The effectiveness of the braking of the loading stock directly depends on the correct operation of the pneumatic system, the central element of which is the brake-lineIncorrectly adjusting this unit on the semi-trailer can lead to the skidding of the train, increasing the braking distance or, conversely, premature wear of the linings due to "grabbing." Drivers and mechanics often face a situation where the brakes on the tractor work perfectly, and the trailer either brakes too sharply or is delayed.
The adjustment process requires not only the presence of a special tool, but also a deep understanding of the principles of pneumatics. Pneumatic system It responds to the slightest pressure change, so even a minimal error in the pressure regulator setting can upset the balance of the entire composition. In this article, we will discuss in detail the algorithm of actions necessary to bring the brake system of the semi-trailer in accordance with the standards.
Safety on the road is a priority, and ignoring the symptoms of a brake crane malfunction is unacceptable. If you notice that the trailer pecks when braking or, on the contrary, pushes the tractor, then the balance is broken. The critical parameter is the pressure difference in the receivers of the axle, which should not exceed 0.2 bar in static. Further material will help you diagnose and fix the problem.
Working principle and braking crane arrangement
The brake force crane, often called a modulator or regulator, controls the compressed air flow to the brake chambers of the wheels. Its main task is to distribute the pressure proportionally depending on the load of the axles and the signal from the tractor brake pedal. regulationwhich provide a smooth braking.
Modern systems are often equipped with electronic control (e-control).EBSHowever, classical pneumatic cranes require physical adjustment of the screws and check the tightness of the joints, understanding the design allows you to quickly find the cause of the malfunction.
It's important to note that the crane responds to the pressure in the control line, and if the signal comes with a delay or insufficient force, the brakes of the semi-trailer will not work in time, which creates a dangerous situation, especially on slippery surfaces.
⚠️ Warning: Before any work on adjusting the crane of brake forces, be sure to turn off the car, install recoil stops under the wheels and completely blow the air from the pneumatic system.
Some of the cranes have built-in safety-valveThey also affect the overall braking efficiency, and if the valve sticks, the pressure may not be released, which will cause the brakes to overheat.
Diagnostics of malfunctions before adjustment
Before you can get a control screw, you need to know exactly what the fault is, and often the problem is not the crane itself, but the adjacent parts of the system. brake.
Look at the pneumonoline for leaks. A characteristic suite or hiss will indicate tube damage or leaky connections. Leaks reduce the overall pressure in the system, making braking sluggish and unpredictable.
Check the brake chambers. The rods must be in compliance with technical regulations. If the rods are skewed or have excessive backlash, the adjustment of the crane will not give the desired result. Mechanical defects must be eliminated first.
Use a pressure gauge to monitor the pressure in the receivers, compare the readings on the tractor and semi-trailer, a significant difference will indicate a problem in the main line or a malfunction of the regulator. double-valve, which often fails.
- 🔍 Visual examination of pneumonia for cracks and scuffs.
- 🔍 Checking the tightness of the compounds with a soap solution.
- 🔍 Control of the brake chamber rods.
- 🔍 Measurement of pressure at control points with a manometer.
Tools and training required
To properly adjust the brake crane, you will need a standard set of locksmiths and specialized equipment. Lack of the right tool can lead to improper adjustment and damage to the threaded joints.
First of all, you'll need a calibrated pressure gauge to measure the pressure in the air system, and without accurate pressure readings, you'll need a divination, and you'll need keys to access the valve's adjusting screws, which are often located in hard-to-reach places.
Use only serviceable pressure gauges with an accuracy class of not less than 1.5. Inaccuracy in readings can lead to erroneous adjustment of the brakes.
Don't forget to prepare clean rags and penetrating lubricant. The threaded joints on the brake valves are often clamped due to dirt and vibration. Careful cleaning and lubrication will facilitate the adjustment process and prolong the life of the unit.
Electronic systems may require a diagnostic scanner that can count errors and test sensors in real time, but basic mechanical adjustment can be done without one.
☑️ Preparation for adjustment
Step-by-step instructions for pressure adjustment
The adjustment process starts with checking the pressure in the receivers, start the engine and wait for the compressor to pump the system to the operating pressure, which is usually about 8-9 bar. Turn off the engine to take measurements.
Find a control screw on the brake crane, it can be protected by a cap or a seal, carefully remove the protection, trying not to damage the seals, turning the screw clockwise usually increases the pressure, against reduces.
Sequence of action:Connect the pressure gauge to the control connection.
2. Push the brake pedal.
Record the pressure gauge readings.
4. adjust the screw to the desired value.
5. Release the pedal and check for pressure relief.
Adjust the pressure smoothly, making small turns of the screw. After each change, check the brakes. The pressure in the brake chambers must correspond to the values specified in the technical documentation of the semi-trailer manufacturer.
Pay special attention to balancing the pressure between the axles. If the pressure on one axle is higher, this will lead to uneven wear of the linings and the trailer will move aside during braking. Balancing of axes - key stage of adjustment.
Table of normative pressure values
To adjust correctly, you need to be factory-oriented. Below is a table with typical pressure values for different parts of the semi-trailer braking system. Remember, there may be some nuances for a particular model.
| System node | Operating pressure (bar) | Opening pressure (bar) | Permissible error |
|---|---|---|---|
| Receivers | 8.0 - 9.0 | - | ±0.5 |
| Brake chambers | 6.0 - 7.5 | 0.2 | ±0.3 |
| Spring-loaded energy accumulators | - | 4.5 - 5.0 | ±0.2 |
| EBS system | Depends on the load. | 0.1 | ±0.1 |
Compliance with these parameters ensures stable operation of the braking system; exceeding the pressure can lead to rupture of the membranes, and insufficient - to ineffective braking, Regular check of these values should become a habit.
If the values are very abnormal even after adjustment, the crane or compressor may be defective, in which case a deeper diagnosis or replacement of the nodes is required.
Typical errors and ways to fix them
One of the most common mistakes is to ignore the condition of air filters. Dirty air enters the tap, causing seal wear and valve sticking. Regularly replacing filters will prevent many problems.
Why is the brake tap whistling?
Whistling can occur due to air leakage through the discharge valve or damaged membrane, and the cause can also be icing of the inner parts in the winter.
Often, mechanics forget to check the work. return-valveIf it doesn't hold the pressure, the air will leave the system when the engine stops, which will cause the pressure in the receivers to drop and the brakes to fail.
Another mistake is the wrong sequence of adjustment, and you always have to start by checking the tightness and the mechanical part, and then you start by setting the pressure, and if you're not going to do it, you can get the picture of the malfunction.
- 🛠️ Ignoring the replacement of air filters.
- 🛠️ Incorrect sequence of adjustment of nodes.
- 🛠️ Use of uncalibrated measuring instruments.
- 🛠️ No check of the return valves.
⚠️ Warning: Do not try to adjust the brake crane on the move or while the train is moving. All work is carried out only in the parking lot with the engine shut off and the wheels fixed.
Also worth mentioning is the importance of using quality parts: cheap crane counterparts are often low-life and can fail at the most inopportune moment.
Frequently Asked Questions (FAQ)
How often should the brake crane be checked and adjusted?
Pressure and leakproofness checks are recommended daily before departure, and full adjustment and calibration should be performed at each scheduled maintenance or when signs of malfunction appear.
Can I adjust the crane without special equipment?
The basic test can be done visually and by ear, but you need a pressure gauge to be adjusted accurately, and you can't set the right pressure in the system without it.
What if the brakes are unevenly adjusted?
Uneven operation may indicate malfunctioning brake chambers, different wear of linings or problems with the balancing bar.
Does the temperature affect the crane?
Yes, at low temperatures, condensation can form in the system, which freezes and blocks the valves, and it is important to regularly drain the condensate from the receivers and use antifreeze for the air systems.
What are the signs that a crane needs to be replaced?
Constant air leaks, inability to hold pressure, mechanical damage to the body or rod, as well as the lack of response to adjustment indicate the need to replace the node.