Overview and working principle of 1 and Parker variable displacement piston pump

The pressure oil of Parker variable displacement piston pump enters the lower cavity of the variable displacement housing through the oil hole on the pump body and the variable displacement housing through the one-way valve. When the pull rod moves downward, it pushes the servo piston to move downward, and the upper valve port of the servo valve opens. The pressure oil in the lower cavity of the variable housing enters the upper cavity of the variable housing through the oil hole in the variable piston. Because the area of the upper cavity is larger than that of the lower cavity, the hydraulic pressure pushes the piston to move downwards, driving the pin shaft to rotate the variable head around the center of the steel ball, and changing the inclination angle (increasing) of the variable head. Parker, on the contrary, when the pull rod moves upward, the inclination angle of the variable head changes in the opposite direction, and the flow rate of the pump also changes. When the inclination angle becomes zero, the variable lift changes to the direction of negative deflection angle, the liquid flow changes direction, and the oil inlet and oil outlet of the pump change.

2. Common faults of Parker variable piston pump

1. The output flow of hydraulic pump is insufficient or there is no oil output.

(1) Insufficient inspiration. The reason is that the resistance on the oil suction pipeline is too large or the oil supply is insufficient. For example, the pump speed is too high, the oil tank level is too low, the oil inlet pipe leaks oil, and the oil filter is blocked.

(2) The leakage is too large. The reason is that the clearance of the pump is too large and the seal is poor. If the oil distribution plate is scratched by metal chips, iron chips, etc. , end oil leakage; The sealing surface of one-way valve in variable mechanism is not well matched, and there are sand holes or wear marks on the bearing surface of pump body and oil distribution plate. The damaged part of the pump can be determined by checking the foreign matter 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, so it is necessary to adjust the variable piston and increase the inclination angle of the swash plate.

2. The oil displacement is not zero in the middle position.

Parker variable axial piston pump is called neutral when the inclination of its swash plate is zero, and the output flow of the pump should be zero. But sometimes the median deviates from the midpoint of the regulation mechanism, and there is still flow output at the midpoint. The reason is that the position of the controller is offset, loose or damaged and needs to be reset, fastened or replaced. This phenomenon may also be caused by insufficient angle retention of the pump and wear of the trunnion of the tilt angle.

3. Output flow fluctuation

The fluctuation of output flow is related to many factors. Variable displacement pump can be considered as the result of poor control of variable mechanism, such as foreign matter entering variable mechanism, leaving step marks, wear marks and scars. Resulting in unstable movement of the control piston. The motion of the control piston will be unstable due to the lack of energy of the amplifier or the damage of parts, and the poor efficiency of the damper of the control piston with spring. Unsteady flow is often accompanied by pressure fluctuation. This kind of fault generally needs to disassemble the hydraulic pump, replace the damaged parts, increase damping, improve spring stiffness and control pressure.