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Forklift truck brake troubleshooting: forklift truck walking brake system is composed of vacuum pump, vacuum tank, vacuum supercharger, brake master pump, brake sub-pump, wheel brake and brake pedal, etc. The brake type is vacuum booster, hydraulic drive, internal expansion front wheel brake.
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The common faults of forklift brake are as follows:
1. When stepping on the brake pedal of the forklift truck, it has no braking effect
Possible causes: There is no oil in the main brake pump, the brake system pipeline leaks oil, and the main pump leather bowl breaks and wears, resulting in oil leakage; The piston ring of the main pump is damaged, swollen or worn too much; The main pump piston ring is inverted; The piston of the branch pump leaks oil or the oil seal of the half shaft is damaged, resulting in oil in the brake drum, resulting in brake drum and friction lining brake failure; Brake shoe friction lining wear too much, so that the rivet exposed or loose off.
2. There is elastic resistance when stepping on the brake pedal of the forklift truck, and the braking force is insufficient
Possible cause: Air in the braking system; Insufficient brake fluid in the main pump; The supercharger return valve is damaged or dirty; The brake fluid does not build up enough pressure to stop even if the brake pedal is pressed to the bottom; The clearance between brake drum and friction lining is too large; Brake shoe loose, etc.; The brake shoe is not properly installed and the brake clearance is not properly adjusted.
3. Forklift brake pedal
It has rebound force and poor braking effect
When stepping on the brake pedal, should listen to the vacuum supercharger with or without air inlet hiss, if there is no sound, the booster low pressure oil pipe release, and then step on the brake pedal, if the oil pipe does not produce oil or oil is weak, it is the main pump to the vacuum supercharger oil circuit blockage, or the main pump is not working well, otherwise the supercharger itself is faulty.
Possible causes: the pipeline is blocked, can be the main pump to the booster of the low-pressure oil pipe removed, with compressed air blowing, if not blown is blocked pipeline; Otherwise, the main pump is not working well. The poor performance of the main pump is that the oil pressure is low (the standard is 3MPA, can be measured by pressure gauge), the main pump cup and the leather ring are swollen; The oil outlet valve is not working well, or there is no gap between the main pump push rod and the piston, and the oil return hole is blocked, so that the brake fluid cannot return to the oil storage chamber; When the brake pedal is relaxed, the piston cannot return quickly. When the brake pedal is continuously pressed, the pedal does not return and gradually rises, and the feeling is very hard when stepping down. The oil inlet hole of the supercharger control cylinder is blocked, and the atmospheric valve cannot be opened when stepping the brake pedal, so the supercharging effect cannot be achieved; The intake valve seal ring expands or leaks, at this time the position of the brake pedal will become higher, and the feeling is very hard when the forklift walks.
4, brake drag, long time walking
Rear brake drum heats up
Possible causes: supercharger parts stuck, improper adjustment of brake stroke; The oil return hole of the brake master pump is blocked (covered by the swollen leather bowl or blocked by the dirt in the brake fluid), resulting in poor oil return resulting in wheel brake lag; The brake fluid is dirty and the oil return is too slow; The leather bowl of the main pump is swollen, and the leather bowl cannot be returned quickly after the brake pedal is relaxed. The sealing ring of the control valve expands, causing the air valve to close loosely, the exhaust of the air chamber in the tympanic membrane of the power cylinder is delayed, and the tympanic membrane cannot be quickly returned. The copper tube between the brake master pump and the supercharger is deformed or squeezed flat, making the oil return slow, resulting in brake drag.
5. The braking is not smooth
Possible causes: the brake drum is not round, the gap between the brake drum and the brake shoe is abnormal; Brake shoe adjustment is not
6. It's hard to step on the brake pedal
Possible causes: the main pump cup or the main pump piston skin ring is swollen; The copper pipe between the main pump and the supercharger is deformed or squeezed flat, making the inner hole smaller and the oil flow is not smooth; The copper pipe leading to the wheel pump is deformed, resulting in small aperture and poor oil flow; The control cylinder skin ring expands; Brake fluid deterioration, too thick and poor flow.
7. Braking deviation
Possible causes: The braking force of the left and right wheels is not balanced, so that the forklift truck is biased to one side when braking (which side is to check the brake gap or the pump condition of which side is to be seized when braking; Irregular running, left and right, if the braking first left and then right, you should first check the left wheel braking situation, otherwise check the right wheel first); Or the brake shoe friction plate or brake drum has oil.
8, oil leakage (including external leakage, internal leakage) - the main pump, sub-pump, supercharger, pipeline, as long as there is a oil leak, it will reduce the braking efficiency or brake failure.
Possible causes: the main pump, the sub-pump oil leakage, mostly due to the use of the leather bowl, leather ring for too long due to wear and tear caused by leakage; If you feel very light when you step on the brake pedal, it is generally the main pump bowl wear oil leakage; The sealing of the piston cup, the piston ring or the piston push rod ring and the control valve bowl is poor, which will cause oil leakage; The brake shoe is too thin or the brake gap is too large, and when the brake pedal is pressed hard, the pump leather bowl will often turn over and cause oil leakage.
9. Excessive brake oil consumption
Possible causes: Pipeline leakage; The oil leakage from the leather bowl of the brake slide valve in the transmission shift control valve enters the transmission. At this time, the smell of brake oil can be smelled from the transmission oil checking hole, and the check can confirm whether the brake oil is leaking. Vacuum supercharger booster cylinder piston bowl, skin ring or piston push rod skin ring and control valve bowl seal is poor, will cause excessive brake oil consumption, open the supercharger power room brake oil will leak out, serious when the vacuum pump lubricating oil pipe leakage into the engine oil pan, oil is diluted, or be sucked into the cylinder and burned off.
10, vacuum supercharger failure
This kind of fault can be judged from whether the supercharger is admitted or not and the brake oil pressure at the brake branch pump is detected.
Possible causes: the supercharger is working normally, the oil pressure at the brake pump should reach 11~13MPa(can be connected to the pressure gauge detection), if the pressure is lower than this value, the supercharger is faulty; Remove the vacuum tube of the supercharger, plug the tube mouth by hand, start the engine for a moment, feel no suction or little suction, it is the vacuum tank, vacuum tube there is a leak, or the vacuum pump is not working well; The vacuum pump can be measured by a vacuum gauge. The normal vacuum value should be -0.08-0.085MPa. If the vacuum degree is lower than this value, the vacuum pump is faulty. After inspection, the vacuum pump, vacuum tank, vacuum tube are normal, the supercharger still does not work, it is the vacuum supercharger air filter is seriously blocked (because the machine supercharger air filter is directly installed on the supercharger, located under the car, the working environment is bad, this failure often occurs), or the air valve can not be opened, resulting in the atmosphere can not enter the power room caused by.
The brake device of forklift includes two ways: hand brake and foot brake. Hand brake has disc type, drum type and belt type, and its transmission part is mostly mechanical. The foot brake has hydraulic type and pneumatic type, of which the hydraulic type is divided into general hydraulic type and vacuum booster hydraulic type. Although there are many kinds of foot brake forms, the fault phenomena are basically the same. The common faults of hydraulic brake system are analyzed and judged here. The hydraulic brake system of forklift truck is mainly composed of brake pedal, brake master pump, brake sub-pump, wheel brake and oil pipe. The common faults are: poor braking effect, sudden braking failure, braking lag and braking deviation.
First, poor braking
1, the fault phenomenon: the forklift is driving, step on the brake pedal can not immediately slow down and stop.
2. Cause of failure
2.1 Faults belonging to the main pump are:
(1) The leather bowl is swollen or damaged by aging.
(2) The main pump piston and cylinder wear is excessive, so that the clearance is too large.
(3) The oil valve spring is too soft, broken or the oil valve seal is poor.
(4) The oil return valve is poorly sealed.
(5) The oil return hole is blocked.
(6) The vent hole of the brake hydraulic oil chamber is blocked or the brake hydraulic oil is too small.
(7) The return spring of the main pump piston is too soft.
2.2 Sub-pump faults are:
(1) The branch pump cup is aging and swollen.
(2) The gap between the piston of the branch pump and the cylinder is too large.
(3) the piston equivalent spring of the branch pump is too soft or broken.
2.3 Brake failures are:
(1) The gap between the brake shoe friction plate and the brake drum is too large.
(2) The contact area between the brake shoe friction plate and the brake drum is too small, the friction plate is greasy, the water is wet, hardened or the rivets are exposed.
(3) Brake drum wear deformation or grooves.
(4) Air permeates into the brake pipeline, the tubing is dented or the brake hose is not smooth.
3. Analysis and judgment
The reasons for the poor hydraulic braking effect can generally be judged according to the size of the brake pedal travel of the forklift truck, the size of the pedal reaction, the stability after stepping off the pedal, and the pedal height increase during continuous multi-foot braking.
(1) The pedal height is too low during foot braking, and the braking effect is poor. If two or several feet brake continuously, the pedal height increases and the braking effect improves, indicating that the gap between the brake drum and the friction disc or the main pump piston and the push rod is too large.
(2) After one or two feet brake, the brake pedal cannot maintain the height of the brake, and it slowly or rapidly drops, indicating that the brake pipeline is broken somewhere or the joint is leaking oil, the sub-pump bowl is badly sealed, the main pump bowl, the leather ring, and the oil inlet and outlet valves are badly sealed. In this case, you can first step on the brake pedal to observe whether there is brake hydraulic oil leakage. If the outside is normal, check the internal faults of the sub-pump and the main pump.
(3) When the pedal height is low and soft for several consecutive feet of braking, the oil inlet hole of the main pump or the oil storage chamber is blocked or the brake hydraulic oil is seriously lacking.
(4) The pedal height is slightly increased and has a sense of elasticity when a few feet brake, indicating that there is air in the brake pipeline.
(5) When one or two feet brake, the pedal height is appropriate, but it is too hard and the braking effect is poor. The wheels of each forklift should be checked.
