Kawasaki K3V112S-1NCJ-12 Hydraulic Pump K3V112S For EX100 EX120-2/3 PC120-6 PC130-7

1.Working principle: The axial piston pump with sliding shoe structure is currently widely used. The plunger placed in the cylinder body is in contact with the swashplate through the sliding shoe. When the transmission shaft drives the cylinder body to rotate, the swashplate pulls the plunger out of the cylinder body or pushes it back, completing the oil suction and discharge process. The oil in the working chamber composed of the plunger and cylinder hole is connected to the suction and discharge chambers of the pump through the oil distribution plate. The variable mechanism is used to change the inclination angle of the swashplate, and the displacement of the pump can be changed by adjusting the inclination angle of the swashplate.

2. Maintenance of plunger pumps: Swash plate axial piston pumps generally adopt the form of cylinder rotation and end face flow distribution. There is a friction pair composed of a bimetallic plate and a steel oil distribution plate embedded on the end face of the cylinder block, and most of them use a flat flow distribution method, making maintenance more convenient. The oil distribution plate is one of the key components of an axial piston pump. When the pump is working, on the one hand, the high-pressure oil in the working chamber pushes the cylinder body towards the oil distribution plate, and on the other hand, the oil film pressure between the oil distribution plate and the cylinder body forms a hydraulic reverse thrust on the cylinder body, causing the cylinder body to deviate from the oil distribution plate. The design hydraulic compression force 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, i.e. Fn/Ff=1.05-1.1, allowing the pump to operate normally and maintain high volumetric efficiency.

In fact, due to oil contamination, slight wear often occurs between the oil distribution plate and the cylinder block. Especially under high pressure, even slight wear can increase the hydraulic reverse thrust Ff, thereby damaging Fn.

III. Common fault handling

1. Insufficient or no oil output from hydraulic pump

(1) Insufficient suction capacity: The reason is due to excessive resistance on the suction pipeline or insufficient oil replenishment. If the pump speed is too high, the liquid level in the oil tank is too low, the oil inlet pipe leaks, and the oil filter is blocked.

(2) Excessive leakage: The reason is due to excessive clearance and poor sealing of the pump. If 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, and there are sand holes or grinding marks on the supporting surface of the pump body and oil distribution plate. The damaged part of the pump can be identified by checking for foreign objects mixed in the hydraulic oil inside the pump body.

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

2. When the oil discharge is not zero in the middle position, the displacement of the swash plate of the variable displacement axial piston pump is called the middle position, and the output flow rate of the pump should be zero at this time. But sometimes there is a phenomenon of deviation 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 deviates, becomes loose or damaged, and needs to be reset, tightened or replaced. Insufficient angle maintenance of the pump and wear of the inclined angle trunnion can also cause this phenomenon.

3. The fluctuation of output flow is related to many factors. The variable pump can be considered to be caused by poor control of the variable mechanism, such as foreign objects entering the variable mechanism, causing step marks, wear marks, scars, etc. on the control piston, causing unstable movement of the control piston. Due to insufficient energy or damaged components of the amplifier, as well as poor effectiveness of dampers containing springs in the control piston, unstable movement of the control piston can be caused. The unstable flow rate is often accompanied by pressure fluctuations. This type of fault usually requires disassembling the hydraulic pump, replacing damaged components, increasing damping, increasing spring stiffness, and controlling pressure.

4. Abnormal output pressure: 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 with abnormal output pressure.

(1) When the output pressure is too low, when the pump is in a self priming state, if there is air leakage in the oil inlet pipeline or significant leakage in the hydraulic cylinder, one-way valve, directional valve, etc. in the system, it will cause the pressure to not rise. This requires identifying the leak, tightening, and replacing the seal to increase the pressure. If there is a malfunction or low adjustment pressure in the overflow valve, and the system pressure cannot rise, the pressure should be readjusted or the overflow valve repaired. If the deviation between the cylinder body of the hydraulic pump and the port plate causes a large amount of leakage, and in severe cases, the cylinder body may break, the matching surface should be reground or the hydraulic pump should be replaced.

(2) Excessive output pressure: If the circuit load continues to rise and the pump pressure also continues to rise, it is considered normal. If the load is constant and the pump pressure exceeds the required pressure value for the load, hydraulic components other than the pump should be checked, such as directional valves, pressure valves, transmission devices, and return pipelines. If the maximum pressure is too high, the overflow valve should be adjusted.

5. Vibration and noise: Vibration and noise occur simultaneously. They not only pose a threat to the operators of the machine, but also cause pollution to the environment.

(1) Mechanical vibration and noise: If the pump shaft and motor shaft are not concentric or locked, the bearings and couplings of the rotating shaft are damaged, the elastic pad is damaged, and the assembly bolts are loose, noise can be generated. For pumps that operate at high speeds or transmit large amounts of energy, regular inspections should be conducted 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, it will cause resonance, and the pump speed can be changed to eliminate resonance.

(2) The noise generated by the liquid flow inside the pipeline can be caused by the oil inlet pipeline being too thin, the flow capacity of the oil inlet filter being too small or blocked, the intake pipeline absorbing air, the oil gap being too high, the oil level being too low and the oil absorption being insufficient, and the liquid hammer generated in the high-pressure pipeline. Therefore, it is necessary to design the fuel tank correctly, select the oil filter, oil pipe, and directional valve correctly.

6. Hydraulic pump overheating: There are two reasons for hydraulic pump overheating, one is mechanical friction heat generation. Due to the fact that the moving surface is in a dry or semi dry friction state, the moving parts generate heat by friction with each other. The second is the heat generated by liquid friction. High pressure oil passes through various gaps.

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