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Striking Features in a New Sliding Door

15th November 1935
Page 80
Page 80, 15th November 1935 — Striking Features in a New Sliding Door
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Light in Weight and Simple in Operation, the Dorvac System Appears to Provide for All Contingencies

KNOWN as the Dorvac system, a new eiectro-vacuum or air-pressure door-operating mechanism for buses and coaches has recently been marketed by George Johnston, Ltd., 66, Grove Road, Sutton, Surrey. Incorporating ingenious features, the mechanism may be applied to any type of sliding door without modification to the existing coachwork. The system niay be operated under pressure or by vacuum and a storage. tank is provided.

Mounted in a convenient position in the driver's cab is a control valve having three nozzles ; the centre one is connected to the vacuum tank,, the forward nozzle to the front of the operating. cylinder and the rear one to the back of the operating cylinder. The valve is also connected to a solenoid, which, when energized, returns the valve to the "open" position.

The solenoid is actuated by an ingenious "accident cushion" on the door pillar, which consists of a rubber buffer having within it electrical contacts. The method of operation is such that should anything become caught in the door, or should a passenger grip the pillar in an endeavour to mount the bus as the door is closing, the 'electric circuit is immediately completed, the solenoid energized and the control valve thrown into the " open " position.

On a model demonstrated to us by Mr. Johnston, we found that, despite a pressure of over 150 lb., one could safely allow one's hand to be trapped by the closing door, the efficiency of the " accident-cushion " device being such that the door opened again after but slight pressure on the hand.

In addition to this safeguard, an emergency handle is provided, also a remote control in the form of one or more push buttons. Both these safety devices are wired to the solenoid, and the push buttons may be placed in any convenient place in the bus for control, in case of emergency, by the conductor or passengers. .

Mounted alongside the driver's control lever is a main switch for the elec./deal circuit and a tell-tale light which glows when the door is open. 2 The wiring for the electrical part of the apparatus is extremely simple, whilst a further point is that, apart from the tell-tale lamp, current is used only the instant when the emergency handle, accident cushion or push buttons are operated, the current being automatically switched off so soon as the door opens. In the event of a breakdown in either the vacuum or electrical system, or both, the door can still be operated by hand in the usual manner. .

The mechanism is light in weight, and in its heaviest form, for a curved sliding door, the complete equipment weighs" but 36 lb., plus 30 lb. for a pressure or vacuilm tank for an oil-engined bus, or 20 lb. for a suitable tank for a petrol-engined vehicle.

Examples of this interesting device are on view at the Commercial Motor Show on a Leyland trolleybus, with an air-pressure jack-knife door (Stand 118), and on a Bristol bus with a vacuum-operated door of the sliding type (Stand 13).

Tags

People: Johnston
Locations: Surrey, Bristol

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