Modern trucks will either be fitted with air or hydraulic brake systems. The braking system is a vital part of a truck and must be reliable and effective.
Although each of these systems has its strengths and weakness, they are both excellent systems. But are air brakes better than hydraulics?
Air brakes are better suited for larger trucks that will be towing heavy loads. Hydraulic brakes are best used on smaller delivery trucks less than 26,000 pounds. Air brakes will automatically apply the brakes if there is a leak in the hose, while hydraulic brakes will fail.
Read on to learn the differences between the two braking systems and where they are best suited.
Air vs Hydraulic Brakes – A Full Comparison
All tucks have a brake system fitted to each of the truck’s wheels. When the driver applies a force to the brake pedal, this force is transmitted through the lines to the brakes.
There are two ways in which this can be achieved; this is either with air or hydraulics. To determine which brake system is better, we must compare them against each other.
We’re going to go compare the following things:
- Truck Size
- Cost
- Failures
- Special Licenses
- Components
Air Brakes vs Hydraulics: Truck Size
The size and weight of a particular truck will influence which brake system will be utilized.
Air Brakes
Air brakes are best suited on trucks exceeding 26,000 pounds GVWR but can also be used on lighter trucks.
They are praised for their robust stopping power under towing conditions and are ideal for trailers.
Hydraulic Brakes
Hydraulic brakes are commonly found on trucks that weigh less than 33,000 pounds.
When using hydraulic brakes on heavier tucks, they can be pushed beyond their limitations resulting in a greatly reduced performance.
For trucks that travel at a low speed due to lots of stop-and-go traffic, hydraulic brakes are better.
Air Brakes vs Hydraulics: Cost
All trucking companies want to keep their expense as low as possible to increase profits. An effective and low-cost brake system will be at the top of their list.
Air Brakes
Air brakes cost, on average, $1500 to $2500 more than hydraulic brakes. This is due to all the extra components that are required for the initial setup.
The maintenance cost is significantly reduced due to the easy accessibility of the components. This can be done in a quarter of the time compared to a hydraulic system.
Hydraulic Brakes
Hydraulic brakes are considerably cheaper to install than an air brake system. There are fewer components making the system easier to install.
The maintenance cost may be higher due to the specific pressure hoses used.
Air Brakes vs Hydraulics: Failures
The braking system on a truck is used to slow and stop, but what happens when they fail? What can cause this to happen?
Air Brakes
An air brake system has the advantage of having a fails safe if there is a drop in air pressure. If there is a leak in the air brake system, it is replenished by the air compressor. Thus always having enough pressure is not a problem unless an entire airline is severed.
If the air pressure in the system drops too low for the brakes to function, the brakes automatically activate and slow the truck or trailer down. This will happen incrementally as the pressure drops and eventually stop the truck.
Under heaving towing conditions, the brakes will heat up, but because the air is constantly being replaced, it maintains enough pressure for the brakes to function.
Hydraulic Brakes
Hydraulic brakes, unfortunately, have a fatal flaw. If there is a leak in a hydraulic brake line, the fluid pressure can be reduced so low that there is not enough force acting on the brake pad to slow the wheel down effectively.
If the leak is not repaired, the truck may lose all braking functionality on that part of the braking system.
Under heaving towing conditions, hydraulic brakes can heat up beyond their optimal working temperature. This will cause brake fade, and this greatly reduces the stopping distance.
When the brakes reach these high temperatures, it can cause the hydraulic fluid to boil, which will cause air bubbles in the lines.
Air that is trapped in a hydraulic line will reduce the pressure acting on the brake pads.
Air Brakes vs Hydraulics: Special Licenses
There are different license requirements for a truck that weighs over a specified weight, trailer type, and the number of axils. But are special licenses required for the different brake systems?
Air Brakes
If the truck is equipped with an air brake system, the driver will require a commercial driver’s license (CDL) to operate it. This will include trucks under 26,000 pounds, such as light delivery trucks.
The air brake system works differently from the standard hydraulic system, and additional safety operations will need to be learned.
Hydraulic Brakes
Hydraulic brakes all function under the same principle, whether on a small hatchback, utility truck, or delivery vehicle.
Due to its simplicity, only a standard driver’s license is required to use a truck with a hydraulic brake system.
Air Brakes vs Hydraulics: Components
There is a significant difference in the types of components used in an air brake system compared to a hydraulic system. The more components there are, the higher the complexity of the system.
Air Brakes
- Air Compressor – The air compressor pumps atmospheric air to the air storage tank. It is controlled by a belt system connected to the engine’s crankshaft.
- Air Compressor Governor – the air compressor governor controls the pressure the compressor pushes into the storage tank.
- Air Dryer – the air dryer is an essential component as it removes the moisture in the air to prevent condensation build up in the system.
- Air Storage Reservoir – the air reservoir stores the air from the compressor. It keeps the specific pressure available so that the brakes can be used several times if the air compressor fails.
- Brake Pedal – The brake pedal is used by the driver to actuate the air pressure into the system.
- Dirt Collector – the dirt collector filters the air so no contaminants can enter the system and cause blockages.
- Brake Cylinder – the brake cylinder consists of a piston and a cylinder over which the compressed air pressure is applied to push the brake pads together.
- Brake Valve – the brake valve regulates the release and build-up of air pressure inside the brake lines. It will regulate the required force as the driver applies on the brake pedal.
- Brake drum/disk – the brake drum contains the frictional components which apply the frictional brake force. Inside the drum is a brake shoe that comes into contact with the drum lining providing a frictional braking force.
Hydraulic Brakes
- Brake Pedal or leaver – The brake pedal is used by the driver to apply pressure to the system. It is connected directly to the master cylinder.
- Master Cylinder – The master cylinder uses a basic piston arrangement to convert mechanical force into a more substantial hydraulic pressure.
- Brake fluid Reservoir – The brake fluid reservoir is connected to the master cylinder and contains the brake fluid needed for the system.
- Brake Lines – The brake lines are hollow high-pressure metal tubes that connect the master cylinder to the disk caliper cylinder at the wheels.
- Disc Rotors – The disc rotor is a metal disk that is fitted to the wheel hub. It rotates with the wheel, and the brake pads rub against it to create a frictional stopping force.
- Disc Calipers – The disc caliper forces the brake pads against the frictional surface of the disc rotor.
Conclusion
Air brakes are better suited to larger trucks that will be towing heavy loads as there is a fail-safe built into the brake system. Air brakes are expensive as many additional components must be installed.
Hydraulic brakes are more suited to lighter trucks under 26,000 pounds that will have more stop-and-go driving. Hydraulic brakes are much more simplistic, but they do suffer from excessive heat, which may cause brake fading.