The Analysis and Maintenance of Failure Causes of Hydraulic Check Valves (Part Two)

2.3 Finding and confirming the failure
(1) The inspection of the valve body
The pipeline was opened and it was found that the valve plate was in the middle state. The valve plate was knocked lightly with a copper rod and nothing happened, indicating that the drive part of the valve plate has jammed and caused the valve body to fail to move (Figure 4).
 

Figure 4 The jamming of the valve plate
 

(2) The inspection of the hydraulic station

The globe valve, one-way valve, throttle valve, overflow valve, three-way electromagnetic exchange valve, electromagnetic exchange valve, lifting cylinder, locking cylinder and stroke switch were checked and it was found that the needle of the manual needle-shaped globe valve was bent and led to leakages and not being unable to maintain pressure. See Figure 5.

 
Figure 5 Bending and deformation of the needle valve's needle

(3) The inspection of the control

The feedback contact signal and the indicator light of the control cabinet were checked. The connecting terminal between the terminal of the control cabinet and that of the hydraulic station was measured. The connecting terminals between the hydraulic station's terminal and the solenoid valve's terminal as well as the terminal of the control cabinet and control switch were checked. No abnormal bending and deformation of the needle valve's needle in Figure 5 were found.
 
2.4 Troubleshooting
(1) Cleaning up rust
The rust on the surface of the valve body was cleaned up, and the loosening fluid was sprayed on the drive shaft and soaked it. After the rust was cleaned up, used the copper rod to gently hit the valve plate. The switch was flexible and the jam was eliminated.
(2) Mapping and processing needle valve needles
After detailed inspection and measurement, the deformation of the valve needle couldn't be eliminated. By looking up the original drawings and actual surveying and mapping, the needle valve's needle was machined. After the processing was completed, the valve needle was assembled and checked by a pressure test, which could meet the requirement for the operating pressure.
 
3. The functional identification of hydraulic check valves
3.1 The inspection of the accumulator
According to the technical documents, the accumulator supplementary nitrogen was adjusted, and the pressure was maintained at 5.2 plus 0.2MPa.

3.2 Manual pressure tests
① Each check valve, throttle valve and globe valve was checked and the sealing rubber ring of each valve was replaced to ensure that there was no leakage. ② Checked whether or not the hydraulic cylinder piston, sealing ring, sealing surface and rubber ring were installed correctly. ③ Used the lever to perform a pressure test and the pressure should be normal.
 
3.3 The inspection and confirmation of adjustment
(1) Confirming the wiring
Checked and confirmed the connection according to the electrical schematic diagram and the wiring terminal connection diagram. Switched on the power, and the indicator light was on. Pressed the "Starting the Oil Pump" button. Checked whether the motor's rotation direction was correct; if it was opposite, it should be adjusted.
(2) Controlling the hydraulic station
Pressed the "Starting the Oil Pump" button to make the indicator light on; when the oil pressure reached the set upper limit, the motor automatically stopped.
(3) Controlling the energy storage
When the internal pressure of the hydraulic station was lower than the set lower limit, the oil pump automatically ran to store pressure for the accumulator; when the pressure reached the set upper limit, the oil pump stopped operating and stored the pressure for the accumulator.
(4) Controlling the opening of the valve
Pressed the local button; clicked the "valve opening" button, and the indicator light of the oil pump would be on; after the locking cylinder was raised to the position, the valve's closed position indicator light went out, and the valve's open position indicator light was on. The lock indicator light frequently flashed when the button was pushed. This indicated that the lock cylinder failed. Readjusted the upper limit switch of the counterweight to make the lock switch in the normal lock position.
(5) Controlling the closing of the valve
Pressed the "Closing of valves" button, and the indicator light of the valve's opening in place went out, which needed to rely on the heavy hammer to complete the closing of the valve; when the fully closed position was in place, the valve's closing indicator light was on.

(6) Remote control

Pressed the "remote control" button to open or close the valve according to the control command, and the process was fine.
 
4. Conclusion
The hydraulic check valve was disassembled and repaired. The correctness of the failure analysis was verified and the valve's function and stable operation were ensured. The following conclusions were obtained through analysis:

(1) The reason for the frequent starting and stopping of the hydraulic check valve was that the valve needle of the manual pressure relief globe valve was bent, which caused the valve to leak and the system pressure not to be maintained. 

(2) In the valve's opening process, the valve body didn't move because the valve drive shaft was corroded, causing the valve body to jam.

(3) Through the maintenance of the hydraulic check valve, the practical experience for the maintenance of the other two valves of the same model was provided, avoiding such failures occurring repeatedly, and at the same time, technical reserves for the later maintenance of hydraulic check valves were provided.