Part 3 (1/2)

The header is used by placing the gauge or guide end within the flue, and with your light hammer the flue can be calked or beaded down against the flue sheet. Be careful to use your hammer lightly, so as not to bruise the flues or sheet. When you have gone over all the expanded flues in this way, you, (if you have been careful) will not only have a good job, but will conclude that you are somewhat of an expert at it. I never saw a man go into a firebox and stop the leak but that he came out well pleased with himself. The fact that a firebox is no pleasant workshop may have had something to do with it. If your flues have been leaking badly, and you have expanded them, it would be well to test your boiler with cold water pressure to make sure that you have a good job.

How are you going to test your boiler? If you can attach to a hydrant, do so, and when you have given your boiler all the pressure you want, you can then examine your flues carefully, and should you find any seeping of water, you can use your beader lightly untill such leaks are stopped. If the waterworks will not afford you sufficient pressure, you can bring it up to the required pressure, by attaching a hydraulic pump or a good force pump.

In testing for the purpose of ascertaining if you have a good job on your flues, it is not necessary to put on any greater cold water pressure than you are in the habit of carrying. For instance, if your safety valve is set at one hundred and ten pounds, this pressure of cold water will be sufficient to test the flues.

Now, suppose you are out in the field and want to test your flues. Of course you have no hydrant to attach to, and you happen not to have a force pump, it would seem you were in bad shape to test your boiler with cold water. Well, you can do it by proceeding in this way: When you have expanded and beaded all the flues that were leaking, you will then close the throttle tight, take off the safety valve (as this is generally attached at the highest point) and fill the boiler full, as it is absolutely necessary that all the s.p.a.ce in the boiler should be filled with cold water. Then screw the safety valve back in its place.

You will then get back in the firebox with your tools and have someone place a small sheaf of wheat or oat straw under the firebox or under waist of boiler if open firebox, and set fire to it. The expansive force of the water caused by the heat from the burning straw will produce pressure desired. You should know, however, that your safety is in perfect order. When the water begins to escape at the safety valve, you can readily see if you have expanded your flues sufficiently to keep them from leaking.

This makes a very nice and steady pressure, and although the pressure is caused by heat, it is a cold water pressure, as the water is not heated beyond one or two degrees. This mode of testing, however, cannot be applied in very cold weather, as water has no expansive force five degrees above or five degrees below the freezing point.

These tests, however, are only for the purpose of trying your flues and are not intended to ascertain the efficiency or strength of your boiler.

When this is required, I would advise you to get an expert to do it, as the best test for this is the hammer test, and only an expert should attempt it.

PART SIX __

Any young engineer who will make use of what he has read will never get his engine into much trouble. Manufacturers of farm engines to-day make a specialty of this cla.s.s of goods, as they endeavor to build them as simple and of as few parts as possible. They do this well knowing that, as a rule, they must be run by men who cannot take a course in practical engineering. If each one of the many thousands of engines that are turned out every year had to have a practical engineer to run it, it would be better to be an engineer than to own the engine; and manufacturers knowing this, they therefore make their engines as simple and with as little liability to get out of order as possible. The simplest form of an engine, however, requires of the operator a certain amount of brains and a willingness to do that which he knows should be done; and if you will follow the instructions you have already received, you can run your engine as successfully as any one can wish as long as your engine is in order, and, as I have just stated, it is not liable to get out of order, except from constant wear, and this wear will appear in the boxes, journals and valve. The bra.s.ses on wrist pin and cross-head will probably require your first and most careful attention, and of these two the wrist or crank box will require the most; and what is true of one is true of both boxes. It is, therefore, not necessary to take up both boxes in instructing you how to handle them. We will take up the box most likely to require your attention. This is the wrist box. You will find this box in two parts or halves. In a new engine you will find that these two halves do not meet on the wrist pin by at least one-eighth of an inch. They are brought up to the pin by means of a wedge-shaped key. (I am speaking now of the most common form of wrist boxes. If your engine should not have this key, it will have something which serves the same purpose.) As the bra.s.ses wear you can take up this wear by forcing the key down, which brings the two halves nearer together. You can continue to gradually take up this wear until you have brought them together. You will then see that it is necessary to do something, in order to take up any more wear, and this ”something”

is to take out the bra.s.ses and file about one-sixteenth of an inch off of each bra.s.s. This will allow you another eighth of an inch to take up in wear.

Now here is a nice little problem for you to solve and I want you to solve it to your own satisfaction, and when you do, you will thoroughly understand it, and to understand it is to never allow it to get you into trouble. We started out by saying that in a new engine you would most likely find about one-eighth of an inch between the bra.s.ses, and we said you would finally get these bra.s.ses, or halves together, and would have to take them out and file them. Now we have taken up one-eighth of an inch and the result is, we have lengthened our pitman just one-sixteenth of an inch; or in other words, the center of wrist pin and the center of cross-head are just one-sixteenth of an inch further apart than they were before any wear had taken place, and the piston head has one-sixteenth of an inch more clearance at one end, and one-sixteenth of an inch less at the other end than it had before. Now if we take out the boxes and file them so we have, another eighth of an inch, by the time we have taken up this wear, we will then have this distance doubled, and we will soon have the piston head striking the end of the cylinder, and besides, the engine will not run as smooth as it did. Half of the wear comes off of each half, and the half next to the key is brought up to the wrist pin because of the tapering key, while the outside half remains in one place. You must therefore place back of this half a thin piece of sheet copper, or a piece of tin will do. Now suppose our boxes had one-eighth of an inch for wear. When we have taken up this much we must put in one-sixteenth of an inch backing (as it is called), for we have reduced the outside half by just that amount. We have also reduced the front half the same, but as we have said, the tapering key brings this half up to its place.

Now we think we have made this clear enough and we will leave this and go back to the key again. You must remember that we stated that the key was tapering or a wedged shape, and as a wedge, is equally as powerful as a screw, and you must bear in mind that a slight tap will bring these two boxes up tight against the wrist pin. Young engineers experience more trouble with this box than with any other part of the engine, and all because they do not know how to manage it. You should be very careful not to get your box too tight, and don't imagine that every time there is a little knock about your engine that you can stop it by driving the key down a little more. This is a great mistake that many, and even old engineers make. I at one time seen a wrist pin and boxes ruined by the engineer trying to stop a knock that came from a loose fly-wheel. It is a fact, and one that has never been satisfactorily explained, that a knock coming from almost any part of an engine will appear to be in the wrist. So bear this in mind and don't allow yourself to be deceived in this way, and never try to stop a knock until you have first located the trouble beyond a doubt.

When it becomes necessary to key up your bra.s.ses, you will find it a good safe way to loosen up the set screw which holds the key, then drive it down till you are satisfied you have it tight. Then drive it back again and then with your fist drive the key down as far as you can. You may consider this a peculiar kind of a hammer, but your boxes will rarely ever heat after being keyed in this manner.

KNOCK IN ENGINES

What makes an engine knock or pound? A loose pillow block box is a good ”knocker.” The pillow block is a box next crank or disc wheel. This box is usually fitted with set bolts and jam nuts. You must also be careful not to set this up too tight, remembering always that a box when too tight begins to heat and this expands the journal, causing greater friction. A slight turn of a set bolt one way or the other may be sufficient to cool a box that may be running hot, or to heat one that may be running cool. A hot box from neglect of oiling can be cooled by supplying oil, provided it has not already commenced to cut. If it shows any sign of cutting, the only safe way is to remove the box and clean it thoroughly.

Loose eccentric yokes will make a knock in an engine, and it may appear to be in the wrist. You will find packing between the two halves of the yoke. Take out a thin sheet of this packing, but don't take out too much, as you are liable then to get them too tight and they may stick and cause your eccentrics to slip. We will have more to say about the slipping of the eccentrics.

The piston rod loose in cross-head will make a knock, which also appears in the wrist, but it is not there. Tighten the piston and you will stop it. The piston rod may be keyed in cross head, or it may be held in place by a nut. The key is less liable to get loose, but should it work loose a few times it may be necessary to replace it with a new one. And this is one of the things that cause a bad break when it works out or gets loose. If it gets loose it may not come out, but it will not stand the strain very long in this condition, and will break, allowing the piston to come out of cross head, and you are certain to knock out one cylinder head and possibly both of them. The nut will do the same thing if allowed to come off. So this is one of the connections that will claim your attention once in a while, but if you train your ear to detect any unusual noise you will discover it as soon as it gives the least in either key or nut.

The cross-head loose in the guides will make it knock. If the cross-head is not provided for taking up this wear, you can take off the guides and file them enough to allow them to come up to the cross-head, but it is much better to have them planed off, which insures the guides coming up square against the cross-head and thus prevent any heating or cutting.

A loose fly-wheel will most likely puzzle you more than anything else to find the knock. So remember this. The wheel may apparently be tight, but should the key be the least bit narrow for the groove in shaft, it will make your engine b.u.mp very similar to that caused by too much or too little ”lead.”

LEAD

What is lead? Lead is s.p.a.ce or opening of port on steam end of cylinder, when engine is on dead center. (Dead center is the two points of disc or crank wheel at which the crank pin is in direct line with piston and at which no amount of steam will start the engine.) Different makes of engines differ to such an extent that it is impossible to give any rule or any definite amount of lead for an engine. For instance, an engine with a port six inches long and one-half inch wide would require much less lead than one with a port four inches long and one inch wide.

Suppose I should say one-sixteenth of an inch was the proper lead. In one engine you would have an opening one-sixteenth of an inch wide and six inches long and in the other you would have one-sixteenth of an inch wide and four inches long; so you can readily see that it is impossible to give the amount of lead for an engine without knowing the piston area, length of port, speed, etc. Lead allows live steam to enter the cylinder just ahead of the piston at the point of finis.h.i.+ng the stroke, and forms a ”cus.h.i.+on,” and enables the engine to pa.s.s the center without a jar. Too much lead is a source of weakness to an engine, as it allows the steam to enter the cylinder too soon and forms a back pressure and tends to prevent the engine from pa.s.sing the center. It will, therefore, make your engine b.u.mp, and make it very difficult to hold the packing in stuffing box.

Insufficient lead will not allow enough steam to enter the cylinder ahead of piston to afford cus.h.i.+on enough to stop the inertia, and the result will be that your engine will pound on the wrist pin. You most likely have concluded by this time that ”lead” is no small factor in the smooth running of an engine, and you, as a matter of course, will want to know how you are to obtain the proper lead. Well don't worry yourself. Your engine is not going to have too much lead today and not enough tomorrow. If your engine was properly set up in the first place the lead will be all right, and continue to afford the proper lead as long as the valve has not been disturbed from its original position; and this brings us to the most important duty of an engineer as far as the engine is concerned, viz: Setting the Valve.

SETTING A VALVE.

The proper and accurate setting of a valve on a steam engine is one of the most important duties that you will have to perform, as it requires a nicety of calculation and a mechanical accuracy. And when we remember also, that this is another one of the things for which no uniform rule can be adopted, owing to the many circ.u.mstances which go to make an engine so different under different conditions, we find it very difficult to give you the light on this part of your duty which we would wish to. We, however, hope to make it so clear to you that by the aid of the engine before you, you can readily understand the conditions and principles which control the valve in the particular engine which you may have under your management.

The power and economy of an engine depends largely on the accurate operation of its valve. It is, therefore, necessary that you know how to reset it, should it become necessary to do so.