A New Heater Plug
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Bosch, Ltd., Introduces 2pole Pre-heating Plugs for Starting Oil Engines TO obviate the need for a separate 2-volt accumulator, or for tapping one cell of the main battery, for supplying current to the normal single-pole heater plugs used for starting-up certain makes of compression-ignition engine, Bosch, Ltd., Lardeti Road, London, W.3, is now marketing double-pole plugs which may be connected up in series.
In the new plug, type GS2D4, the element is mounted in the usual manner in the central conductor and the body of the plug. As it is now necessary to insulate the body from the cylinder, two sleeves, separated from the main part by mica, are pressed on to form that portion which locates the plug in the cylinder, seats on the coned joint and receives the pressure of the lock-nut.
These sleeves abut against the two faces of a flange formed on the body and are similarly insulated from In A nut on the outer end of the body, an insulating distance piece and a terminal nut on the end of the central conductor serve to secure the connections.
For use in conjunction with these beater plugs a starter switch and a resistance and tell-tale unit are provided. Their purposes are to indicate to the driver that current is flowing through the plugs, and to reduce the resistance of the plug circuit when the starter motor is siitghed on. This is simply accomplisherWy putting a short resistance, in addition to the tell-tale coil, in circuit with the plugs during preheating, and short-circuiting it as the motor is brought into use. Thus the switch has three positions, namely, off, heating plugs on, and plugs and starter on.
Incidentally, the tell-tale coil is secured by a pair of ingenious quickacting spring-operated terminals and can be released by giving each a quarter of a turn.
We are informed that no trouble has been experienced through short circuits occurring across the narrow strip of insulation exposed to combustion.