Forklift vacuum booster hydraulic brake system is mainly composed of brake pedal, brake master cylinder, vacuum booster, brake cylinder, wheel brake and pipeline. As shown in the figure. Its working principle is as follows: The braking force acts on the master cylinder through the pedal and the linkage mechanism, so that the outlet produces a fluid flow with a certain pressure; the pressure further increases after the fluid enters the vacuum booster, and finally passes through the pipeline to the brake. The sub-pump; the brake cylinder generates thrust to open the brake shoe to both sides, and the brake shoe generates a braking force when the shoe contacts the brake hub.

Forklift brake system often has four kinds of faults such as brake failure, bad braking effect, brake running deviation and brake dragging. The diagnosis methods are as follows.

1. Braking failure is manifested as the forklift cannot slow down or stop while braking. The diagnosis and exclusion are as follows:

If you step on the brake pedal several times in a row and the pedal does not rise and feel no resistance, check the brake master cylinder for brake fluid. If it is lacking, add the brake fluid of the same type and remove the air in the pipeline; if not, check whether there is any leakage or damage to each brake pipe and repair or replace it as appropriate.

Depress the brake pedal. If there is no linkage feeling, the connection between the pedal and the master cylinder may be disconnected. Check the connection mechanism and connect it.

If the brake pedal is depressed, although there is a certain resistance, the position of the pedal cannot be maintained, it is obviously sinking, and the main pump has a phenomenon of leakage or ejection. The reason is that the brake master cylinder seal is broken. The master cylinder should be disassembled and the master pump seal replaced.

If the above checks are all normal, the master pump seal may be lost. At this time, the master cylinder should be disassembled and the master pump seal of the same type should be replaced.

2. Bad braking effect This fault has 3 kinds of phenomena: First, step on the foot brake pedal several times, the forklift cannot slow down and stop; Second, the pedal height is normal when stepping, but it feels stepless and cannot be stopped immediately; Third, the pedal is felt when stepping on the pedal. High, hard or even rebound, but the braking effect is poor. The diagnosis and troubleshooting of this fault are as follows:

If you step on the brake pedal several times, the pedal will gradually rise, and after raising, you will continue to step down without lifting your foot. You can feel that the pedal has elasticity. You can release the pedal and stop for a while and then step on it. If it is still the brake There is air in the system and it should be vented.

The sequence of the discharge air should start with the master cylinder and then the brake cylinders. The sequence of the discharge of the air from each of the sub-pumps shall start from the nearest sub-pump to the master cylinder and be discharged one by one. Exhaust method: One person is responsible for stepping on the brake pedal and the other one is responsible for exhaust. After the brake pedal is pressed to the end, it does not relax, and then the exhaust screw is released. After the brake fluid mixed with air is sprayed, the pressure can be lowered, and then the bleeder screw can be tightened to relax the brake pedal. After the brake pedal is fully returned, press the brake pedal again to the end and continue to vent. This will be repeated several times to completely discharge the air.

If the brake pedal does not work well when stepping on one foot, the position of the brake pedal is gradually increased with a few feet, and the braking effect is good, indicating that the free travel of the pedal is too large or the gap between the friction plate and the brake hub is too large. At this point should first check the free travel of the adjustment pedal to within the specified range, and then check the adjustment of friction plate and brake hub clearance.

If the brake pedal is pressed continuously, the position of the pedal can be gradually increased. If the pedal is not stepped on, the pedal is not depressed, but there is a sense of sinking, indicating that the brake system has oil leakage or the brake master cylinder is out of oil. The valve does not close tightly. At this point should check the pipe joints for any leakage of the place, if any leakage, it should take fastening, welding or replacement and other methods.

When the pedal is depressed, if the pedal position is very low, and even a few pedals are pressed, the position cannot be increased. Generally, the brake master cylinder vent hole or the brake fluid compensation hole is blocked, and the clearing should be checked. If the pedal height meets the requirements, the treadle will not be weak and sink, but if the brake effect is poor, the wheel brake will be faulty and the wheel brakes shall be dismantled for inspection.

If the foot brake is used, if the brake pedal is high, hard or bouncing, the vacuum booster may be defective. Should first check whether each vacuum tube is in good condition, whether the connection is reliable, and then check the vacuum booster. During the inspection, the brake pedal may be depressed first, and then the engine may be started and idle for a few seconds. If the brake pedal feels a little lower, the vacuum booster is good; if the brake pedal does not decrease by itself, then the vacuum booster is indicated. The device is not working properly and the vacuum booster should be replaced.

3. Brake runaway faults are manifested in the fact that the two wheels cannot act at the same time or the braking force is not equal in magnitude during braking, which causes the forklift to deflect to one side when braking. The diagnosis and troubleshooting of this fault are as follows:

During the road test, if the forklift is moving to the right during braking, it means that the brake on the left wheel is slow or the brake force is insufficient; otherwise, the brake on the right wheel is slow or the braking force is insufficient.

If it is determined that the brake of a wheel is sluggish or the braking force is insufficient, check whether there is any collision or leakage of the brake pipe in the wheel. If any, check the cause and remove it. If the wheel line is intact, the wheel cylinder can be vented. If the phenomenon of exhausted brake deviation is eliminated, this indicates that there is air resistance in the wheel cylinder or pipeline. If there is no air resistance phenomenon, check and adjust the gap between the wheel friction plate and the brake hub.

If there are no problems with the above inspections, it means that the fault is inside the wheel brakes. The wheel brakes shall be dismantled, and the wear of the brake pads and the working condition of the brake cylinders shall be checked. If necessary, repairs or replacements shall be made.

4. Braking delay This fault is manifested by the fact that after the brake pedal is raised, all or individual wheel brakes cannot be completely released immediately, which will affect the forklift restart or drive. The diagnosis and troubleshooting of this fault are as follows:

After the forklift has worked for a period of time, touch each wheel brake hub. If all the wheel hubs are hot, it means that the fault occurred in the master cylinder; if the individual wheels are hot, the fault is in the wheel brake.

If it is determined that the fault is in the main pump, first check the free travel of the pedal. If the free stroke does not meet the requirements, the free travel of the pedal shall be adjusted as required; if the free stroke meets the requirements, the cover of the oil storage chamber of the master cylinder can be opened to observe the return of the master pump. If the oil cannot be returned or the return oil is slow, The main pump should be dismantled for maintenance and replaced if necessary.

If the fault is in the wheel brake, loosen the exhaust screw first. If there is rapid ejection of the brake fluid and the brake shoes return, the pipeline shall be blocked and the pipeline shall be opened; if the brake shoes cannot return, the gap between the brake pads of the brake pads shall be adjusted.

If there is no effect after adjustment by the above inspection, the brake hub should be removed and the condition of the piston seal, return spring and brake shoe pin of the cylinder pump should be checked and repaired and replaced if necessary.