A New Heater Plug THERE are two obvious methods of
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L overcdming the difficulties inseparable from the practice of supplying current at 2 volts to the normal type of single-pole heater plug. They are the employment of 12-volt plugs connected in parallel or the use of plugs of the double-pole type for 2 volts or 3 volts—in the case of six-cylindered and four-cylindered engines respectively—connected in series.
Beru A.-G., Ludwigsburg, Germany, having found by experiment that 12volt heater coils are of less durability than those for lower voltages, has de
veloped a double-pole plug in 2-volt and other types. The standard coils used are composed of twisted strands which afford a larger total heating surface than does a coil formed from a single heavy-gauge wire, although the latter is also available.
Consisting of two separable units, the Bent plug has an outer body which is threaded to screw into the cylinder casting and provided with a cone seating. Pressed into it and insulated
from it by a mica sleeve is the hollow intermediate conductor. A recess is turned on the upper part of the lastnamed for the attachment of one lead, and its base has a conical mouth.
This assembly forms the first unit and the other is composed of the central conductor, a short sleeve pressed on to its lower end over a mica wrapping, and the heater coil, one end of which is fixed in the central conductor, the other, in the short sleeve. The last-named is turned conical to seat in the intermediate conductor.
With the plug assembled the upper
end of the central conductor is located by an insulating ring on to which a nut is screwed down to hold the two units together. A terminal nut is provided for the other lead. The Bern preheating equipment includes a controlling resistance, short circuited when the starter motor is switched on, a tell-tale and switch gear. Resistances and heater plugs for voltages for engines with various numbers of cylinders are available.