Maintenance of hydraulic brake master cylinder

1. Remove the hydraulic brake master cylinder from the forklift, remove the brake pedal, clutch pedal return spring, two pushrods, and oil outlet pipe on the master cylinder, remove the fixing bolts from the master cylinder, and remove the master assembly of the brake master cylinder.

2. For the decomposition of the brake master cylinder, the hydraulic brake master cylinder produced in the early stage is integrated with the clutch hydraulic master cylinder. The parts in the two chambers should be placed separately during the decomposition to prevent the wrong installation. The steps are as follows:

1) Remove the dust cover clamp, remove the piston push rod and dust cover, clean the outside, unscrew the oil filler plug and drain the internal brake oil.

2) Remove the lock ring, take out the thrust washer, piston, and cup, return spring and oil outlet valve; Remove the oil outlet and return valve from the return spring and remove the sealing ring from the piston.

3) Remove the pump cover and oil pipe joint, clean the internal parts with alcohol, and dredge the oil return hole, compensation hole, small hole on the piston head, and vent hole on the refueling plug.

3. Maintenance of master cylinder parts.

If the star valve plate on the piston is loose, it should be riveted tightly. The degree of freedom of the positioning spring in the master cylinder is 107mm. Under the pressure of 53 -. 9-68.6n, the compression length shall not be less than 67mm. Otherwise, it shall be replaced. The leather cup, sealing ring, dust cover and oil outlet, and return valves shall be replaced with new parts.

4. Assembly and test of brake master cylinder.

1) All accessories shall be cleaned before assembly and then assembled in the reverse order of subsection. After reassembly, push the plug several times with the push rod to check whether the piston moves flexibly and freely in the cylinder barrel and whether there is card clamping. After loosening the pushrod, use a skinny steel wire to check whether the oil return hole and compensation hole are unblocked in the liquid storage chamber. If the oil return hole is closed by a leather cup, the washer at the back should be thinned to eliminate the fault. Otherwise, a braking seizure will occur or replace the return spring with a large elastic force.

2) For the test of the master cylinder, it is best to conduct a pressure test after reassembly. Check whether all parts are sealed, leaking oil, and working usually. Otherwise, it shall be eliminated first and then loaded for use. For pressure test, fill the master cylinder with brake fluid, and then turn the handle to make the oil pressure reach 8820kpa for 3min. The master cylinder and wheel cylinder shall not leak oil, and the oil pressure drop shall not exceed 294kpa. Otherwise, it shall be reassembled.

5. Maintenance of wheel cylinder. The hydraulic brake wheel cylinder is installed on the wheel brake, and the maintenance method is the same as that of the master cylinder. The inner diameters of two-wheel cylinders on the same wheel shall be the same, and the leather cup and sealing ring shall be replaced after removal. The free length of the spring in the wheel cylinder is 42mm. Under the pressure of 24.5-34.3n, the compression length should not be less than 17mm. Otherwise, it should be replaced. After reassembly, the pressure test shall be conducted with the master cylinder, and there shall be no oil leakage.

6. The oil level in the oil tank is too low, or the oil filter in the oil tank is blocked, resulting in insufficient oil absorption, shaking, and abnormal noise, resulting in the inadequate lift of the hydraulic cylinder. Add hydraulic oil, thoroughly clean the oil filter and keep the oil clean. If it is found that the oil inlet pipe has poor sealing, aging, and deformation and is easy to be sucked flat, tighten or replace the high-quality pipe in time.

7. When replacing the hydraulic pump, if the oil suction port is mistaken for the oil discharge port, the hydraulic pump reverses, and the pressure is insufficient, it shall be corrected in time. In addition, when repairing the hydraulic system, disassemble the hydraulic pump to make its internal oil flow out. Before assembly, the same hydraulic oil must be injected into the pump, and the pump body must be continuously rotated to fill it. Otherwise, the hydraulic pump will be burned.

8. If the opening pressure of the safety valve is too low (< 15.5mpa), the primary safety valve cannot be adjusted blindly. The safety pressure valve must be disassembled to check whether the spring in the pilot cone valve is broken, whether the main oil valve is stuck, whether the conical oil inlet valve is flexible, and whether the damping hole is blocked. If there is no problem, adjust the opening pressure of the safety valve. The adjustment method is: install a pressure gauge on the system, add 120% of the rated load, and adjust the overflow valve in the multi-way directional valve. When the forklift lifts the goods to a seemingly Nonrising state, the pressure should be 16.0mpa. Otherwise, one of the reversing valves shall be reversed, the unloading port of the overflow valve shall be cut off to make it in a working state, and then the adjusting screw shall be rotated until the required pressure value is reached.

9. Methods for removing air from forklift hydraulic system:

1) Fill the hydraulic oil specified for the forklift to the oil level set on the scale, and lift the lifting cylinder when filling the hydraulic oil;

2) Make the load of the forklift reach 1 / 10-1 / 8 of the rated load, loosen the vent plug on the lifting cylinder, lift and drop the fork several times until there is no bubble at the vent plug, and then tighten the vent plug;

3) Tilt the tilt cylinder forward and backward to the maximum several times to eliminate the air in the tilt cylinder.

Forklift maintenance personnel shall check the fault causes and fault components one by one and then use the troubleshooting method to troubleshoot or determine the parts that are easier to study. This will focus on several more complex parts and then use the replacement method to replace the qualified components of the exact specification with the questionable parts for the test. Generally, through the above process, the general faults of the forklift hydraulic system can be effectively and accurately diagnosed and repaired.

I hope this blog is helpful. Please click here for more about our forklift parts.