When a hydraulic cylinder fails to operate, first check the hydraulic oil level, pump operation status, and suction filter blockage (power source). Then verify control signals, solenoid valve energization/function, valve spool sticking, and pilot pressure (control system). Finally, inspect cylinder line blockage/leakage, internal seal failure, and mechanical binding in the load or mounting (actuator).
1. Check the hydraulic power source (oil pump and oil tank)
(1) Check the hydraulic oil volume:
Observe the oil level gauge of the hydraulic oil tank. Is the oil level below the minimum scale? If the oil volume is insufficient, immediately add clean hydraulic oil of the same brand and viscosity grade to the specified range. Severely contaminated or emulsified oil needs to be completely replaced.
(2) Check the operating status of the hydraulic pump:
① Confirm whether the motor power is connected and whether the motor rotates normally.
② Check whether the coupling or transmission device between the pump and the motor is intact and the connection is reliable.
③ If the pump makes a serious abnormal noise, stop the pump and check whether it is damaged.
④ Listen to the sound of the hydraulic pump: Normally, it is a uniform “buzzing” sound.
⑤ Abnormal situation: sharp whistling (possibly suction or cavitation), no sound (pump not started), abnormal knocking sound (inside the pump is damaged).
(3) Check the oil suction pipeline and filter element:
① Observe whether the pressure difference indicator of the oil suction filter element (in the oil tank or pipeline) alarms (turns red).
②Listen to see if there is a clear suction sound (“hissing”) at the pump inlet.
③Handling: Blockage of the suction filter is one of the most common reasons. Clean or replace the blocked suction filter immediately. Ensure that all connections of the suction pipeline are well sealed and leak-free.
2. Check the control system (valves and signals)
(1) Check the operation input signal:
① Check the input devices such as the operating handle, button, foot switch, remote control, etc.
② Confirm that the device itself is not mechanically stuck or damaged.
③ Use a multimeter to measure whether its output signal (voltage/current) is normally delivered to the control valve (such as the solenoid valve coil terminal).
④ Check whether the relevant control circuit is open, short-circuited, or loose.
(2) Check the function of the directional control valve:
① Use a pressure gauge to measure whether the control oil pressure reaches the starting pressure value required by the valve.
② The pilot pressure is insufficient and the main valve core cannot be switched normally. It is necessary to check whether the pilot pressure source (such as the pressure reducing valve, pilot pump) is normal.
③ Try to tap the valve body (pay attention to safety and do it after the system is depressurized). Sometimes a slightly stuck valve core can be shaken loose.
④ If it does not work, the valve core and the inside of the valve body need to be disassembled and cleaned to remove contaminants. The valve needs to be replaced if it is severely worn or damaged.
⑤ When the power is on, touch the solenoid valve coil housing with your hand. It should feel warm and vibrate slightly, and you can usually hear a clear “click” sound.
Handling: Measure the coil resistance to determine whether it is open circuit/short circuit. Replace the damaged coil. Check the power supply line.
3. Check the cylinder body and load
(1) Check the cylinder pipeline and connection:
① Visually check the two main oil pipes connecting the cylinder inlet and outlet.
② Confirm that the pipeline has no serious bends or flattening that may cause oil blockage.
③ Check whether there is obvious external leakage at the pipe joints and cylinder port seals.
(2) Check for internal leakage in the cylinder (be careful):
① Move the cylinder piston rod to the end of the stroke.
② Remove the oil pipe joint of the other chamber (rodless chamber or rod chamber) (the system must be completely depressurized first!).
③ Operate the control valve to try to make the cylinder move (supply oil to the chamber where the joint is removed).
If a large amount of oil continues to flow out of the disassembled interface, it means that the internal seal (piston seal) of the cylinder has been severely damaged, and the high-pressure oil leaks directly from one chamber to another, resulting in the inability to establish thrust. The internal seal of the cylinder needs to be removed and replaced.
(3) Check the mechanical load and installation:
① Check whether the load driven by the cylinder is mechanically stuck, the guide rail is severely deformed, or there is foreign matter blocking it.
② Check whether the mounting bracket, earrings, and pin of the cylinder itself are broken, deformed, or severely loose.