Maintenance and Overhaul of Master Cylinder and Sub-Cylinder in Hydraulic Braking System of Forklift
Repair of Hydraulic Brake Master Cylinders
1. Remove the hydraulic brake master cylinder from the forklift. Remove the brake pedal, clutch pedal return spring, two push rods on the master cylinder and oil outlet pipe; remove the fixing bolts on the master cylinder, and take off the brake master cylinder assembly.
2. Decomposition of the brake master cylinder. The hydraulic brake master cylinder and the clutch hydraulic master cylinder produced in the early stage are integrated. When disassembling, the parts in the two chambers should be placed separately to prevent wrong installation.
①Remove the dust cover clip, remove the piston push rod and dust cover, clean the outside, unscrew the oil filler plug, and release the brake fluid inside.
②Remove the lock ring, take out the thrust sting ring, the piston and the leather cup, the return spring and the oil outlet valve; remove the outlet and oil return valve from the return spring, and remove the sealing ring from the piston.
③Remove the pump cover and the oil pipe joint, clean the internal parts with alcohol, and at the same time clear the oil return hole, compensation hole in the master pump, the small hole in the piston head and the air hole on the refueling screw plug.
3. Overhaul of master cylinder parts
①If the star valve plate on the piston is loose, it should be riveted.
②The free length of the return spring in the master cylinder is 107mm. Under the pressure of 53.9~68.6N, the compression length should not be shorter than 67mm, otherwise it should be replaced.
③The oil outlet valve, oil return valve, leather cup, sealing ring, dust cover, etc. should be replaced with new ones.
4. Assembly and test of brake master cylinder
①All parts should be cleaned before assembly, and then assembled in the reverse order of disassembly. After reassembly, push the piston several times with the push rod to check whether the piston moves flexibly and freely in the cylinder, and whether there is a card issue. After loosening the push rod, use a very thin wire to check whether the oil return hole and the compensation hole are unobstructed in the liquid storage chamber. If the oil return hole is closed by the leather cup, the washer at the back should be thinned to eliminate it; otherwise, the brake bite phenomenon will occur, and the return spring with greater elasticity can also be replaced.
②The test of the master cylinder: After reassembly, carry out the pressure test. Check whether the parts are sealed, whether there is oil leakage, and whether the work is normal. When carrying out the pressure test, the master cylinder should be filled with brake fluid, and then the handle should be turned to make the pressure of the oil reach 8820kPa for 3min.
Overhaul of the sub-pump
The hydraulic brake cylinder is installed on the wheel brake, and the maintenance method is the same as that of the master cylinder. The size of the inner diameter of the two cylinders on the same wheel should be the same. After disassembly, the leather cup and apron should be replaced. The free length of the spring in the sub-pump is 42mm. Under the pressure of 24.5~34.3N, the compression length should not be shorter than 17mm, otherwise it should be replaced. After the reassembly, carry out the pressure test together with the master cylinder, and there shall be no oil leakage.
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