Service brakes, as required by Specification MIL-M-8090 on towed equipment, must operate in response to the driver of the tractor. Hydraulic brakes connected to the brake system of the towing vehicle, electric brakes, and air-over-hydraulic brakes all have disadvantages; mainly the required compatibility between all towed and towing vehicles. The problem of providing service brakes is best resolved by using the AEROL surge type brake actuator. This device responds to any decelerating force of the tractor pintle hook on the lunette eve of the trailer tow-bar, to actuate the hydraulic brakes of the towed vehicle. Whether the force of the tractor on the tow-bar is the result of deceleration, excessive lurching, or descending a grade, the surge of the trailer against the tractor will actuate the brakes. It is from this function of the system that its name is derived.
The surge system is designed to accommodate sudden shock loads on the lunette eye without actuating the brakes so that they are not spasmodically applied while the equipment is towed over rough terrain. An additional feature of the surge system is an automatic hydraulic by-pass that deactivates the brakes when the trailer is operated in the reverse direction. A fail-safe feature is available, in the form of a mechanical linkage that applies the brakes to bring the trailer to a safe stop, in the event of failure of the pintle hook and safety chains.
The “Hydraulic Brake Actuator” is available in 5 sizes covering a range of gross trailer weights up to 22,000 pounds. However, each installation must be tailored for the job for maximum efficiency. In general, the springs and orifices used in the surge unit are selected so that the lowest operating pressure may be used that will satisfy the performance specifications. For this reason, the following information is required: