Hydraulic pump Fault Diagnosis Summary

Summary of common problems with hydraulic pumps

H-STAR

6/18/20122 min read

Faulty input signal from pump control source to control module – Check input control signal, repair or replace related parts if necessary.
Faulty control linkage or blocked control orifice in pump displacement control module – Adjust or repair control module, replace if necessary.
Multifunction valve leakage – Swap the two multifunction valves; if the system fault changes direction, replace the damaged valve.

Low oil level in tank – Add hydraulic oil to proper level.
Radiator insufficient – Check air flow and temperature through radiator; clean, repair or replace.
Low charge pressure – Measure charge pressure, check and adjust charge pressure relief valve, replace if necessary; or repair charge pump with excessive leakage.
High vacuum in charge pump suction line – Check vacuum; if too high, inspect suction filter and replace; check suction line diameter, length and fittings.
System relief valve set too low – Check high-pressure relief valve or pressure limiter setting, adjust or replace multifunction valve.
Excessive internal leakage in motor – Block flush valve spool; without flush valve, observe motor case drain flow; if too high, replace motor.
System pressure too high – Measure system pressure and reduce load if necessary.

Faulty input signal to control module – Check input control signal, repair or replace if necessary.
Control linkage fault or blocked orifice – Adjust, repair control module, replace if necessary.
Faulty pressure limiter, high-pressure relief valve or charge check valve – Swap multifunction valves; if fault changes direction, replace damaged one.
Shuttle valve spool of flush valve stuck, causing low charge pressure in one direction – Measure charge pressure in forward/reverse; check or repair circuit flush valve.

Low oil level – Add oil.
Faulty input signal – Check and repair/replace.
Control linkage/orifice fault – Adjust, repair or replace control module.
Bypass valve open – Close bypass valve, replace multifunction valve if damaged.
Low charge pressure at neutral – Measure charge pressure at neutral; if low, adjust charge relief valve.
Charge pressure drops excessively when off-neutral – Check flush relief valve or system relief valve setting; adjust/replace; else check charge pump.
Charge relief valve faulty or set too low – Adjust or replace.
Clogged charge pump suction filter – Inspect and replace.
Charge pump failure – Repair or replace.
Low system pressure due to faulty multifunction valve – Repair or replace.

Low pressure at motor inlet (multifunction valve set too low) – Measure inlet pressure; increase valve setting if necessary.
Variable motor stuck at minimum displacement – Check control supply pressure or repair displacement control module; check for blocked orifice.
Excessive internal leakage – Check seals (O-rings, gaskets, fittings); repair or replace components with excessive leakage.

Low oil level – Add oil.
Incorrect pump output flow (swashplate off position) – Measure pump flow and speed; ensure pump reaches full displacement.
Variable motor displacement control failure – Check if displacement adjustment responds; if not, repair or replace control module.
Excessive internal leakage – Check seals; repair or replace components.

Low oil level causing cavitation – Add oil.
Air in system (bubbles) – Check for foam in tank and leaks in suction line; let oil settle after repair; run system at low speed repeatedly to exchange oil.
High suction vacuum (clogged filter or undersized suction line) – Check and replace filter; check suction line diameter.
Loose coupling – Replace coupling or pump/motor.
Misalignment of shafts – Realign shafts.