Created on:2021-12-30 10:08

Fault analysis and troubleshooting of axial piston pump

Fault analysis and troubleshooting of axial piston pump

1. The oil cannot be drained or the flow is insufficient, and the pressure is low

(1) Failure cause analysis.

1) The steering is wrong or the inlet and outlet are connected reversely.

2) The oil filter of the oil suction pipe is blocked.

3) The hydraulic oil level in the oil tank is too low.

4) The oil temperature is too high or the oil viscosity is too low.

5) There is dirt between the oil distribution plate and the cylinder block or there is poor contact between the oil distribution plate and the cylinder block.

6) The joint surface between the oil distribution plate and the cylinder block is roughened and grooved.

7) Axial grooves are worn and pulled between the plunger and the plunger hole.

8) The center spring is damaged and the plunger cannot extend.

9) Air leakage at suction end.

10) The variable mechanism of the is faulty, so that the inclination angle of the swashplate is fixed at the minimum position.

11) The oil distribution plate hole is not aligned with the locating pin installed on the pump cover.

(2) Exclusion method.

1) Rotate according to the direction indicated on the pump body, check and check the oil suction port and oil pressure port.

2) Remove the oil filter and clean it carefully.

3) Add oil to the specified scale mark.

4) Check the cause of oil temperature rise or the quality of hydraulic oil and replace it as appropriate.

5) Disassemble, clean, reassemble or check whether the spring is invalid and replace it as appropriate.

6) Grind and then polish the joint surface between the oil distribution plate and the cylinder block.

7) If the fit clearance is too large, grind the cylinder hole and electroplate the outer circle of the column plug.

8) Replace the center spring.

9) Check and tighten the pipe joint to strengthen the sealing.

10) Adjust or reassemble the variable piston and variable head to make them move freely and correct the adjustment error.

11) During disassembly, repair and assembly, the direction shall be identified, the pin hole shall be aligned, and the locating pin shall not expose the oil distribution plate.

2. The pump cannot rotate

(1) Cause analysis.

1) The plunger is stuck in the cylinder due to pollutants or too large changes in oil temperature.

2) The sliding shoe is stuck with the plunger ball head or the sliding shoe falls off.

3) The plunger ball head is broken due to the above reasons.

(2) Exclusion method.

1) Find out the causes of pollutants and replace with new oil.

2) Replace or reassemble the sliding shoes.

3) Replace the plunger.

3. Failure of variable mechanism or pressure compensation variable mechanism

(1) Cause analysis.

1) The check valve spring is broken.

2) The wear between the swashplate and the circular arc surface of the bearing bush on the variable housing is serious and the rotation is not flexible.

3) The control oil pipeline is blocked by pollutants.

4) The servo piston or variable piston is stuck.

5) The servo valve core does not cover the oil port in the differential piston enough.

6) The end of the servo valve core is broken.

(2) Exclusion method.

1) Replace the spring.

2) If the wear is slight, it can be scraped before assembly. If it is serious, it should be replaced.

3) Disassemble it for cleaning and blow it clean with compressed air.

4) Try to make the servo piston or variable piston flexible, and pay attention to whether the assembly clearance is appropriate.

5) Check the coverage of the servo valve core to the oil port in the differential piston and adjust it properly.

6) Replace the servo valve element.

4. The pump has large noise and pressure fluctuation (vibration)

(1) Cause analysis.

1) Air is introduced into the oil suction pipe of the pump, resulting in large pump noise and pressure fluctuation (vibration).

2) The servo piston or variable piston is inflexible, with occasional or frequent pressure fluctuations.

3) For variable displacement pump, the flow may be reduced and the internal leakage may be relatively increased due to the small deflection angle of variable mechanism. Therefore, it is impossible to continuously supply oil to the outside, and the flow pulsation will cause pressure pulsation.

4) Loose fit between plunger ball head and sliding shoe.

5) The valve plate and triangular groove repaired by flat grinding become shorter, resulting in oil trapping, resulting in relatively large noise and pressure fluctuation.

(2) Exclusion method.

1) Check and tighten the pipe joint to strengthen the sealing; Check and eliminate the poor sealing at the oil inlet. Check and clean the oil filter to prevent the oil filter from being blocked. Check the oil suction pipe to prevent pumping air and air intake caused by too long and too much bending of the oil suction pipe.

2) Try to make the servo piston or variable piston flexible, and pay attention to whether the assembly clearance is appropriate. In case of accidental pressure fluctuation, it is mostly caused by too dirty hydraulic oil pollution and dirt jamming the piston. The dirt flushing fork returns to normal. At this time, the hydraulic oil can be cleaned and replaced. In case of frequent pulsation, it may be the strain or other force of the mating parts. At this time, the parts shall be removed for research and assembly or replaced.

3) Check the variable mechanism of variable displacement pump. At this time, appropriately increase the deflection angle of variable mechanism to eliminate internal leakage.

4) Check the matching relationship between the plunger ball head and the sliding shoe and rivet it properly.

5) Carefully check the valve plate repaired by flat grinding, and repair the size of the triangular groove with a assorted triangular file.

5. The pump heating oil temperature rises too high

(1) Cause analysis.

1) Due to wear and strain between the plunger of the plunger pump and the cylinder block hole and the joint surface between the port plate and the cylinder block, the internal leakage increases, which is converted into heat energy and causes the temperature to rise.

2) The moving pair in the plunger pump is seriously worn and roughened, or the burr is not cleaned, the mechanical friction is large, the looseness is not strong, and heat is generated, resulting in high oil temperature.

3) When the plunger pump often operates under zero eccentricity or the system working pressure is lower than 8Mpa, the leakage of the pump is too small and the pump body is heated.

4) High viscosity of oil, small capacity of oil tank, excessive leakage of hydraulic pump or hydraulic system and other reasons lead to heating and temperature rise.

5) The pump bearing is seriously worn, the transmission is not strong, and the transmission torque increases and heats up.

(2) Exclusion method.

1) Check and grind the connecting surface between the plunger and the cylinder block hole of the plunger pump, the port plate and the cylinder block to make it close, and ensure the matching clearance between the plunger and the cylinder block hole.

2) Check, repair or replace worn parts.

3) Measures to reduce the heat generation of the pump body due to too small leakage: a branch pipe is shunted from the return pipe of the hydraulic system valve and led into the oil drain at the lower part of the pump return port to make the pump body produce forced circulation cooling.

4) In case of heating and temperature rise due to large oil viscosity, too small oil tank capacity, too large leakage of hydraulic pump or hydraulic system, corresponding measures can be taken according to the actual situation. If the hydraulic oil with appropriate viscosity is selected, the oil tank with large capacity is redesigned or replaced, the causes of increased internal leakage shall be checked and measures shall be taken.

5) Check the cause, replace the bearing and ensure that the motor shaft is concentric with the pump shaft.

6. The oil leakage of hydraulic pump drain pipe is serious (internal and external leakage)

(1) The internal leakage of cylinder block and port plate, plunger and cylinder block hole increases due to wear, and leaks from the oil drain pipe, which can be repaired according to the actual situation.

(2) The variable piston or servo piston is worn, resulting in leakage. In case of serious wear, it can be grinded after brush plating, or replaced.

(3) If the O-ring seal at each joint is invalid, damaged or damaged, and the cylinder head screw is loose, replace the seal and tighten the screw to solve the external leakage.

(4) The outer mattress at the pump shaft oil seal can be disposed according to the situation.

7. The joint surface of port plate and cylinder block is worn or burned

(1) The hydraulic oil is not filtered when adding, and there are dirt and impurities in the hydraulic oil, which enter the bonding surface during operation.

(2) Before starting the hydraulic pump, the pump was not filled with working oil, resulting in dry friction between the port plate and the cylinder block. Generally, the plunger pump must be filled with oil before it can be started.

(3) The end face hardness of the port plate is not enough. The port plate is made of 38crmoaia. After heat treatment, the surface nitriding depth is 0.4mm, and the hardness is hv900 ~ 1100. When the heat treatment is not good and there is no nitrided layer, the surface hardness is not enough and it is easy to burn, so it must be re nitrided to meet the technical requirements. When the thickness of the polished port plate exceeds the nitrided layer, it must be nitrided again and then put into final assembly.

(4) The cylinder block is made of qal9-4 copper. When the material is poor and the hardness is uneven, it is easy to wear and burn out. Strictly check the material quality and replace it if necessary.

(5) The port plate generates deformation stress at high temperature. In addition to controlling the oil temperature, the port plate shall be placed on a flat plate with secondary accuracy, ground and leveled with M10 alumina, and then washed in kerosene and polished to ensure that the parallelism of both ends is within 0.01mm and the flatness is within 0.005mm.

(6) Some holes on the cylinder block matching with the plunger are not deep enough or have taper, which causes the plunger to jam in the cylinder block hole and burn the joint surface between the port plate and the cylinder block. In this case, the holes on the cylinder block matching with the plunger should be studied and repaired to eliminate the taper and make it meet the technical requirements.

(7) The flatness error between the port plate and the small end face of the cylinder block is out of tolerance and concave. Refer to item (5) for repair.

(8) The coaxiality between the inner support hole of the pump shell and the transmission shaft is out of tolerance (especially when the pressure difference in the high pressure direction is negative), the pump shall be disassembled to check the coaxiality between the inner support surface on the pump shell and the transmission shaft. If the out of tolerance is too large, the pump shell or transmission shaft shall be replaced.

(9) If the fit clearance between the cylinder block and the bearing is too large, the bearing can be replaced with a new one.

(10) The fit clearance between the spline hole of the cylinder block and the spline of the transmission shaft is too small. Do not tighten it. Replace the pump shaft or properly grind the spline of the pump shaft.

(11) The oil distribution surface of the cylinder block is not perpendicular to its bearing support surface. The bearing support surface can be corrected or the oil distribution surface of the cylinder block can be polished.

(12) If the transmission shaft is bent or the large and small bearings are not aligned, straighten or replace the transmission shaft and reinstall the large and small bearings.

(13) The high and low pressure transition zone between the port plate and the cylinder block is seriously trapped with oil, so it can be appropriately elongated with a assorted triangular file to make the transition zone ideal for pressure relief.

8. The contact surface between the sliding shoe and the variable head (or swashplate) is worn or burned

(1) If the hydraulic oil is not clean and impurities and dirt are sucked into the gap between the sliding shoe and the variable head by the hydraulic pump, causing galling and wear, clean the hydraulic pump and replace the hydraulic oil.

(2) The column plug hole or sliding shoe hole is blocked by impurities and dirt, resulting in dry friction between the sliding shoe thrust plate and the variable head, resulting in wear or burning of the mating surface between the sliding shoe and the variable head. At this time, compressed air or fine steel wire with a diameter of 0.8mm can be used to pass through the small hole of the sliding shoe and clean it.

(3) When the variable head (material is 40Cr) has insufficient hardness or poor machining accuracy after heat treatment (flatness and surface roughness do not meet the requirements), it is easy to wear and burn. If the damage is slight, it shall be ground and polished, and if it is serious, it shall be ground and polished first, or replaced.

(4) If the thickness of the sliding shoe shoulder on a pump is inconsistent, the thickness of the shoulder shall be ground to be consistent with a special die.

(5) If the accuracy and surface roughness of the hydrostatic bearing surface of the sliding shoe are poor, it is necessary to apply a special fixture for re flat grinding to make the flatness and surface roughness meet the requirements. If it is slightly worn, it only needs polishing.

(6) The plane of the plunger ball head is too small. At the maximum deflection angle, the pressure oil is blocked by the spherical surface, and the moving surface of the thrust plate and variable head cannot be lubricated with oil, resulting in burning, so the plane of the large ball head can be polished.

(7) If the 7 holes of the return disc are not equally divided or the size is inconsistent, the 7 holes can be reground with a special die.

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