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Insufficient pressure
① The oil did not enter the hydraulic cylinder and connected the cylinder body to the oil pressure circuit. After giving an action command, the piston rod still did not move; Connect a pressure gauge near the oil port of the cylinder block, and there is no pressure display. The reasons are as follows:
a. The directional valve is not reversing. It is generally caused by poor lubrication, stuck or damaged springs, oil stains or impurities sticking to the sliding parts, and other reasons.
b. If the intake and exhaust holes of the electromagnetic pilot valve are blocked by impurities such as oil sludge, not tightly sealed, the movable iron core is stuck, and there is a circuit malfunction, it can cause the directional valve to not be able to reverse normally.
c. Circuit faults are generally divided into two types: control circuit faults and electromagnetic coil faults. Before checking for circuit faults, the manual knob of the directional valve should be turned a few times to see if the directional valve can reverse normally at the rated air pressure. If it can reverse normally, it indicates a circuit fault. During inspection, an instrument can be used to measure the voltage of the electromagnetic coil to see if it has reached the rated voltage. If the voltage is too low, further checks should be made on the power supply and associated travel switch circuits in the control circuit. If the directional valve cannot reverse normally at the rated voltage, the connector (plug) of the electromagnetic coil should be checked for looseness or poor contact. The method is to unplug the plug and measure the resistance of the coil. If the resistance is too high or too low, it indicates that the electromagnetic coil is damaged and should be replaced.
d. The system is not supplying oil. Check and eliminate the causes of faults in the hydraulic pump and main hydraulic valves.
First, check if the hydraulic pump can output oil. If there is no oil output, it may be due to the incorrect steering of the hydraulic pump, severe wear or damage to accessories, high resistance or air leakage in the suction pipe, resulting in the hydraulic pump being unable to deliver oil.
If there is oil flowing out of the pump, check each return pipe to see which component is causing the overflow. If the overflow valve malfunctions, disassemble it, clean it, inspect or replace the spring, and restore its working performance.
After inspecting the overflow valve (safety valve) and cleaning it, if the fault still persists, disassemble the relevant valve, clean and inspect the size of the sealing gap and various sealing devices, and replace the damaged sealing devices.
② Although there is oil, there is no pressure
a. Mainly due to pump or overflow valve malfunction. If there is a specific pressure that can be adjusted by the relief valve, but the pump's oil delivery volume significantly decreases with the increase of pressure. If the pressure does not reach the required value, it may be due to increased clearance after pump wear. The elimination method is to measure the volumetric efficiency of the pump to determine whether the pump can continue to operate. For those with severe wear and tear, repair or replace them.
b. Serious internal leakage. Add a shut-off valve or similar valve to the open oil circuit from the cylinder block to the fuel tank to close it, and install a pressure gauge at this location to measure its pressure rise. If the pressure rises to the supply pressure, it can be determined that there is an internal leak in the cylinder block. One reason for internal leakage is that the piston nut or bolt is loose, the bolt neck is damaged, and the bolt is not tightened enough. The bolt is cut off, causing the piston and piston rod to loosen; Secondly, due to severe damage to the seals. At this point, tighten the active.