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What are the common faults of variable piston pumps?

What are the common faults of variable piston pumps?

[Abstract]:
The variable plunger pump has insufficient intake. The reason is that the resistance on the suction line is too large or the amount of oil is insufficient. If the speed of the pump is too large, the liquid level in the fuel tank is too low, the inlet pipe leaks, and the oil filter is clogged.
1. Variable piston pump output flow is insufficient or does not output oil
 
(1) The variable plunger pump has insufficient intake. The reason is that the resistance on the suction line is too large or the amount of oil is insufficient. If the speed of the pump is too large, the liquid level in the fuel tank is too low, the inlet pipe leaks, and the oil filter is clogged. filter is clogged.
 
(2) The displacement of the variable plunger pump is too large. The reason is that the pump gap is too large and the seal is poor. If the oil distribution plate is scratched by metal fragments, iron filings, etc., the oil leakage on the end face; the sealing surface of the one-way valve in the variable mechanism is not well matched, and the bearing surface of the pump body and the oil distribution plate has sand holes or grinding marks. The damaged part of the pump can be identified by checking the foreign matter mixed in the hydraulic fluid in the pump body.
 
(3) The tilting angle of the tilting disc is too small, and the displacement of the pump is small. This requires adjusting the variable piston to increase the inclination of the swash plate.
 
2. The oil discharge is not zero at the middle position.
 
When the swashplate inclination angle of the variable axial displacement piston pump is zero, it is called the neutral position, and the output flow rate of the pump should be zero. However, there is sometimes a phenomenon in which the median deviates from the midpoint of the adjustment mechanism, and there is still flow output at the midpoint. The reason is that the position of the controller is deviated, loose or damaged and needs to be re-zeroed, tightened or replaced. This is also the case with insufficient pump angular retention and tilted trunnion wear.
 
3. variable plunger pump output flow fluctuation
 
Output flow fluctuations are related to many factors. The variable displacement piston pump can be considered as the poor control of the variable mechanism. For example, if the foreign matter enters the variable mechanism, the step marks, wear marks, and scratches are drawn on the control piston, resulting in unstable control piston movement. Due to insufficient energy or damage to the amplifier, the damper performance of the spring-containing control piston is poor, causing the control piston to be unstable. Unsteady flow is often accompanied by pressure fluctuations. This type of failure generally requires disassembling the hydraulic pump, replacing the damaged components, increasing the damping, increasing the spring stiffness and controlling the pressure.
 
4. variable plunger pump output pressure is abnormal
 
The output pressure of the pump is determined by the load and is approximately proportional to the input torque. There are two types of faults in output pressure abnormalities.
 
(1) The output pressure is too low
 
When the pump is in the self-priming state, if the oil inlet line leaks or the hydraulic cylinder, check valve, reversing valve, etc. in the system have a large leak, the pressure will not rise. This requires finding the leak, tightening and replacing the seal to increase the pressure. If the relief valve is faulty or the adjustment pressure is low and the system pressure is too high, the pressure should be readjusted or the relief valve should be overhauled. If the cylinder of the hydraulic pump deviates from the distribution plate and causes a large amount of leakage, if the cylinder may be broken in severe cases, the mating surface should be re-ground or the hydraulic pump should be replaced.
 
(2) The output pressure is too high
 
If the loop load continues to rise, the pump pressure will continue to rise, which is normal. If the load is constant and the pump pressure exceeds the pressure required by the load, check the hydraulic components other than the pump, such as the directional valve, pressure valve, transmission, and return line. If the maximum pressure is too high, adjust the relief valve.
 
5. vibration and noise
 
Vibration and noise are present at the same time. They not only cause harm to the operator of the machine, but also pollute the environment.
 
(1) Mechanical vibration and noise
 
If the pump shaft and the motor shaft are not concentric or top dead, the bearings of the rotating shaft, the joints are damaged, the elastic pads are damaged, and the assembly bolts are loose. Noise is generated. For pumps that operate at high speeds or that transmit large amounts of energy, periodically check and record the amplitude, frequency, and noise of each component. If the pump's rotational frequency is the same as the natural frequency of the pressure valve, it will cause resonance and change the pump's speed to eliminate the resonance.
 
(2) Noise generated by the flow in the pipeline
 
The variable plunger pump inlet pipe is too thin, the inlet oil filter has a small flow capacity or blockage, the intake pipe draws in air, the oil liquidity is too high, the oil level is too low, the oil is insufficient, and the high pressure pipe produces liquid hammer. Both generate noise. Therefore, the tank must be properly designed to properly select the oil filter, tubing and directional valve.
 
6. variable plunger pump overheating
 
There are two reasons for excessive heating of the variable displacement piston pump. One is mechanical friction to generate heat. Since the moving surface is in a dry friction or a semi-dry friction state, the moving parts rub against each other to generate heat. The second is the friction of the liquid to generate heat. High-pressure oil leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy loss is converted into heat. Therefore, the correct selection of the gap between the moving parts, the tank volume and the cooler can eliminate the excessive heat generation of the pump and the excessive oil temperature. In addition, the oil return filter is clogged and the back pressure is too high, which may cause the oil temperature to be too high and the pump body to overheat.
 
7. Oil leakage Variable piston pump oil leakage mainly has the following reasons:
 
(1) The spindle oil seal is damaged or the shaft is defective or scratched;
 
(2) The internal leakage is too large, causing the pressure at the oil seal to increase, and the oil seal is damaged or flushed out;
 
(3) The drain pipe is too long and too long to leak oil at the seal;
 
(4) The external oil pipe of the pump is loose, the pipe joint is damaged, the gasket is aged or cracked;
 
(5) The variable adjustment mechanism bolt is loose and the seal is broken;
 
(6) The cast iron pump casing has blisters or poor welding.