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Large-flow plunger pump common fault solutions and maintenance methods

14 May 2021Email

Large flow plunger pump is an important device of hydraulic system. It relies on the reciprocating movement of the plunger in the cylinder to change the volume of the sealed working chamber to achieve oil absorption and pressure. The high-pressure and large-flow plunger water pump has the advantages of high rated pressure, compact structure, high efficiency and convenient flow adjustment. It is widely used in high-pressure, large-flow Tianjin high-pressure pumps and occasions where flow needs to be adjusted, such as hydraulic presses, planers, broaching machines, In oil fields, construction machinery and ships. This article shares 7 common problems and maintenance methods of plunger pumps.

 

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

(1) The suction volume is insufficient, because the resistance on the suction pipe is too large or the oil supplement is insufficient. If the speed of the pump is too high, the liquid level in the oil tank is too low, the oil inlet pipe is leaking, and the oil filter is blocked.

(2) The leakage is too large, the reason is that the gap of the pump is too large, and the sealing is not good, such as the oil distribution plate is scratched by metal fragments, iron filings, etc., and the end surface is leaking; the sealing surface of the one-way valve in the variable mechanism is not well matched , The supporting surface of the pump body and the oil distribution plate has blisters or grinding marks. The damaged part of the pump can be judged by checking the abnormality mixed in the hydraulic oil in the pump body.

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

 

2. The oil discharge is not zero at the neutral position

When the inclination angle of the swash plate 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. However, sometimes the midpoint deviates from the point of the adjustment mechanism, and the flow rate is still 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 phenomenon can also be caused by insufficient pump angle maintenance and wear of the tilt angle trunnion.

 

3. The output flow fluctuates

The 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, scratching the plug on the control piston, marking steps, wear marks, etc., resulting in unstable motion of the control piston.

Due to insufficient amplifier energy or damaged parts, the poor performance of the damper of the control piston containing the spring will cause the control piston to move unstable. Unstable flow is often accompanied by pressure fluctuations. Such failures usually require disassembling the hydraulic pump, replacing damaged parts, increasing damping, increasing spring stiffness and control pressure.

 

4. The output pressure of the high-pressure and large-flow plunger pump is abnormal

(1) The output pressure is too low

In the self-priming state, if the oil inlet pipe leaks or the hydraulic cylinders, check valves, reversing valves, etc. in the system have large leaks, the pressure will not rise. This requires finding out where the air is leaking, tightening, and replacing the seals to increase the pressure.

If the overflow valve is faulty or the adjustment pressure is low, and the system pressure cannot rise, the pressure should be readjusted or the overflow valve should be overhauled. If the cylinder body of the plunger pump and the valve plate have a large amount of leakage, and the cylinder body may be broken in severe cases, 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 pump pressure also continues to rise, which is normal. If the load is constant and the pressure of the pump exceeds the pressure required by the load, hydraulic components other than the pump should be used, such as directional valves, pressure valves, transmissions and oil return pipelines. If the maximum pressure is too high, the relief valve should be adjusted.

 

5. Vibration and noise of large flow plunger pump

Vibration and noise occur at the same time. They not only cause harm to the operator of the machine, but also cause pollution to the environment.

(1) Mechanical vibration and noise

If the pump shaft and the motor shaft are different in core or die, the bearings and couplings of the rotating shaft are damaged, the elastic cushion is damaged, and the transfer bolts are loosened, which will cause noise.

For pumps that run at high speeds or transmit energy, check regularly 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, resonance will be caused, and the pump speed can be changed to eliminate resonance.

(2) Noise generated by the liquid flow in the pipeline

The oil inlet pipe is too thin, the flow capacity of the oil inlet filter is too small or blocked, the oil inlet pipe sucks in air, the oil temperature is too high, the oil level is too low, the oil suction is insufficient, and the high-pressure pipe produces liquid shock, etc., which all produce noise. Therefore, the fuel tank must be designed correctly, and the oil filter, oil pipe and directional valve must be correctly selected.

 

6. Overheating of large flow plunger pump

There are two reasons for the excessive heating of the plunger pump. One is the heat generated by mechanical friction. Because 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 the friction and heat generation of the hydraulic body. High-pressure oil leaks into the low-pressure cavity 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 oil tank volume and the cooler can prevent the overheating of the pump and the overheating of the oil. In addition, the oil return pressure is too high due to the clogging of the oil return filter, which will also cause the oil temperature to be too high and the pump body to overheat.

 

7. Oil leakage of large flow plunger pump

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 aged or cracked;

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

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