Chap. XXI. STEAM CONSIDERED AS A MOVING POWER.
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Water Gauge is an instrument attached to the steam-engine boiler for the purpose of regu-lating the quantity of water and fuel, as well as the combustion and elasticity of the steam.
The Glass Gauge attached to steam-engine boilers is either of flat or tubular glass :the first description consists of a smallwindow, made of very thick glass, insertedin the boiler, at the place up to which thewater should rise.
The Tubular Glass Gauge is a small pipeof glass, about £ inch in diameter internally,and 11 inches thick: it is placed outsidethe boiler, and communicates at the top andbottom by stopcocks with the interior of theboiler: the higher stopcock enters wherethe steam is a little above the surface of thewater, so that the water, standing in the glasstube on the same level with the water in theboiler, is shown to the attendant.
Feeding Apparatus for Boilers is for the purpose of supplying it with water, in lieu ofthat passing off continually as steam : a simple form, adapted to a low-pressure engine, mayhave the water conducted into the reservoir of about 18 inches diameter, with a pipeto conduct from it into the boiler : the top of this pipe may be closed by a conical plug,hanging at the end of a rod Vr, from a lever supported at /,and having two weights W and u; that of W rests on thesurface of the water in the boiler, which falls whenever thewater is below its proper level. The arm L is pulled down by
j. 1981. WINDOWCLASS GAUGE.
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Fig. 1983.
FEEDING APPARATUS.
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the rod LW, which passes through a steam-tight stuffing-box;by the same motion the lever L ascends and opens the valveV, and allows the water to descend to replenish the boiler.
This description of valve answers when the boiler is low-pressure, or w'hen the reservoir is more than 26 inches above ^2* self-regulating1, - r . f. , r. feeding apparatus.
the surface of the w’aterlor every pound ot pressure per square
inch of the boiler; for the height of the water in the cistern should be sufficient to balancethe strength of the steam, and if this height be too small, the water in the boiler will beforced up the feed-pipe, and driven by the steam out of the valve. Water at a temperatureof 60°, 2-94 feet in height, is equivalent to one pound on the circular inch, but the waterin the feed-pipe is about 212°, so that 3 feet is required in height for every pound onthe circular inch : it is necessary that the stone float should be placed in that part of theboiler where the steam will least affect it, and the feed-pipe should be as far away as possiblefrom where the greatest quantity of steam is produced.
In High-Pressure Engines , the water is supplied to the boiler by a forcing-pump, workedby a lever connected with one of the reciprocating portions of the engine, and the watersupplied by a pipe that traverses the steam which escapes, so as to become raisedin temperature before it is admitted to the boiler: in order to proportion accurately thequantity of water to be supplied, we must remember that there is exactly one cubic inch ofwater for each cubic foot of atmospheric steam given to the engine, or one cubic footequal to six gallons per horse-power per hour : but as the evaporation does not proceeduniformly, in consequence of variation in the intensity of the fire, which causes steamof greater or less density to pass into the engine, the steam sometimes falling below thestandard and at others escaping through the valve, it is necessary to have some furthermeans of regulating its supply. In some engines this is effected by a float; a stop-cockattached to the pipe of the feed pump will enable the attendant to regulate the
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