How Do You Troubleshoot a Hydraulic Pump

Troubleshooting a hydraulic pump requires a systematic approach to identify whether the issue lies with the pump itself or other hydraulic components. Below is a step-by-step guide to diagnose common hydraulic pump failures.

1. Initial Checks (Quick Diagnostics)

A. Visual & Basic Inspections

✔ Check Hydraulic Fluid

Is the oil level adequate (Low oil → Cavitation)

Is the oil contaminated (Dark, milky, or gritty = waterdirt ingress)

Is the viscosity correct (Too thick → Poor flow; too thin → Leakage)

✔ Listen for Unusual Noises

WhiningHissing → Cavitation (air in system)

GrindingKnocking → Bearing or internal component failure

✔ Check for Leaks

External leaks (shaft seals, fittings)

Internal leaks (excessive case drain flow)

✔ Verify Drive System

Is the motorengine running at the correct RPM

Is the pump shaft rotating (Sheared key or coupling failure)

2. Performance Testing

A. Pressure Test

Install a pressure gauge at the pump outlet.

Deadhead the pump (block flow temporarily) – pressure should spike to the system relief valve setting.

No pressure → Pump failure, relief valve stuck open, or major leakage. 

Low pressure → Worn pump, internal leakage, or faulty compensator.

B. Flow Test

Disconnect the outlet hose and direct flow into a container.

Measure flow at rated RPM (compare to pump specs).

No flow → Clogged inlet, pump failure, or suction leak.

Low flow → Worn internals, air ingress, or incorrect speed.

C. Case Drain Flow Check

Measure flow from the case drain port (if applicable). 

Normal 10% of rated flow

Excessive flow (15%) → Severe internal wear (pistons, vanes, or gears).

3. Component-Specific Troubleshooting

A. Gear Pumps (G2, G3, AZPF Series)

Symptom Possible Cause Solution

No pressure Broken shaft, clogged inlet Inspect drive coupling, clean suction filter

Low flow Worn gears, excessive clearance Replace gearsside plates

Loud noise Cavitation, air leaks Check suction line, prime pump

B. Vane Pumps (PV7, PVV Series)

Symptom Possible Cause Solution

Pressure drop Worn vanescam ring Replace vanes, inspect cam profile

Erratic operation Contaminated oil Flush system, replace filter

Overheating Internal leakage Check case drain flow

C. Axial Piston Pumps (A10V, A4V, A7V Series)

Symptom Possible Cause Solution

No pressure Swashplate stuck, servo piston failure Inspect control mechanism

High case drain flow Worn pistonsbarrel Rebuild pump

Unstable pressure Dirty control valve Clean or replace valve

4. Advanced Diagnostics

A. Cavitation Check

Symptoms Whining noise, low flow, pump overheating.

Causes 

Clogged inlet filter 

Restricted suction line

Oil viscosity too high

Fix

Check vacuum at inlet (should be  -0.5 bar)

Use a larger suction hose if needed

B. Air Ingression Test

Symptoms Foamy oil, erratic actuator movement.

Causes

Loose suction line fittings 

Low oil level 

Shaft seal leak

Fix 

Tighten connections

Replace seals

C. Contamination Analysis

Symptoms Sticking valves, scoring on components. 

Test

Check ISO cleanliness code (should be ≤181613)

Use a patch test to inspect for metal particles.

Fix

Replace filters 

Flush system

5. Repair or Replace

Repair If

Minor sealO-ring leaks

Contamination is the only issue (flush & replace filters)

 Wear is within tolerance (e.g., gear backlash 0.1mm)

Replace If

Major scoring on pistonsgears

Housing is cracked

Cost of repair 60% of a new pump

6. Preventive Maintenance Tips

- Monitor oil temperature (ideal 40–60°C)

- Use proper filtration (5µm absolute)

- Check alignment (misalignment 0.05mm causes wear)

- Inspect hosesfittings annually

Need More Help

If you provide

Pump model (e.g., A10VSO 45)

Symptoms (noise, pressure loss, etc.)

System details (pressure, flow rate)

I can guide you through specific disassembly steps or recommend replacement parts!

Elephant Fluid Power has dozens of standard parts and seal production workshops, We stock an extensive inventory of OEM & new aftermarket replacement piston pump parts for mobile and industrial applications. The piston pump spares include pumps from manufacturers such as Bosch, Vickers, Rexroth, Kawasaki, Hitachi, Denison, Linde, Komatsu, Sundstrand, Parker, Oilgear, and more.