The directional valve is not reversing. This is usually caused by poor lubrication, a stuck or damaged spring, or the sliding part being obstructed by oil污 or impurities.
b. If the inlet and outlet holes of the electromagnetic pilot valve are blocked by oil sludge or other debris, if the valve is not sealed properly, if the moving core is stuck, or if there is a circuit fault, all these issues can cause the directional valve to fail to change direction normally.
c. Circuit failures are generally categorized into control circuit failures and electromagnetic coil failures. Before inspecting circuit failures, the manual knob of the directional valve should be turned a few times to check if the valve can change direction normally under the rated pressure. If it can, there is likely a circuit fault. During inspection, use a meter to measure the voltage of the electromagnetic coil to see if it reaches the rated voltage. If the voltage is too low, further inspect the power supply and associated travel switch circuit in the control circuit. If the directional valve cannot change direction normally at the rated voltage, check if the connections (plugs) of the electromagnetic coil are loose or not making good contact. The method is to remove the plug, measure the resistance of the coil, and if the resistance is too high or too low, it indicates that the electromagnetic coil is damaged and should be replaced.
d. The system was not supplied with oil. Investigated and rectified the causes of failure in the hydraulic pump and main hydraulic valves.
First, check if the hydraulic pump can output oil. If no oil is being produced, it may be due to the incorrect orientation of the pump, severe wear or damage to the components, high resistance or leakage in the suction pipe, which prevents the hydraulic pump from outputting oil.
If the pump has oil output, inspect all return oil lines to determine the component causing overflow. If the overflow valve is faulty, disassemble the valve, clean it, inspect or replace the spring, and restore its operational performance.
After inspecting and cleaning the overflow valve (safety valve), if the fault persists, disassemble the relevant valve, clean and inspect the size of the sealing gaps and various sealing devices, and replace any damaged sealing devices.
② Oily, but no pressure
a. Primarily, there is a fault with the pump or relief valve. If a specific pressure can be adjusted by the relief valve but the pump's oil flow rate significantly decreases with increasing pressure, and the pressure does not reach the required value, it may be due to increased clearance after the pump wears. The method to rule this out is to measure the pump's volumetric efficiency, which will determine if the pump can continue to operate. For more severe wear, repairs or replacements are conducted.
b. A severe internal leak has been detected. A shut-off valve, such as a cutoff valve, should be added to the open oil path leading to the oil tank to close it off. A pressure gauge should then be installed at this location to measure the pressure increase. If the pressure rises to the supply pressure, it can be clearly determined that there is an internal leak in the cylinder. The internal leak is caused either by loose piston bolts or piston pins, damaged bolt necks, insufficient bolt torque, the bolt being sheared, resulting in the piston and piston rod becoming loose; or by severe damage to the sealing components. At this point, tighten the piston and piston rod and replace the sealing components.
