Hydraulic Drift
It is the load slowly moving on its own while the control lever is in neutral. A boom held in the air lowering within minutes is the typical example. The cause is either internal leakage past the valve spool, leakage at the cylinder piston, or the lock valve holding the load failing to do its job.
Diagnosis requires isolating where the leakage is, and there is a simple method for this:
- With the load held in the air, both hoses of the cylinder are closed off. If the drift stops, the leakage is on the valve or line side.
- If the load still descends with the hoses closed, the leakage is inside the cylinder; the piston seal is passing.
- If there is a load holding valve, its cleanliness and seating are checked first; even a single particle trapped under the spool is enough to cause leakage.
Drift is not only a comfort issue; on a machine with a suspended load it is a safety matter. Never work under the load, and always support the load mechanically before maintenance.
If drift is seen on a machine fitted with a wireless proportional remote control, do not look for the source in the kit: the kit moves the lever and does not touch the hydraulic circuit. If the lever stays in neutral but the load moves, the problem is in the vehicle's own valve and must be solved there.
Where this term is used: What Is a Hydraulic Lever Retrofit Kit? Definition, Components, Operating Principle