A Catechism of the Steam Engine Part 35

The fire box or furnace is simply a square box or furnace of any required dimensions; it is nothing more than a water s.p.a.ce surrounding the fire, stay-bolted as all water s.p.a.ces are. It is made of boiler plate in the usual manner. The water s.p.a.ce extends only 2/3 of the height, the balance being a single sheet. The bottom of this fire box is crossed by grate bars to support the fuel; in its rear side are fire doors, inserted for firing.

The internal arrangements of the boiler are composed of a large number of tubes, lying across in a horizontal position, put together in sections with return bends resembling the coils for heating buildings. These coils are of small pipe (say one inch in diameter), and as numerous as may be necessary.

They give the required amount of steam. They are secured to wrought-iron plates at each end by rivets. These plates lie close to the box, and are secured to it, top and bottom. These tubes are wrought iron, firmly screwed into the bends, so as to prevent any possible breaking.

The box has a hole through both sheets, in the same manner as a hollow stay-bolt, through which the coil pipe pa.s.ses, having no connection with the box. After pa.s.sing into the box it divides into two pipes, then subdivides into four, and so on, until its numbers equal the number of coils in the box, and to which each limb is attached. The upper ends of these coils are the same in number, and are carried through at the top or nearly the top of the box. They then run down outside to the steam chamber, or rather water s.p.a.ce, as the box is both steam chamber and water s.p.a.ce.

These pipes empty their contents into the box, steam and water, as it may come, all together. It will be observed that these coils of tube are sufficiently separated to allow the fire to pa.s.s between them freely, and cover their whole surface.

The mode of operation of this boiler is this: The fire box is filled 2/3 full of water. The coils are dry at starting; the s.p.a.ce for fuel being filled with good wood, the fire is lighted, and in a few moments the engineer moves his hand pump, which takes its water from the box to which it is attached, and forces it through the coils. By this means steam is generated in from 3 to 5 minutes, so as to start the engine.

It will be seen that the water performs a complete circuit; it is taken from the box and pa.s.sed through the coils; what is steam remains in the steam chamber, and what is not (if any) drops back into the box from where it started. Hence it will be seen that a large surface is exposed to a small quant.i.ty of water, and in a way that it is entirely controllable. All the engineer has to do to surcharge his steam, is to reduce the speed of the pump (which is independent of the main engine). By raising the heat and quant.i.ty of water, any degree of elasticity can be given to the steam, and that, too, with the least amount of waste heat in giving a natural draft.

Hence the great economy of this boiler.

The next feature of this engine is, it has no wood work about it to perish with the heat and roughness of the streets. All the wheels are wrought iron; and, as yet, these are the only ones that have stood a steam fire engine. The frame is wrought iron; truck, on which the front wheel is hung, wrought iron. The axles are cast steel. The engine and pump is a double-acting piston pump direct, without any rotary motion; with a perfect balance valve, it is balanced at all times, and hence the engine remains quiet without blocking, when at work. The engine is mounted on three wheels, which enables it to be turned in a very short s.p.a.ce.

Many engines have been constructed by the Messrs. Latta for the fire companies, of different cities, and have been in successful compet.i.tion with other engines; the farthest throw ever made by one of their first-cla.s.s engines was 310 feet from a 1-5/8 inch nozzle; steaming time, starting from cold water, 3-1/2 minutes.

[Ill.u.s.tration: Fig. 74 AMOSKEAG STEAM FIRE ENGINE.]

Fig. 74 is a representation of one cla.s.s of steam fire engine, as built by the Amoskeag Manufacturing Company, at Manchester, N.H. The boiler is an upright tubular boiler, of a peculiar construction, the patent right to which is vested in the Amoskeag Manufacturing Company. This boiler is very simple in its combination, and for safety, strength, durability, and capacity for generating steam is unsurpa.s.sed. No fan or artificial blower is ever used or needed, the natural draft of the boiler being always sufficient. Starting with cold water in the boiler, a working head of steam can be generated in _less than five minutes_ from the time of kindling the fire. The engine "Amoskeag," owned by the city of Manchester, has played two streams in _three minutes and forty seconds_ after touching the match, at the same time drawing her own water. The boilers are made and proved so as to be safely run at a steam pressure of 140 to 150 lbs. to the square inch; but the engines are constructed so as to give the best streams at a pressure of about 100 lbs. to the square inch, and for service at fires a steam pressure of about 60 lbs. to the square inch is all that is required.

The various styles of engine are all _vertical_ in their action, and in all the pumps and steam cylinders are firmly and directly fastened to the boiler, the steam cylinders being attached directly to the steam dome. This arrangement obviates the necessity of carrying steam to the cylinders through pipes of considerable length, and the machine has very little vibratory motion when in operation--so little that it is not necessary to block its wheels to keep it in its place, or to take the weight off the springs before commencing work.

The pumps are placed on the engines as near the ground as they can be with safety, and are arranged so as to attach the suction and leading hose to either or both sides of the machine, as may be most convenient or desirable, so that less difficulty will be found in placing an engine for work, and when required to draw its own water, it has only to draw it the shortest possible distance.

Each engine has two "feed pumps" for supplying the boiler, and also a connection between the main forcing pumps and the boiler, so that it can be supplied from that source if desirable. The tank which carries the water for supplying the boiler is so placed that the water in it is always above the "feed pumps," an advantage that insures the almost certain working of these pumps. These pumps are of bra.s.s, the best locomotive pattern, and one of them running with the engine, when at work, furnishes an ample supply of water to the boiler.

[Ill.u.s.tration: Fig. 75.]

The engines are exceedingly portable; they can be turned about or placed for service in as contracted a s.p.a.ce as any hand engine, and two good horses will draw a first-cla.s.s engine with the greatest ease, carrying at the same time water for the boiler, a supply of fuel sufficient to run the engine two hours, the driver, the engineer, and the fireman.

Fig. 75 is a representation of the cla.s.s of steam fire engine built by Silsbee, Mynderse & Co., Seneca Falls, N. Y. under Holly's patent.

The boiler is vertical, with vertical water tubes pa.s.sing directly through the fire. These tubes are closed at the bottom and open at the top, where they pa.s.s through a water-tight plate, and communicate with the water in the boiler. The arrangement of the tubes causes a constant current, the water rising on the outside of the tubes as they are heated, and its place being supplied by a current flowing downward through the tube to the boiler. The smoke and flame pa.s.s among the tubes up through flues.

Both engine and pump are rotary, and of the same type. They consist essentially of two elliptical rotary pistons, cogged and working into one another in an air-tight case. The pistons fit close to the inside of the case, and gear into each on the line of their conjugate diameters. The action is somewhat similar to the old-fashioned rotary pump, consisting of two cog wheels in gear with, each other, the s.p.a.ces at the side of the case being filled with water, which at the centre are occupied by the teeth in gear. In Holly's pump, instead of uniform teeth, and depending on the fit of the teeth with the side of the case and with each other for the packing, there are two large teeth in each piston opposite each other, which have slide pistons, and intermediate with these large teeth are small cogs, which continue the motion of the rotary pistons. The machine works very smoothly, and performs the work necessary, in ordinary service, under a pressure of 50 to 60 lbs.

There are many other makers of fire engines in this country; but sufficient examples are given to ill.u.s.trate the cla.s.s; so successful have they been, that they are fast superseding hand engines, even in the smaller cities.

Under a paid department, the following is, in the city of Boston, Ma.s.s., the comparative cost of running the two kinds of engines, viz.:

STEAM FIRE ENGINE.

1 engineer........................................... $720 00 1 fireman............................................ 600 00 1 driver............................................. 600 00 1 foreman of hose.................................... 150 00 8 hos.e.m.e.n, at $125 each.............................. 375 00 -- -------- 7 men................................................ $2,445 00 Keeping of 2 horses.................................. 315 00 -------- Total......................................... $2,760 00

HAND ENGINE.

1 foreman............................................ $150 00 1 a.s.sistant foreman.................................. 125 00 1 clerk.............................................. 125 00 1 steward............................................ 125 00 3 leading hos.e.m.e.n, at $125 each...................... 375 00 33 men, at $100 each................................. 3,300 00 -- --------- 40 men............................................... $4,200 00

Here the engineer, fireman, and driver are constantly employed, the hos.e.m.e.n have other employment in the neighborhood, but all the company sleep in the engine house.

In the city of Manchester, N.H., a steam fire engine company is composed of fourteen men, all told, one of whom, acting as driver and steward, is constantly employed, remaining at the engine house with a pair of horses always ready to run out with the engine in case of an alarm of fire. The other members of the company have other employments, and turn out only on an alarm of fire.

STEAM FIRE ENGINES.

"Amoskcag," Expenditures..................... $864 32 "Fire King," " ..................... 855 78 "E.W. Harrington," " ..................... 496 09

The above expense includes pay of members, team expenses, cost of gas, wood, coal, and all necessities incident to service. The "E.W. Harrington"

is a second-cla.s.s engine, stationed in the outskirts of the city, and was run cheaper from the fact that no horses were kept for it by the city.

A first-cla.s.s hand-engine company is allowed to number, all told, fifty men, and the members of the company are paid as follows:

FIRST-CLa.s.s HAND-ENGINE COMPANY.

1 foreman.......................................... $35 00 1 a.s.sistant foreman............................... 28 00 1 clerk........................................... 28 00 1 steward........................................ 68 00 46 men, at $18 each................................ 828 00 -------- 50 men. Total.............................. $987 00

By this it will be seen, that in a city like Manchester, with from twenty to twenty-five thousand inhabitants, a first-cla.s.s steam fire engine can be run at an expense not to exceed that of a first-cla.s.s hand engine, while in service it will do at least _four times_ the work. The cost of repairs is found by experience to be no greater on the steam fire engines than on hand engines.

The Excavator, fig. 76, is the invention of the late Mr. Otis, an application of the spoon dredging machine of the docks to railway purposes, with very important modifications. The machine consists of a strong truck, _A_, _A_, mounted on railway wheels, on which is placed the boiler _C_, the crane _E_, and the requisite gearing. The excavator or shovel, _D_, is a box of wrought iron, with strong points in front to act as picks in loosening the earth, and its bottom hung by a hinge at _d_, so that, by detaching a catch, it may fly open and discharge the material raised. To operate the machine, suppose the shovel _D_ to be in the position shown in the cut; it is lowered by the chains _o_, _o_, and thrown forward or backward, if necessary, by the drum _B_, and handle _S_, till the picks in the front of the shovel are brought in proper contact with the face of the cut; motion forward is now given to the shovel by the drum _B_ and handle _S_, and at the same time it is raised by the chains _o_, _o_. These two motions can be so adjusted to each other, as to give movement to the shovel to enable it to loosen and sc.r.a.pe up a shovelful of earth. The handle _S_ is now left free, and the shovel _D_ is raised vertically by the chains _o_, _o_. The crane is now turned round, till the shovel comes over a rail car on a side track; the bottom of the shovel is opened, and the dirt deposited in the car. All these motions are performed by the aid of a steam engine, and are controlled by a man who stands on a platform at _f_.

[Ill.u.s.tration: Fig 76.]

692. _Q._--Having now described the most usual and approved forms of engines applicable to numerous miscellaneous purposes for which a moderate amount of steam power is required, will you briefly recapitulate what amount of work of different kinds an engine of a given power will perform, so that any one desiring to employ an engine to perform a given amount of work, will be able to tell what the power of such engine should be?

_A._--It will of course be impossible to recapitulate all the purposes to which engines are applicable, or to specify for every case the amount of power necessary for the accomplishment of a given amount of work; but some examples may be given which will be applicable to the bulk of the cases occurring in practice.

693. _Q._--Beginning, then, with the power necessary for threshing,--a 4 horse power engine, with cylinder 6 inches diameter, pressure of steam 45 lbs., per square inch, and making 140 revolutions per minute, will thresh out 40 quarters of wheat in 10 hours with a consumption of 3 cwt. of coals.

_A._--Although this may be done, it is probably too much to say that it can be done on an average, and about three fourths of a quarter of wheat per horse power would probably be a nearer average. The amount of power consumed varies with the yield.

Messrs. Barrett, Exall, and Andrewes give the following table as ill.u.s.trative of the work done, and the fuel consumed by their portable engines; but this must be regarded as a maximum performance:--

Number of | Weight of | Quarters of | Quant.i.ty of | Quant.i.ty of Horse Power.| Engine. | Corn thrashed| Coals consumed| Water required | | in 10 Hours. | in 10 Hours. | for 10 Hours | | | | in Gallons.

------------|-----------|--------------|---------------|--------------- |Tons. Cwts.| | Cwts. | 4 | 2 0 | 40 | 3 | 360 5 | 2 5 | 50 | 4 | 380 6 | 2 10 | 60 | 5 | 460 7 | 2 15 | 70 | 6 | 540 8 | 3 0 | 80 | 7 | 620 10 | 3 10 | 100 | 9 | 780 -----------------------------------------------------------------------

694. _Q._--In speaking of horses power, I suppose you mean indicator horse power?

_A._--Yes; or rather the dynamometer horse power, which is the same, barring the friction of the engine. At the shows of the Royal Agricultural Society, the power actually exerted by the different engines is ascertained by the application of a friction wheel or dynamometer.

695. _Q._--Can you give any other examples of the power necessary for grinding corn?

_A._--An engine exerting 23-1/3 horses power by the indicator works two pairs of flour stones of 4 feet 8 inches diameter, two pairs of stones grinding oatmeal of 4 feet 8 inches diameter, one dressing machine, one pair of fanners, one dust screen, and one sifting machine. One of the flour stones makes 85, and the other 90 revolutions in the minute. One of the oatmeal stones makes 120, and the other 140 revolutions in the minute. To take another case:--An engine exerting 26-1/2 indicator horses power works two pairs of flour stones, one dressing machine, two pairs of stones grinding oatmeal, and one pair of sh.e.l.ling stones. The flour stones, one pair of the oatmeal stones, and sh.e.l.ling stones, are 4 feet 8 inches diameter. The diameter of the other pair of oatmeal stones is 3 feet 8 inches. The length of the cylinder of the dressing machine is 7 feet 6 inches. The flour stones make 87 revolutions in the minute, and the larger oatmeal stone 111 revolutions, but the smaller oatmeal stone and the sh.e.l.ling stone revolve faster than this. At the time the indicator diagram was taken, each pair of flour stones was grinding at the rate of 5 bushels an hour; each pair of oatmeal stones about 24 bushels an hour; and the sh.e.l.ling stones were sh.e.l.ling at the rate of about 54 bushels an hour. The fanners and screen were also in operation.

696. _Q._--Have you any other case to enumerate?

_A._--I may mention one in which the power of the same engine was increased by giving it a larger supply of steam. The engine when working with 8.65 horses power, gives motion to one pair of oatmeal stones of 4 feet 6 inches diameter, and one pair of flour stones 4 feet 8 inches diameter. The oatmeal stone makes 100 revolutions in the minute, and the flour stone 89.

The oatmeal stones grind about 36 bushels in the hour, and the flour stones 5 bushels in the hour. The engine when working to 12 horses power drives one pair of flour stones, 4 feet 8 inches diameter, at 89 revolutions per minute and one pair of stones of the same diameter at 105 revolutions, grinding beans for cattle. The flour mill stones with this proportion of power, being more largely fed, ground 6 bushels per hour, and the other stones also ground 6 bushels per hour. When the power was increased to 18 horses, and the engine was burdened in addition with a dressing machine having a cylinder of 19 inches diameter, the speed of the flour stone fell to 85, and of the beans stone to 100 revolutions per minute, and the yield was also reduced. The dressing machine dressed 24 bushels per hour.

697. _Q._--What is the power necessary to work a sugar mill such as is used to press the juice from canes in the West Indies?

_A._--Twenty horses power will work a sugar mill having rollers about 5 feet long and 28 inches diameter; the rollers making 2-1/3 turns in a minute. If the rollers be 26 inches diameter and 4-1/2 feet long, 18 horses power will suffice to work them at the same speed, and 16 horses power if the length be reduced to 3 feet 8 inches. 12 horses power will be required to work a sugar mill with rollers 24 inches diameter and 4 feet 2 inches long; and 10 horses power will suffice if the rollers be 3 feet 10 inches long and 23 inches diameter. The speed of the surface of sugar mill rollers should not be greater than 16 feet per minute, to allow time for the canes to part with their juice. In the old mills the speed was invariably too great. The quant.i.ty of juice expressed will not be increased by increasing the speed of the rollers, but more of the juice will pa.s.s away in the bega.s.s or woody refuse of the cane.

698. _Q._--What is the amount of power necessary to drive cotton mills?