The hydraulic pump is the power component of the hydraulic system. It is driven by an engine or an electric motor, sucks oil from the hydraulic oil tank, forms pressure oil and discharges it, and sends it to the actuator. Hydraulic pumps are divided into gear pumps, piston pumps, and vane pumps according to their structure. The following will explain the problems frequently encountered during hydraulic pump repair and maintenance.
One of the hydraulic pump problems: leakage
1. Leakage classification: leakage is divided into internal leakage and external leakage. According to the degree of leakage, there are various manifestations such as oil film leakage, leakage, dripping and spraying. Oil film leakage occurs between relative moving parts, such as the sliding pair of the rotating body, reciprocating movement (such as the piston rod of the hydraulic cylinder, the spool extension of the manual reversing valve, etc.); leakage occurs in the end cover valve plate joint And so on; dripping and leakage mostly occur in pipe joints, etc.; spraying and leakage mostly occur in pipe ruptures, leaking installation and sealing.
2. The hazards of oil leakage: external leakage causes work environment pollution and wastes resources, internal leakage causes temperature rise, efficiency drop, work pressure, system weakness, slow motion speed and other faults.
3. Causes of oil leakage
(1) The seal is ineffective due to poor quality, improper assembly and damage, long-term aging and deterioration, and incompatibility with the working medium;
(2) The wear of the relative motion pair increases the clearance and internal leakage, or the internal and external leakage due to strain on the mating surface;
(3) The oil temperature is too high;
(4) The system pressure is too high;
(5) Incorrect size design of the sealing part, poor processing accuracy, and poor assembly will cause internal and external leakage.
On the basis of finding out the causes of internal and external leakage, take symptomatic measures
The second problem frequently encountered in hydraulic pump maintenance: the pressure of the hydraulic system is abnormal, and the pressure cannot go up or down
Pressure is one of the two most basic parameters of the hydraulic system, which largely determines the performance of the hydraulic system. This fault is manifested as: when the pressure of the hydraulic system is adjusted, the adjustment failure occurs. The system pressure cannot be established, the pressure is insufficient, or even no pressure at all, or the pressure cannot be adjusted, or the pressure falls after rising, and the adjusted pressure is unstable , Pressure fluctuations and other phenomena.
- The impact of stress disorders
(1) Actuating components (such as hydraulic cylinders, hydraulic motors) do not move, or although they move, they stop moving or become weak when loaded, and cannot overcome the load and do work;
(2) The hydraulic system cannot realize the correct working cycle, especially in the sequential action loop of pressure control
(3) Some valves that rely on pressure control cannot work, such as hydraulic reversing valves, hydraulic control check valves, cartridge valves, pressure relays, etc., which also cause the hydraulic system to fail to work normally:
(4) The speed of the actuator is reduced due to insufficient load flow.
(5) Failures including safety accidents due to uncontrolled pressure regulation.
2. Causes of stress disorder
(1) The hydraulic pump causes no flow output or insufficient output flow:
- The steering of the hydraulic pump A is wrong, there is no pressure oil output at all, and the system pressure does not rise at all;
B. Because the motor speed is too low, the power is insufficient, or the hydraulic pump is used for a long time, the internal wear is large, the leakage is large, and the volumetric efficiency is low, resulting in insufficient output flow of the hydraulic pump and insufficient system pressure.
C. hydraulic pump inlet and outlet ports are installed reversely, and the pump is a non-reversible pump, which not only cannot be oiled, but also breaks the pump shaft oil seal.
D. Other reasons, such as the pump suction pipe is too small, the suction pipe is poorly sealed and leaks, the oil viscosity is too high, the oil filter is blocked by impurities and dirt, which causes the pump suction resistance to be large, and the suction phenomenon occurs, which makes the pump output flow. Not enough, the system pressure can’t rise.
(2) Failure of pressure regulating valve such as overflow valve
For example, the spool of the overflow valve is stuck in the large opening position, and the pressure oil output by the hydraulic pump flows back to the oil tank through the overflow valve, that is, the pressure oil is shorted to the oil return path; it may also be that the orifice of the pressure control valve is blocked or adjusted. The pressure spring breaks and other reasons cause the system to be pressureless. On the contrary, when the relief valve spool is stuck in the position of closing the valve port, the system pressure will not come.
(3) It is found that the pressure does not rise or fall during the working process. It is likely that the reversing valve fails, causing the system to be unloaded or closed; or it is caused by serious internal leakage between the valve core and the valve body hole.
(4) The unloading valve is stuck in the unloading position, the system is always unloaded, and the pressure cannot rise.
(5) Leakage inside and outside the system.
(6) Inside the valve mounting plate (manifold block) there is a position where the pressure oil channel and the oil return channel are in series.
(7) The spool of the reversing valve does not move in place, causing the pressure oil cavity and the oil return cavity to channel.
(8) The lock nut connecting the piston of the hydraulic cylinder and the piston rod is loosened, and the piston runs out of the piston rod, making the two chambers of the hydraulic cylinder communicate with each other.
3. Elimination methods for pressure disorders
(1) Replace the motor wiring, correct the rotation direction of the hydraulic pump, and replace the motor with matching power.
(2) Correct the direction of the inlet and outlet of the hydraulic pump, especially for non-reversible pumps.
(3) Properly increase the size of the suction pipe of the pump, strengthen the seal at the joint of the suction pipe, and clean the oil filter.
(4) Troubleshoot the directional valve. If the unloading valve is installed, troubleshoot the unloading valve.
(5) Find out the specific locations of internal and external leakage, and eliminate internal and external leakage faults.
(6) Check the hydraulic cylinder.
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