1. Hydraulic oil contamination
Hazards of hydraulic oil pollution:
① Solid particles in hydraulic oil, such as molding sand, chips, abrasives, welding slag, rust flakes, paint skins, fibers, etc., are the most harmful, resulting in deterioration of system performance, wear of components, damage to seals, shortening of service life and even damage.
② The water mixed into the hydraulic oil includes various chemical solvents, precipitates and surface active substances, which will corrode the components, reduce the viscosity, deteriorate, freeze and emulsify the hydraulic oil.
③ Mixing air will cause cavitation, cavitation, vibration, noise, response deterioration and crawling of the system.
75% of system faults are caused by hydraulic oil pollution, so attention should be paid to the problem of hydraulic oil pollution.
2. Hydraulic pump failure
① Pump noise.
② The pump does not discharge oil or the oil discharge is insufficient. Insufficient pump speed; Insufficient oil absorption; Air leakage at oil suction port; The oil filter or oil suction pipe is blocked; The oil level is too low; Poor oil absorption due to too high oil viscosity; The oil viscosity is too small, resulting in too large internal leakage (internal leakage).
③ The pump pressure is insufficient and weak. Constant pressure of overflow valve is too low; Leakage of other control elements and actuators; Insufficient or no oil absorption of the pump; Serious leakage in the pump; Incorrect installation of vane pump blades, etc.
④ The pump temperature is too high. Improper design, assembly, adjustment and use, improper system unloading, excessive pipeline flow rate, excessive pressure loss, etc. The oil temperature should be 55 ° C, and the pump can be 65 ° C.
⑤ Leakage in the pump. It is caused by parts processing (unloading groove position, groove depth, etc.), improper assembly (tightness or scratch), improper use (wrong import and export installation), etc.
3. Hydraulic motor failure
① The output torque of the hydraulic motor is insufficient and the operation slows down. It is caused by insufficient oil supply caused by pump failure.
② Large internal leakage. It is mainly related to working pressure difference, oil viscosity, structural form of hydraulic motor, displacement and processing and assembly, especially at low speed.
③ Leakage (leakage). It is mainly caused by too small sealing and oil viscosity.
④ Crawl. It is caused by uneven friction resistance, improper oil viscosity, air entry, hydraulic oil pollution and component wear.
⑤ The motor is disengaged and bumped. It is mainly caused by insufficient back pressure and other reasons.
⑥ Noise. Mechanical noise: caused by looseness and collision of bearings, couplings or other moving parts. Hydraulic noise: mainly due to pressure and flow pulsation, volume change, cavitation and hydraulic impact.
4. Hydraulic cylinder failure
① Insufficient thrust or ineffective action. Due to internal leakage, poor cylinder processing and assembly problems.
② Crawl. It is caused by air mixing, non concentricity between piston rod and piston, bending of piston rod, rust or roughening of cylinder barrel (including iron filings, impurities, etc.) and excessive clearance between parts.
③ Impact and vibration. It is caused by excessive buffer clearance, too tight moving seal, poor assembly of parts, etc.
④ Leak. Due to poor sealing, strain and hydraulic oil viscosity.
5. Overflow valve failure
① Pressure fluctuations. It is caused by too small or deformed spring rigidity, poor contact of cone valve, inaccurate pressure gauge, insensitive action of slide valve and unclean hydraulic oil.
② Vibration and noise. It is caused by spring deformation, air entry, excessive oil return resistance and excessive oil volume.
③ Oil leak. It is caused by poor contact or wear of cone valve, excessive clearance of slide valve, etc.
④ The pressure can't rise. It is caused by broken spring, clamping of slide valve, blockage of damping hole, reverse connection of inlet and outlet, etc.
1. Pressure reducing valve failure
① The pressure reducing valve fails. The main valve is jammed due to hydraulic oil pollution and the damping hole of the main valve is blocked, or it is caused by poor contact between the cone valve and the valve seat and spring deformation.
② The valve core is clamped radially. It is caused by hydraulic oil pollution and manufacturing accuracy problems.
③ Pressure pulsation. It is caused by unstable oil inlet (such as oil pressure pulsation from hydraulic pump) and air.
2. Sequence valve failure
① The sequence pressure is inconsistent with the set pressure. Improper adjustment of pressure regulating spring; The spring is deformed and the high pressure cannot go up; The slide valve is stuck; After disassembly and washing, the valve body is installed in the wrong direction, etc.
② Vibration and noise. Improper oil pipe and excessive oil return resistance.
3. Hydraulic control check valve failure
① Noise. Resonance with other valves; The oil flow exceeds the allowable value.
② Poor sealing during countercurrent. There is a gap between the valve core and the valve seat; Dirt at the valve port; The valve port is worn.
③ Poor control. The control pressure is too low.
4. Hitachi excavator solenoid directional valve failure
① No commutation. Contamination in the system; The flow exceeds the set value of the valve; Electrical failure; Electromagnet is damaged or suction is insufficient; The spring force exceeds the electromagnetic suction force; The spring is broken.
② The heating of solenoid coil is too high or burnt out. Poor coil insulation; Improper electromagnet core; Coil short circuit; The voltage is too high.
③ AC solenoid valve noise. It is mainly because the electromagnet has poor contact.
④ Leakage. The sealing ring or protective ring is damaged; Loose bolt connection; The solenoid valve is damaged.
5. Fault of Electro-hydraulic Directional Valve
① The valve core cannot move. The valve core is damaged; Deformation of valve body; Insufficient control pressure; The return spring is broken.
② The electromagnet is burnt out. Poor insulation; Improper electromagnet core; The voltage is too low; The reversing pressure, flow and oil port back pressure are too high; The push rod is too long or too short.
6. Multi way directional valve failure
① Pressure fluctuation and noise. The spring is bent and too soft; The damping hole of overflow valve in the valve is blocked; The check valve is not tightly closed.
② The valve stem does not work properly. The return spring is damaged, etc.
③ Leak. Poor contact between cone valve and valve seat; The stud screws are not tightened.
7. Pipeline failure
① Leakage due to loose connectors.
② Blockage in the pipe, caused by sundries, oxidation and corrosion, etc.
③ The pipe diameter becomes smaller.
④ Too many turns, too small angle.
