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Understanding horsebox air brakes

If you already use them horsebox air brakes are something we all take for granted. It is easy to forget how daunting they can seem to customers moving up to larger vehicles and encountering them for the very first time!

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 exactly the same controls as a car, with a foot brake and hand brake. The handbrake differs only slightly in operation but is very easy to use. It is a very safe and simple system which consists of service brakes, parking brakes, a control pedal, hand brake, air pump and air storage tanks with gauges on the dashboard.
From turning on the ignition the driver will see gauges with air pressure levels in the storage tanks. If these levels are low the brakes will automatically be on and a warning symbol and buzzer will warn that the pressure is down. For safety, it is not possible to move the vehicle until the pressure has built up and the warning symbol and buzzer have gone off. In the event of a failure in the brake system, for safety any loss of air will automatically engage the brakes.

Load sensing valves

In addition to Horsebox air brakes, load sensing valves are a completely separate yet vital safety system that also deserves a little explanation.
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 more quickly.
MOT tip – this may be of help if you take your own vehicle for MOT. Many horseboxes fail the MOT test on the rear brakes. This is because they test them all the way to locking up on a rolling road. So if you test with no load in the horse area, the rear brakes will lock more easily and fail the test. It is a good idea to add some load over the rear axle so the load sensing valve directs more braking to the rear wheels. You cannot take horses!

Anti lock brakes

Anti lock brakes have been 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. Hopefully it’s a feature you will be glad to have and never need!


Any queries or questions?