Why do lorries have air brakes

There are many graduates who entered the diesel program as complete beginners and leave ready to tackle entry-level diesel technician jobs. Students accepted into this manufacturer-paid program can learn how to work on tractors from Fendt, part of the AGCO Corporation.

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Air brakes, which we'll break down in the next section, use air to operate their brakes. Let's look at the differences. In a hydraulic system, fluid is stored in a reservoir commonly referred to as a master cylinder.

When you push the brake pedal, fluid is pumped through brake hoses or lines into pistons mounted on each wheel. These brake pistons either push against two brake shoes , which expand and cause friction inside a brake drum , or against a brake pad , which clamps down on a brake rotor.

Below are the components in a hydraulic disc brake system. Before disc brakes, cars relied on drum brakes. The principal mechanics were the same, but drum brakes used brake shoes set inside a drum that was mounted on the hub, versus a rotor. Disc brakes increase stopping power, as they are more easily cooled and have more surface area to grasp.

In addition, brake dust, which forms as the brake pads wear and decreases braking ability, is vented more easily with disc brakes than with drum brakes.

Now that we understand the fundamentals of brakes in trains and cars, let's talk about the big rigs and the buses. Foundation brakes are the most common air-brake systems found in trucks and buses and work the same way as in rail cars. Using the triple-valve principle, air builds up inside the brake pipes or air lines, releasing the brakes.

Virtually all of the roadgoing vehicles equipped with air brakes have a graduated release system where a partial increase in pressure dictates a proportional release in brakes. At idle foot off the brake and vehicle's air system charged , air pressure overcomes the diaphragm or the s-cam is in the closed position, resulting in a released brake system. As soon as you depress the brake pedal, the air pressure decreases, turning the s-cam and spreading the brake shoes against the drum.

The compressor refills the reservoir tanks and when you allow the pedal to retract, the air pressure increases back to the original state.

Emergency air brakes complement standard air-brake systems and can be activated by pulling a button on the dash near the one with the light that we saw in the introduction.

Before you can drive a vehicle with air brakes, you must push in the emergency brake button to fill the system with air. As long as the emergency system is pressurized, the emergency brake will remain free. If the system has a leak, the pressure can decrease enough to engage the emergency brake. In addition, heavy trucks are often equipped with an exhaust brake that aids the braking process, but this relies on the engine, not the air-brake system.

We've learned how air brakes work. Now let's look at how to maintenance can prevent brake failure in the next section. Have you ever wondered why trucks and buses make those funny squeaking and hissing sounds? The squeaking is the air escaping after braking and the ppssss sound is the automatic bypass safety valves at work, ensuring the air pressure remains at the correct level.

Since a main advantage of air-brakes systems is their ability to use air to operate, the compressor is constantly kicking on and kicking off to refill the reservoirs with pressurized air.

When the compressor builds too much air, the valves open, producing that loud hiss. Every state in the U. Here are some steps you'll want to take before heading out on the road:. You'll also want to watch for water in the air-brake system, a byproduct of the condensed air. To prevent this problem, many of the modern systems have automatic drain valves installed in each air tank. Air couplers can also pose a problem. Worn rubber seals will cause air to escape. While the compressor can overcome a small leak, running compressors too hard can lead to failure.

For truck drivers, getting stranded in the middle of a mountain pass probably isn't on the itinerary. Brake sensitivity, another byproduct of air brakes, can lead to accidents, especially for inexperienced drivers. Air-brake systems are designed to work on vehicles carrying heavy loads. Have you ever wondered where all those dual skid marks on the expressway come from? Probably the worst fear for a truck driver is jackknifing.

Trucks traveling in rain and snow can easily jackknife if too much brake is applied. Most modern vehicles with air brakes use a dual system. In essence, such equipped vehicles have two systems in case one should fail. Anti-lock brakes can now be found in tractor-trailer rigs and work much the same way as ABS systems found in passenger cars.

Fundamentally speaking, air brakes are efficient and reliable. Air-brakes systems occupy too much space and attention to be considered practical in cars.

Just look at a Peterbilt truck as it saunters down the interstate. Have you seen the big tanks tucked behind the fuel tanks? Try finding a place for those under the hood of a Honda Civic. As the driver of the cement truck approached an intersection at the end of a downhill off ramp, his brakes failed and the truck barreled into the intersection, striking the Subaru and killing its driver.

The National Transportation Safety Board investigated the incident and found several problems with the truck, notably reversed brake lines and a secondary system failure. The parking brake system is the one you employ when you put the truck in park. This is engaged when the truck needs to be shut off for loading or unloading purposes. This system continues to operate with minimal power requirements.

This totally locks the brake pads in place for ingress and egress purposes. The emergency brake system is the most important brake system as it uses both the service brake system and parking system to completely immobilize the truck in the rare event that the air brake system fails. This automatically kicks in if the system senses that there is anything wrong with the delivery of the compressed air through the hoses.

Trucks nowadays are also equipped with ABS to prevent the wheels from locking in place during hard braking or emergency situation. This prevents jack-knifing, excessive skidding and other brake-related issues while operating your truck on the public road. Weather conditions usually prevent trucks from leaving the garage as too much cold can compromise the air brake system.

This is added to the compressor to reduce the risk of compressed air lethargy which could seriously hamper your ability to stop. Air brake system failure can also originate from the standard hoses used in trucks. These can be replaced with high-performance, high-pressure tensile hoses.

Aside from their inherent durability and resistance to cuts from external factors, they can also ensure a consistent supply of compressed air from the air compressor to the air brake chamber. Trucks are usually relegated to the slow lane when driving in busy areas. Keep a safe distance between you and the truck behind you by at least three car lengths. Better yet, get out of its lane. It can be done but it would take too much space.

Sedans are light vehicles that can effectively stop with conventional brake systems. Disc brakes are often enough to provide more stopping power. A truck jackknifes when the trailer exceeds a degree angle to the tractor. Hard braking when these road hazards are met usually results to jack-knifing.