The instability which causes caravans to snake is generally the result of overloading. The recommended towed weight should be no more than 85% of that of the car. Unfortunately many motorists exceed this figure. Once snaking begins the conventional system of braking – `the hitch’ – is virtually ineffective, as it can only brake the caravan while it stays in a straight line. With the introduction of a British invention called Trail-Air, the situation has now changed.
Trail-Air is designed to overcome snaking by permitting the use of the caravan brakes through an electro-pneumatic device. The invention applies the caravan brakes only, and does not rely on the normal over-run system to operate it.
Only light pressure to the foot brake in the tow vehicle is needed. This ensures that only the brake lights are operated and not the tow vehicle’s brakes. Under normal application of the tow vehicle’s brakes, the caravan’s brakes will operate before the tow vehicle’s, retarding the caravan first.
The device operates via a small compressor through an Asco Joucomatic solenoid valve, an air pressure switch and check valve combination, and a pressure brake chamber operating through a linkage mounted underneath the caravan and connected into the existing brake rods. The unit does not interfere with the normal over-run braking system and is therefore failsafe.
Under normal braking the device operates so quickly that the over-run system does not compress the hitch to operate the over-run brakes. However, should there be a failure of the device, such as broken or disconnected electrical connections between car and caravan, the normal over-run brakes would operate.
Due to the way the unit is linked into the brake rods it actually improves the normal over-run braking system under normal braking as it is electrically operated and does not rely on momentum.