Created on:2021-09-01 14:12

Fault diagnosis and maintenance of marine hydraulic equipment_ Fault of luffing hydraulic system of cargo crane

Fault diagnosis and maintenance of marine hydraulic equipment_ Fault of luffing hydraulic system of cargo crane

A ship's cargo crane adopts single hydraulic cylinder luffing, and the boom can not be lifted in use.

(1) Working principle of luffing system

The hydraulic schematic diagram of luffing system is shown in Figure g, and its working principle is as follows.

Hydraulic pump 3 sucks oil from oil tank 1 through filter 2. When 4 is in the middle position, the hydraulic pump is unloaded and luffing hydraulic cylinder 9 does not move; When the change-over valve is in the right position, the oil discharged from the hydraulic pump enters the lower chamber of the hydraulic cylinder through the check valve 7 and the hydraulic control check valve 8 to make the piston of the hydraulic cylinder move upward and jack up the boom; When the change-over valve is in the left position, the oil discharged by the hydraulic pump enters the upper chamber of the hydraulic cylinder to move the piston downward and lower the boom.

(2) Fault diagnosis

① The possible causes of the failure can be seen from the hydraulic schematic diagram. The reasons for the failure of the boom are the following: A. insufficient oil level in the oil tank; b. Wrong rotation of motor; c. The hydraulic pump cannot work normally; d. Reversing valve failure; e. Failure of safety valve 10 and overflow valve 13; f. Internal leakage of hydraulic cylinder.

② A. check whether the oil level of oil tank is correct; b. The motor turns correctly; c. The hydraulic pump operates stably without noise and overheating; d. The inspection of internal leakage is simpler than that of directional valve, safety valve and overflow valve, so check whether the hydraulic cylinder has internal leakage first. Open the pipe joint of the upper chamber of the hydraulic cylinder 9, connect the oil with the oil bucket, place the reversing valve 4 on the right, and the lower chamber of the hydraulic cylinder enters the oil. It is found that a large amount of oil flows out of the upper chamber of the hydraulic cylinder and the piston does not move, indicating that the hydraulic cylinder leaks.

(3) Repair of hydraulic cylinder

① Disassemble the hydraulic cylinder and its structure is shown in Figure h. It is found that the piston of the hydraulic cylinder has been broken and its section is rectangular. After measurement, the outer diameter of the sealing ring - the inner diameter of the hydraulic cylinder d1152.4mm; Inner hole of sealing ring - outer diameter of piston d = 127mm; Seal ring length H1 = 17mm.

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② Replace the sealing ring. The sealing ring can not be bought in China. The domestic polyurethane hole is replaced by a Y-shaped sealing ring with its outer diameter φ 150mm; Inner hole selection φ 17. 8mm; Length h2 = 14mm. The outer diameter of the selected Y-shaped seal ring is 2.4mm smaller than the inner hole of the hydraulic cylinder, and the inner hole is 10.8mm larger than the piston. Add two steel sleeves, as shown in figure I, and its inner hole is φ= 127-0.05-0.10, interference fit with piston, outer circle is φ= 137.8 + 2.4 = 140.2mm, soak the Y-shaped sealing ring on the steel sleeve with hot water and support it so that its outer circle is 152.4mm.

③ Reinstall the hydraulic cylinder. The inner hole of the hydraulic cylinder is provided with a keyway. When installing the piston, the lip of the Y-shaped seal ring is embedded in the keyway and is gnawed. A ring is prepared according to the size of the keyway, which is equally divided into three sections. Stick it in the keyway with glycerol and fill it. The piston can be smoothly installed into the hydraulic cylinder. Then take out the three sections of ring and reinstall the hydraulic cylinder. After test run, the boom can rise and fall freely, and the fault can be eliminated.

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