Chapter VIII: Section 24: “Lever safety valves to be attached to marine boilers shall (1)

have an area of not less than one square inch to two square feet of the grate surface in the boiler, and the seats of all such safety valves shall have an angle of inclination of forty-five degrees to the centre line of their axis.

“The valves shall be so arranged that each boiler shall have one separate safety valve, unless the arrangement is such as to preclude the possibility of shutting off the communication of any boiler with the safety valve or valves employed. This arrangement shall also apply to lock-up safety valves when they are employed.

“Any spring-loaded safety valves constructed so as to give an increased lift by the operation of steam, after being raised from their seats, or any spring-loaded safety valve constructed in any other manner, or so as to give an effective area equal to that of the aforementioned spring-loaded safety valve, may be used in lieu of the common lever-weighted valve on all boilers on steam vessels, and all such spring-loaded safety valves shall be required to have an area of not less than one square inch to three square feet of grate surface of the boiler, and each spring-loaded valve shall be supplied with a lever that will raise the valve from its seat a distance of not less than that equal to one-eighth the diameter of the valve opening, and the seats of all such safety valves shall have an angle of inclination to the centre-line of their axis of forty-five degrees. But in no case shall any spring-loaded safety valve be used in lieu of the lever-weighted safety valve, without first having been approved by the Board of Supervising Inspectors.”

The following size “Pop” Safety Valves are required for boilers having grate surfaces as below:

2 inch “Pop” Valve for 9.42 square feet of grate surface.
2-1/2 inch “Pop” Valve for 14.72 square feet of grate surface.
3 inch “Pop” Valve for 21.20 square feet of grate surface.
4 inch “Pop” Valve for 37.69 square feet of grate surface.
5 inch “Pop” Valve for 58.90 square feet of grate surface.
6 inch “Pop” Valve for 84.82 square feet of grate surface.

PROFESSOR RANKIN’S RULE.—Multiply the number of pounds of water evaporated per hour by .006, and the product will be the area in square inches of the valve.

The U. S. Steamboat Inspection Law requires for the common lever valve one square inch of area of valve for every two square feet of area of grate surface.

United States Navy Department deduced from a series of experiments the following rule: Multiply the number of pounds of water evaporated per hour by .005, and the product will be the area of the valve in square inches.

Rule adopted by the Philadelphia Department of Steam Engine and Boiler Inspection:

1. Multiply the area of grate in square feet by the number 22.5. 2. Add the number 8.62 to the pressure allowed per square inch. Divide (1) by (2) and the quotient will be the area of the valve in square inches. This is the same as the French rule.

The maximum desirable diameter for safety valves is four inches, for beyond this the area and cost increase much more rapidly than the effective discharging around the circumference.

There should not be any stop valve between the boiler and safety valve.

The common form of safety valve is shown in Fig. 96.

Here the load is attached to the end _B_ of the lever _A_, _B_, the fulcrum of which is at _c_. The effective pressure on the valve, and consequently the blowing off pressure in the boiler can be regulated within certain limits, by sliding the weight _W_ along the arm of the lever. In locomotive engines, as well as on marine boilers, the weight would on account of the oscillations, be inadmissible and _a spring_ is used to hold down the lever.

In the calculations regarding the lever safety valve, there are five points to be determined, and it is necessary to know four of these in order to find the fifth. These are: (1) The Steam Pressure, (2) The Weight of Ball, (3) The Area of Valve, (4) The Length of Lever, (5) The Distance from the Valve Centre to the Fulcrum.

In making these calculations it is necessary to take into account the load on the valve due to the weight of the valve-stem and lever. The leverage with which this weight acts is measured by the distance of its centre of gravity from the fulcrum. The centre of gravity is found by balancing the lever on a knife edge, and the weight of the valve-stem and lever can be found by actual weighing. This load can also be found by attaching a spring balance to the lever exactly over the centre of the valve stem when they are in position. The following examples will be computed under these conditions: (1) Steam Pressure, 120 pounds; (2) Weight of Ball, 100 pounds; (3) Weight of Valve and Lever, 60 pounds, weighed in position; (4) Length of Lever, 45 inches; (5) Length of Distance from Valve Centre to Fulcrum, 5 inches; (6) Area of Valve, 8 square inches.

_To find the area of the valve:_

RULE.—Multiply the length of the lever by the weight of the ball, and divide the product by the distance from the valve centre to the fulcrum, and to the quotient add the effective weight of the valve and lever, and divide the sum by the steam pressure.

_Example._

45 inches, length of the lever,
100 pounds, weight of the ball,
----
Fulcrum, 5 in. )4500
----
900
60 pounds, weight of valve and lever,
----
Steam pressure 120 lbs. )960 (8 square inches, area of valve.
960

_To find the pressure at which the valve will blow off:_

RULE.—Multiply the length of the lever by the weight of the ball; divide this product by the distance from the valve centre to the fulcrum, and to the quotient add the effective weight of the lever and valve, and divide the sum by the area of the valve.

_Example._

45 inches, length of lever,
100 pounds, weight of ball,
----
Fulcrum, 5 in. )4500
----
900
60 pounds, weight of valve and lever,
----
Area of Valve 8 ) 960
----
120 pounds, pressure at which valve will blow.

_To find the weight of ball:_

RULE.—Multiply the steam pressure by the area of the valve, and from the product subtract the effective weight of the valve and lever, then multiply the remainder by the distance from the valve centre to the fulcrum, and divide the product by the length of the lever.

_Example._

120 pounds, steam pressure,
8 inches, area of valve,
----
960
60 pounds, weight of valve and lever,
----
900
5 inches, fulcrum,
----
Length of lever, 45 in. )4500
----
100 pounds, weight of ball.

_To find the length of lever:_

RULE.—Multiply the steam pressure by the area of the valve, and from the product subtract the effective weight of the valve and lever, then multiply the remainder by the distance from the valve centre to the fulcrum, and divide the product by the weight of the ball.

_Example._

120 pounds, steam pressure,
8 inches, area of valve,
----
960
60 pounds, weight of valve and lever,
----
900
5
----
100)4500(45 length of lever.

Every boiler should be provided with two safety valves, one of which should be put beyond the control of the attendant.

Safety valves that stick will do so even though tried every day, if they are simply lifted and dropped to the old place on the seat again. _If a boiler should be found with an excessively high pressure, it would be one of the worst things to do to start the safety valve from its seat unless extra weight was added_, for should the valve once start, it would so suddenly relieve the boiler of such a volume of steam as would cause a rush of water to the opening, and by a blow, just the same as in water hammer, rupture the boiler.

Such a condition is very possible to occur of itself when a safety valve sticks. The valve holds the pressure, that gets higher and higher, until so high that the safety valve does give way and allows so much steam to escape that the sudden changing of conditions sets the water in motion, and an explosion may result.

The noise made by a safety valve when it is blowing off may be regarded in two ways. First, by it is known that the valve is capable of performing its proper function, and that there is, therefore, a reasonable assurance that no explosion will result from excessive pressure of steam or other gas, and on the other hand too much noise of this kind indicates wasted fuel.

The hole of the safety valve may be 2, 3 or 4 inches; that does not say that the area is 3.1416, 7.06 or 12.56 square inches, but the area is that which is inside of the joint. The valve opening may be, say 2 inches, but _the circle of contact of valve to seat_ may be of an average diameter of 2-1/8 inches, if so, all the close calculations otherwise will not avail. In the first place, the area of 2 inches equals 3.1416; that of 2-1/8 diameter equals 3.5466, showing a difference of .4 square inches.

NOTE.

Very extended rules issued by the U. S. Government for calculating the safe working pressure, dimensions and proportions of the safety valves for marine boilers are reprinted in “Hawkins’ Calculations” for engineers.

When a safety valve is described as a “2 inch safety valve,” etc., it means that two inches is _the diameter_ of the pipe; hence the following rule and examples for finding the area.

RULE FOR FINDING AREA OF VALVE OPENING.

Square the diameter of the opening and multiply the product by the decimal .7854.

EXAMPLE.

What is the area of a three inch valve? Now then:

3 × 3 = 9 × .7854 = 7.06 square inches, Ans.

NOTE.—A shorter method of calculating by .7854 in larger sums is to multiply by 11 and divide by 14, for decimal .7855 = the fraction 11/14th. Note: .7854 is the area of a circular inch.

When valves rise from their seats under increasing steam pressure they do so by a constantly diminished ratio which has been carefully determined by experiment and reduced to the following table.

+----------------+----------------+
|Pressure in Lbs.| Rise of Valve. |
+----------------+----------------+
| 12 | 1-36 |
| 20 | 1-48 |
| 35 | 1-54 |
| 45 | 1-65 |
| 50 | 1-86 |
| 60 | 1-86 |
| 70 | 1-132 |
| 80 | 1-168 |
| 90 | 1-168 |
+----------------+----------------+

The following useful table was prepared by the Novelty Iron Works, New York.

+----------------+----------------+
|Boiler Pressure |Area of Orifice |
| in Lbs. Above | in Sq. In. for |
|the Atmosphere. |Each Sq. Ft. of |
| |Heating Surface.|
+----------------+----------------+
| 0.25 | .022794 |
| 0.5 | .021164 |
| 1. | .018515 |
| 2. | .014814 |
| 3. | .012345 |
| 4. | .010582 |
| 5. | .009259 |
| 10. | .005698 |
| 20. | .003221 |
| 30. | .002244 |
| 40. | .001723 |
| 50. | .001389 |
| 60. | .001176 |
| 70. | .001015 |
| 80. | .000892 |
| 90. | .000796 |
| 100. | .000719 |
| 150. | .000481 |
| 200. | .000364 |
+----------------+----------------+

FEED WATER HEATERS.

There are two forms of feed water heaters: (1) _The closed heater_, where the feed water passes through tubes, which are enclosed in a shell, through which the exhaust steam passes.(2) _The open heater_, in which the steam and water come into contact. In the latter the water is sprayed into a space, through which the exhaust steam passes, or is run over a number of inclined perforated copper plates, mingled with the exhaust steam.

The original feed water heater called a “pot heater,” consisted of a vessel so constructed that the feed water was sprayed through the exhaust steam into a globe formed tank, from the bottom of which the heated water was pumped into the boiler; its name was originally the “pot heater,” but as it was open to the air through the exhaust pipe, it was, with its successively improved forms called the open heater.

All the heat imparted to the feed water, before it enters the boiler, is so much saved, not only in the cost of fuel, but by the increased capacity of the boiler, as the fuel in the furnace will not have this duty to perform. There are two sources of waste heat which can be utilized for this purpose: the chimney gases and the exhaust steam. The gases escaping to the chimney after being reduced to the lowest possible temperature contain a considerable quantity of heat. This waste of heat energy may be largely saved by the device illustrated on page 186.

How much saving is obtained under any given condition is a question requiring for its solution a careful calculation of all of the conditions which have a bearing on the subject. Exhaust steam under atmospheric pressure only has a sensible temperature of 212 degrees, but exhaust steam contains also a large number of heat units which are given up when the steam is condensed into water; for this reason it might be thought possible to raise the temperature of the feed water a few degrees higher even than the sensible temperature of the exhaust steam. But this should not be expected, on account of the radiation of heat that would occur above that of the steam.

The steam which escapes from the exhaust pipe dissipates into the atmosphere or discharges into the condenser over nine tenths of the heat it contained when leaving the boiler. This can be best utilized by _exhaust feed water heaters_, for the use of live steam heaters represents no saving in fuel, as all the heat imparted to the feed water by their use comes directly from the boiler. The purpose for which they are used is to elevate the temperature of the feed water above the boiling point, so as to precipitate the sulphate of lime and other scale forming substances, and prevent them from entering the boiler. Neither does the heat in the feed water introduced by an injector represent saving, as it comes from the boiler and was generated by the fuel.

It is important to note these two statements: 1, That neither live steam feed water heaters, nor 2, injectors save the heat from the escaping steam.

It is also well to remember that it requires _a pound of water_ to absorb 1.146 heat units, and that this quantity of heat is distributed through the whole quantity of water, and _as a pound of steam is the same as a pound of water_, it may be understood that at 212° each pound of exhaust steam contains 1,146 heat units; ten pounds of steam contain 11,460 heat units distributed through the mass, etc.: thus, to explain still further:

To evaporate water into steam, it must first be heated to the boiling point, and then sufficient heat still further added to change it from the liquid to the gaseous state, or steam. Take one pound of water at 32 degrees and heat it to the boiling point, it will have received 212° - 32° = 180 heat units. A heat unit being the amount of heat necessary to raise one pound of water through one degree at its greatest density. To convert it into steam after it has been raised to the boiling point, requires the addition of 966 heat units, which are called latent, as they cannot be detected by the thermometer. This makes 180 + 966 = 1146 heat units, which is the total heat contained _in one pound of water_ made into steam at the atmospheric pressure. And at atmospheric density the volume of this steam is equal to 26.36 cubic feet, and this amount of steam contains 1,146 units of heat, distributed throughout the whole quantity, while the temperature at any given point at which the thermometer may be inserted is 212 degrees. If two pounds of water be evaporated, making a volume of 52.72 cubic feet, then the number of heat units present would be doubled, while the temperature would still remain at 212, the same as with one pound.

If by utilizing the heat that would otherwise go to waste, the temperature of the feed water is raised 125 degrees, the saving would be 125/1146 of the total amount of heat required for its evaporation, or about 11 per cent. Thus it can be seen the percentage of saving depends upon the initial temperature of the feed water, and the pressure at which it is evaporated.

For example, a boiler carrying steam at 100 pounds pressure has the temperature of the feed water raised from 60 to 200 degrees, what is the percentage of gain?

By referring to a table pressure of “saturated steam,” it will be seen that the total heat in steam at 100 pounds pressure is 1185 heat units. These calculations are from 32 degrees above zero, consequently the feed must be computed likewise.

In the first case, the heat to be supplied by the furnace is the total heat, less that which the feed water contains, or 1185 - 28 = 1157 heat units. In the second case it is 1185 - 168 = 1017 heat units, the difference being 1157 - 1017 = 140, which represents a saving of 140/1157 or about 12 per cent.

Where feed water is heated no more than 20 degrees above its normal temperature the gain effected cannot amount to more than 2%, not sufficient to pay for the introduction and maintenance of a feed water heating device, no matter how simple, but if the temperature of the water can be increased 60 degrees the gain will be in the neighborhood of 5%. To make feed water heating practical and economical it would be necessary to increase the temperature of the water about 180 degrees at least, and to do this, using the exhaust from a non-condensing engine without back pressure, would require such a capacity of heater as would give fully 10 square feet of heating surface to each horse power of work developed, and to raise the temperature above this would require a certain amount of back pressure or an increased capacity of heater, so that the subject resolves itself into a question of large capacity of heater, or a higher temperature of the exhaust steam, which could only be obtained through a given amount of back pressure.

In the same way has been calculated the following table, showing percentages of saving of fuel by heating feed-water to various temperatures by exhaust steam, otherwise waste:

_Percentage of saving._ (_Steam at 60 pounds gauge pressure._)

-----+--------------------------------------------------------------
Final| Initial Temperature of Water (Fahrenheit).
Temp.+--------+--------+--------+--------+--------+--------+--------
Fahr.| 32 Deg.| 40 Deg.| 50 Deg.| 60 Deg.| 70 Deg.| 80 Deg.| 90 Deg.
-----+--------+--------+--------+--------+--------+--------+--------
60 | 2.39 | 1.71 | 9.86 | … | … | … | …
80 | 4.09 | 3.43 | 2.59 | 1.74 | 0.88 | … | …
100 | 5.79 | 5.14 | 4.32 | 3.49 | 2.64 | 1.77 | .90
120 | 7.50 | 6.85 | 6.05 | 5.23 | 4.40 | 3.55 | 2.68
140 | 9.20 | 8.57 | 7.77 | 6.97 | 6.15 | 5.32 | 4.47
160 | 10.90 | 10.28 | 9.50 | 8.72 | 7.91 | 7.09 | 6.26
180 | 12.60 | 12.00 | 11.23 | 10.46 | 9.68 | 8.87 | 8.06
200 | 14.36 | 13.71 | 13.00 | 12.20 | 11.43 | 10.65 | 9.85
220 | 16.00 | 15.42 | 14.70 | 14.00 | 13.19 | 12.33 | 11.64
-----+--------+--------+--------+--------+--------+--------+--------
|100 Deg.|120 Deg.|140 Deg.|160 Deg.|180 Deg.|200 Deg.|
-----+--------+--------+--------+--------+--------+--------+--------
60 | … | … | … | … | … | … |
80 | … | … | … | … | … | … |
100 | … | … | … | … | … | … |
120 | 1.80 | … | … | … | … | … |
140 | 3.61 | 1.84 | … | … | … | … |
160 | 5.42 | 3.67 | 1.87 | … | … | … |
180 | 7.23 | 5.52 | 3.75 | 1.91 | … | … |
200 | 9.03 | 7.36 | 5.62 | 3.82 | 1.96 | … |
220 | 10.84 | 9.20 | 7.50 | 5.73 | 3.93 | 1.98 |
-----+--------+--------+--------+--------+--------+--------+--------

A good feed-water heater of adequate proportions should readily raise the temperature of feed-water up to 200° Fahr., and, as is seen by inspection of the table, thus effect a saving of fuel, ranging from 14.3 per cent. to 9.03 per cent., according as the atmospheric or normal temperature of the water varies from 32° Fahr. in the height of winter, to 100° Fahr. in the height of summer.

The percentage of saving which may be obtained from the use of exhaust steam for heating the feed water, with which the boiler is supplied, will depend upon the temperature to which the water is raised, and this, in turn, will depend upon the length of time that the water remains under the influence of the exhaust steam. This should be as long as possible, and unless a sufficient amount of heating surface is employed in the heater best results cannot be expected.

It does not necessarily require all the exhaust steam—or the whole volume of waste steam passing from the engine to bring the feed water up to the temperature desired, and the larger the heating appliance the smaller proportion is needed—hence heaters are best made with two exits nicely proportioned to avoid back pressure and at the same time utilize enough of the exhaust to heat the feed water.

An impression prevails among many who are running a condenser on their engine that a feed water heater can not be used in connection with it; large numbers of heaters running on condensing engines with results as follows: the feed water is delivered to the boiler at a temperature of 150° to 160° Fahr., depending on the vacuum: the higher the vacuum the less the heat in the feed water.

A heater applied to a condensing engine generally increases the vacuum one to two inches.

When cold water is used for the feed water, the saving in fuel by the use of the heater is from 7 to 14 per cent.

When feed water is taken from the hot well, it will save 7 to 8 per cent.

Where all the steam generated by a boiler is used in the engine and the exhaust passed through a heater it is found by actual experiment, where iron tubes are used in the heater, that approximately ten square feet of heating surface will be required for each 30 lbs. of water supplied to the boiler at a temperature of 200 degrees Fahr.

Ten square feet of heating surface in the feed water heater also represents one horse power.

CAPACITY OF CISTERNS.

The following table gives the capacity of cisterns for each twelve inches in depth:

_Diameter._ _Gallons._
25 feet 3671
20 „ 2349
15 „ 1321
14 „ 1150
13 „ 992
12 „ 846
11 „ 710
10 „ 587
9 „ 475
8 „ 376
7 „ 287
6-1/2 „ 247
6 „ 211
5 „ 147
4-1/2 „ 119
4 „ 94
3 „ 53
2-1/2 „ 36
2 „ 23

Supposing it was required to find the weight of the water in any cistern or tank; it can be ascertained by multiplying the number of gallons by the weight of one gallon, which is 8-1/3 pounds, 8.333. For instance, taking the largest cistern in the above table containing 3671 gallons: 3671 × 8.33 = 30579.43 pounds.

The table above gives the capacities of round cisterns or tanks. If the cistern is rectangular the number of gallons and weight of water are found by multiplying the dimensions of the cistern to get the cubical contents. For instance, for a cistern or tank 96 inches long, 72 inches wide, and 48 inches deep, the formula would be: 96 × 72 × 48 = 331,776 cubic inches.

As a gallon contains 231 cubic inches; 331,776 divided by 231 gives l,436 gallons, which multiplied by 8.33 will give the weight of water in the cistern.

For round cisterns or tanks, the rule is: Area of bottom on inside multiplied by the height, equals cubical capacity. For instance, taking the last tank or cistern in the table: Area of 24 inches (diameter) is 452.39, which multiplied by 12 inches (height) gives 5427.6 cubic inches, and this divided by 231 cubic inches in a gallon gives 23 gallons.

Supposing the tank to be 24 inches deep instead of 12 inches, the result would be, of course, twice the number of gallons.

RULE FOR OBTAINING CONTENTS OF A BARREL IN GALLONS.

Take diameter at bung, then square it, double it, then add square of head diameter; multiply this sum by length of cask, and that product by .2618 which will give volume in cubic inches; this, divided by 231, will give result in gallons.

WATER METERS.

Water meters, or measurers (apparatus for the measurement of water), are constructed upon two general principles: 1, an arrangement called an “_inferential meter_” made to divert a certain proportion of the water passing in the main pipe and by measuring accurately the small stream diverted, _to infer_, or estimate the larger quantity; 2, _the positive meter_; rotary piston meters are of the latter class and the form usually found in connection with steam plants. They are constructed on the positive displacement principle, and have only one working part—a hard rubber rolling piston—rendering it almost, if not entirely, exempt from liability to derangement. It measures equally well on all sized openings, whether the pressure be small or great; and its piston, being perfectly balanced, is almost frictionless in its operation.

Constructed of composition (gun-metal) and hard rubber, it is not liable to corrosion. An ingenious stuffing-box insures at all times a perfectly dry and legible dial, or the registering mechanism which is made of a combination of metals especially chosen for durability and wear, and inclosed in a case of gun-metal.

Fig. 99 is a perspective view of the meter, showing the index on the top. It is shown here as when placed in position. The proper threads at the inlet and outlet make it easy of attachment to the supply and discharge pipes.

The hard rubber piston (the only working part of the Meter) is made with spindle for moving the lever communicating with the intermediate gear by which the dial is moved.

The water, through the continuous movement of the piston, passes through the meter in an unbroken stream, in the same quantity as with the pipe to which it is attached when the opening in the meter equals that of the service pipe; the apparatus is noiseless and practically without essential wear.

“POINTS” RELATING TO WATER METERS.

In setting a meter in position let it be plumb, and properly secured to remain so. It should be well protected from frost.

If used in connection with a steam boiler, or under any other conditions where it is exposed to a back pressure of steam or hot water, it must be protected by a check valve, placed between the outlet of the meter and the vessel it supplies.

It is absolutely necessary to blow out the supply pipe before setting a new meter, so that if there be any accumulation of sand, gravel, etc., in it, the same may be expelled, and thus prevented from entering the meter. Avoid using red lead in making joints. It is liable to work into the meter and cause much annoyance by clogging the piston.

This engraving, Fig. 100, shows the counter of the Meter. It registers cubic feet—one cubic foot being 7-48/100 U. S. gallons and is read in the same way as the counters of gas meters.

The following example and directions may be of service to those unacquainted with the method:

If a pointer be between two figures, the smallest one must always be taken. When the pointer is so near a figure that it seems to indicate that figure exactly, look at the dial next below it in number, and if the pointer there has passed 0, then the count should be read for that figure. Let it be supposed that the pointers stand as in the above engraving, they then read 28,187 cubic feet. The figures are omitted from the dial marked “ONE,” because they represent but tenths of one cubic foot, and hence are unimportant. From dial marked “10,” we get 7; from the next marked “100,” we get 8; from the next marked “1,000,” we get the figure 1; from the next marked “10,000,” the figure 8; from the next marked “100,000,” the figure 2.

THE FISH TRAP used in connection with water meters is an apparatus (as its name denotes) for holding back fishes, etc.

THE STEAM BOILER INJECTOR.

For safety sake, every boiler ought to have two feeds in order to avoid accidents when one of them gets out of order, and one of these should be an injector.

This consists in its most simple form, of a steam nozzle, the end of which extends somewhat into the second nozzle, called the combining or suction nozzle; this connects with or rather terminates in a third nozzle or tube, termed the “forcer.” At the end of the _combining tube_, and before entering the forcer, is an opening connecting the interior of the nozzle at this point with the surrounding area. This area is connected with the outside air by a check valve, opening outward in the automatic injectors, and by a valve termed the overflow valve.

The operation of the injector is based on the fact, first demonstrated by Gifford, that the motion imparted by a jet of steam to a surrounding column of water is sufficient to force it into the boiler from which the steam was taken, and, indeed, into a boiler working at a higher pressure. The steam escaping from under pressure has, in fact, a much higher velocity than water would have under the same pressure and condition. The rate of speed at which steam—taking it at an average boiler pressure of sixty pounds—travels when discharged into the atmosphere, is about 1,700 feet per second. When discharged with the full velocity developed by the boiler pressure through a pipe, say an inch in diameter, the steam encounters the water in the combining chamber. It is immediately condensed and its bulk will be reduced say 1,000 times, but its velocity remains practically undiminished. Uniting with the body of water in the combining tube, it imparts to it a large share of its speed, and the body of water thus set in motion, operating against a comparatively small area of boiler pressure, is able to overcome it and pass into the boiler. The weight of the water to which steam imparts its velocity gives it a momentum that is greater in the small area in which its force is exerted than the boiler pressure, although its force has actually been derived from the boiler pressure itself.

The following cut 101 represents the outline of one of the best of a large number of injectors upon the market, from which the operation of injectors may be illustrated.

S. Steam jet. V. Suction jet.
R. Ring or auxiliary check.
M. Steam valve and stem, handle.
X. Overflow cap.
C-D. Combining and delivery tube.
P. Overflow valve. O. Steam plug.
N. Packing nut. K. Steam valve

Fig. 101.]

The steam enters from above, the flow being regulated by the handle K. The steam passes through the tube S and expands in the tube V, where it meets the water coming from the suction pipe. The condensation takes place in the tubes V and C, and a jet of water is delivered through the forcer tube D to the boiler. Connection passages are made to the chamber surrounding the tubes C, D, and to the end of tube V. If the pressure in this surrounding chamber becomes greater than that of the atmosphere, the check valve P is lifted and the contents are discharged through the overflow.

So long as the pressure in this chamber is atmospheric, the check valve P remains closed, and all the contents must be discharged through the tube D.

There are three distinct types of live steam injectors, the “simple fixed nozzle,” the “adjustable nozzle,” and the “double.” The first has one steam and one water nozzle which are fixed in position but are so proportioned as to yield a good result. There is a steam pressure for every instrument of this type at which it will give a maximum delivery, greater than the maximum delivery for any other steam pressure either higher or lower. The second type has but one set of nozzles, but they can be so adjusted relative to each other as to produce the best results throughout a long range of action; that is to say, it so adjusts itself that its maximum delivery continually increases with the increase of steam pressure.

The double injector makes use of two sets of nozzles, the “lifter” and “forcer.” The lifter draws the water from the reservoir and delivers it to the forcer, which sends it into the boiler. All double injectors are fixed nozzle.

All injectors are similar in their operation. They are designed to bring a jet of live steam from the boiler in contact with a jet of water so as to cause it to flow continuously in the direction followed by the steam, the velocity of which it in part assumes, back into the boiler and against its own pressure.

As a thermodynamical machine, the injector is nearly perfect, since all the heat received by it is returned to the boiler, except such a very small part as may be lost by radiation; consequently its thermal efficiency should be in every case nearly 100 per cent. On the other hand, because of the fact that its heat energy is principally used in warming up the cold water as it enters the injector, its mechanical efficiency, or work done in lifting water, compared with the heat expended, is very low.

The action of the injector is as follows: Steam being turned on, it rushes with great velocity through the steam nozzle into and through the combining tube. This action induces a flow of air from the suction pipe, which is connected to the combining tube, with the result that a more or less perfect vacuum is formed, thus inducing a flow of water. After the water commences to flow to the injector it receives motion from the jet of steam; it absorbs heat from the steam and finally condenses it, and thereafter moves on into the forcer tube simply as a stream of water, at a low velocity compared with that of the steam. At the beginning of the forcer tube it is subjected only to atmospheric pressure, but from this point the pressure increases and the water moves forward at diminished velocity.

“POINTS” RELATING TO THE INJECTOR.

In nine cases out of ten, where the injector fails to do good service, it will be either because of its improper treatment or location, or because too much is expected of it. The experience of thoroughly competent engineers establishes the fact that in almost every instance in which a reliable boiler feed is required, an injector can be found to do the work, provided proper care is exercised in its selection.

The exhaust steam injector is a type different from any of the above-named, in that it uses the exhaust steam from a non-condensing engine. Exhaust steam has fourteen and seven-tenths (14.7) pounds of work, and the steam entering the injector is condensed and the water forced into the boiler upon the same general principle as in all injectors.

The exhaust steam injector would be still more extensively used were it not for a practical objection which has arisen—it carries over into the boiler the waste oil of the steam cylinder.

Some injectors are called by special names by their makers, such as ejectors and inspirators, but the term injectors is the general name covering the principle upon which all the devices act.

The injector can be, and sometimes is, used as a pump to raise water from one level to another. It has been used as an air compressor, and also for receiving the exhaust from a steam engine, taking the place in that case of both condenser and air pump.

The injector nozzles are tubes, with ends rounded to receive and deliver the fluids with the least possible loss by friction and eddies.

Double injectors are those in which the delivery from one injector is made the supply of a second, and they will handle water at a somewhat higher temperature than single ones with fixed nozzles.

The motive force of the injector is found in the heat received from the steam. The steam is condensed and surrenders its latent heat and some of its sensible heat. The energy so given up by each pound of steam amounts to about 900 thermal units, each of which is equivalent to a mechanical force of 778 foot pounds. This would be sufficient to raise a great many pounds of water against a very great pressure could it be so applied, but a large portion of it is used simply to heat the water raised by the injector.

The above explanation will apply to every injector in the market, but ingenious modifications of the principles of construction have been devised in order to meet a variety of requirements.

That the condensation of the steam is necessary to complete the process will be evident, for if the steam were not condensed in the combining chamber, it would remain a light body and, though moving at high speed, would have a low degree of energy.

Certain injectors will not work well when the steam pressure is too high. In order to work at all the injector must condense the steam which flows into the combining tube. Therefore, when the steam pressure is too high, and as a consequence the heat is very great, it is difficult to secure complete condensation; so that for high pressure of steam good results can only be obtained with cold water. It would be well when the feed water is too warm to permit the injector to work well, to reduce the pressure, and consequently the temperature of the steam supplied to the injector, as low pressure steam condenses much easier, and consequently can be employed with better result. Throttling the steam supplied by means of stop valves will often answer well in this case. The steam should not be cold or it will not contain heat units enough to allow it to condense into a cross section small enough to be driven into the boiler. This is the reason why exhaust injectors fail to work when the exhaust steam is very cold. It also explains why such injectors work well when a little live steam is admitted into the exhaust sufficient to heat it above a temperature of 212°.

Leaks affect injectors the same as pumps, and in addition, the accumulation of lime and other mineral deposits in the jets stops the free flowing of the water. The heat of the steam is the usual cause of the deposits, and where this is excessive it would be well to discard the injector and feed with the pump.

The efficient working of the injector depends materially upon the size of the jet which should be left as the manufacturer makes it; hence in repairs and cleaning a scraper or file should not be used.

For cleaning injectors, where the jets have become scaled, use a solution of one part muriatic acid to from nine to twelve parts of water. Allow the tubes to remain in the acid until the scale is dissolved or is so soft as to wash out readily.

The lifting attachment, as applied to any injector, is simply a steam jet pump. It is combined with the injector proper and is operated by a portion of the steam admitted to the instrument. Nearly all the successful injectors on the market are made with these attachments, and will raise water about 25 feet, if required, from a well or tank below the boiler level.

Where an injector is required to work at different pressures it must be so constructed that the space between the receiving tube and the combining tube can be varied in size. As a rule this is accomplished by making both combining and receiving tubes conical in form and arranging the combining tube so that it can be moved to or from the receiving tube, and the water space thereby enlarged or contracted at will. The adjustment of the space between the two tubes by hand is a matter of some difficulty, however; at least it takes more time and patience than the average engineer has to devote to it, and the majority of the injectors in use are therefore made automatic in their regulation.

The injector is not an economical device, but it is simple and convenient, it occupies but a small amount of space, is not expensive and is free from severe strains on its durability; moreover, where a number of boilers are used in one establishment, it is very convenient to have the feeding arrangements separate, so that each boiler is a complete generating system in itself and independent of its neighbors.

LAWS OF HEAT.

Heat is a word freely used, yet difficult to define. The word “heat” is commonly used in two senses: (1) to express the sensation of warmth; (2) the state of things in bodies which causes that sensation. The expression herein must be taken in the latter sense.

Heat is transmitted in three ways—by _conduction_, as when the end of a short rod of iron is placed in a fire, and the opposite end becomes warmed—this is conducted heat; by _convection_ (means of currents) such as the warming of a mass of water in a boiler, furnace, or saucepan; and by _radiation_, as that diffused from a piece of hot metal or an open fire. Radiant heat is transmitted, like sound or light, in straight lines in every direction, and its intensity diminishes inversely as the square of the distance from its center or point of radiation. Suppose the distance from the center of radiation to be 1, 2, 3 and 4 yards, the surface covered by heat rays will increase 1, 4, 9 and 16 square feet; the intensity of heat will diminish 1, 1/4, 1/9, and 1/16. and so on in like proportions, until the heat becomes absorbed, or its source of supply stopped.

Whenever a difference in temperature exists, either in solids or liquids that come in contact with or in close proximity to each other, there is a tendency for the temperature to become equalized; if water at 100° be poured into a vessel containing an equal quantity of water at 50°, the tendency will be for the whole to assume a temperature of 75°; and suppose the temperature of the surrounding air be 30°, the cooling process will continue until the water and the surrounding air become nearly equal, the temperature of the air being increased in proportion as that of the water is decreased.

The heat generated by a fire under the boiler is transmitted to the water inside the boiler, when the difference in the specific gravities, or, in other words, the cold water in the pipes being heavier than that in the boiler sinks and forces the lighter hot water upward. This heat is radiated from the pipes, which are good conductors of heat to the air in the room, and raises it to the required temperature. That which absorbs heat rapidly, and parts with it rapidly, is called a good conductor, and that which is slow to receive heat, and parts with it slowly, is termed a bad conductor.

The following tables of conductivity, and of the radiating properties of various materials, may be of service:

CONDUCTING POWER OF VARIOUS SUBSTANCES.—DESPRITZ.

_Material._ _Conductivity._
Gold 100
Silver 97
Copper 89
Brass 75
Cast iron 56
Wrought iron 37
Zinc 36
Tin 30
Lead 18
Marble 2.4
Fire clay 1.1
Water 0.9

RADIATING POWER OF VARIOUS SUBSTANCES.—LESLIE

_Radiating_
_Material._ _Power._

Lampblack 100
Water 100
Writing paper 98
Glass 90
Tissue paper 88
Ice 85
Wrought lead 45
Mercury 20
Polished lead 19
Polished iron 15
Gold, silver 12
Copper, tin 12

From the above tables, it will be seen that water, being an excellent radiator, and of great specific heat, and iron a good conductor, these qualities, together with the small cost of the materials, combine to render them efficient, economic and convenient for the transmission and distribution of artificial heat.

By adopting certain standards we are enabled to define, compare and calculate so as to arrive at definite results, hence the adoption of a standard unit of heat, unit of power, unit of work, etc.

The standard unit of heat is the amount necessary to raise the temperature of one pound of water at 32° Fahr. one degree, _i.e._, from 32° to 33°.

Specific heat is the amount of heat necessary to raise the temperature of a solid or liquid body a certain number of degrees; water is adopted as the unit or standard of comparison. The heat necessary to raise one pound of water one degree, will raise one pound of mercury about 30 degrees, and one pound of lead about 32 degrees.

TABLE OF THE SPECIFIC HEAT OF EQUAL WEIGHTS OF VARIOUS SUBSTANCES.

_Specific_
_Solid bodies._ _Heat._
Wood (fir and pine) 0.650
„ (oak) 0.570
Ice 0.504
Coal 0.280
Charcoal (animal) 0.260
„ (vegetable) 0.241
Iron (cast) 0.241
Coke 0.201
Limestone 0.200
Glass 0.195
Steel (hard) 0.117
„ (soft) 0.116
Iron (wrought) 0.111
Zinc 0.095
Copper (annealed) 0.094
„ (cold hammered) 0.093
Tin 0.056
Lead 0.031
_Liquids._
Water 1.000
Alcohol 0.158
Acid (pyroligneous) 0.590
Ether 0.520
Acid (acetic) 0.509
Oil (olive) 0.309
Mercury 0.033

_Gases._
Hydrogen 3.409
Vapor of alcohol 0.547
Steam 0.480
Carbonic oxide 0.245
Nitrogen 0.243
Oxygen 0.217
Atmospheric air 0.237
Carbonic acid 0.202

THE STEAM PUMP.

It is difficult to overestimate the importance, in connection with a steam plant, of the appliance which supplies water for the boiler, not only, but a hundred other uses. Upon the steady operation of the pump depends the safety and comfort of the engineer, owner and employee, and indirectly of the success of the business with which the “plant” is connected. Hence the necessity of acquiring complete knowledge of the operation of a device so important.

Pumps now raise, convey and deliver water, beer, molasses, acids, oils, melted lead. Pumps also handle, among the gases, air, ammonia, lighting gas, and oxygen. Pumps are also used to increase or decrease the pressure of a fluid.

Pumps are made in many ways, and defined as rope, chain, diaphragm, jet, centrifugal, rotary, oscillating, cylinder.

Cylinder pumps are of two classes, single acting and double acting. In single acting—in effect is _single ended_—in double acting, the motion of the cylinder in one direction causes an inflow of water and a discharge at the same time, in the other; and on the return stroke the action is renewed as the discharge end becomes the suction end. The pump is thus double acting.

A _direct pressure_ steam pump is one in which the liquid is pressed out by the action of steam upon its surface, without the intervention of a piston. A direct acting steam pump is an engine and pump combined.

A cylinder or reciprocating pump is one in which the piston or plunger, in one direction, causes a partial vacuum, to fill which the water rushes in pressed by the air on its head.

NOTE.—A _suction valve_ prevents the return of this water on the return stroke of the piston, and a _discharge valve_ permits the outward passage of the fluid from the pump but not its return thereto or to the reservoir through the suction pipe.

The force against which the pump works is gravity or the attraction of the earth which prevents the water from being lifted. This is shown by the fact that water can be led, or trailed, an immense distance, limited only by the friction, by a pump.

NOTE.—It may be noted that the difference between a fluid and _liquid_ is shown in the fact that the latter can be poured from one vessel to another, thus: air and water are both fluids, but of the two water alone is liquid: air, ammonia, etc., are _gases_, while they are also fluids, _i.e._, they flow.

The idea entertained by many that water is raised by suction, is erroneous. Water or other liquids are raised through a tube or hose by the pressure of the atmosphere on their surface. When the atmosphere is removed from the tube there will be no resistance to prevent the water from rising, as the water outside the pipe, still having the pressure of the atmosphere upon its surface, forces water up into the pipe, supplying the place of the excluded air, while the water inside the pipe will rise above the level of that outside of it proportionally to the extent to which it is relieved of the pressure of the air.

If the first stroke of a pump reduces the pressure of the air in the pipe from 15 pounds on the square inch to 14 pounds, the water will be forced up the pipe to the distance of 2-1/4 feet, since a column of water an inch square and 2-1/4 feet high is equal in weight to about 1 pound. Now if the second stroke of the pump reduces the pressure of the atmosphere in the pipe to 13 pounds per inch, the water will rise another 2-1/4 feet; this rule is uniform, and shows that the rise of the column of water within the pipe is equal in weight to the pressure of the air upon the surface of the water without.

There are pumps (Centrifugal) especially designed for pumping water mingled with mud, sand, gravel, shells, stones, coal, etc., but with these the engineer has but little to do, as they are used mostly for wrecking and drainage.

The variety of pattern in which pumps are manufactured and the still greater variation in capacity forbids an attempt to fully illustrate and describe further than their general principles, and to name the following general

CLASSIFICATION OF PUMPS.

1st. Pumps are divided into Vertical and Horizontal.

Vertical pumps are again divided into:

1. Ordinary Suction or Bucket Pumps.
2. Suction and Lift Pumps.
3. Plunger or Force Pumps.
4. Bucket and Plunger Pumps.
5. Piston and Plunger Pumps.

Horizontal Pumps are divided into:

1. Double-acting Piston Pumps.
2. Single-acting Plunger Pumps.
3. Double-acting Plunger Pumps.
4. Bucket and Plunger Pumps.
5. Piston and Plunger Pumps.

A—Air Chamber.
B—Water Cylinder Cap.
C—Water Cylinder with Valves and Seats in.
D—Rocker Shafts, each, Long or Short.
E—Removable Cylinders, each.
F—Water Piston and Follower, each.
„—Water Piston Followers, each.
G—Rocker Stand.
H—Suction Flange, threaded.
I—Discharge Flange, threaded.
J—Intermediate Flanges, each.
K—Water Cylinder Heads, each.
L—Concaves complete, with Stuffing Boxes, each.
M—Steam Cylinder, without Head, Bonnet and Valve.
N—Steam Cylinder Foot.
O—Crosshead Links, each.
P—Steam Piston complete with Rings and Follower, each.
m—Steam Piston Head.
n—Steam Piston Follower.
Steam Piston Rings, including Spring and Breakjoint.
Q—Side Water Cylinder Bonnet, each.
R—Steam Chest Bonnet, each.
S—Steam Chest Stuffing Box Gland, each.
T—Steam Slide Valve, each.
U—Piston Rods, each.
V—Crossheads, each.
W—Rocker Arms, each, Long or Short.
X—Valve Rod Links, each, Long or Short.
Y—Steam Valve Stems, each.
Z—Steam Cylinder Heads, each.
aa—Piston Rod Nuts, each.
hh—Piston Rod Stuffing Glands, each.
ii—Water Valve Seats, each.
jj—Rubber Valves, each.
kk—Water Valve Stems, each.
ll—Water Valve Springs, each.
gg—Removable Cylinder Screws, each.
b—Steam Valve Stem Forks, each.
c—Steam Valve Stem Fork Bolts, each.
e—Valve Rod Link Bolts, each.
d—Rocker Arm Pins, each.
f—Crosshead Link Bolts, each.
o—Collar Bolts, each.
pp—Brass Steam Cylinder Drain Cocks, each.
Water Packings, each.
Brass Piston Rods, each.
Brass Lined Removable Cylinders, extra, each.
Piston Rod Stuffing Gland Bolts, each.
Water Cylinder Cap Bonnets, each.
Top Valve Caps, each.
Valve Cap Clamps, each.
]

In Figs. 102 and 103 are exhibited the outlines of _the double acting steam pump_, which is undoubtedly the pattern most thoroughly adapted for feeding steam boilers, as it is equipped for the slowest motion with less risk of stopping on a centre.

From the drawing with reference letters may be learned the terms applied generally to the parts of all steam pumps: example: “k” shows the water valve stems, “K” the water cylinder heads.