Notes, Rules and Tables.

One H. P. is 33,000 pounds raised one foot high in one minute, or 33,000 foot pounds per minute.

A heat unit or H. U. or British thermal unit or B. T. U. is the heat required to raise one pound of water at 39.1° one degree.

According to Joule's experiments I heat unit was equal to 772 foot pounds, but further experiments have demonstrated that one heat unit is equal to 778 foot pounds, 33,000 foot pounds per minute divided by 778 = 42.62 heat units per H. P. per minute, or 42.62 X 60 = 2557.20 heat units per hour.

A pound of carbon contains 14,500 H. U. A pound of coal having 10% of ash will have remaining 13,050 H. U.

A good boiler with a good fireman should get 75% of this into steam, which allows 8% for radiation and losses from air leaks, etc., and 17% loss of heat in gases going up the chimney, which leaves 9787.5 H. U. in steam per pound coal. Of this, 2257.20 is converted into. work, the remainder, or 7230.30, going out in the exhaust.

This is providing that I pound coal produces 1 H. P. If it requires 2 pounds, then the total H. U. will be

Keep the Boiler Clean.

9787.5 X 2 = 19575 out in the exhaust.

=

2557.2 17017.8 H. U. going

=

As the H. U. in 1 pound coal with 10% of ash is 13050, this number divided by 2557.20 5.1 H. P. that would be obtained with one pound coal, if all the heat could be converted into work, or if the heat put into steam, 9787.5 H. U. could be converted into work, it would make

The efficiency of the boiler will depend upon the ease with which it can be kept clean, the tightness of its setting in preventing air leaks, the thinness of the heating surface, the draft and the circulation.

The latter point is very important. The greater the difference in temperature between the water within. the boiler and the fire the more rapid the absorption of heat. The more rapid the water flows over the heating surface bringing fresh water into contact, the greater will be this difference, and the more rapid the movement of the water the easier will be the disengagement of the steam.

Wrought iron expands I-150000 of an inch per inch. for each degree.

A pipe 300 feet long and 150 lbs. pressure would expand as follows: 300 ft. is 3600 inches. Temperature of room 80°. Temperature of steam at 150 lbs. pressure 366° less the 80° 286° difference in temperature of

3600 X 286

pipe.

I 50000

=

6.86 inches the pipe would expand.

Standards of Pressure.

All pressures are measured or standardized by the weight of mercury.

The atmosphere sustains mercury 30" high.

One cubic inch of mercury weighs .49 of a pound. 30 X .49 = 14.7.

Weight of water.

A pressure of one pound is exerted per square inch by a column of water 2.3093' high, and one atmosphere, or 14.7 pounds, by a column 33.947′ high.

The pressure multiplied by 2.3093 will give the height of a column of water due to that pressure.

A column ' high has a pressure of .433 pounds. Height, multiplied by .433 equals the pressure.

The efficiency of an engine depends upon the small amount of heat required to do a certain amount of work. The engine that has the lowest terminal pressure in proportion to the mean effective pressure will require the least heat, or, put in another way, the lowest amount of heat will go out in the exhaust.

An engine that requires a large amount of compression to secure quiet running will have a rounded cutoff corner on the diagram, and this, together with the compression, will make the terminal pressure higher.

An engine having a slow piston speed will condense a large amount of steam when it enters the cylinder, and this will be re-evaporated towards the end, bringing the terminal pressure high.

Too slow piston speed will give too much time for a cylinder to cool off and cause cylinder condensation, with consequent re-evaporation.

Should we wish to get a high piston speed we have the problem of rotation speed to contend with.

To get a piston speed of 800' per minute we can

About Clearance.

build an engine with 6' stroke and 66 revolutions. This number of revolutions will require no more compression than is necessary to lap the exhaust valves to have them seated properly when the steam valves open, the indicator card will show nearly square corners all around, which will be the theoretic and practical card for economy.

Should we conclude that this stroke is too long, we can divide it by 4, making it 18" stroke and a rotative speed of 266 revolutions. The piston speed is the same, but the compression required will increase as the square of the number of the revolutions, the card from the engine will have round corners and the terminal pressure will be higher.

Clearance plays an important part.

Clearance is that portion that exists between the piston and cylinder head, between the valves and cylinder in the steam parts and in any depressions in the piston or heads.

The clearance spaces are filled with steam at each stroke and are emptied, doing only the work that the steam in them expands, and are finally emptied, the unexpanded portion doing no work. The effect is to increase the terminal pressure.

The clearance spaces are filled and emptied at each stroke.

The shorter the stroke, the greater the percentage of clearance.

The nearer the valve is to the cylinder, and the shorter and smaller the port, provided it is of ample area for the passage of the steam, the less will be the clearance, which is the reason for the four-valve engine.

The quicker the cut-off valve closes, the sharper will be the cut-off and the lower will be the terminal

pressure.

Compression-Lap-Lead.

The terminal pressure will be the lowest in proportion to the mean effective pressure when the engine is cutting off at about 4 stroke, so that an engine loaded. to that amount will be at its most economical load.

Compression is the vapor enclosed within the cylinder by the closing of the exhaust valve before the crank reaches the center.

Its object is to absorb the inertia of the moving parts gradually and allow them to come to a state of rest without jar.

Lap of a valve is the amount that the valve travels beyond the port more than is necessary to cover the same. Its office is to cover the port, or space beyond, sufficiently to insure tightness, and in a steam valve to provide for cutting off the steam.

In an exhaust valve, to give compression.

Lead is the amount the valve opens before the crank reaches the center.

Pre-release is sometimes applied to the exhaust valve and is the same thing as lead on the steam valve.

An eccentric is a wheel placed off the center, and is used to be placed on a shaft to give motion to the valves of an engine.

The distance it will move a rod or valve is the extreme movement between the distance of its circumference on both sides of the shaft, and is termed the throw of the eccentric.

The travel of the valve is the total distance the valve moves.

If the eccentric rod be attached direct to valve the throw of eccentric and travel of valve will be the same. The travel of the valve should be the width of the