Created on:2021-05-17 14:34

Common faults of hydraulic pump and general methods of diagnosis and elimination

Common faults of hydraulic pump and general methods of diagnosis and elimination

Fault phenomenon

Cause analysis

Exclusion method

A. The pump does not deliver oil

1. The pump doesn't work

(1) Motor shaft not rotating

① Power supply not connected

② Electrical circuit and component failure

Check the electrical and control system and remove the fault

(2) Motor heating trip

① Insufficient motor drive power

② The pressure regulating value of the system relief valve is too high or the valve core is blocked and overloaded, then the pump is shut down

③ The pump outlet check valve is installed reversely or the valve core is blocked and the pump is blocked

④ Motor fault

① Increase motor power

② Adjust the pressure value of relief valve and overhaul the valve

③ Maintenance of check valve

④ Repair or replace the motor

(3) There is no connecting key on pump shaft or motor shaft

① Missing packing

② Break off

① Replacement key

② Change key

(4) The internal sliding part of the pump is stuck

① The fit clearance is too small

② Poor precision of parts, poor assembly quality, too large coaxiality error between gear and shaft, plunger head stuck, poor verticality of blade, too large swing error of rotor, wound in rotor groove or blade scar, fracture and stuck after stress

① Disassemble and repair, and select the clearance according to the requirements

② Replace the parts and reassemble to make the fit clearance meet the requirements

2. Pump reverse

Motor steering error

① Electrical wiring error

② Pump body up rotation arrow error

① Correct the electrical wiring

② Correct the upward rotation arrow of the pump body

The pump shaft can still be turned

Internal fracture of pump shaft

① Poor shaft quality

② The sliding pair in the pump is stuck

① Check the cause and replace with a new shaft

② Exclusion method: A.L. (4)

4. The pump does not absorb oil

(1) The oil level in the oil tank is too low

(2) The oil suction filter is blocked

(3) Valve on pump suction pipe not opened

(4) The pump or oil suction pipe is not tightly sealed

(5) The suction height of the pump exceeds the standard, and the suction pipe is slender and has too many elbows

(6) The filtering accuracy of the oil suction filter is too high or the remote flow area is too small

(7) The viscosity of the oil is too high

(8) The blade of vane pump is not extended or stuck

(9) Vane pump variable mechanism action is not flexible or wear, so that the stator and rotor eccentricity is zero

(10) There is no seal between oil distribution plate and pump body of vane pump

(11) Piston pump variable mechanism failure or wear, such as poor machining accuracy, poor assembly, too small fit clearance, too large internal friction resistance of pump, servo piston, variable piston and spring mandrel stuck, individual oil passage leading to variable mechanism blocked, oil too dirty, high oil temperature, thermal deformation of parts, etc

(12) There is no seal between piston pump cylinder and valve plate (e.g. the center spring of piston pump is broken)

(1) Oil level to oil level line

(2) Clean or replace the filter element

(3) Check and open the valve

(4) Check and tighten the joint, tighten the screw of the pump cover, apply grease on the joint of the pump cover and the joint, or inject oil into the oil suction port of the pump first

(5) Reduce the suction height, replace the pipe, reduce the elbow

(6) Select appropriate filter precision and increase filter specification

(7) Check the viscosity of the oil, change the appropriate oil, and check the effect of the heater in winter

(8) Disassemble and clean, select the clearance reasonably, check the oil quality, filter or replace the oil

(9) Repair, adjust or replace the variable mechanism

(10) Disassemble, clean and reassemble

(11) Take apart and check, repair or replace parts, reasonably select the clearance, filter or replace the oil, check the effect of cooler, check the oil level in the oil tank and add it to the oil level line

(12) Replace the spring

B. Insufficient pump output

1. Low volumetric efficiency

(1) The sliding parts inside the pump are seriously worn

① The gear end face and side plate are seriously worn

② The bearing of gear pump is damaged, which makes the hole of pump wear seriously

③ The end face of valve plate of vane pump is seriously worn

④ Plunger and cylinder bore of plunger pump are seriously worn

⑤ Piston pump valve plate and cylinder face wear seriously

(1) Disassemble, clean, repair and replace

① Grinding repair or replacement

② Replace the bearing and repair it

③ Grinding the end face of valve plate

④ Replace the plunger and match it, and reassemble it after cleaning

⑤ Grind the two end faces to meet the requirements and reassemble after cleaning

(2) Poor assembly of pump

① The clearance between gear and pump body, gear and side plate, stator and rotor, plunger and cylinder body is too large

② The screw tightening torque on the cover of gear pump and vane pump is uneven or loose

③ Reverse installation of blade and rotor

① Reassemble according to the technical requirements

② Retighten the screws to achieve uniform force

③ Correct the direction and reassemble

(3) The viscosity of the oil is too low (e.g. the wrong oil is used or the oil temperature is too high)

(3) Change the oil, check the cause of high oil temperature and take cooling measures

2. Suction phenomenon of pump oil

See E.1., 2

See E.1., 2

3. The internal mechanism of the pump does not work well

See e.4

See e.4

4. Insufficient oil supply

The auxiliary pump of non self priming pump is insufficient or faulty

Repair or replace the auxiliary pump

C. The pressure is insufficient or cannot rise


See B.1

See B.1


(1) The motor output power is too small

① Unreasonable design

② There is something wrong with the motor

(1) Check the motor power and check the motor

① Check the motor power, if it is insufficient, replace it

② Check the motor and remove the trouble


(2) The output power of mechanical driving mechanism is too small, resulting in insufficient power of driving mechanism or motor

(2) Calculate the driving power and replace the driving mechanism, and recalculate the matching flow, pressure and power to make it reasonable

D. Abnormal pressure or flow


See E.1., E.2

See E.1., E.2


Individual blades are jammed or difficult to expand and contract in the rotor slot

Filter or change oil


(1) The clearance of individual blades in the rotor slot is too large, resulting in high pressure

The oil flows to the low pressure chamber

(2) Individual blade in the rotor slot clearance is too small, causing stuck

Or it's hard to stretch

(3) The fit clearance between individual plunger and cylinder bore is too large, resulting in internal friction

Large leakage


(1) Dismantle, wash, repair or replace the blades, and reasonably select the clearance

(2) Repair, make blade movement flexible

(3) Make the clearance meet the requirements after repair


See e.4

See e.4


The auxiliary pump of the non self priming pump is faulty

Repair or replace the auxiliary pump

E. The hydraulic pump is noisy


(1) The oil absorption filter is partially blocked and the oil absorption resistance is large

(2) The oil suction pipe is close to the liquid level

(3) Oil suction position too high or tank level too low

(4) The sealing of pump and oil suction pipe is not tight

(5) Oil viscosity too high

(6) Pump speed too high (improper use)

(7) The flow area of oil absorption filter is too small

(8) The auxiliary pump of non self priming pump is insufficient or faulty

(9) The air filter on the oil tank is blocked

(10) Pump shaft oil seal failure

(1) Clean or replace the filter

(2) Adjust the length of the oil suction pipe properly

(3) Reduce the installation height of the pump or increase the liquid level height

(4) Check the sealing of the joint and joint surface, and tighten them

(5) Check oil quality and select oil viscosity as required

(6) Control below the maximum speed

(7) Replace the filter with large flow area

(8) Repair or replace the auxiliary pump

(9) Clean or replace the air filter

(10) Replacement


(1) Oil dissolved in a certain amount of air, in the process of work

And then the bubbles are formed

(2) oil return vortex strongly generates foam.

(3) There is air in the pipe or in the pump casing

(4) The depth of the oil suction pipe into the oil surface is not enough

(1) A baffle plate is added in the oil tank to pass the return oil through the baffle plate

After defoaming, absorb again and add defoamer into the oil

(2) The oil suction pipe and the oil return pipe should be separated from each other for a certain distance

The oil pipe should be inserted below the oil level

(3) Carry out no-load operation to remove air

(4) Lengthen the oil suction pipe to inject oil into the oil tank to raise its liquid level


(1) The bearing in the pump is seriously worn or damaged

(2) The internal parts of the pump are damaged or worn

① The gear has low precision and large swing

② The inner surface of stator ring is seriously worn

(1) Disassemble, clean and replace

(2) Replace or repair

① Research, repair or replace

② Replace the stator ring


(1) Large flow pulsation and pressure pulsation are caused by trapped oil

① Poor design of unloading slot

② Poor machining accuracy

(2) Poor operation of variable mechanism of variable displacement pump (too small clearance, poor machining accuracy, serious oil pollution, etc.)

(3) Abnormal operation of pressure distribution valve of double stage vane pump (too small clearance, poor machining accuracy, too dirty oil, etc.)

(1) Improve design and machining accuracy

① Improve the design, improve the unloading capacity

② Improve machining accuracy

(2) Disassemble, wash, repair, reassemble, meet the performance requirements, filter or replace the oil

(3) Disassemble, wash, repair, reassemble, meet the performance requirements, filter or replace the oil


(1) Coaxiality difference between pump shaft and motor shaft

(2) Poor installation of coupling, poor coaxiality and looseness

(1) Re installation to meet the technical requirements, coaxiality should generally be within 0.1 mm

(2) Re install to meet the technical requirements and fasten with set screws

F. Abnormal heating of hydraulic pump

1. Poor assembly

(1) Improper clearance selection (e.g. too small clearance between gear and side plate, blade and rotor slot, stator and rotor, plunger and cylinder block, resulting in overheating and burn of sliding parts)

(2) The assembly quality is poor. The coaxiality of the transmission part does not meet the technical requirements, and the operation is not smooth

(3) Poor bearing quality or damaged during assembly, or not cleaned during installation, resulting in poor operation

(4) The lubricating oil drain through the bearing is not smooth

① Return port plug not open (not connected with pipe)

② The oil passage was not cleaned and blocked by dirt during installation

③ There are too many elbows or flattening of oil return pipe during installation

(1) Disassemble and clean, measure the clearance, and re grind to reach the specified clearance

(2) Disassemble, clean and reassemble to meet the technical requirements

(3) Disassemble, inspect, replace and reassemble the bearing

(4) Re install, clean or replace

① Install the oil return pipe

② Clean the pipe

③ Replace the pipe and reduce the elbow

2. Poor oil quality

(1) The viscosity temperature characteristic of oil is poor, and the viscosity changes greatly

(2) Oil contains a lot of water, resulting in poor lubrication

(3) Serious oil pollution


(1) Select hydraulic oil according to regulations

(2) Replace the qualified oil and clean the inside of the oil tank

(3) Change the fluid

3. Pipeline fault

(1) The leaking oil pipe is deformed or blocked

(2) The leaking oil pipe is too thin to meet the requirements of oil drainage

(3) The oil suction pipe is thin and the oil suction resistance is large

(1) Cleaning or replacement

(2) Change the design, change the pipe

(3) Increase pipe diameter, reduce elbow, reduce oil absorption resistance

4. Influence of external conditions

The external heat source is high and the heat dissipation condition is poor

Remove external influence and add heat insulation measures

5. Large internal leakage, low volumetric efficiency and heating

See B.1

See B.1

G. Oil leakage of shaft seal hydraulic pump

1. Poor installation

(1) Seal lip reversed

(2) The skeleton spring falls off

① The chamfer of the shaft is not appropriate, and the sealing lip is turned over, which makes the spring fall off

① When installing the shaft, the spring falls off

(3) Foreign body stuck on sealing lip

(4) The sealing lip is pulled when passing through the spline shaft

(5) Oil seal slanting

① The inner diameter of groove is too small

② Groove chamfer too small

(6) Serious deformation of oil seal during assembly

(7) Too small shaft chamfer or too rough shaft chamfer causes the sealing lip to roll over

(1) Remove and re install. Do not damage the lip during disassembly. If there is deformation or damage, it should be replaced

(2) Reprocess the shaft and re install the spring

① Reprocessing according to the processing drawing

② Re install

(3) Remove, clean and reassemble

(4) Replace and re install

(5) Reprocessing grooves

① Check the groove size and re process as required




2. 轴和沟槽加工不良
















3. 油封有缺陷



4. 容积效率过低



5. 泄漏油孔被堵



6. 外接泄漏油管过细或管道过长



7. 未接泄漏油管




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