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The Analysis For Rexroth A4VSO Piston Pump Appearance's Common Breakdown
Date:2018-06-14

The Analysis For Rexroth A4VSO Piston Pump Appearance's Common Breakdown

 

The Overview And Working Principle Of Rexroth a4vso Series Variable Piston Pump: The pressure oil of the German REXROTH A4VSO series variable displacement piston pump enters the lower chamber of the variable housing through the check valve through the oil hole in the pump body and casing variable casing. The REXROTH hydraulic pump pushes the servo piston when the pull rod moves downwards. Move down and the upper valve opening of the servo valve opens. The pressure oil in the lower chamber of the variable housing enters the upper chamber of the variable housing through the oil hole in the variable piston. Because the upper chamber area is larger than the lower chamber, the hydraulic pressure pushes the piston downward. , Drive the pin to rotate the variable head around the center of the ball, change the tilt angle (increase) of the variable head, and the flow of the A4VSO pump increases. If the rod moves upwards, the tilt angle of the variable head changes in the opposite direction, and the flow of the pump also changes. When the angle of inclination changes to zero, the head of the variable changes in the direction of the negative declination angle, the flow changes, and the pump inlet and outlet ports change. 

Although A4VSO is robust pump with very long service life, but on the running of the A4VSO pumps, especially it has been a long running, there will meet several breakdown as following:

1. Hydraulic pump output flow is insufficient or does not output fluid

(a) Inadequate inhalation: The reason is that the resistance in the suction pipe is too large or the amount of oil is insufficient. If the speed of the pump is too high, the liquid level in the tank is too low, the intake pipe leaks, and the oil filter is blocked. (b) Excessive leakage: The cause is excessive clearance of the pump and poor sealing. If the oil pan is scratched by metal fragments, iron scraps, etc., the end surface leaks oil; the one-way valve sealing surface in the variable mechanism is not well-matched, and the bearing surface of the pump body and the oil pan is blistering or grinding marks. It is possible to discriminate where the pump is damaged by checking for foreign matter in the hydraulic fluid in the pump body. (c) The inclination of the swash plate is too small and the displacement of the pump is small. This requires adjusting the piston of the variable and increasing the swash plate inclination.

 

2. Oil leak

Rexroth A4VSO piston pump oil leakage mainly has the following reasons: (a) The spindle oil seal is damaged or the shaft has defects or scratches; (b) The internal leakage is too large, causing the pressure at the oil seal to increase, and the oil seal is damaged or washed out; (c) ) If the drain pipe is too long, oil leaks from the seal; (d) The external oil pipe of the pump is loose, the pipe joint is damaged, and the gasket is aged or cracked; (e) The loose bolt of the adjusting mechanism and the seal is damaged; (f) Cast iron pump The shell has trachoma or poor welding.

 

3. Output flow fluctuations

Output flow fluctuations are related to many factors. Variable pumps can be considered to be caused by poor control of the variable mechanism. For example, when foreign objects enter the variable mechanism, step marks, wear marks, and scars are marked on the control piston, resulting in unstable control piston movement. Due to the lack of energy in the amplifier or the damage to the parts, the damper of the control piston with springs is poor in performance, which can cause unstable control piston movement. Unsteady flow is often accompanied by pressure fluctuations. This kind of fault generally needs to disassemble the hydraulic pump, replace the damaged parts, increase the damping, increase the spring stiffness and control the pressure.

 

4. Hydraulic pump overheated

There are two reasons why the A4VSO hydraulic pump overheats. One is that mechanical friction generates heat. Because the moving surface is in a state of dry friction or semi-dry friction, moving parts rub against each other to generate heat. The second is liquid friction heat. High-pressure oil leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy is lost to heat energy. Therefore, the correct selection of the gap between the moving parts, the volume of the fuel tank and the cooler can prevent excessive heating of the pump and high oil temperature. In addition, blockage of the return filter causes high back pressure on the return oil, which can also result in high oil temperatures and overheating of the pump body.

 

5. Vibration and noise

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.

(a)Mechanical vibration and noise: If the pump shaft and the motor shaft are not concentric or top dead, the bearings and joints of the rotating shaft may be damaged, and damage to the elastic mat and loosening of the mounting bolts may generate noise. For pumps that operate at high speeds or that transmit large amounts of energy, they must be periodically checked to record the amplitude, frequency, and noise of each component. If the rotational frequency of the pump is the same as the natural frequency of the pressure valve, resonance will occur and the pump speed can be changed to eliminate resonance. (b) The noise generated by the flow in the pipeline: The inlet pipeline is too thin, the inlet flow capacity of the inlet filter is too small or blocked, the intake pipe intakes air, the oil level is too high, the oil level is too low, and the oil pressure is insufficient and high pressure If liquid strikes in the pipeline, noise will be generated. Therefore, the fuel tank must be properly designed to properly select the oil filter, tubing, and directional valve.

 

6. Abnormal output pressure

The output pressure of the A4VSO pump is determined by the load and is approximately proportional to the input torque. There are two kinds of faults in the output pressure abnormality.

(a) The output pressure is too low: When the pump is in the self-priming state, if the inlet pipe leaks or the hydraulic cylinder, one-way valve, and reversing valve in the system have large leakage, the pressure will not rise. This requires finding leaks, tightening, and replacing seals to increase pressure. If the relief valve is faulty or the adjustment pressure is low and the system pressure does not rise, the pressure should be readjusted or the relief valve checked. If the deviation between the cylinder and the valve plate of the hydraulic pump results in a large amount of leakage, and if the cylinder block may be broken when it is serious, the mating surface or the hydraulic pump should be replaced. (b) Output pressure is too high: If the loop load continues to rise, the pump pressure 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, such as directional valves, pressure valves, transmissions and return lines, should be checked. If the maximum pressure is too high, adjust the relief valve.

 

7. When the median position, the oil discharge is not zero

When the swash plate inclination angle of the variable displacement axial piston pump is zero, it is referred to as the neutral position, and the output flow rate of the pump at this time should be zero. However, sometimes there is a phenomenon that the median deviation deviates from the midpoint of the adjustment mechanism, and there is still a flow output at the midpoint. The reason for this is that the position of the controller is deviated, loosened or damaged and needs to be re-zeroed, tightened or replaced. This phenomenon can also be caused by the insufficient maintenance of the angle of the pump and the wear of the tilted trunnion.

 

In all words, in order to avoid above problems, the end users should be check and maintain the operation of the hydraulic system.

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