Mechanics of the Household. E. S. Keene
if not, fill through the funnel. Let the water run until the gage-glass shows about half full of water.
In the first filling, after the water has boiled, get up a pressure of at least 10 pounds, draw the fire and blow off the boiler under pressure through draw-off cock to remove oil and sediment, after which refill with fresh water to the water line. This is best done usually by the steam-fitter.
The damper regulator will control the pressure of steam, closing the damper when the pressure is raised beyond the desired point and opening the damper when the pressure falls below that point. By removing the weight on the lever, different degrees of pressure can be kept up. The regulator should be allowed to control the drafts without interference.
Examine the water glass often to see that the water line is at the proper height. If lower than normal open the supply pipe until the water runs in and stands at the proper level. It is best when no water stands in the glass, nor shows at the bottom of the try-cock, to quickly dump the grate and do not put water into the boiler again until it is cooled off.
If there is one or more shut-off valves on the main or return pipes, before starting a fire see that one line of piping at least (main and return) is open to circulate the steam.
To Control Radiators.
—When it is desired to shut off steam from any radiator (if the regular radiator valves are used), close the valve tight, and when it is turned on see that the valve is wide open. A valve partly turned off will cause the radiator to fill with water. This rule applies only to one-pipe heating systems.
The Air Valves.
—If little keyed air valves (sometimes called “pet-cocks”) are used, follow generally the same directions as outlined for hot-water radiators on page 49—only, of course, in releasing the air from the radiator open the valve with the key provided and close it just as soon as the steam unmixed with air comes through the nose of the valve.
If “automatic” air valves are used they must be carefully adjusted by the steam-fitter and then left to operate without undue interference.
End of the Season.
—At the close of the heating season fill the steam boiler with water to the safety valve and let it thus stand through the summer.
Also thoroughly clean all the fire and flue surfaces of the boiler and at the opening of the next season withdraw the water and refill with fresh water to the water line, starting the boiler as before.
It is advisable to have a competent steam-fitter blow off the boiler under pressure and thus give the inside a thorough cleaning when the boiler is first set up and ready for fire.
A low-pressure boiler, using good water, rarely needs blowing off after it is once cleaned at time of setting up.
THE RIGHT CHIMNEY FLUE
The area of the flue should never be less than 8 inches in diameter if round, or 8 by 8 inches if square—unless for a very small heating boiler or tank heater. Nine or 10 inches round, or 8 by 12 rectangular is a good average size. The flue should generally have a little more area than that of the connecting smoke pipes.
Draft force depends very much on the height of the flue.
The chimney top should run above the highest part of the roof and should be so located with reference to any higher buildings nearby that the prevailing wind currents will not form eddies which will force the air downward in the shaft. Often a shifting cowl which will always turn the outlet away from the source of adverse currents will promote better draft.
The flue should run as nearly straight up from the base to the top outlet as possible. It should have no other openings into it but the boiler smoke pipe. Sharp bends and offsets in the flue will often reduce the area and choke the draft. The flue must be free of any feature which prevents a free area for the passage of smoke. The outlet must not be capped with any device which makes the area of the outlet less than the area of the flue.
The best form of flue is a round tile—in such there is less friction than in the square form and the spiral ascent of the draft moves in the easiest and most natural manner.
If the flue is made of brick only, the stack should be at least two 4-inch courses in thickness.
If there is a soot pocket in the flue below the smoke-pipe opening, the clean-out door should always be closed. If this soot pocket has other openings in it—from fireplaces or other connections—such arrangements are very liable to check the draft and prevent best action in the boiler.
The smoke pipe should not extend into the flue beyond the inside surface of the flue, otherwise the end of the pipe cuts down the area of the flue and injures its drawing capacity.
The inside of a flue should be smooth (pointed or plastered). When the courses are laid with the mortar bulging out from the joints the friction within the flue is very much increased. Often a troublesome flue is corrected by lowering some sharp-edged weight by a rope which should be worked against the sides of the flue until the clogging is scraped off.
A new chimney when “green” will not have a good drawing capacity. Short use dries out the mortar and better results follow.
“Smokey” Chimneys.
—The failure of draft in flues may be due to a variety of causes, one of which is illustrated in Fig. 57b. The short chimney on the left side of the roof shows the course of the wind as it passes over the ridge of the roof and why the draft in such a chimney is retarded whenever this condition exists. The force of the wind, as it comes into contact with the roof, causes a compression of the air on the windward side and a rarification on the lee side. This inequality of pressure causes a downward sweep of the wind as indicated by the arrows. The effect on the low chimney is to retard the draft and sometimes the pressure is great enough to reverse the action of the flue and force the smoke into the house. The only remedy for such a condition is an extension of the chimney that will raise its top above the ridge.
Fig. 57b.—Effect of the wind in causing down draft in low chimneys.
The same effect is often produced by a neighboring building or a border of trees that are higher than the chimney and dense enough to effect the wind pressure.
Конец ознакомительного фрагмента.
Текст предоставлен ООО «ЛитРес».
Прочитайте эту книгу целиком, купив полную легальную версию на ЛитРес.
Безопасно оплатить книгу можно банковской картой Visa, MasterCard, Maestro, со счета мобильного телефона, с платежного терминала, в салоне МТС или Связной, через PayPal, WebMoney, Яндекс.Деньги, QIWI Кошелек, бонусными картами или другим удобным Вам способом.