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and permanent perfect condition of this vital part of a boiler apparatus, will be seen at a glance to characterise the design of this absolute safety-valve.
The chief feature of novelty, however, which distinguishes this improved safety-valve from all others hitherto proposed, consists in the peculiar and simple manner in which the motion of the water in the boiler is employed, as the agent by which the valve is prevented from ever getting set fast in its seat. The swaying to-and-fro sort of motion which at all times accompanies the ebullition of water in boilers, is made to act upon a sheet-iron appendage to the weight directly attached to the valve; and as the rod which connects this sheet-iron appendage and weight to the valve is inflexible, it will be easily seen how any slight pendulous motion given to the sheet-iron appendage is directly transferred to the valve; and as that portion of the valve which rests in the seat is spherical, the valve not only admits of, but receives, a continual slight motion in its seat in all directions, as the result of the universal pendulous motion of the appended weight, as acted upon by the incessant swaying motion of the water during ebullition. It will be seen that, as the spherical portions of the valve and seat are of equal width, the edges of their respective surfaces pass and repass each other continually, and so maintain and continually tend to improve the perfect spherical fit and agreement between the valve and its seat.
It may be proper to observe, that when the steam is nearly up to the desired pressure, the valve rests on its seat with a pressure next to no pressure at all, and is then, as it were, floating on steam. This action is common to all good valves; but the observation may tend to show how a slight movement of the water affects the valve in its seat. A pipe may lead the steam escaping from this valve to the manager's-office, and there give audible notice of its escape by acting in a steam-whistle there placed.
Still further to obviate the risk of boilers exploding from a dangerous pressure, "fusible plates" are introduced sometimes on the top of the boiler. These are made of a composition calculated to melt at a comparatively low temperature. Fusible plugs are also introduced into apertures on the boiler below water-line; these melting when the water gets too low, allow the steam to pass off. Little reliance, however, is to be placed on these contrivances.
All boilers are supplied with gauge-cocks, the nature of which has been already described; by these the level of the water in the boiler is ascertained.
Mercurial pressure-gauges are frequently used to indicate the exact degree of pressure in the boiler. A glass tube is placed in a small cistern filled with mercury; one end is closed, the other opens to the interior of boiler in the steam space: the steam passing down the tube presses on the surface of the mercury; by this means the air in the upper part of the tube is compressed, and in proportion to the compression so is the pressure in the boiler. In improved gauges, a scale is attached which shows the temperature of the steam as well as its pressure in the boiler. In fig. 82 an improved pressure-gauge is shown: aa is the pipe introducing steam from the boiler; b the pipe for leading off the water of condensation; cc the snugs for fixing the gauge in any convenient position. In mercurial gauges adapted for low-pressure boilers, the mercury is placed in a syphon tube, one end of which opens into the boiler, and the other is open to the atmosphere; the pressure of the steam raises the mercury in the short leg of the
PRESSURE IN to
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syphon, and acts on a small plug floating on it; to this is attached a pointer, which shows on an index the degree of pressure. When the steam gets of very high pressure, the mercury is blown out of the tube; in this way acting as a safety-valve.
The consumption of smoke arising from the fuel used to raise the steam in the furnaces of boilers, has long been a favourite project among inventors; and the adoption of a good plan to effect this desideratum, always of importance, has more recently attracted earnest attention, from the fact of many Corporations making it imperative on those who employ steam-engines to consume their own smoke. We cannot pretend to notice all the plans introduced for this purpose, but must content ourselves with noticing only one; that, however, the most recently invented, and which has already taken a high place in the rank of effective plans. This, the invention of Mr. John Lee Stevens of London, is shown in the diagram in fig. 83. "The invention," says Mr. Lee, in his prospectus, from which our diagrams are taken, "consists in the combination of two sets of fixed fire-bars, the first of which is fed by the scoria and cinders voided from the second or upper set of fire-bars, with a calorific plate, as shown in the diagram; by which arrangement, the current of air entering at the lower part of the furnace passes through two strata of fire, and thence between the calorific plate and the bridge; and is thus so intensely heated, as continuously to produce the entire combustion of the gaseous products of the fuel, without the formation of smoke." In fig. 83, b the first and a the second set of bars; c the calorific plate, faced with fire-bricks; d the bridge, e the furnace-flue, h the furnacedoor; i shows the direction of the current of air: this diagram shows the application of the principle to the Cornish boiler for land-engines. In fig. 71 the application is shown to marine boilers; the same letters of reference apply to this diagram as to fig. 83.
Still further to make the steam-engine automaton or self-acting in its arrangements, mechanism has been introduced by which the labour of the fireman or stoker is suspended, and the furnace supplied with fuel in proportion as required. Numerous contrivances have been introduced for this purpose; we shall only notice one, and that patented by Mr. Dean of Stockport, and in which neighbourhood it has been introduced with success. "It consists, first, of a double self-acting feed-apparatus, one side of which is caused to supply the furnace with fuel, whilst the other is at rest, and vice versa, alternate; and, secondly, in placing a partition-wall in the fur
nace, between the fire doors and the bridge of the same, and employing two dampers, at or about the bridge, which are opened and closed alternately by certain levers and rods connected with the feeding apparatus." In
addition, therefore, to acting as an automaton feed-apparatus to supply the furnace with fuel, it insures the combustion of the smoke and economisation of fuel. In fig. 84, we give an end view of a steam-boiler and furnace,
with the feeding mechanism applied; in fig. 85, a plan or horizontal section below the boiler; and in fig. 86, a transverse section in front of the bridge of the furnace. "a a is the foundation brick-work supporting the boiler, bb, cc the dead plate' of the furnace, dd the fire-bars. e is the main driving-shaft, to which motion is communicated (by the engine) by a strap passing round the pulley é at its upper-end, or by any other convenient means. Upon the main driving-shaft e is a pulley f, which, by means of the cross-belts g and n, drives alternately the shaft i of the right-hand feeding-apparatus, and the shaft j of the left-hand feeding apparatus. These shafts have each a fast and loose pulley at the upper-end; and the requisite shifting of the straps from the fast on to the loose pulley is effected
in the following manner: A small crank k is caused to revolve by means of a worm on the driving-shaft e, actuating the worm gearing 1; this crank k has a lever attached to it, furnished with two studs, m and n, which, as the crank revolves, causes the strap lever o to vibrate, and throw one strap on the loose pulley, and the other on the fast one, thus alternately setting in motion and stopping each feeding apparatus. It will be seen in figs. 85 and 86, that there is a partition-wall p in the furnace, reaching from the fire-bars to the bottom of the boiler; and extending from the bridge about half way to the fire-doors; and that there are two dampers q and r behind the bridge of the same, one of which is open and the other closed. The dampers are connected to the strap lever o by cranks and levers, so that when one side of the feeding-apparatus is supplying fuel to the fire, the damper upon that side is closed, and the damper on the other side open, and vice versa. In the drawings the right-hand feeding-apparatus
of the furnace, and will thereby be consumed. It will be evident that, when by the revolution of the crank k, the feeding-apparatus and damper on the other side of the furnace are brought into action, the passage of the
is represented at work, and that upon the left hand as stationary. The right-hand damper being closed, the smoke, &c. from the fresh coal will have to pass round the partition-wall p, and over the fire at the left hand