Triple-line Braking System for Leyland Freightline Tractive Units
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ANEW triple-kine braking system has been introduced by Leyland Motors Ltd. on tractive units throughout the new Freightline range.
Basic components consist of a main and an auxiliary reservoir on the tractive unit with another air reservoir on the semi-trailer; a footbrake control with dual valve; a hand-operated emergency brake control; and the standard Leyland power-assisted handbrake, There are dual diaphragm chambers on the tractive unit front axle and the semi-trailer rear axle(s), with single diaphragm chambers on the tractive unit rear axle(s).
The air pressure is supplied by an engine-mounted compressor through an unloader valve and via non-return valves to the main and auxiliary reservoirs on the tractive unit. When the brake pedal is depressed one half of the dual valve allows air through the primary line to operate the front and rear brakes on the tractor. Air is passed through the other side of the dual valve at the same time, and via the service line to the relay emergency valve on the trailer; this in turn diverts air pressure from the trailer reservoir to the trailer brakes. Should either of the footbrake valves fail, there will still be a braking system from the brake pedal. If the air supply from the main reservoir is lost, the auxiliary reservoir still supplies air to the second valve on the footbrake by which the brakes on the trailer can be applied.
The auxiliary reservoir also feeds the emergency line to pressurize the trailer reservoir. This emergency line is coupled to a hand-operated emergency brake control and the handbrake pull-valve, operation of the former allowing air through an auxiliary line direct to the brakes on the front axle of the tractor and—independent of the trailer reservoir —to the trailer brakes.
Self-sealing couplings are fitted to the three connecting hoses, and are of different design to guarantee correct coupling. The service line has a male C-type coupling, the emergency line a female C-coupling and the auxiliary line a special palm-type coupling with selfsealing device. in the event of a fracture in the emergency line, or should the trailer break away, the relay emergency valve automatically opens and applies the brakes on the semi-trailer.