A Catechism of the Steam Engine

by C. E. John Bourne

A.--In tubular boilers a good deal of care is required to prevent the ends of the tubes next the furnace from becoming coated with scale. Even when the boiler is tolerably clean in other places the scale will collect here; and in many cases where the amount of blowing off previously found to suffice for flue boilers has been adopted, an incrustation five eighths of an inch in thickness has formed in twelve months round the furnace ends of the tubes, and the stony husks enveloping them have actually grown together in some parts so as totally to exclude the water.

731. Q.--When a tubular boiler gets incrusted in the manner you have described, what is the best course to be adopted for the removal of the scale?

A.--When a boiler gets into this state the whole of the tubes must be pulled out, which may be done by a Spanish windlass combined with a pair of blocks; and three men, when thus provided, will be able to draw out from 50 to 70 tubes per day,--those tubes with the thickest and firmest incrustations being, of course, the most difficult to remove. The act of drawing out the tubes removes the incrustation; but the tubes should afterward be scraped by drawing them backward and forward between the old files, fixed in a vice, in the form of the letter V. The ends of the tube should then be heated and dressed with the hammer, and plunged while at a blood heat into a bed of sawdust to make them cool soft, so that they may be riveted again with facility. A few of the tubes will be so far damaged at the ends by the act of drawing them out, as to be too short for reinsertion: this result might be to a considerable extent obviated by setting the tube plates at different angles, so that the several horizontal rows of tubes would not be originally of the same length, and the damaged tubes of the long rows would serve to replace the short ones; but the practice would be attended with other inconveniences.

732. Q.--Is there no other means of keeping boilers free from scale than by blowing off?

A.--Muriatic acid, or muriate of ammonia, commonly called sal-ammoniac, introduced into a boiler, prevents scale to a great extent; but it is liable to corrode the boiler internally, and also to damage the engine, by being carried over with the steam; and the use of such intermixtures does not appear to be necessary, if blowing off from the surface of the water is largely practised. In old boilers, however, already incrusted with scale, the use of muriate of ammonia may sometimes be advantageous.

733. Q.--Are not the tubes of tubular boilers liable to be choked up by deposits of soot?

A.--The soot which collects in the inside of the tubes of tubular boilers is removed by means of a brush, like a large bottle brush; and the carbonaceous scale, which remains adhering to the interior of the tubes, is removed by a circular scraper. Ferules in the tubes interfere with the action of this scraper, and in the case of iron tubes ferules are now generally discarded; but it will sometimes be necessary to use ferules for iron tubes, where the tubes have been drawn and reinserted, as it may be difficult to refix the tubes without such an auxiliary. Tubes one tenth of an inch in thickness are too thin: one eighth of an inch is a better thickness, and such tubes will better dispense with the use of ferules, and will not so soon wear into holes.

734. Q.--If the furnace or flue of a boiler be injured, how do you proceed to repair it?

A.--If from any imperfection in the roof of a furnace or flue a patch requires to be put upon it, it will be better to let the patch be applied upon the upper, rather than upon the lower, surface of the plate; as if applied within the furnace a recess will be formed for the lodgment of deposit, which will prevent the rapid transmission of the heat in that part; and the iron will be very liable to be again burned away. A crack in a plate may be closed by boring holes in the direction of the crack, and inserting rivets with large heads, so as to cover up the imperfection. If the top of the furnace be bent down, from the boiler having been accidentally allowed to get short of water, it may be set up again by a screw jack,--a fire of wood having been previously made beneath the injured plate; but it will in general be nearly as expeditious a course to remove the plate and introduce a new one, and the result will be more satisfactory.

735. Q.--In the case of the chimney being carried away by shot or otherwise, what course would you pursue?