TH Series Air Over Hydraulic Trailer Kits – with ABS, Product Description

Air Over Hydraulic

The air over hydraulic system is a common application for trailers being towed by light and medium duty commercial vehicles equipped with air brake systems. Components of the air/hydraulic system are trailer-mounted and consist of a compressed air storage tank, a control valve, an air chamber/master cylinder assembly, hydraulic lines and hydraulic disc or drum brakes. The towing vehicle supplies compressed air to the trailer storage tank as well as a modulated control signal through tubing and gladhands or quick connects mounted on the tow vehicle and trailer.

When the operator applies the tow vehicle service brakes, the tow vehicle air brake system provides a signal pressure in proportion to the tow vehicle's service brake pressure. The trailer control valve receives this signal and compressed air from the trailer-mounted storage tank, modulated by the trailer control valve, is applied to an air chamber/master cylinder assembly producing a corresponding hydraulic pressure in the trailer brake system.

Typical applications for air/hydraulic brake systems are pintle hitch and gooseneck drawn multi-axle equipment and utility trailers towed with air brake equipped vehicles. The trailer brakes may be applied independently of the tow vehicle brakes. ABS and spring actuated emergency braking and parking for FMVSS 571.121 compliance can be incorporated.


An Antilock Braking System (ABS) is a sub-system designed to modulate the braking force at the vehicle wheels to prevent the wheels from sliding. The system monitors the rotational speed of the wheels on one or all axles, depending on the system specified, and automatically modulates brake pressure to give the most available braking force without the loss of wheel rotation and the resultant loss of control and tire flat spotting. ABS allows for maximum effort braking on slippery surfaces to bring the vehicle to a safe, controlled stop. The system is available in single or all axle configurations.