.
Oil temperature matters
A cold machine that holds the boom but noticeably drifts when hot shows a typical sign of internal leakage.
What you can observe
Which function lowers, and how fast? Is it different cold and hot? Does the rate change with the load? Is there an external leak, and does it move with the joystick fully neutral?
Related problems
Further service support
Problem still there?
If these checks have not identified the cause or the fault returns, contact TSV Servis. The more initial information you provide, the sooner we can identify the next diagnostic direction.
What to send us
Send the machine model, affected function, drift rate, oil temperature, load and cylinder, control valve and load-holding valve test results.
Include the make and model, S/N or a nameplate photo, engine model if known, operating hours, exact code or display photo and when the fault occurs.
Also tell us what you have already checked or replaced and the results. Include a photo or short video of the symptom where useful.
+420 722 307 850 · tsvcz@seznam.cz