Forklift vacuum boost 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 brake master cylinder through the pedal and the linkage mechanism, so that its outlet generates a liquid flow with a certain pressure; after the liquid flow enters the vacuum supercharger, the pressure further increases, and finally passes to the brake Cylinder; the brake cylinder generates thrust to spread the brake shoes to both sides, and the shoes are close to the brake hub to generate braking force.
Forklift brake system often has four kinds of failures, such as brake failure, poor braking effect, brake deviation and brake drag. The diagnostic methods are described as follows.
1. Braking failure
Shows that the forklift cannot slow down or stop when braking. The diagnosis and elimination methods are as follows:
If you step on the brake pedal several times in a row, the pedal does not rise and feel no resistance, you should first check whether the brake master cylinder lacks brake fluid. If it is missing, the brake fluid of the same model should be added, and the air in the pipeline should be excluded; if it is not missing, check each brake pipeline for leakage or damage, and repair or replace as appropriate.
Depress the brake pedal. If there is no linkage, the pedal to the master cylinder may be disconnected. Check the connection mechanism and connect it.
If you step on the brake pedal, although you feel a certain resistance, but the pedal position can not be maintained, it sinks obviously, and the master cylinder leaks or sprays. The main reason is that the brake master cylinder seal is broken. The brake master cylinder should be disassembled and the master cylinder seal replaced.
If the above inspections are normal, it may be that the master cylinder seal is out of position. At this time, the brake master cylinder should be disassembled and the master cylinder seal of the same type should be replaced.
2. Poor braking effect
There are three phenomena of this fault: one is that the forklift cannot slow down by stepping on the foot brake pedal several times; the second is that the pedal height is normal when the pedal is stepped on, but the pedal is not strong enough to stop immediately; the third is that the pedal feels high, hard or even Rebound, but the braking effect is poor. The troubleshooting and troubleshooting methods for this are as follows:
If you step on the brake pedal a few times in a row, the pedal gradually rises, and after raising it, you do n’t lift your foot and continue to step down. You can feel the pedal springy. You can release the pedal and stop it for a while, then step on it. There is air in the system and it should be vented.
The sequence of exhausting air should start from the master cylinder and then to the brake cylinders. The order of air discharge from each cylinder should start from the cylinder closest to the master cylinder and discharge one by one. Exhaust method: one person is responsible for stepping on the brake pedal, and the other person is responsible for exhausting. Press the brake pedal to the end and do not release it, then loosen the exhaust screw. After the brake fluid mixed with air is sprayed out and the pressure drops, tighten the bleed screw to release the brake pedal. After the brake pedal is fully returned, depress the brake pedal to the end and continue to deflate. Repeat this several times to completely expel the air.
If the brake does not work when you step on the brake pedal, the position of the brake pedal will increase gradually and the brake effect is good, which means that the pedal free travel is too large or the friction between the friction plate and the brake hub is too large. In this case, first check the free stroke of the adjustment pedal to make it within the specified range, and then check the clearance between the adjustment friction plate and the brake hub.
If the position of the pedal can be gradually increased by continuously pressing the brake pedal, without lifting the foot and continuing to step down, the pedal does not feel elastic, but there is a feeling of sinking, indicating that the brake system has oil leakage or the brake master cylinder is out of oil The valve is not closed tightly. At this time, it should be checked whether there is any leakage in the pipe joint. If there is leakage, it should be treated by tightening, welding or replacement.
