Zwicker's Revised Practical Instructor
The steam engine indicator is an instrument for showing the pressure of steam in the cylinder at all points of the stroke, or for producing actual diagrams. The indicator consists of a small cylinder accurately bored out, and fitted with a piston, capable of working in the (indicator) cylinder with little or no friction, and yet be practically steam-tight. The piston has an area of just of a square inch, and its motion in the cylinder is 25/32 of an inch.
The piston-rod is connected to a pair of light levers, so linked together that a pencil carried at the center of the link moves in nearly a straight line through a maximum distance of 31/8 inches. A spiral spring placed in the cylinder above the piston, and of a strength proportioned to the steam pressure, resists the motion of the piston; and the elasticity of this spring is such that each pound of pressure on the piston causes the pencil to move a certain fractional part of an inch. The pencil in this case is made of a piece of pointed brass wire, which retains its sharpness for a considerable time, and yet makes a well-defined line upon the prepared paper generally used with the indicator.
The paper is wound around the drum, which has a diameter of 2 inches, and is capable of a semi-rotary motion upon its axis to such an extent that the extreme length of diagram may be 5 inches. Motion is given to the drum in one direction, during the forward stroke of the engine, by means of a cord connected indirectly to the cross-head of the engine, and the drum is brought back again during the return stroke of the engine by the action of a coiled spring at its base.
The conical stem of the instrument permits it to be turned around and fixed in any desired position, and the guide-pulleys attached to the instrument under the paper drum may also be moved around so as to bring the cord upon the drum-pulley from any convenient direction.
The upper side of the piston is open to the atmosphere; the lower side may, by means of a stop-cock, be put into communication either with the atmosphere or with the engine cylinder.
When both sides of the piston are pressed upon by the atmosphere, the pencil, on being brought into contact with the moving paper, describes the atmospheric line. When the lower side of the piston is in communication with the engine cylinder, the position of the pencil is determined by the pressure of the steam existing in the cylinder; and on the pencil being pressed against the paper during a complete double stroke of the engine, the entire indicator diagram is described.
In order that the diagram shall be correct, the motion of the drum and paper shall coincide exactly with that of the engine piston; second, that the position of the pencil shall precisely indicate the pressure of steam in the cylinder; third, that the pendulum must be from 1 to 3 times as long as the stroke of the engine piston; fourth, that the pendulum must be plumb when the piston is at half-stroke; fifth, that the cord around the drum must be attached to the pendulum at right angles, or square with the indicator; sixth, the pendulum must be attached with an inch wooden pin to the ceiling or floor at one end, the other end to the cross-head by means of a screw bolt in the wrist-pin and a slot in the pendulum; seventh, that the two holes tapped in the cylinder are directly opposite the steam ports, and centrally between the piston-head and cylinder head, when the engine is at the dead center, or, in other words, in the center of clearance; eighth, that the piping should be as short as possible, and inch pipe if not over one foot long. If longer the pipe should be larger close to the cylinder, and covered so as not to allow too much condensation, as it affects the diagram. The best way to take a diagram is to tap a hole in each cylinder-head and take each end separately. The cord must be attached to the pendulum, so the paper drum will move in proportion to the piston.
An indicator shows the highest and the lowest pressure reached, also the cut-off and lead. If there is a great difference, say more than five pounds, between the boiler pressure and the initial pressure upon the piston, the connecting pipes may be taken as being too small, too abrupt, or the steam ports too contracted. The full pressure of steam should come upon the piston at the very beginning of its stroke. Should the admission corner be rounded, the valve is wanting in 'lead,' or, in other words, the port for the admission of steam is uncovered too late in the stroke.
The steam line should be parallel or straight with the atmospheric line up to the point of cut-off, or nearly so. Should it (the steam line) fall as the piston advances, the opening for the admission of steam is insufficient, and the steam is 'wire-drawn.'
The point of cut-off should be sharp and well defined; should it be otherwise, the valve does not close quick enough. The bevel line leading from the cut-off line to the end of the stroke is called the expansion line.
Q. Which is the standard indicator?
A. The Tabor's improved.
Q. Are there any other makes?
A. Yes; Richard's, McNought's, Thompson's and others.
Rule for telling the power of a diagram: Set down the length of the spaces formed by the vertical lines from the base in measurements of a scale accompanying the indicator, and on which a tenth of an inch usually represents a pound of pressure; add up the total length of all the spaces, which will give the main length, or the main pressure upon the piston in pounds per square inch; to do this, lay a card taken by the indicator off in ten parts, by drawing lines from top to bottom. Find out what the scale is; suppose it is 60, the number of ordinates 10, and that the sum of their length is 6 inches; so 6 and 10 ordinates = 6/10 or 6 x 60 = 36.0. Answer, 36 pounds pressure upon the piston.
Rule for finding and deducting friction: Multiply N. H. P. by . 13 and subtract the answer from N. H. P., which gives I. H. P.
Q. What is N. H. P.?
A. It is nominal horse power.
Q. What is I. H. P.?
A. It is indicated horse power.
Q. What is meant by cutting off steam at 6 inches?
A. It means that the valve closes and cuts off the live steam from the boiler at 6 inches of the piston's travel; then the engine gets its power, from the time the valve closes or cuts off until the exhaust opens, by the expansion of the steam closed up in the cylinder.
Standard multipliers, with examples:
1.For the Area of a Circle, Multiply sq. of diam. by
2.For Circumference of a Circle, Multiply diameter by 3.1416.
3.For Diameter of a Circle, Multiply circum. by .31831.
4.For the surface of a Ball, Multiply Sq. of Diam. by 3.1416.
5.For the Cubic Inches in a Ball, Multiply Cube of diam. by .5236.
1. RULE for finding the area of any circle, Always multiply the diameter by itself, then by .7854, then cut off 4 decimals to the right.
2. RULE for finding the circumference of anything round. Multiply the diameter by 3.1416, and cut off 4 decimals.
3. RULE to find diameter of circle. Multiply circumference by
EXAMPLE: The circumference 9.4248 x .31831- 3.000008088= 3 inches diameter.
4.RULE to find the surface of a sphere, globe or ball. EXAMPLE: 9 inches diameter x 9-81 x 3.1416-254.4696.
5.RULE to find the cubic inches in a ball. Multiply cube of the
diameter by .5236; the answer equals its solid contents.
EXAMPLE: Ball 3 inches in diameter; 3 X 3=9, 9 X 3=27 X .5236=14 1372/10000 solid contents.
Rule to find pressure on the crown sheet of a hanging fire-box boiler. Multiply the width by the length in inches, then multiply by steam gauge pressure and divide by 2.
Crown sheet 46 x 33 in. 46 Pressure 85 1b. 33 Iron in. 1518 85 If iron is in. div. by 4. 2)129030 If iron is 5/8 in. div. by 2.66 2000)64515 lbs. press'e. 32.257 tons '
Rule to find how much water a boiler will contain. For 2-flue boiler, 2/3 full of water, find 2/3 of the area of the boiler in inches inside; multiply by length in inches; then find area of flues, thickness of iron added; then multiply by 2, if two flues; multiply by length in inches, subtract area of flues from 2/3 contents, and divide by 231 (number of cubic inches in a standard gallon); the answer will be the number of U. S. gallons.
Boiler 48 inches. 48 Two flues, 16 in. each. 48 Length 20 feet, 2304 16 .7854 16 3)1809.5616 area of Boiler. 256 603.1872 One-third of area. .7854 2 201.0624 1206.3744 Two-thirds of area 2 240 Length in inches. 402.1248 239529.8560 240 96509.9520 Sub. Area of Flues, 96509.9520 231)193019.9040 835.5940 No. of Gallons.
Rule to find the amount of water required, when the average pounds of coal used per hour is known. Divide the coal by 7.5; the answer will be cubic feet; then multiply by 7.5, and that gives the number of U. S. standard gallons.
117 lbs. of coal used per hour, 7.5]117.0 15-6 7.5 117-0=117 gals.
Q. How many cubic feet in 1 lb. of air?
A. 13817/1000 cubic feet.
Q. How much air does it take to consume 1 pound of coal?
A. It takes 18 pounds, or 248 817/1000 cubic feet.
Q. How would you tell the amount of water any tank contained?
A. If the tank was large at the bottom and narrow at the top, lay the tank off in 10 parts from top to bottom, then take the diameter 4/10 from the large end of the tank, square it, then multiply by .7854; that gives the area; then multiply quotient by full depth of tank and divide by 1728, which gives the number of cubic feet; multiply answer by 7.5, and the number of U. S. gallons will be given. The example must be done in inches; 1728 is the number of inches in a cubic foot, and 7.5 is the number of gallons in a cubic foot.
Tank 2 feet diam. 24 inches diameter. Tank 3 feet deep, 24 ' ' 576 .7854 452.3904 area in inches. 36 inches deep. 1728)16286.0544 9.4248 cubic feet. 7.5 No. gals, in a cub. ft. 70.86000 U. S. gals, in tank.
Rule how to mark engineer's tools. Warm the tool and allow a thin coat of beeswax to cover the place to be marked; after the beeswax is cold, take a dull scriber and do the marking; then apply some nitric acid, after a few moments wash off the acid with water, then heat the tool to melt the beeswax, and you will find well defined marks.
Rule for chimneys. Chimneys should be round inside, instead of square, to insure a good draft. The opening should be one-fifth larger than the area of the flues or tubes combined; if less, the draft will not be free. The opening from the bottom should increase in size to the top, and be smooth inside.
Rule for making good babbitt metal, for high and low speed, in parts.
HIGH SPEED COMMON. MEDIUM. Martin's Nickel.. 10 Copper.............. 12 Copper.............. 60 Copper.............. 16 Antimony........... 4 Antimony........... 25 Antimony........... 4 Tin..................... 84 Tin..................... 15 Tin..................... 70 100 100 100
Rule for babbitting a box. Nearly every engineer has his own way; but the best and quickest way is to chip out all the old babbitt in the cap and box, then put the journal or shaft that is to run in the box in its place; put enough liners in between the shaft or journal and edge of box until level, square and in line; put thick putty around the shaft and against the box, so the babbitt can not run out; then heat the babbitt until it runs free, and pour accordingly; the cap is then bolted in its place upon 1/16 inch thick liner, and putty placed as before; then pour metal through the oil holes, which will have to be drilled out afterwards.
Rule to determine the capacity of any size pump, single or double action. Multiply the area of the water piston-head face or plunger in inches, by its stroke in inches, which gives the number of cubic inches per single stroke; the answer divided by 231 (the cubic inches in a gallon) will give the number of standard gallons per single stroke. But remember, all pumps throw less water than their capacity, which depends upon the condition and quality of the pump. This loss arises from the rise and fall of the valves; from a bad fit or leakage, and in some cases from there being too much space between valves, piston or plunger. The higher the valves have to rise to give the proper opening, the less work the pump will perform.
Q. Will a boiler 60 inches in diameter,
3/8 inch iron, stand as much pressure as a
boiler 48 inch diameter, 3/8 iron?
A. Because the pressure in the large boiler has more surface, and will not allow it. It is the same as a long bar and a short bar of the same thickness; it takes less strain to break the long one than the short one.
Rule for finding safe working pressure of steam boilers. Always use .56 for single riveted and .70 for double riveted side seams. A radius means the diameter and 1/5 of tensile strength is safe load. U. S. standard is 1/6.
Multiply the thickness of iron by single or double rivets, then multiply by safe load, divide by internal radius, and the answer will be the safe working pressure.
Diam. 42 in. .1875 thickness of iron. Iron 3/1 6, in. .70 double riveted. Double riveted .131250 50,000 1bs. tensile str'th. 10000 2)42 20.8125)13125000.00 21 outside radius Safe working pressure, 63.06 . 1875 5 20.8125 inside radius Bursting pressure, 315.30
Rule to find aggregate strain caused by the pressure of steam on the shells of boilers. Multiply the circumference in inches by the length in inches; multiply this answer by the pressure in pounds. The result will be the pressure on the shell of boiler, and divide by 2000, which gives the tons.
Diam. of boiler 48 inches, circumference 150.7968, length 20 feet, or 240 inches, pressure of steam 120 lbs. 150.7968 x 240 x 120=4342947.8400 1bs., divided by 2000=2171 tons strain.
Rule to find the number of feet of 1 inch pipe required to heat any size room with steam. For direct radiation 1 lineal foot (straight foot) to 25 cubic feet of space. For indirect radiation, 1 lineal foot to 15 cubic feet of space, Note, all pipe is measured inside for size.
Room 18 x l8 x l8 to be heated with 1 inch pipe. Direct radiation. All calculating must be done in inches, and divided by 1728 to find the cubic feet.
216 216 46656 1728)10077696 cubic inches. 25)5832 cubic feet. Lineal 2337/2 5- feet of 1 inch pipe.
One cubic foot of boiler is required for every 1500 cubic feet of space to be warmed. One horse power of boiler is enough for 40,000 cubic feet of space.
RULE to find the horse power of a boiler. Always find the number of square inches and divide by 144, which gives the square feet of heating surface, and divide by 15 square feet, which is an average allowance for one horse power of a boiler; divide the HP by 2, you will have the proper grate surface, and allow square inch of safety valve to each square foot of grate surface. Generally, from to of a square foot of grate surface is allowed to each horse power of a boiler.
Q. How do you find the horse power of a
A. Find the number of square feet of heating surface and divide by 15; 15 square feet of heating surface is the general allowance for a HP of a boiler. (See following example.)
Boiler 48 in. x 25 ft. First find circum. of boiler. Two 16 in. flues. 16 in. diam. of 1 flue. 48 diam. of shell. 3.1416 3.1416 50.2656 circ. of 1 flue. 3)150.7968 300 length of flue. 50.2656 one-third circum. 15079.6S0O in inches. ______2 ______2 100.5312 two-thirds ' 30159.3600 heat, sur.2 fl. 300 length or boiler in inches. 30169.3600 No. sq. in. heat. surf. in the shell. 16 in diam. of 1 flue. 16 48 256 48 .7854 2304 201.0624 area 1 flue. .7854 2 3)1809.6616 area of 1 head. 402.1248 area 2 flues, 603.1872 one-third area of 1 hd. 2 2 804.2496 both ends. 1206.3744 two-thirds area of 1 hd. 2 2412.7488 two- thirds area of both heads. No. sq. in. heat. surf, in shell, 30159.3600 ' ' ' flues, 30159.3600 Two-thirds area both heads, 2412.7488 Total, 62731.4688 Subtract area of flues, 804.2496 This boiler is 28 h. p. An 144)61927.2192 engine uses about of boiler's 15(430. sq. ft. h. s. h. p.. making this boiler 2(28.____h. p. sufficiently large enough 2(14.____grate surf. to supply engine of 56 h. p. 7. area s'fty v.
Number sq. feet of heating surface allowed for tubular boilers are 12 sq. feet. Flue boilers 15 sq. feet. Cylinder boilers 7 sq. feet.
Rule to find the horse power generated in any kind of boiler when running. First, notice how long it will take to evaporate 1 inch of water in the glass gauge, divide this into 60, which gives the number of inches evaporated in one hour; second, multiply the average diameter where evaporation took place by the length of the boiler in inches; this multiplied by the number of inches evaporated, and the answer divided by 1728 gives the cubic feet of water evaporated in one hour.
As a rule, 1 cubic foot of water evaporated is generally allowed for 1 horse power; also the capacity of a pump, or injector for any boiler should deliver 1 cubic foot of water each horse power per hour, and an engine uses one-third of a cubic foot of water per horse power.
Length of boiler 216 inches. 216 Average diam. 40 inches. __40 One inch evaporated in 15(60 8640. 15 minutes. 4 ____4 1728)34.560(20 h. p.
WEIGHT OF SQUARE SUPERFICIAL FOOT OF BOILER PLATE WHEN THICKNESS IS KNOWN
Thickness. Weight, Thickness. Weight,
5/1 6 = .3125
1/1 6 = .0625
3/8 = .375
3/3 2= .0937
7/1 6 = .4375
1/8 = .125
9/16 = .5625
3/1 6= .1875
5/8 = .625
7/3 2 = .2187
7/8 = .875
9/3 2 = .2812
1 = .1
Q. Explain how the above fractional parts of
whole numbers are made to read as decimalstake 3/16 of an inch for
A. To do this take 100 as a whole number; divide 16 into 100=6, reads .625=1/16 of 100. 3/16 would read, 3 x .625=. 1875. This principle answers for all the rest.
Rule for safety. To find the distance ball should be placed on lever, when the weight is known, or the distance is known and weight is not known. Multiply the pressure required by area of valve, multiply the answer by the fulcrum; subtract the weight of the lever, valve and stem, and divide by the weight of ball for distance, or divide by distance for weight of ball with the same example as follows:
Weight of ball, 60 1bs. 100 lbs. pressure. Pressure, 100 ' _3 area of valve. Wt. of L.V.& steam, 30 ' 300 Fulcrum, 4 inch,___4 fulcrum. Area of valve, 3 ' '1200 ___30 wt. of L. Y. & st. 60)1170 19 inch ball should be hung on lever.
The mean effective weight of valve, lever and stem is found by connecting the lever at fulcrum, tie the valve-stem to lever with a string, attach a spring scale to lever immediately over valve, and raise until the valve is clear of its seat, which will give the mean effective weight of lever, valve and stem.
Rule for figuring the safety valve and to know the pressure when the area of valve, the weight of lever, valve and stem, the distance fulcrum is from valve, and weight of ball is known.
Divide fulcrum into length of lever, multiply answer by weight of ball, add weight of lever, valve and stem, and divide by area of valve. Answer will be steam pressure.
Weight of ball, .50 lbs. 2.25 4)20 Wt. of L.V. and stem,30 lbs. 2.25 5 Fulcrum, 4 in. 5.0625 50 Diam. of valve. 2 in. .7854 250 Length of lever, 20 in. 3.97608750 area. 30 Add as many ciphers to the dividend 3.9)280.0 as there are decimels in the divisor, 1bs. press. 71.3 1/3 9 and divide as whole numbers.
To measure or mark off the lever, you measure the fulcrum and
make notches the same distance as fulcrum; if fulcrum is 4 inches,
each notch must be 4 inches apart.
Q. What is meant by a fulcrum?
A. The distance valve stem is from where the lever is connected.
Rule To Gear A Lathe for Screw-Cutting. Every screw cutting lathe contains a long screw called the lead screw, which feeds the carriage of the lathe while cutting screws; upon the end of this screw is placed a gear to which is transmitted motion from another gear placed on the end of the spindle; these gears each contain a different number of teeth, for the purpose of cutting different threads, and the threads are cut to a certain number to the inch, varying from one to fifty. Therefore, to find the proper gears to cut a certain number of threads to the inch, you will first multiply the number of threads you desire to cut to the inch by any small number, 4 for instance, and this will give you the proper gear to put on the lead screw. Then with the same number 4, multiply the number of threads to the inch in the lead screw, and this will give you the proper gear to put on the spindle. For example, if you want to cut 12 to the inch, multiply 12 x 4, and it will give you 48. Put this gear on the lead screw, then with the same number 4, multiply the number of threads to the inch in the lead screw. If it is 5, for instance, it will give you 20; put this on the spindle and your lathe is geared. If the lead screw is 4, 5, 6, 7 or 8, the same rule holds good. Always multiply the number of threads to be cut first.
Some in deed, most small lathes are now made with a stud geared into the spindle, which stud only runs half as fast as the spindle, and in finding the gears for these lathes you will first multiply the number of threads to be cut, as before, and then multiply the number of threads on the lead screw as double the number it is. For instance, if you want to cut 10 to the inch, multiply by 4, and you get 40; put this on the lead screw, then, if your lead screw is 5 to the inch, you call it 10, and multiply by 4, and it will give you 40. Put this on your stud and your lathe is geared, ready for cutting.
Rule For Cutting A Screw In An Engine Lathe.In cutting V-thread screws, it is only necessary for you to practice operating the shipper and slide screw-handle of your lathe before cutting. After having done this until you get the motions, you may set the point of the tool as high as the center, and if you keep the tool sharp you will find no difficulty in cutting screws. You must, however, cut very light chips, mere scrapings in finishing, and must take it out of the lathe often, and look at it from both sides very carefully, to see that the threads do not lean like fish scales. After cutting, polish with a stick and some emery and oil.
Rule For Cutting Square Thread Screws.In cutting square thread screws, it is always necessary to get the depth required with a tool somewhat thinner than one-half the pitch of the thread, after doing this make another tool exactly the pitch of the thread and use it to finish with cutting a slight chip on each side of the groove. After doing this, polish with a pine stick and some emery. Square threads for strength should be cut one-half the depth of their pitch, while square threads for wear mayand should beout three-fourths the depth of their pitch.
Rule For Mongrel Threads.Mongrel, or half V half square threads, are usually made for greater wear, and should be cut the depth of their pitch, and for extraordinary wear they may be cut 1 the depth of the pitch. The point and the bottom grooves should be in width the depth of their pitch. What is meant here by the point of the thread is the outside surface, and the bottom of the groove is the groove between the threads. In cutting these threads, it is proper to use a tool the shape of the thread, and in thickness about V5 less than the thread is when finished. As it is impossible to cut the whole surface, at once, you will cut it in depth about 1/16 at a time then a chip off the sides of the thread, and continue in this way alternately till you have arrived at the depth required. Make a gauge of the size required between the threads and finish by scraping with water. It is usually best to leave such screws as these a little large until after they are cut, and then turn off a light chip, to size them; this leaves them true and nice.
Rule To Temper Tools Used Daily, Such As Chisels, Taps, Reamers, Twist Drills, Common Flat Drills, and Lathe Tools.To temper flat, cape or side chisels, and common flat drills, put the tool to be tempered in the fire and heat slowly to a cherry red color, about 4 inches from the point. Then take it out and put it in the water, point first, about three or four inches, then draw it back quick about an inch from the point, and leave it so until the water will barely dry on the chisel, then take it out, polish it with a piece of sand stone, and let the heat that is left in the body of the tool force its way toward the point; it will be noticed immediately in the change of color. The color of temper for chisels to cut cast iron should be a dark straw, turning to a blue. The temper of chisels to cut wrought iron or steel should be plunged into water after the dark straw color has disappeared and the blue begins to show itself, and left in the water to cool off. In some cases, where the tool is too cold and the temper will not draw, put the tool in and out of the fire often, until the temper shows itself, then cool immediately. If the temper gets to the point of tool before it is polished, it will have to be heated over again. The above rule answers for lathe, plainer and shaper tools as well.
Taps, dies, reamers and twist drills should be tempered in oil. After being heated to a cherry red all over equally, drop the tool into a bucket of oil (plumb) and leave it there until cold; then take it out and brighten it with emery cloth; be careful not to drop it, because it is brittle and liable to break. To draw the temper of taps, reamers and twist drills, heat a heavy ring red hot and enter the tool centrally in the ring, so the heat will be equal from all sides. The hole in the ring should be about three times the diameter of the tool. An old pulley hub would be about right. The color for reamers, taps and twist drills should be dark straw, turning to a blue near the shank; where the color is changing too fast, drop a little water on it; after the right color is obtained, cool off in water. To draw the temper in dies after being cooled in oil, set them (the threads up) on a piece of red-hot iron and draw temper the same color as taps.
For tempering a spring, heat it cherry red and put it in oil; after it is cool, take it out and hold it over the fire until the oil burns off; then put the spring in the oil again, then in the fire; do this three times; after the last time, plunge it into water and cool off.