In the application of manual power to the working of fire-engines, the principal object is, to apply the greatest aggregate power to the lightest and smallest machine; that is, suppose two engines of the same size and weight, the one with space for 20 men to work throws 60 gallons per minute; and the other, with space for 30 men, throws 80 gallons in the same time; the latter will be the most useful engine, although each man is not able to do so much work as at the former.
The reciprocating motion is generally preferred to the rotary for fire-engines.
Independent of its being the most advantageous movement, a greater number of men can be employed at an engine of the same size and weight; there is less liability to accident with people unacquainted with the work, and such as are quite ignorant of either mode of working, work more freely at the reciprocating than the rotary motion. To these reasons may be added, the greater simplicity of the machinery.
Various sizes of engines, of different degrees of strength and weight, have been tried, and it is found that a fire-engine with two cylinders of 7 inches diameter, and a stroke of 8 inches, can be made sufficiently strong at 17-1/2 cwt. If 4 cwt.
be added for the hose and tools, it will be found quite as heavy as two fast horses can manage, for a distance under six miles, with five firemen and a driver.
Fig. 1. Fire-Engine used by the London Fire Brigade. Longitudinal section,— with the Levers turned up for travelling. Fig. 1. Fire-Engine used by the London Fire Brigade. Longitudinal section,—with the Levers turned up for travelling.
This size of engine has been adopted by the Board of Admiralty and the Board of Ordnance, and its use is becoming very general.
When engines are made larger, it is seldom that the proper proportions are preserved, and they are generally worked with difficulty, and soon fatigue the men at the levers.
Fig. 2. Transverse section. Fig. 2. Transverse section.
When an engine is large, it not only requires a considerable number of men to work it, but it is not easily supplied with water; and, above all, it cannot be moved about with that celerity on which, in a fire-engine establishment, everything depends. When the engine is brought into actual operation, the effect to be produced depends less on the quantity of water thrown than upon its being made actually to strike the burning materials, the force with which it does so, and the steadiness with which the engine is worked. If the water be steadily directed upon the burning materials, the effect even of a small quantity is astonishing.
When a large engine is required in London, two with 7-inches cylinders are worked together by means of a connecting screw, thus making a jet very nearly equal (as 98 to 100) to that of an engine with cylinders 10 inches diameter.
It is also an advantage not unworthy of consideration, that two 7-inch engines may be had nearly for the price of one 10-inch one; so that if one happens to be rendered unserviceable the other may still be available.
The usual rate of working an engine of the size described is 40 strokes of each cylinder per minute; this gives 88 gallons. The number of men required to keep steadily at work for three or four hours is 26; upwards of 30 men are sometimes put on when a great length of hose is necessary. The lever is in the proportion of 4-1/4 to 1. With 40 feet of leather hose and a 7/8 inch jet, the pressure is 30 lb.
on the square inch; this gives 10.4 lbs. to each man to move a distance of 226 feet in one minute. The friction increases the labour 2-1/2 per cent. for every additional 40 feet of hose, which shows the necessity of having the engine, and of course the supply of water, as close to the fire as is consistent with the safety of the men at the levers.
In order that the reader may have a distinct idea of such a fire-engine, I shall here endeavour to give a description, chiefly taken from those made by W. J.
Tilley,[K] fire-engine maker, London.
The engravings (figs. 1 and 2) represent a fire-engine of 7-inch barrels and 8- inch stroke.[L] The cistern marked A is made of mahogany or oak. The upper work, B, and side-boxes or pockets, C, are of Baltic fir. The sole, D, upon which the barrels stand, and which also contains the valves, is of cast-iron, with covers of the same material, which are screwed down, and the joints made good with leather or india-rubber. The pieces E, at each end of the cast-iron sole D, are of cast brass, and screwed to the cast-iron sole D, with a joint the same as above. In one of these pieces is the screwed suction-cap F, and to the other is attached the air-vessel G, made of sheet-copper, and attached to the piece E by a screw. The exit-pipe H is attached to the under side of the casting E by a swivel. The valves at I are of brass, ground so as to be completely water-tight. The barrels K are of cast brass. The engine is set on four grasshopper springs M. The shafts or handles O, of the levers P, are of lancewood. The box S, under the driving seat, is used for keeping wrenches, cord, &c.; in the fore part of the cistern A, and the box B above the cistern, the hose is kept; the branch and suction-pipes are carried in the side-boxes or pockets C; the rest of the tools and materials are kept along with the above-mentioned articles, in such situations as not to interfere with the working of the engine.
The cistern is made of oak or mahogany, for strength and durability; but, for the sake of lightness, the upper work and side-boxes are made of Baltic fir, strength in them being of less importance.
As the valve cannot be made without a rise for the lid to strike against, there is a small step at each of the valves, and the sole is carried through as high as this step, to admit of the water running off when the engine is done working. If constructed in a different manner, the water will lodge in the bottom, and produce much inconvenience in situations where the engine is exposed to frost.
The valve-covers are of cast-iron, fastened down with copper screws, a piece of leather or india-rubber being placed between them and the upper edges of the sole.
The pieces at each end of the sole are of cast-brass, instead of sheet-copper, with soft-solder joints, which are very apt to give way.
The screwed suction cap with iron handle admits the water in two different directions, according as it is open or closed: the one to supply the engine when water is drawn from the cistern, the other for drawing water through the suctionpipe.
The valves are brass plates, truly ground to fit the circular brass orifice on which they fall. The brass being well ground, no leather is used for the purpose of making them tight. The longer they are used the better they fit, and by having no leather about them they are less liable to the adhesion of small stones or gravel.
The whole valve is put together and then keyed into a groove in the sides and bottom of the sole, left for that purpose.
The barrels are of cast-brass, with a piston made of two circular pieces of the same metal, each put into a strong leather cup, and bolted to the other. The bottoms of the cups being together, when the piston becomes loose in the barrels, and there is not sufficient time to replace the cups by new ones, they are easily tightened by putting a layer of hemp round the piston between the leather and the brass. This operation, however, requires to be carefully performed; for if more hemp is put into one part than another it is apt to injure the barrels. The barrels are fixed to the cast-iron sole by copper screws, a little red lead being placed between the bottom flange of the barrel and the sole.
When the engine is likely to be dragged over rough roads or causeways, it is of importance to have it set on springs, to prevent the jolting from affecting the working part of the engine, everything depending on that being right.
The engines used in Paris are mounted on two wheels, the carriage and the engine being separate, the latter being dismounted from the former before it can be used. In Paris, where the engines are managed by a corps of regularly-trained firemen, this may answer well enough; but if hastily or carelessly dismounted by unskilful persons, the engine may be seriously damaged. It is also worthy of remark, that the proper quantity of hose, tools, &c., can be more easily attached to and carried on a four-wheeled engine.
In order that the men may work more easily at the handles, and suffer less fatigue, the engine is not higher than to enable them to have the levers easily under their command. The shafts of the levers are of lancewood, being best calculated to bear the strain to which they are exposed when the engine is at work, and they are made to fold up at each end for convenience in travelling.
The air-vessel should be placed clear of any other part of the engine, excepting only the point where it is attached.
The fore-carriage of the engine is fitted with a pole, and is made to suit the harness of coach-horses, these being, in large towns, more easily procured than other draught cattle; this can be altered, however, to suit such harness as can most readily be obtained. Where horses are seldom used to move the engines, a drag-handle is attached, by which one or two men are able easily to direct the progress of the engine.
Two drag-ropes, each twenty-five feet long, of three-inch rope, with ten loops to each, are attached, one to each end of the splinter-bar, by means of which the engines are dragged; and to prevent the loops collapsing on the hand, they are partly lined with sheet-copper.
The whole of the brass work of an engine should be of the best gun-metal, composed of copper and tin only. Yellow brass should never be used; even at first it is far inferior to gun-metal, and after being used for some time it gets brittle. The whole of the materials used in the construction of a fire-engine should be of the best description.
In London for some years past a hand-pump has been carried with each engine.
They have been found of the greatest service in keeping doors, windows, &c., cool. They throw from six to eight gallons per minute, to a height of from thirty to forty feet, and can be used in any position. The idea of the hand-pumps I took from the old-fashioned squirt, or "hand-engine." When fire-engines are unserviceable it arises more frequently from want of care in keeping in order than from any damage they may have received in actual service or by the wearing out of the materials; so it is quite plain that this important part of the duty has not generally had that degree of attention paid to it which it deserves.
Although an engine were to be absolutely perfect in its construction, if carelessly thrown aside after being brought home from a fire, and allowed to remain in that state till the next occasion, it would be in vain (especially in small towns, where alarms are rare) to expect to find it in a serviceable condition; some of the parts must have grown stiff, and if brought into action in this state something is likely to give way.
When an engine is brought back from a fire, it ought to be immediately washed, the cistern cleaned out, the barrels and journals cleaned and fresh oil put on them, the wheels greased, and every part of the engine carefully cleaned and examined, and if any repairs are needed they should be executed immediately.
When all this has been attended to clean hose should be put in, and the engine is again fit for immediate service. Besides this cleaning and examination after use, the engine ought to be examined and the brass part cleaned once a week, and worked with water once a month whether it has been used or not.
In addition to the keeping of the engine always in an effective state, this attention has the advantage of reminding the men of their duty, and making them familiar with every part of the mechanism of the engine; thus teaching them effectually how the engines ought to be protected when at work, by enabling them to discover those parts most liable to be damaged, and to which part damage is the most dangerous. It is more troublesome generally to get the engines well kept when there are no fires, than when there are many. But the only effectual method of inducing the men to keep them in good order, in addition to the moral stimulants of censure and applause, is to fine those who have the charge of them for the slightest neglect.
When the engine has been properly placed, before beginning to work the forecarriage should be locked. This is done by putting an iron pin through a piece of wood attached to the cistern, into the fore-carriage. This prevents the wheels from turning round, and coming under the shafts, by which the latter might be damaged, and the hands of the men at work injured.
Small stones, gravel, and other obstructions, sometimes find their way into the nozzle of the branch-pipe, from having dropped into the hose before being attached, or having been drawn through the suction-pipe or from the cistern.
Whenever the engine is found to work stiffly, it should be stopped and examined, otherwise the pressure may burst the hose, or damage some part of the engine. If anything impedes the action of the valves the pistons must be drawn, and if a person's hand be then introduced they may easily be cleared—constant care and attention to all the minutiæ of the engine and apparatus being absolutely indispensable, if effective service be expected from them.
Considerable attention ought to be paid to the selecting a proper situation for an engine-house. Generally speaking, it ought to be central, and on the highest ground of the district it is meant to protect, and care should be taken to observe when any of the streets leading from it are impassable.
If, in addition to these advantages, the engine-house can be had adjoining to a police watch-house, it may be considered nearly perfect, in so far as regards situation. These advantages being all attained, the engine can be conveyed to any particular spot by a comparatively small number of men, while the vicinity of a police watch-house affords a facility of communicating the alarm of fire to the firemen not to be obtained otherwise. When the engine-house is placed in a low situation the men who first arrive must wait till the others come forward to assist them to drag the engine up the ascent, and many minutes must thus be lost at a time when moments are important.
After choosing a proper situation for the engine-house, the next care should be directed towards having it properly ventilated, as nothing contributes more to the proper keeping of the engines and hose than fresh and dry air. For this purpose a stove should be fitted up, by which the temperature may be kept equal. When engines are exposed to violent alternations of heat and cold, they will be found to operate very considerably on the account for repairs, besides occasioning the danger of the engine being frozen and unserviceable when wanted.
There ought to be at least half a dozen keys for each engine-house, which should be kept by the firemen, watchmen, and those connected with the establishment, that the necessity of breaking open the door may not occur.
© Copyright 2020 Qouh - All Rights Reserved