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of the pump, the exhaust steam may escape through them and thus no flooding of the engine can occur.

The whole apparatus is self-contained and only requires pipes to make the necessary connections.

The following list gives the proportions of these pumpcondensers. Their own steam may be included in their condensation, or may be made use of for feed-heating :

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The ability of these pumps to elevate the heated discharge renders the apparatus of special value in certain cases, while the pump may be readily arranged to act as a fire-pump in emergencies. For sugar factories they are especially suitable.

Falling-column Condensers.—A simple adaptation of the forces due to gravity may be made to produce most excellent results at much less cost than the foregoing, in the shape of a condenser known as the falling-column condenser, in forms invented by Korting, Ledward, Bulkley, and Ransom.

In these the primary necessity is plenty of water, at least

25 times the feed, but should a natural fall of water of about 30 feet be available for use a high economy may be reached with any of the above-mentioned apparatuses.

In the two latter a closed cold-water tank is situated at the top of a pipe of 33 feet height. To the tank the exhaust is led from the engine. The water pours freely into the upper part of the tank on to a perforated plate about half way down its depth. The exhaust is introduced below this plate and entire condensation takes place. The resultant body of water condensing and condensed water drops down the pipe, and the natural suction due to 33 feet fall is thus almost entirely made use of.

In Korting's and Ledward's apparatuses the tank is dispensed with, and the height of the pipe may be reduced to 15 feet. The exhaust steam passes through an ejector pointing down the vertical pipe, and, issuing from the ejector, it draws with it cold water from a chamber surrounding the ejector. Condensation ensues just as the resultant body of water enters the down-fall pipe.

With an ample water-supply I have seen one of these ejector-condensers registering steadily a vacuum of 29.4 inches of mercury for hours together, the work of the engine varying greatly all the time, as it was employed on saw-mill work.

Surface Condensers.—This is the best form of condenser for reliable and complete results. It is the method universally adopted at sea, and in very many cases on land.

The exhaust steam is passed through a large number of thin metal tubes, over which water is caused to flow.

For industrial purposes it is not always necessary to have a complete self-contained apparatus. Excellent surfacecondensers for many large mills are arranged in any convenient spot, to which the exhaust is led by a pipe.

Over the condenser pipes a supply of water is allowed to flow, and this can be exactly proportioned to the require

ments or economy of the case. Thus the water may be reduced in volume and thereby increased in total temperature, or the hottest portion of the condenser pipes may be set apart with this view, whereby enough water may be heated to nearly boiling-point to make up the amount required to feed the boiler in addition to the condensed steam.

The rule in marine engines is to proportion the condensing surface to the heating surface of the boilers, thus,

Heating surface X 0.7 = condensing surface. For land purposes one-half the boiler heating surface may be considered sufficient. For further information, see Chapter XXIV. ** Gain in Condensation.-A good idea of the relative advantage to be gained from adopting condensation with a single-cylinder engine is afforded by the following comparative table of engines of very widely used sizes : COMPARATIVE TABLE OF SINGLE-CYLINDER ENGINES WITH AND

WITHOUT CONDENSATION.

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Heating Factories by Exhaust Steam.-Much economy results from the use of exhaust steam to warm factories, heat drying rooms and closets, and dry cement floors, etc.

Data for arriving at the amount thus to be made use of are as follows:

To raise the temperature of a room from freezing-point to 60°, and there maintain it (say 30° rise), allow i superficial foot of steam-pipe for each 6 superficial feet of glass in the windows; or, allow i superficial foot of steam-pipe to every 120 square feet of wall and ceiling.

SURFACE OF TUBES IN SQUARE FEET PER ONE-Foot LENGTH.

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Water Required for Surface Condensing.–The amount of water required for surface condensing of course varies with the amount used by the engine. If the engine is wasteful, or with work much below its normal duty, it may stand as high as 20 lbs. of water per minute per horse-power, but with a good compound engine, doing regular work, it will fall to 12 to 15, and with high class triple compounds as low as 1o lbs.

The friction of the condenser tubes and the velocity of the entrance of the water is equivalent to a head of 5 to 10 feet, which must be added to the work of the pump supplying the cooling water.

The speed of this water is safely taken at 10 feet per second through the pipes, while in the navy they use 15.

and centrifugal pumps are commonly employed for this purpose, the best speed for them being 150 revolutions per minute.

The air-pump capacity in surface-condensing engines may be as low as Xth of the low-pressure cylinder.

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