APPLIED MECHANICa 



[FLOATS, OAPOE-COCKS, ETC- 



Dot the only danger of an over-heated flno ; fur on the 

 wat.T again covering it, the enormous volume of steam 

 MI. Meuly generated produces an excess of pressure, and 

 causes an explosion of the boiler. We believe almost 

 very ease of explosion can be traced to some circum- 

 stance connected with a deficient supply of water ; and, 

 therefore, too much caution cannot bo used in watching 

 the condition of the wator-level, and providing the 

 proper supply or feed. 



BOILER FITTINGS. In order to ascertain the 

 water-level within the boiler, several kinds of apparatus 

 are employed. Tho float A (Fig. 158) consists of a stone 



suspended by a wire passing through the top of the 

 boiler, and connected, by a chain led over a pulley, with 

 a counter-balance, sufficient to balance BO much of the 

 weight of the float-stone that it shall always lie at the 

 surface of tho water. Should the water-level vary, the 

 position of the float-stone, which rises or falls with it, is 

 marked by an index on the pulley. 



Oauge-cocks B C are two stop-cocks fitted into the face 

 of a boiler, one above and the other below the proper 

 water-level When these cocks are opened, steam should 

 blow through the upper, and water through the lower 

 one. The objection to gauge-cocks consists in the cir- 

 cumstance that, in order by them to ascertain the level, 

 the attendant must open them. 



The glass gauge consists of two stop-cocks, D and F, 

 fitted in the face of a boiler, one above and the other 

 below the water-line. These cocks are connected by a 

 glass tube E, in which the level of the water is distinctly 

 seen. A stop-cock G is provided at the lower end of 

 the glass tube ; and this being occasionally opened, the 

 sediment that may collect in the tube or passages of the 

 cocks is blown out by the pressure within the boiler. 

 Should the glass tubo burst, the stop-cocks D and F can 

 be closed until a new tubo is litted, or they can be em- 

 ployed as gauge-cocks. 



Occasionally the float is connected with a whistle, in 

 micli a manner that when tho level of the water becomes 

 too low, it opens a small stop-cock, which permits steam 

 to blow through the whistle, and thus give audible warning 

 Hi tlio danger. 



In many boilers a precaution is taken against the dan. 

 geroiu consequences of insufficiency of water, by the use 

 of fusible metal plugs. A hole is made in the highest 

 part of the fire-box or flue, which is filled up with a plug 

 or rivet of metal fusible at a temperature not greatly ex- 

 ceeding that of boiling-water. So long as this plug is 

 covered with water, its temperature cannot attain the 

 melting point ; but should it bo left bare, the heat of 

 tli- fire playing upon it causes it to melt out, and thus to 

 leave a hole, through which the steam escapes into the 

 flue. Not only does the rush of the escaping steam give 

 warning of the circumstance, but it also relieves the 

 steam- preiuni re within the boiler, and prevents the ex- 

 plosion which might otherwise result from the over-heat- 

 ing of the ' 



! >. In low-prwwuro boilers, the float occasionally 

 ii made to act as a self -feeding apparatus. A (Fig. 150) is 



a cistern constantly supplied with water, and fitted at 

 bottom with a valve opening downwards into a pipe pass- 

 ing down to nearly the bottom of the boiler ; the II 

 is connected by a wire and lever with the valve, so that 

 when the water-level is too low, the descent of the float 

 causes the valve to open, and thus pi-units the passage of 

 water from the cistern into the boiler. This arrange- 

 ment can only be adopted when the pressure of the 

 steam within the boiler does not exceed that of the 

 column of water in the feed-pipe. For high-pressure 

 boilers, the height of cistern and feed-pipe would be in- 

 conveniently great to overcome the pressure ; accord- 

 ingly, for these and for marine boilers, the supply 

 of water is effected by means of a 

 force-pump, called the feed-pump, 

 Fig. 159. 



worked by the en- 

 gine, and regulated 

 by suitable cocks or 

 valves. An appara- 

 tus for feeding boil- 

 ers with water, called 

 an Injector, hiis also 

 been very success- 

 fully applied in many 

 cases. The force of a certain quantity of steam issuing 

 from the boiler by properly arranged dinnneN ami valves, 

 is made to cause a proportional quantity of water to 

 enter the boiler. 



The quantity of water required for a boiler may be 

 generally taken at 1 cubic foot per horse- power por hour ; 

 or, as 1 cubic foot contains about (ij gallons, and weighs 

 about G3 Ibs., we may take 1 Ib. of water per minute, or 

 1 gallon every 10 minutes, as the nc ;-essary supply for 

 each horse-power. The actual quantity of water required 

 for generating steam to work an engine of 1 horse-power, 

 depends much upon the construction of the engine, the 

 extent to which the steam is used expansively, the 

 amount of power derived from condensation, or the 

 amount of resistance to the egress of waste steam, if not 

 condensed ; but the above estimate is tolerably correct 

 for non-condensing engines worked without much ex- 

 pansion, and is in excess for condensing engines, and 

 such engines as those in which the expansive force of 

 tho steam is taken advantage of, so as to produce great 

 effect with small expenditure of steam. 



It has been found by experiment, that 1 Ib. of ordinary 

 fuel coal or coke is capable of turning from 8 to 10 

 Ibs. of water into steam, according to tho capabiliti. 

 the boiler. Taking the lower estimate, we should 

 reckon that as 63 Ibs. of water are required per horse- 

 power per hour, about 8 Ibs. of fuel per horse-power per 

 hour would be consumed. In condensing engine-;, 

 working expansively and under the must 

 circumstances, the consumption of fuel has been i. -In.-, -<l 

 so low as from 2J Ibs. to 3 Ibs. per horse-power per liour. 

 In non-condensing engines, when the steam is used to a 

 considerable extent expansively, from 6 Ibs. to 7 Ibs. of 

 fuel per horse-powor per hour is nearly the average 

 consumption. 



SAFETY-VALVE. It may be readily conceived, 

 that when water contained in a vessel or boiler of limited 

 strength, is subjected to heat in such a manner as to 



