Modern Machine-Shop Practice Part 230

IN THE MORNING.--In starting up a banked fire in the morning, first close the fire door and open the damper, so as to give the fire all the draught possible, and let it burn up a little; then, if it has been piled up at the back of the furnace, clean out the ashes by pa.s.sing the T bar beneath the fire, and spread it over the grate, letting it burn up a little before making up a fire.

BOILER-FEED.--The fireman should endeavor, if possible, to so regulate the boiler feed that it is kept going as nearly continuously as possible while maintaining a uniform quant.i.ty of water in the boiler, and this, with uniform firing, will give the greatest economy.

When pumps are used to feed with, the amount of the lift of the valves can be regulated by a screw, so as to vary the amount of water the pump will deliver, and in this case it is comparatively easy to set them so that the pump may be kept going without putting too much water in the boiler.

When injectors are used, however, the feed will be intermittent, and a uniform quant.i.ty of water in the boiler is best obtained by feeding at short intervals, stopping the feed when the fire door is opened much, as when cleaning the fire.

If the feed water is dirty, the gauge gla.s.s should be kept clean by first shutting off the upper c.o.c.k and opening the lower one, so as to let the water blow through the lower c.o.c.k, and then shutting off the lower c.o.c.k from the boiler, and opening the upper one, which will let the steam blow all the water out of the gla.s.s. This should be done two or three times a day, so as to keep the holes in the boiler and those in the c.o.c.ks from closing up with fur or scale.

If the water falls in the gla.s.s, or if the gauge c.o.c.ks show the water to be falling, notwithstanding that the feed pump has been started, it is evident that the pump is not working.

This may occur from a stuck valve, a leak in the suction pipe, from the feed water being too hot, or from the pump failing to start in action from leaky or choked valves.

A stuck valve may generally be relieved by striking a few blows on the outside of the pump with a hammer and a block of wood, or if this does not answer, with the hammer only. Check valves are the ones most likely to stick.

If a pump fails to work by reason of the feed water being too hot, the remedy is to open the pet c.o.c.k to let the steam out of the pump, but if this does not succeed, cold water may be poured on the outside of the pump, which will start it, after which, in most cases, the pump will keep going and the pet c.o.c.k may be closed.

If the suction pipe has a joint, a leak there will impair the action of the pump, and, if the leak is great enough, will stop it; the remedy is to make the joint tight.

Plunger pumps sometimes fail to act because the plunger has worn so small in diameter that there is sufficient air between the plunger and the pump barrel to expand and compress without lifting the valve; the remedy is obviously a new plunger of as large diameter as the pump gland will admit of, boring the gland out to admit the new plunger.

All the impurities in the water are left in the boiler when the water has evaporated, and it is obvious these impurities must be blown off or they will form scale on the internal surface of the boiler and the external surface of the tubes or flues.

This scale obstructs the pa.s.sage of the heat from the iron to the water, and if let get thick enough will cause the iron to rapidly burn out.

To prevent the formation of scale, two princ.i.p.al methods are employed, one being to purify the feed water, and the other to occasionally blow the impurities out of the boiler.

Feed-water heaters generally serve also as purifiers, and their effectiveness is increased in proportion as the water can pa.s.s quietly through them, and has a large area on which the impurities can settle.

Horizontal heaters have the advantage that they have a large settling area, and a less distance for the impurities to fall through. The water-gauge gla.s.s and the lower gauge c.o.c.k are usually set so as to have a margin of about three inches of water above the tubes or crown sheet of the fire box, hence if it is known that the water is but just below the bottom of the gauge gla.s.s or gauge c.o.c.k, there is no positive danger, although it is improper to let it get so low.

If the water is out of sight, and it is not known exactly how low it is, then it is dangerously low, and every minute is of vital importance.

Should the water get dangerously low in the boiler, the most dangerous thing to do is to lift the safety valve or pump in cold water, especially if it is not known how much water there is in the boiler.

As quickly as possible cover the fire with ashes, coal, earth, sand, or anything that is at hand that will smother the fire, then close the draught to the fire, leaving the fire door and the chimney damper open.

Leave all the steam outlets just as they are, and also the feed.

PRIMING.--Priming, which is also called "foaming," is that the steam carries up water into the steam s.p.a.ce. This may arise from several causes, but it is well known that what will stop priming in some cases will cause it in others.

The known causes of priming are--first, too little room for the steam in the boiler, and it follows that a high water level may cause priming; second, it may be caused by a difference of temperature between the water and the steam in the boiler. Suppose, for example, that the pressure of the steam and water in the boiler is 160 lbs. by gauge, and its sensible temperature will be 370 degrees. Suppose then that enough steam is permitted to escape from the boiler to reduce the steam pressure to 140 lbs., and its temperature will be reduced to 361 degrees. But the water will remain at 270 degrees, and the result will be that it will pa.s.s into steam so rapidly that it will carry up the water and hold it in suspension among the steam. The water will pa.s.s with the steam into the engine cylinder, and the boiler will be said to "prime," "foam," or "work water." The same thing may happen if the water is heated very rapidly.

Priming is wasteful because it rapidly empties the boiler of its water, and dangerous because it may cause the piston to knock out the cylinder head or cover.

When the safety valve blows off, priming may be induced, especially if the engine is at work, because in this case the boiler is being forced, or, in other words, is making steam more rapidly than it is designed to do, and the pa.s.sage of so large a body of steam through the water is apt to lift it.

Muddy water will sometimes cause foaming or priming, as will also insufficient circulation of the water in the boiler or sometimes the presence of grease or oil.

Priming may be detected from the discharge of water with the steam when the gauge c.o.c.k is opened, the steam looking white and fluttering as it escapes, and also by violent motion of the water in the gauge gla.s.s, or by a thump or pound at the ends of the piston stroke.

To stop priming, the steam from the boiler should be decreased by slackening the speed of the engine, or if necessary, by stopping it. The true water level can then be seen, and if there is too much water in the boiler some of it may be blown off, while if the quant.i.ty of water in the boiler will permit it, the feed may be put on.

If the boiler has a surface blow-off c.o.c.k, or a mechanical boiler cleaner, it is best to blow off from that, as it carries off the sc.u.m at the same time as relieving the boiler.

To prevent priming, a steady and uniform rate of boiler feed, the use of pure water, a clean boiler, and steady firing are the best means, turning on the steam slowly so as not to violently disturb the water in the boiler.

The engine as well as the boiler requires attention when the boiler primes. Thus the cylinder c.o.c.ks should be opened to let out the water from the cylinder and prevent breakage of the cylinder cover.

SCALE IN BOILERS.--The steam leaves behind it all the impurities that the water contained, and these impurities deposit in form of mud and scale, which must be got rid of because it causes a loss of fuel, and if allowed to get thick enough will cause the boiler to burn.

The use of boiler compounds or scale preventatives may be resorted to with advantage, providing they are of a nature to suit the water, but mechanical cleaning must also be resorted to at periods determined by the nature of water.

Boilers are cleaned in two ways--first, by blowing off the impurities before they have formed into scale; and second, by removing at certain intervals whatever scale has formed.

Blowing down may be done in two ways--first, from the surface of the water by means of mechanical cleaners; and second, by blowing out from the bottom of the boiler.

The first draws off the impurities as they are thrown to the surface, the second draws them off after they have become more condensed and sink to the bottom.

How often a boiler should be blown down depends upon the kind of water fed to the boiler; where purifiers are used, less blowing down is obviously needed.

It is best to blow off from the bottom of the boiler when no steam is being used, as during dinner time, letting the water blow down about a quarter of the gla.s.s, or from the upper to the middle gauge c.o.c.k.

As no steam is being used, the feed can then be put on to restore the quant.i.ty of water without reducing the temperature of the boiler so much. The feed should be gradual and the fire regulated to keep the steam pressure even.

How often a boiler should be washed out and cleaned depends upon the quality of the water it uses, and varies from about once a week to once a month, according to whether bad and unpurified water or purified water is used.

The first thing to do is to draw the fire, leaving the chimney damper open and closing all the other dampers so that as little cold air as possible can get into the boiler, while the heat can pa.s.s away up the chimney.

Let the steam and water all remain in the boiler until there is a gauge pressure of about 5 lbs. in the boiler.

Then open the blow-off c.o.c.k and let out the water. If the water is blown off under a high pressure, then after the waste is all out the iron is hot enough to dry up the scale, making it hard and very difficult to remove.

After all the water is blown off, take out all the mud plugs and the man-hole and hand-hole covers, and wash out the boiler under as much water pressure as can be had, directing the hose so to reach all parts of the boiler and tubes, and continuing the washing until the water leaves the boiler clean.

Then with a wooden hoe on a piece of gas-pipe of small diameter for a handle, and small enough to pa.s.s through the hand-hole, draw all the loose scale to the hand-hole and remove it, letting the water run slowly, so as to carry the small pieces of scale towards the hand-hole as fast as the hoe disturbs it.

Then get inside the boiler, and a few blows with a light ball-pened hammer will loosen the scale, and a steel sc.r.a.per will remove more, which must be washed down and drawn out with a hoe.

After the cleaning and scaling are complete, the engineer, with lamp in hand, should carefully examine the interior of the boiler and of the fire box, paying especial attention to the stays to see that they are not broken.

The hammer test should also be applied. It consists of sounding the boiler by light blows given by a light ball-pened hand hammer, the sound indicating defective places.

CHAPTER x.x.xVII.--THE STEAM ENGINE.