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through the automatic valve K K'. This chamber is in communication with the air pump by means of a passage L.

During the forward stroke a charge of air is drawn into the air chamber, which on the return stroke is slightly compressed, and enters the combustion chamber by means of the automatic air valve (this valve acts independently of the gas valve). If this return stroke were the exhausting one, the expulsion of the products must necessarily be assisted to a considerable extent, and the combustion chamber be almost filled with pure air. During the compression and explosion strokes there is a slight gain of power owing to the heating of the air, but as this heating is very slight, the gain cannot be reckoned upon.

Fig. 50 is a diagram taken from the air pump cylinder of a 30 H.P. NOM. engine. S is the suction line and C the compression lines, coinciding for both back strokes till the admission valve opens; then on the exhaust stroke the discharge line D D' is horizontal, till the piston nearly comes to rest, when the drop is very rapid, owing to the exhaust valve being nearly full open, and the gases in the pipe in motion.

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Fig. 51 is a light spring card taken from the motor cylinder

of the same engine; the effect of the entrance of air in the cylinder is shown at A, near the end of the stroke.

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FIG. 52.-150 I.H.P. PREMIER' TANDEM ENGINE (WITH SCAVENGER)

The area of the air pump piston is 1.65 time that of the motor piston, or a difference of area of 0.65 time the motor

piston, which fraction multiplied by the mean pressure in the pump will give the equivalent deduction to be made from the effective pressure in the latter, in order to allow for loss of power in the pump.

The work absorbed in forcing the air through is, owing to free passages, very slight, as a reduction of to 1 lb. per square inch from the indicator card will cover it.

From a mechanical point of view the air cylinder is advantageous, as the front end of the piston remains cool and offers a large surface for taking the lateral thrust of the connecting rod, and a cool bearing for the piston pin.

Fig. 52 is an external elevation of a tandem 'scavenging' engine, which will indicate 150 H.P. with coal gas, and onefifth less with Dowson gas. With Sandiacre gas, the consumption is 15 cubic feet per I.H.P. per hour.

With Sandiacre

Referring to fig. 52, it will be seen that the two pistons are coupled by side rods passing through the cylinder jacket, though not in contact with the cooling water. The pistons are well supported by a slide block working between the two cylinders. A governor of the centrifugal type mounted on the crank shaft actuates the gas pecker lever on each cylinder. When working at full power an impulse is obtained for each revolution of the crank shaft.

The design of this engine is well thought out, and is admirably adapted for hard work without undue heating.

Clarke, Chapman & Co. (Limited), Gateshead-on-Tyne

All the engines described have been worked on the 'Otto' cycle, with fixed air and gas inlet, the latter being in some cases varied by a graduated cam, tube ignition, and side shaft for operating valve levers. In this engine there is a new departure, inasmuch as the lifting drop valves and tube ignition is dispensed with, the system adopted being known as 'Butler's.'

Fig. 53 is an external elevation; fig. 54 a sectional plan, and fig. 55 a cross section, clearly show the whole arrangement.

It will be seen that only one four-chambered equilibrium valve is used, the speed of which is one-fourth that of the crank, and controls the various functions of the supply of gas, air, and exhaust. The gas and air pass through an inspirator, where they get properly mixed on their way to the combustion chamber.

The speed regulator is actuated by a flywheel governor, which opens or closes the regulator valve so as to admit a larger or smaller charge of unvarying richness, and is capable of easy adjustment by hand while the engine is running,

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enabling any required speed to be maintained in the manner obtained in ordinary steam engine practice, the governor automatically keeping the engine at that speed. The charge is exploded at the end of the compression stroke by an electric spark from an induction coil excited by a bichromate battery, which is charged about every other day with 1 lb. of acid mixture in the form of a damp red paste.

Figs. 56 and 57 are diagrams taken from a 33 B.H.P. engine, and show the remarkable speed obtained with a variation in load from 32 to 5 B.H.P. Fig. 58 is a diagram taken when the engine is running light.

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SPEED REGULATOR

FIG. 54

FIGS. 54, 55.-CLARKE, CHAPMAN & Co.'s ENGINE

FIG. 55

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