1. There is no pressure in the system
① The oil is too dirty or the damping hole of the slide valve is not cleaned during assembly, so that the damping hole is blocked and the slide valve cannot move. Filter or replace the hydraulic oil and clean the slide valve to make the damping hole unblocked.
② The spool valve spring is broken or bent, and the spool valve cannot be reset. Replace the spring.
③ The spool valve is stuck in the open position. Disassemble for maintenance. If the slide valve is rusted or roughened, it can be polished with metallographic sandpaper. If the valve body has burrs, it needs to be repaired.
④ The pilot valve spring is broken. Replace.
⑤ The pilot valve body is damaged. Replace.
⑥ The oil inlet and outlet are installed reversely, and there is no pressure oil to push the slide valve to move. Replace the oil inlet and outlet pipes.
⑦ The oil at the hydraulic control port is directly connected to the oil tank. Plug the hydraulic control port and protect the seal to prevent leakage.
2. Large pressure fluctuation
① The slide valve is roughened or bent and deformed, so that the slide valve does not move flexibly in the valve body hole, and sometimes it is stuck. Deburr or replace the spool valve.
② The oil is not clean, so that the damping hole is blocked and connected from time to time. Replace the oil and remove the impurities in the valve body and the dirt in the damping hole.
③ The damping aperture is too small and the damping effect is poor. The original damping hole can be closed and the damping hole can be reprocessed (generally about 1mm).
④ There is air in the hydraulic system. Remove air from the system.
⑤ The cone valve is damaged, the cone valve does not fit well with the valve seat, and the wear is uneven. Replace the cone valve and grind the valve seat.
⑥ The spring is deformed or too soft, making it difficult for the spool valve to reset. Replace the appropriate spring.
⑦ The screw adjusting the pressure changes the pressure due to the loosening of the lock nut. Lock the lock nut immediately after pressure regulation.
⑧ The pressure and flow of the hydraulic pump fluctuate greatly, which makes the overflow valve unable to balance. Replace or repair the hydraulic pump.
3. Noise generation
① The roundness error between the slide valve and the valve body hole is large or the gap is too large, resulting in leakage. Grind the valve body hole, reconfigure the slide valve, and make each precision meet the technical requirements.
② The clearance between the slide valve and the valve body hole is too small and the slide valve does not move flexibly. Grind the slide valve or grind the valve body hole to control the clearance within the required range.
③ The pressure regulating spring is bent and deformed. Replace.
④ The lock nut is loose. Tighten the lock nut immediately after pressure regulation.
⑤ Poor contact between pilot valve and valve seat hole. The surface is rough and the roundness error is large, which makes the force of the pressure regulating spring unbalanced, intensifies the oscillation of the cone valve and produces a scream. Grind the valve seat hole, control the roundness error of sealing oil within 0.005 ~ 0.01mm, and the surface roughness Ra < 0.8fzm. The surface roughness of the grinding cone valve shall reach 0.4mmo
⑥ The vertical error between the axis line of the pilot valve spring and the end face tilts the cone valve and makes the contact with the valve seat uneven. Replace the spring whose end face is grinded and perpendicular to the axis line to prevent the cone valve from toppling.
⑦ The oil inlet of the hydraulic pump is not smooth and the oil supply is insufficient. Remove the filter dirt at the oil inlet and appropriately increase the oil inlet area.
⑧ The oil return pipe of the valve is not smooth. Adjust the height of the oil return pipe to be more than 50mm from the bottom of the oil tank.
4. Hitachi excavator leaks seriously
① The fit clearance between slide valve and valve body hole is too large. Remake slide valve and match grinding.
② The seal is damaged. Replace.
③ Poor contact or serious wear between cone valve and valve seat hole. Grind the cone valve and grind the valve seat hole to make it fit closely.
④ The fit clearance between valve cover and valve body hole is too large. Refit the bonnet to control the fit clearance.
⑤ The oil resistant paper pad at the joint surface is broken. When replacing the oil resistant paper pad, pay attention not to cover the oil hole to ensure that the oil hole is unobstructed.
⑥ The screws at each connection are not tightened. Tighten the screws at each connection.
