Common hydraulic pump failure analysis and solutions

The hydraulic pump is the “heart” of the hydraulic system. When a hydraulic system has problems, the first thing that comes to mind is the hydraulic pump. The hydraulic pump is an important component in hydraulic equipment. According to different structures, it can be divided into gear pumps, vane pumps, and plunger pumps. If the hydraulic pump fails, the hydraulic system will not work properly.

Although there are many types of hydraulic pumps, the working principles and functions of hydraulic pumps are the same, so hydraulic pumps can be studied as a single object. After investigating and analyzing the common faults in the work of various hydraulic pumps, the common faults of hydraulic pumps are summarized as follows.

1. The hydraulic pump cannot output oil or has no pressure

The reasons are:

• The direction of the prime mover and the hydraulic pump does not match.
• The oil level in the oil tank is too low.
• The oil suction pipe or oil filter is blocked.
• The speed at startup is too low.
• The oil viscosity is too high, or the blades are not flexible. 
• There is air leakage at the oil inlet.
• The assembly screws are too loose.

Corresponding solutions:

• Adjust the direction of the prime mover and the hydraulic pump to be consistent.
• Add oil to the oil mark position.
• Clean the oil suction pipeline or oil filter to keep it unobstructed.
• Ensure that the speed at startup reaches above the minimum speed of the hydraulic pump.
• Check and replace the appropriate hydraulic oil or increase the oil temperature to reduce the oil viscosity.
• Replace the seal or joint to prevent air leakage.
• Tighten the screws.

2. Insufficient flow or pressure cannot be increased

When the flow and pressure of the hydraulic pump are insufficient, the speed and pressure of the actuator are unstable, and the external work cannot be achieved. Therefore, the cause should be found to stabilize the flow and increase the pressure.

The reasons are:

• The suction pipe or oil filter is partially blocked.
• The suction end connection is not sealed tightly, air enters, and the suction position is too high
• The pump cover screws are loose.
• System leakage
• The axial and radial clearances of the gear pump are too large.
• The inner surface of the vane pump stator is worn.
• The plunger pump plunger and the cylinder body or the oil distribution plate and the cylinder body are worn, the plunger return is insufficient or cannot return, causing the cylinder body and the oil distribution plate to lose the sea.
• The variable mechanism of the plunger pump fails.
• The side plate end is seriously worn and the leakage increases
• The overflow valve fails.

Corresponding solutions:

• Remove dirt to ensure smooth oil suction.
• Apply oil to the connection at the oil suction end. If there is improvement, tighten the connection parts or replace the seal to reduce the oil suction height.
• Tighten appropriately.
• Check the system in sequence.
• Find out where the gap is too large and take measures.
• Replace parts.
• Replace the plunger, grind the contact surface between the oil distribution plate and the cylinder body to ensure good contact, and check or replace the center spring.
• Check the variable mechanism and correct its adjustment error.
• Replace parts.
• Repair the overflow valve.

3. Severe noise and pressure fluctuation

The reasons are:

• The oil suction end connection is not sealed tightly, air enters, and the oil suction position is too high

• Air enters from the pump shaft oil seal

• The pump cover screws are loose

• The pump and the coupling are not concentric or loose

• The oil viscosity is too high, and there are bubbles in the oil

• The suction port oil filter has a small passing capacity

• The speed is too high

• The pump body cavity is blocked

• The axial clearance of the gear pump is too small, the verticality of the gear inner hole and the end face or the parallelism of the two holes on the pump cover is out of tolerance, and the overflow valve is blocked. The holes are clogged
• The oil suction pipe or oil filter is partially blocked

Corresponding solutions:

• Remove dirt to make the oil suction pipe unobstructed

• Apply oil to the connection of the oil suction end. If there is improvement, tighten the connector or replace the seal to reduce the oil suction height

• Replace the seal

• Tighten appropriately

• Reinstall it to make it concentric and tighten the connector

• Change the hydraulic oil with appropriate viscosity to improve the oil quality

• Use an oil filter with larger passing capacity

• Reduce the speed to below the maximum allowable speed

• Clean or replace the pump body

• Inspect and repair related parts and disassemble the overflow valve for cleaning.

4. Hydraulic pump overheating

The reasons are:

•  Oil viscosity is too high or too low.
•  Side plate and sleeve are in serious friction with gear end face.
•  Poor oil cleanliness, aggravated internal wear, reduced volumetric efficiency, oil leakage from internal gaps and throttling to generate heat.
• The oil tank volume is too small, poor heat dissipation.
• System overload, mainly manifested in high pressure or speed.

Corresponding solutions:

•  Replace with hydraulic oil with suitable viscosity.
• Repair or replace side plate and sleeve.
• Change oil
• Increase the oil tank and expand the heat dissipation area
• Adjust the pressure and speed.

5. Hydraulic pump leakage

The reasons are:

• The central spring of the plunger pump is damaged, causing the cylinder body and the oil distribution plate to lose sealing
• The oil seal or sealing ring is damaged
• The sealing surface is poor
• The parts in the pump are worn and the gap is too large.

Corresponding solutions:

• Replace the spring
• Replace the oil seal or sealing ring
• Inspect and repair