1. Internal leakage
When the internal leakage of the multi-way reversing valve occurs, the working oil passage is connected to the oil return passage or the oil overflow passage, and the hydraulic oil flows directly back to the oil tank. The operation cannot be completed, causing the lifting hydraulic cylinder to be weak or unable to lift, and the forks move on their own Failures such as sliding down and the mast tilting forward. The causes and elimination methods of internal leakage are:
(1) The wear gap between the valve stem and the valve body is too large
There are three grooves on the lifting and tilting stems of the multi-way reversing valve. The grooves and the oil passage can connect or cut off the oil passage and change the working mode. The gap between the valve stem and the valve body of a good distribution valve is very small, and there is very little oil leakage, so the hydraulic cylinder drops or tilts very little, and does not affect the work. However, when the wear gap is too large, the hydraulic oil under the pressure generated by the working pump will cause the oil in the working oil passage to communicate with the oil return passage or the oil spill passage and automatically return to the oil tank. The main reason is that the long-term use of the distribution valve or the unclean oil has accelerated the wear of the valve stem and the valve body, damaged the mating sealing surface, and caused oil leakage. If the valve stem is lightly worn during repair, the valve stem can be chrome-plated and polished; if the valve stem is severely worn, it needs to be replaced.
(2) Oil leakage between valve bodies
Since the working oil passage, the oil return passage, and the oil spill passage run through the three single-piece valve bodies, the sealing requirements between the valve bodies are very high. After the O-ring seal is installed between the valve body and the valve body oil passage, Connect the valve body with bolts to achieve the purpose of sealing.
If the tightening torque of the bolts is different, it may cause the valve body to warp. If the sealing ring fails, internal leakage occurs; if the valve body is damaged or the O-ring is aging or damaged during installation, internal leakage between the valve bodies is also prone to occur under the action of oil pressure. When repairing, if the valve body is damaged, you need to grind, replace the O-ring seal, and tighten the bolts according to the sequence and torque requirements.
(3) The safety valve spring fails
The safety valve is used to adjust the working pressure of the system to keep the pressure within a certain range to prevent damage to the hydraulic system components caused by overload, the hydraulic cylinder piston to the limit position or other reasons. The safety valve is mainly opened and closed by pressing the steel ball on the valve position by the spring force. When the oil pressure output by the hydraulic pump exceeds the specified value, the pressure of the high-pressure oil overcomes part of the high-pressure oil and returns to the oil tank through the safety valve spillway. When the oil pressure reaches the specified value, the spring will press the steel ball against the valve position under the action of its own preload, and the safety valve will be closed.
If the safety valve spring fails, the hydraulic oil can force the steel ball to leave the valve position and flow into the oil spillway when the hydraulic oil is lower than the specified pressure of the system, causing internal leakage and causing system failure. The spring must be replaced when repairing, and then use the adjusting screw to adjust the spring pressure to the specified 14 Mpa. During adjustment, load 7.5t cargo according to the demand at 600mm from the load center. When the cargo appears to be lifted, use the lock nut to lock it. The pressure at this time is the pressure that needs to be adjusted.
(4) Multi-way reversing valve stem cannot be reset
The valve stem return spring of the manual hydraulic pallet truck is installed at the lower end of the valve stem. The spring can be compressed regardless of whether the valve stem is in the upper position or the lower position. When there is no external force, the valve stem can quickly return to its original position due to the elastic force of the spring. . If the valve stem cannot be reset and the groove communicates with the oil passage, internal leakage will occur. One is that the return spring of the valve stem is deformed or damaged, and the spring force is reduced and the valve stem cannot be returned to its original position. The spring must be replaced when repairing; the other is that the valve body and the valve stem are not clean, resulting in greater resistance, and the valve stem It is difficult to reset. Clean the inside of the multi-way directional valve during repair to eliminate resistance.
(5) Cone valve wear
The poppet valve is used to prevent backflow of oil. If the poppet valve is worn and the oil passage is not tightly closed, the hydraulic oil will flow back and the system will fail. When repairing, it should be ground or replaced. Eliminate backflow.
2. Oil leakage from the valve body
The seal between the valve stem and the valve body is achieved by an O-ring seal. If the seal ring is aging or damaged, hydraulic oil will flow out along the valve stem under the action of system pressure, causing oil leakage from the valve body. Only need to replace the O-ring to eliminate this fault.
