New System Synchronizes Trailer and Tractor Brakes
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QYNCHRONIZATION of tractor and trailer brakes without loss of sensitivity is claimed for a new electropneumatic system introduced by the Westinghouse Brake and Signal Co., Ltd., London, N.1. This is achieved by providing an additional pressure-supply point operated instantaneously on the trailer, but controlled by the inlet valve in the driver's control valve on the tractor. The supply is equalized at all times by feeding into the normal service line.
The accompanying drawing shows a typical tractor-trailer installation. This is basically a conventional dual-circuit system, plus a hand reaction valve for the trailer brakes. A tractor-protection valve is included. The electro-pneumatic section consists of an electrical supply and valve switch on the tractor, with a magnet valve, small reservoir and two chokes on the trailer.
Braking Harmonized Depression of the brake pedal opens the air inlet valve in the normal way, but also actuates the switch, which in turn operates the magnet valve on the trailer and admits air to the relay emergency valve in direct proportion to pedal pressure. The degree of .trailer braking is always proportional to the tractor braking, and the closeness of the magnet valve to the service-line port in the relay emergency valve eliminates delay in the pressure build-up.
The small reservoir and two chokes are necessary to ensure correct timing, and their sizes will vary according to the particular installation. The capacity reservoir and one choke are to make sure that operation of the magnet valve does not occasion a pressure drop in the emergency line, as this -would possibly cause an emergency application of the brakes. The other choke ensures that the maximum degree of inshot to the relay valve is obtained when the magnet valve is energized.
Thus the system provides an additional feed from the trailer reservoir in the case of a two-pipe layout, both sources being controlled by the driver's pedal through the tractor control valve and connected by the service line to the relay valve on the trailer. Therefore, feeding from the tractor and trailer simultaneously provides synchronized balanced braking. In the event of an electrical failure, normal two-line braking is retained.
BRISTOL BUS STATION WILL BE READY SOON
THE new £200,000 bus station in Whitson Street, Bristol, is expected to be completed by the end of this month, and services will begin operating from it on a Sunday in September. The official opening date will he announced later. The station, which will accommodate 96
vehicles, will be only for country buses, but city services are to be reorganized.
An inquiry into the applicat on by the Bristol Omnibus Co., Ltd., to alter city routes will be held on September1, andbefore the hearing the Traffic Commissioners and the public works committee will tour some of the roads to assure themselves that the thoroughfares are satisfactory.
BID TO KEEP WORKS OPEN IN another attempt to prevent the Kings i. works of Bristol Commercial Vehicles, Ltd., from being closed, local representatives of the Transport and General Workers' Union and officials of the company are to meet during the coming week. The Ministry of Supply have said that any action to prevent closure should be taken locally.
T.G.W.U. representatives are likely to ask whether the works could be used by the British Transport Commission. Two hundred men at the works who have been on short time since March are now back on a fiveAay week,