Pneumatic/Air Brake | How it works

In simple terms, Brakes are the component in any vehicle which help in reducing the speed or stopping the vehicle. To apply the brakes, we have to either press a pedal or pull a lever. But Just think how this transmission of force happens from pedal/lever to brakes located at wheels? To achieve this we have different systems (Pneumatic/Air Brake) to choose from depending on the requirement:

  • Mechanical – Wherein steel cables will be responsible to apply the brakes at wheels, the moment you pull the brake lever. Ex – Parking brakes of a car or Rear drum brake of a bike is commonly operated via. cables.
  • Hydraulic – Hydraulic oil is responsible to pass on the driver applied force via. pedal or lever to the brake piston which in turn applies the brake on wheels. Ex – Normal Braking system of a car or a Disc Brake on a bike.
  • Pneumatic – As the word speaks for itself, it operates via. Air. Braking system maintain a high pressure air inside it and moment driver applies brake, pressure in the line starts dropping. This results in applying of brakes on wheels. It will sound a bit strange but this is how it works. Ex – Heavy vehicles like Truck, Bus, Trailer or Train. Ever noticed a bus driver on reaching destination, he pulls up a button on dashboard & weird ‘phisshhh’ sound we could hear. With that button he releases the air pressure to engage the brakes, acts as a Parking Brake for heavy vehicles.

Working of Pneumatic Brake

Pneumatic or Air brakes operate on compressed air. Entire braking system pipeline is initially charged up with compressed air to maintain optimum pressure. This charged up brake line makes sure the brakes are dis-engaged. Moment driver applies force on brake pedal, air pressure drop initiates via. driver’s brake valve. Due to this pressure drop, control reservoir gets disconnected from the brake pipe and auxiliary cylinder gets connected to brake cylinder. Compressed air from auxiliary cylinder rushes in to the brake cylinder causing brake to get engaged. This is how pneumatic brakes work in real time operation of brake pedal by driver.

Pneumatic or Air brake_Application phase
Pneumatic or Air brake_Application phase (Image Source:

To apply parking brakes, driver pulls the small hand lever on dashboard which causes air pressure inside brake cylinder to release, resulting in brake spring to expand and in-turn engaging the brake. This is how Parking Brake works in pneumatic braking system of heavy vehicle.

What happens If this system works similar to hydraulic braking

This is very interesting and Important to understand – If on pressing of brake pedal by driver forces the compressed air to the brake cylinder directly as it happens in hydraulic system, then any leakage or damage to the brake pipeline will result in complete loss of control of such heavy duty vehicle. You can Imagine how catastrophic that situation would be If such loss of control happens. To avoid this, pneumatic braking system is developed in such a way that in case of any emergency or leakage to brake lines brakes will engage and bring vehicle to halt. Also, driver would have to apply lot of force on brake pedal to apply the brakes on such heavy and multiple wheeled vehicle which won’t be efficiently done.

Why pneumatic system is not utilized in cars or light-duty vehicles

Even though air braking system is far better than a hydraulic braking in terms of safety as well as braking efficiency. But it requires lot of space to fit in such a huge system which has lot of components  in it. Whereas hydraulic system is light weight and doesn’t require much space for installation. Another reason would be the pricing, it won’t be worth installing a air braking system on light vehicles as it would raise the total manufacturing cost to sky high. For light vehicle or cars, hydraulic braking system just do its job effectively & efficiently.

Most Important point to note here, heavy vehicles require good amount of braking force to achieve stopping which is just not easily possible with hydraulic system. With Pneumatic braking system, driver gets a better sense of control on loaded heavy vehicle even with trailer or on a train.

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