THE INDICATOR.
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.
RULES
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
.7854.
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
.31831.
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.
EXAMPLE:
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.
EXAMPLE:
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.
EXAMPLE:
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.
EXAMPLE:
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. No.
Q. Why?
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.
EXAMPLE:
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.
EXAMPLE:
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.
EXAMPLE:
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
boiler?
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.)
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.
EXAMPLE:
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,
Inches. Dec.
1bs.
Inches. Dec.
1bs.
1/3 2=.03125
1.25
5/1 6 = .3125
12.58
1/1 6 = .0625
2.519
3/8 = .375
15.10
3/3 2= .0937
3.788
7/1 6 = .4375
17.65
1/8 = .125
5.054
= .5
20.20
5/3 2=.1562
6.305
9/16 = .5625
22.76
3/1 6= .1875
7.578
5/8 = .625
25.16
7/3 2 = .2187
8.19
= .75
30.20
.25
10.09
7/8 = .875
35.30
9/3 2 = .2812
11.38
1 = .1
40.40
Q. Explain how the above fractional parts of
whole numbers are made to read as decimalstake 3/16 of an inch for
example?
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:
EXAMPLE:
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.
RULES FOR MACHINISTS
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.
