Understanding horsebox air brakes

Understanding horsebox air brakes can seem intimidating for newcomers transitioning to larger vehicles. Unlike the hydraulic brakes in passenger cars, air brake systems represent a fundamentally different approach to vehicle safety.

Designed specifically for heavier vehicles like horseboxes, these braking systems might initially appear complex, but they offer crucial advantages in safely.

I hope this guide goes some way to demystifying air brakes, by explaining their mechanics and highlighting why they’re the preferred braking technology for larger vehicles.

Brief history

Air brakes have been around for a very long time and were first used in the railway service by George Westinghouse who patented a safer air brake on March 5, 1872. He made numerous alterations over the years to improve his air pressure brake which led to various forms of the automatic brake.

After its advantages were proven in railway use it was adopted by truck manufactures in the early 20th century.

Horsebox air brakes simplified operation

From the driver seat, horsebox air brakes have a foot brake and hand brake just like in a car. The only additions are air tank gauges and audio/visual cues in the form of red warning lights and a buzzer on the dashboard.

When turning on the ignition, the driver will see gauges with the pressure levels of the air brake storage tanks. If these levels are low, the brakes will automatically be on, and audio/visual cues will highlight this. This is normal and before you can move away, you must start the engine and let an automatic air pump fill the air brake system and tanks.

For safety, it is not possible to move the vehicle until the pressure has built up on the gauges and the audio/visual cues have gone off.

Air handbrake/parking brake

If your air brake gauges are at full and all audio/visual cues are off, it works much like your car handbrake and is simply on or off.

However, if the air brake gauges show low air pressure and audio/visual cues are still on, even if you let the handbrake off, the brakes will remain on until the brake system has refilled the air tanks, and audio/visual cues have gone off.

Why air brakes?

The reason air brakes are so safe for larger vehicles is because in the event of a failure or fault in the brake system, rather than a runaway vehicle, any loss of air will automatically engage the brakes and safely stop the vehicle.

Load sensing valves

In addition to horsebox air brakes, you will have a load sensing valve as a completely separate yet vital safety system that also deserves a little explanation. It works automatically in the background and has no gauges and no input from the driver.

If you imagine a horsebox with no horses onboard, this makes the rear of the horsebox light. Under heavy braking the rear wheels would tend to lockup and skid more easily than one with a full load. The load sensing valve monitors the weight distribution and automatically reduces the percentage of baking pressure that can be applied to the rear wheels by increasing the percentage of baking pressure that can be applied to the front wheels.

This stops the rear wheels locking up. As you add weight to the rear axle in the form of horses and tack, the load sensing valve senses this added weight increase and adds more braking pressure to the rear wheels and reduces braking pressure to the front wheels. In effect you can brake harder in an emergency and stop quicker.

MOT tips

This may be of help if you take your own vehicle for MOT. Many horseboxes fail the MOT on the rear brakes because with an unloaded horsebox, your load sensing valve will direct more braking force to the front wheels and less to the rear wheels. As part of the MOT the front and rear axles are actually tested separately on a rolling road until the wheels lock up.

If they do not lock up, they fail the brake test. Therefore, it is best to place a load in the horse area (you cannot take horses!) so that the load sensing valve directs more braking force to the rear wheels and under testing they will lock up.

Anti lock brakes

These are a welcomed safety feature on all modern vehicles including horseboxes and work unseen in the background. Basically, when the vehicle is moving sensors constantly check that the wheels are rotating, if one locks up the system removes braking pressure from that wheel until it rotates again. It does this many times each second on each wheel. This clever system allows maximum breaking and shorter stopping distances.

It’s a safety feature you might never use, but one you’ll be grateful to have in an emergency!

Driving test

As part of your C1 driving tuition you will learn all the necessary information about air brakes. I have tried to simplify this as much as possible and it is only written to assuage some of the fears customers may have about moving up in horsebox size.

See our guide for picking the right horsebox depending on your driving licence.