You must be familiar with this hissing sound unique to intercity buses, city buses, trucks and lorries. We explained the reason for this sudden loud sound that can startle.
While waiting for the departure time of the bus at the resting facility, the one that suddenly appeared when we dived into the distance. hissing sound it can be scary at times. Let’s find out what is the reason for this frequently heard disturbing sound:
The reason for this situation seen in various heavy vehicles It is an air brake system. These vehicles, which are frequently used both in heavy industry and in road transportation, are generally over 10 tons in weight. It is not possible for buses and trucks that are that heavy to stop with the normal braking system of trucks.
When heavy vehicles need to slow down and stop on the road, the driver’s force should be at a minimum.
If it was necessary to stop a bus that can stop with a compressed air brake system with a normal brake, 30-40 times more had to apply pressure. It is impossible to transmit the force applied to the brake pedal to the tires of heavy vehicles. Therefore, the air goes up to the vehicle wheel and creates mechanical movement with pneumatic power before it acts on the drum or brake disc.
Buses are equipped with sensitive air bellows suspensions (shock absorbers) for comfort.
After a certain pressure level, in order to maintain the pressure value of the air accumulated here, must be evacuated. During this process, that famous hissing sound is produced.
This system, which is the cause of the hissing sound; It is a system consisting of compressed air supply unit, continuous brake system, foot brake system, hand brake unit and compressor, brake pedal valve, relief valve, distributor valve, hand brake lever, trailer control valve, relay valve, bellows and emergency bellows, load adjustment. consists of apparatus such as valves.
With the developing technology, the air produced once inside the vehicle has started to be used in other mechanisms besides the brakes.
Thanks to this system, heavy servo conditions in clutch systems have been alleviated with air servo valves. Thus, a pneumatic part was added next to the hydraulic part of the clutch and the air clutch system emerged.
The air produced in the vehicle is also used in suspension systems. like this “air suspension systems” It has replaced mechanical scissor type suspension systems. The basic logic of this system is to provide suspension by placing air-filled balloons between the chassis and the load. It should not be confused with the air-charged shock absorber system used in passenger cars.
ABS, EBS, TEBS High-end systems such as these are now used in heavy vehicles.
noting pressure changes thanks to sensors All the devices mentioned above transmit error reports to the driver display. In addition, with the help of brake diagnostic tools, all malfunctions in the brake system can be revealed with a single tool.
Sources: 1, 2