Variable plunger pump maintenance and use method

I. working principle

The axial plunger pump with slipper shoe structure is the most widely used axial plunger pump at present. The plunger installed in the cylinder block is in contact with the swash plate through the slipper shoe. When the drive shaft drives the cylinder block to rotate, the swash plate will pull the plunger out or push back from the cylinder block to complete the oil suction and discharge process. The oil in the working capacity chamber composed of plunger and cylinder hole is communicated with the suction and discharge Chambers of the pump respectively through the oil distribution plate. The variable mechanism is used to change the inclination of the swash plate. The displacement of the pump can be changed by adjusting the inclination of the swash plate.

Ii. Maintenance of plunger pump

Inclined disc axial piston pump generally adopts the form of cylinder rotation and end face flow distribution. The end face of the cylinder block is mounted with a friction pair composed of a bimetal plate and a steel oil distribution plate. Oil distributor is one of the key components of axial piston pump. When the pump works, on the one hand, the high-pressure oil in the working chamber pushes the cylinder block to the oil distributor, on the other hand, the oil film pressure between the oil distributor and the cylinder block forms the hydraulic reverse thrust to the cylinder block and makes the cylinder block deviate from the oil distributor. The designed hydraulic pressure Fn of the cylinder block on the oil distribution plate is slightly greater than the hydraulic reverse thrust Ff of the oil distribution plate on the cylinder block, that is, Fn/Ff=1.05~1.1, so as to make the pump work normally and maintain a high volume efficiency.

In fact, as a result of oil pollution, often make the oil plate and cylinder body between a slight wear. Especially under high pressure, even slight wear and tear can increase the hydraulic reverse thrust Ff, thus damaging the relationship between Fn>Ff and causing cracks between the oil distribution plate and the cylinder block to fail to work properly. So in the plunger pump overhaul and maintenance process, should focus on the oil distribution plate and cylinder block this pair of friction pair of use, even if there is a slight wear, should also be timely repair.

Three, common fault treatment

1 hydraulic pump output flow is insufficient or does not output oil

(1) insufficient inhalation. The reason is that the resistance on the suction line is too large or insufficient oil. If the speed of the pump is too large, the oil level in the tank is too low, the inlet pipe leaks, the filter is blocked and so on.

(2) excessive leakage. The reason is the pump clearance is too large, poor seal. If the oil distribution plate is scratched by metal fragments, iron filings, oil leakage on the end face; The sealing surface of the one-way valve in the variable mechanism is not well matched. The damaged parts of the pump can be distinguished by examining the mixed foreign matter in the hydraulic oil in the pump body.

(3) the tilt Angle of the inclined plate is too small and the pump displacement is small, which requires adjusting the variable piston to increase the tilt Angle of the inclined plate.

2. Oil displacement is not zero at the middle position

Variable axial piston pump tilt Angle is zero when called the middle, at this time the pump output flow should be zero. But sometimes the phenomenon of the median deviation from the middle point of the adjustment mechanism occurs, and there is still flow output at the middle point. The reason is that the position of the controller is deviated, loose or damaged, which needs to be reset, tightened or replaced. Pump Angle maintenance force is not enough, tilt Angle lug wear will also produce this phenomenon.

3. Output flow fluctuation

The fluctuation of output flow is related to many factors. The variable pump can be considered as the result of poor control of the variable mechanism, such as foreign bodies into the variable mechanism, in the control of the piston to draw a step mark, wear marks, scars, etc., resulting in the control of the piston movement is not stable. The movement of the control piston is unstable due to the insufficient energy of the amplifier or the damage of parts, and the poor effectiveness of the damper containing springs. Flow instability is often accompanied by pressure fluctuations. This kind of failure generally to disassemble the hydraulic pump, replace the damaged parts, increase the damping, improve the spring stiffness and control pressure.

4. Abnormal output pressure

Pump output pressure is determined by the load, and the input torque is approximately proportional. Abnormal output pressure has two kinds of faults.

(1) too low output pressure

When the pump in the state of self-priming, if the oil pipeline leakage or the system of hydraulic cylinder, one-way valve, reversing valve has a larger leakage, will make the pressure rise. This needs to find out the leak, tighten, replace the seal, can increase the pressure. If the overflow valve fails or the pressure is low and the system pressure fails to go up, the pressure should be re-adjusted or the overflow valve should be overhauled. If the hydraulic pump cylinder and distribution plate deviation caused by a large number of leakage, serious, the cylinder may be broken, should be re ground surface or replace the hydraulic pump.

(2) too high output pressure

If the loop load continues to rise, the pump pressure also continues to rise, should be normal. If the load is certain, the pump pressure exceeds the pressure value required by the load, the hydraulic components other than the pump should be checked, such as direction valve, pressure valve, transmission device and return oil pipeline. If the maximum pressure is too high, the overflow valve should be adjusted.

Vibration and noise

Vibration and noise occur together. They not only do harm to the operators of machines, but also pollute the environment.

(1) mechanical vibration and noise

If the pump shaft and motor shaft are of different cores or dead, the bearing and coupling of the rotating shaft will be damaged, the elastic pad will be damaged and the assembly bolt will be loose, which will generate noise. For high speed operation or transmission of large energy pump, to check regularly, recording the amplitude of each component, frequency and noise. If the pump rotation frequency and the natural frequency of the pressure valve at the same time, will cause resonance, can change the speed of the pump to eliminate resonance.

(2) noise generated by liquid flow in the pipeline

Noise will be generated when the oil inlet pipe is too thin, the flow capacity of the oil inlet filter is too small or blocked, the oil inlet pipe inhales air, the oil liquid is too high, the oil level is too low and the oil suction is insufficient, and liquid hammer is generated in the high-pressure pipe. Therefore, the fuel tank must be designed correctly and the oil filter, tubing and directional valve must be selected correctly.

6. Hydraulic pump overheating

Hydraulic pump excessive heat for two reasons, one is the heat generated by mechanical friction. Because the moving surface is in the state of dry friction or semi-dry friction, the moving parts generate heat by friction with each other. Second, liquid friction heat. The high-pressure oil leaks into the low-pressure chamber through various crevices, and a large amount of hydraulic energy is lost to heat energy. So the correct choice of moving parts between the clearance, tank volume and cooler, can put an end to the excessive heat pump and oil temperature too high phenomenon. In addition, back oil filter blockage caused back oil back pressure is too high, will also cause oil temperature too high and pump overheating.

7. The spill

The plunger pump leakage mainly has the following reasons:

(1) the spindle oil seal is damaged or the shaft is defective or scratched;

(2) excessive internal leakage will increase the pressure at the oil seal and damage or flush out the oil seal;

(3) the 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, and the sealing pad is aging or cracks occur;

(5) the bolt of the variable regulating mechanism becomes loose and the seal is damaged;

(6) cast iron pump shell has sand holes or poor welding.

Now a lot of manufacturers of plunger pump, imported parts and domestic parts of the structure is not the same, each pump should be strictly in accordance with the factory operating instructions. In the maintenance of the pump, the first should check the pump in the system installation, proper use, to facilitate the timely detection of the cause of damage, eliminate hidden dangers, ensure the normal operation of the system. The repaired hydraulic pump should be tested by certain testing equipment before use. If the testing conditions are not available, the system should be repeatedly debugged to make it work normally.