1. The output flow of the plunger pump is insufficient or does not output oil

(1) Insufficient suction volume is caused by excessive resistance on the oil suction pipeline or insufficient oil supply. Such as the speed of the pump is too high, the liquid

 level in the fuel tank is too low, the oil inlet pipe leaks, the oil filter is blocked, etc.

(2) The leakage is too large, the reason is that the gap of the pump is too large and the seal is poor, such as the oil distribution plate is scratched by metal fragments, iron

 filings, etc., and the end face leaks oil; the sealing surface of the one-way valve in the variable mechanism is not well matched , There are sand holes or grinding marks on

 the supporting surface of the pump body and the oil distribution plate. The damaged part of the pump can be judged by checking the abnormality mixed in the hydraulic

 oil in the pump body.

(3) The inclination angle of the swash plate is too small, and the displacement of the pump is small, which requires adjusting the variable piston to increase the inclination 

angle of the swash plate.

2. The oil discharge volume is not zero at the middle position

When the swash plate inclination angle of the variable axial piston pump is zero, it is called the neutral position, and the output flow of the pump should be zero at this 

time. But sometimes there will be a phenomenon that the median deviates from the point 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 it needs to be re-zeroed, tightened or replaced. Insufficient angle holding force of the

 pump and wear of the angled trunnion can also cause this phenomenon.

3. The output flow fluctuatesThe output flow fluctuation is related to many factors. The variable pump can be considered to be caused by poor control of the variable mechanism, such as foreign

 matter entering the variable mechanism, scratches on the control piston, scratches on the plug, wear marks, etc., resulting in unstable movement of the control piston

. Insufficient energy of the amplifier or damaged parts, poor performance of the damper of the control piston including the spring, will cause the control piston to move

 unstable. Flow instability is often accompanied by pressure fluctuations. Such failures usually require dismantling the hydraulic pump, replacing damaged parts, 

increasing damping, increasing spring stiffness and controlling pressure, etc.

4. Abnormal output pressure

(1) The output pressure is too low

When in the self-priming state, if the oil inlet pipeline leaks or the hydraulic cylinders, check valves, and reversing valves in the system have large leaks, the pressure will 

not rise. This requires finding the air leak, tightening it, and replacing the seal to increase the pressure. The relief valve is faulty or the adjustment pressure is low, and

 the system pressure cannot go up. The pressure should be readjusted or the relief valve should be overhauled. If the cylinder body of the plunger pump deviates from 

the valve plate and causes a large amount of leakage, in severe cases, the cylinder body may be broken, and the mating surface should be reground or the plunger

 pump should be replaced.

(2) The output pressure is too high

If the circuit load continues to rise, the pressure of the pump will also continue to rise, which is normal. If the load is constant and the pressure of the pump exceeds the

 pressure value required by the load, hydraulic components other than the pump, such as directional valves, pressure valves, transmissions, and oil return pipes, should 

be checked. If the maximum pressure is too high, adjust the overflow valve.

5. Vibration and noise

Vibration and noise appear simultaneously. They are not only a hazard to the operators of the machines, but also pollute the environment.

(1) Mechanical vibration and noise

If the pump shaft and the motor shaft have different cores or are dead, the bearings and couplings of the rotating shaft are damaged, the elastic pads are damaged, and

 the transfer bolts are loose, all of which will generate noise. For pumps running at high speed or transmitting energy, regular inspections should be made to record the 

amplitude, frequency and noise of each component, such as the transmission frequency of the pump and the natural frequency and noise of the pressure valve. If the 

transmission frequency of the pump is the same as the natural frequency of the pressure valve, it will cause resonance, and the pump speed can be changed to eliminate

 the resonance.

(2) Noise generated by liquid flow in the pipeline

The oil inlet pipeline is too thin, the flow capacity of the oil inlet filter is too small or blocked, the oil inlet pipe sucks air, the oil temperature is too high, the oil level is too

 low and the oil absorption is insufficient, and liquid hammer occurs in the high pressure pipeline, etc., all of which generate noise. Therefore, the oil tank must be design

ed correctly, and the oil filter, oil pipe and directional valve must be selected correctly.

6. Overheating of plunger pump

There are two reasons for the overheating of the plunger pump. One is the heat generated by mechanical friction. Since the moving surface is in a state of dry friction or

 semi-dry friction, the moving parts rub against each other to generate heat. The second is that the friction of the hydraulic body generates heat. The high-pressure oil

 leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy loss is converted into heat energy. Therefore, the correct selection 

of the gap between the moving parts, the volume of the oil tank and the cooler can prevent the overheating of the pump and the phenomenon of excessive oil

 temperature. In addition, the blockage of the oil return filter will cause the oil return pressure to be too high, which will also cause the oil temperature to be too high 

and the pump body to overheat.

7. Oil leakage

The main reasons for the oil leakage of the plunger pump are as follows:

(1) The main shaft 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 oil drain pipe is too thin and too long, causing oil leakage at the seal;

(4) The external oil pipe of the pump is loose, the pipe joint is damaged, the gasket is aging or cracked:

(5) The bolts of the variable adjustment structure are loose and the seal is damaged.

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