Modern Machine-Shop Practice Part 229

The first thing to do in taking charge of a stationary engine boiler is to know from personal inspection that the safety fittings and the boiler-feeding apparatus are in good order.

The safety valve is the first thing to inspect, as it is liable to stick in its seat, especially in cases in which it is set at a greater pressure than is got up in the boiler, because in that case it is not lifted from the seat and in time sticks fast there.

In such cases it is proper to lift the valve at least once a day while steam is on. For this purpose a cord may be attached to the lever, pa.s.sing over a pulley directly above the lever, and thence to some convenient place near the boiler, but where it is not liable to get caught and pulled accidentally.

Before lighting the fire, see that there is sufficient water in the boiler. If there is a gauge gla.s.s on the boiler, it should show three-quarters full, or three-quarters of a gla.s.s, as it is called.

The gauge gla.s.s may show a false water level, and to be sure that such is not the case, open the top gauge c.o.c.k and the c.o.c.k at the bottom of the gauge gla.s.s, letting the water run through the gauge gla.s.s. Open and close the c.o.c.k below the gauge gla.s.s two or three times to see that the water comes to the same level each time.

If the steam pressure has been allowed to fall in the boiler without any of the c.o.c.ks being opened, there will be a partial vacuum in the boiler, and air must be let in before the true water level will be shown either by the gauge gla.s.s or by the gauge c.o.c.ks.

Opening the upper gauge c.o.c.k will let in the air, and it should not be closed again until enough steam has been got up in the boiler to expel the air again, or in other words, until steam begins to issue from it.

The grate bars and ash pit should be cleaned of clinker, ashes, etc., and it should be seen that the tubes are clear of ashes, etc., before the fire is laid; if the grate is a shaking one, the lever should be applied to see that the grate will shake properly.

TO LIGHT THE FIRE--In the case of anthracite or hard coal, as it is sometimes termed, first cover the bars with a thin layer of coal and then put in pieces of lighted greasy waste (if it is at hand) distributed about the furnace, taking especial care to light the fire at the fire-door end and in the corners, because the fire will spread from the front end towards the back easier than it will from the back end towards the front.

The fire should light from the bottom and not from the top, hence the thinnest pieces of the wood should be put in first.

If there is any soft coal at hand, a small quant.i.ty of it will accelerate lighting the fire, as it burns easier and quicker than hard coal.

Before putting on the coal the wood should be well lighted, the bottom portion of it having ceased flaming.

This causes the lighted wood to spread over the bars and the fire to light evenly.

Charge the coal lightly, first covering the places that have burned up the most.

FIRING.--The fire door should be kept open as little as possible, as it admits cold air that is detrimental to the combustion, as well as to the draught, hence firing should be done quickly.

A good fireman will maintain as even a temperature as possible in the fire box by charging the coal lightly and quickly.

Some firemen will, after the fire is at its proper depth all over the grates, charge the fire in the front end, that is, at the fire-door end, and push it back as it burns up, to keep up the thickness of the fire at the back.

The thickness of the fire depends upon the size and kind of coal.

With small coal a fire from 4 to 6 inches deep will answer, while, if the lumps are five or six inches in diameter, a fire from a foot to 15 inches deep may be maintained, as is done in some locomotives.

The object is to have the fire thick enough to prevent it from burning through in spots or letting cold draughts of air pa.s.s through it.

The sides of the furnace require particular attention, not only because cold air is more likely to get through there, but also in boilers having fire boxes the cool sides of the box keep the temperature of the fuel down, hence a thicker fire is necessary around the sides than in the middle of the furnace or fire box.

Three things are to be considered in cleaning a fire--first, that the boiler pressure will fall during, and for a short time after, the cleaning; second, that the depth of fire will be diminished by the cleaning; and third, that the temperature of the fire will fall during the cleaning.

SHAKING GRATE BARS.

When a furnace has shaking grate bars, the cleaning of the fire is greatly facilitated, and with bars that shake singly (and good coal) the fire is often not disturbed during the day, except to shake the bars occasionally, pa.s.sing the poker through it and using the hoe to keep it evenly spread.

If the grate shakes in sections, more cleaning will be required to break up the clinker, while, if the bars do not shake, the cleaning a.s.sumes greater importance.

Before cleaning, therefore, see that there is sufficient water in the boiler, that it need not be fed while cleaning, nor just after cleaning the fire.

Prepare for cleaning by having a thick fire on the grate, so that after cleaning it will burn up quickly, and let the cleaning be done as quickly as possible.

[Ill.u.s.tration: Fig. 3288.]

The tools used for cleaning the fire are the slice bar, Fig. 3288, which is pushed along the top of the fire bars to loosen up the fire, and let the ashes fall through the bars.

[Ill.u.s.tration: Fig. 3289.]

[Ill.u.s.tration: Fig. 3290.]

The hoe, Fig. 3289, which is used to push the fire to the back of the furnace and to pull it forward. The poker, Fig. 3290, which dislodges any clinker that may be between the bars, and lets the ashes fall through.

[Ill.u.s.tration: Fig. 3291.]

[Ill.u.s.tration: Fig. 3292.]

The clinker hook or devil's claw, Fig. 3291, which is used to haul clinker out of the fire, and the rake, Fig. 3292, which is used to spread the fire evenly over the bars after it is cleaned.

In cleaning a fire, first use the slice bar to loosen up the fire and let the ashes fall through, and also dislodge clinkers from the surface of the bars. Then push the fire to the back of the furnace. Next use the poker to clean out clinker from between the exposed part of the bars.

Then with the hoe pull a part of the fire forward and pull out the clinker that may be in this part, doing so with the hoe as far as possible, as that will save time, but if it should be necessary, use the clinker hook.

Then pull forward a second portion of the fire, and spread it on the bars, removing the clinker as before. When all the fire has thus been cleaned, use the rake to spread it evenly over the bars, and put on a light charge of coal, covering the brightest parts of the fire first, and taking care that no part of the fire bars is left uncovered.

The cleaning should be done quickly.

DRAUGHT.--The draught should be decreased while the fire is being cleaned, but the damper should never be entirely closed, as this might cause an explosion in the fire box and tubes.

During a temporary interruption, as in the case of the engine stopping, partly close all the dampers, as it is wasteful to make steam and blow it off through the safety valve.

COMBUSTION.--A blue flame is evidence of incomplete combustion, but there may be a blue flame and imperfect combustion at the back end of the furnace, and a white flame and perfect combustion at the other end.

This is likely to occur with heavy firing near the fire door, and a thin fire at the tube sheet end of the fire box. In this case the unconsumed gases produced near the fire door (as evidenced by the blue flame) are consumed in pa.s.sing over the bright fire at the tube plate end of the furnace.

AT NIGHT.--Always leave plenty of water in the boiler when leaving it for the night, not only to allow for any leak, but also because it gives a fair start in the morning and more time to remedy any defect in the feed pump if it arise.

By plenty of water, very nearly a full gauge is meant, or if there is no gauge gla.s.s to the boiler, let the water stand above the second or middle c.o.c.k.

The usual method of leaving the fire for the night is to bank it. There is an element of danger, however, in banking a fire, unless it is done to suit the circ.u.mstances, because steam may generate very rapidly, and perhaps more rapidly than the safety valve can carry it off.

A safe method is to clean the fire, leaving the clinker and ashes covering the front half of the grate and the fire piled up on the back half.

The damper and ash pit door should be closed tight, the fire door open, and the fire well covered with fresh coal, choosing small rather than large coal.

If this method is found not to keep up the fire sufficiently, the same plan may be employed, except that the ashes and clinker may be removed, and if this still leaves too cold a boiler, and too poor a fire in the morning, the fire may be left spread over the grate, but heavily covered with fresh coal, the draught being stopped as much as possible by closing the dampers and opening the furnace door.

To further insure safety, the weight on the safety valve lever should be pushed towards the valve, so as to cause the safety valve to blow off at a less pressure than during the day.