Part 145

Boiler explosions are at all times most serious disasters, for not only is the damage very great, but if any living thing is moderately near at the time the result is almost certain to be fatal, and it is a much-regretted fact that three-fourths or nearly all the terrible accidents of this kind could have been avoided with ordinary care; the reason that this form of accident is so serious is that before the explosion takes place, the steam has to attain sufficient power to burst the boiler, which is from ¼ to ½ inch thick of wrought iron, compared to which the human body is a frail object, and suffers accordingly.

The causes of explosions at present known are, firstly, stoppage in both the circulating pipes, caused by frost or by the terrible practice of putting stop taps in these pipes, which prevents escape of steam generated in the boiler, and steam _must_ and _will_ escape if it bursts the boiler to effect its release.

Secondly, failure of water supply. This is sometimes caused by a hidden or unnoticed leakage, or in country residences where the water is pumped this failure is not an uncommon thing (but only rarely results in an accident). If the want of water is unnoticed for a time, the boiler will empty itself by evaporation and afterwards become red hot; should the water then run in, steam will be generated so rapidly that the pipe outlets will not be sufficient for its free escape, and the boiler bursts; all this happens in much less time than is occupied in explaining it, in fact so quick that there is no time for escape if any one is unfortunately near; this, however, under ordinary circumstances cannot occur with the No. 1 system.

There is another though rare cause of accident (which, however, once came under the writer’s notice) that may occur with either system, and that is the ends of the circulating pipes nearest the boiler becoming stopped by incrustation; this incrustation, as has been before explained, takes place in the greater proportion of boilers, and also to a less extent in the pipes, especially near the boiler, and in course of time the pipes will both become completely stopped, but the reason that accidents from this cause are rare is that abundant notice is given by the steam making a variety of unpleasant noises and sometimes violent shaking, in forcing its way through the partly closed pipes, but this noise must not always be confounded with the sounds produced when pipes are imperfectly run or “trapped” and contain air, but whenever noises are heard a practical man should be consulted at the earliest convenience, and if a tap is opened and no water should flow, after it has been open say one minute, the fire should be immediately extinguished and kept so until the reason of failure of water is discovered and remedied. No alarm need be experienced at the rumbling noise to be heard when the water is boiling, but this water has no need and should not be permitted to boil; when the noise is heard, 4 or 5 gal. should be drawn off, this will be replaced in the tank or cylinder by the same quantity of cold water, and the temperature will be reduced; the damper which regulates the boiler flue should be out only when the water is cool and requires rapid heating; even then it must not be pulled out so far that the flame, &c., roars as it passes under the boiler, as the boiler will not experience the full benefit of the heat.

It has been suggested by some authorities that to prevent the water in pipes becoming frozen (this may be considered the most likely cause of explosion) a tap or taps should be left a little open at night so that the water is kept in motion; this, however, cannot be relied upon in a really severe frost, and it is also a waste of water, which is a consideration where the supply is by manual power, &c. Another method suggested is to empty the whole apparatus every frosty night; this is a very good plan to save damage to pipes as well as prevent accidents, but there is the doubt that but few would care to practise this on account of the trouble, and there is a serious risk if it is forgotten to turn the water on until after the fire is lighted. Tolerable reliance can be put on felting or casing the pipes, but the most efficient remedy is to see that the boiler is fitted with a safety valve, which, as the name betokens, is a source of safety and most probably of comfort also; if it is not convenient to attach a safety valve direct into the boiler, it should be connected by a short length of pipe, which however is a weakness, as the pipe may eventually be stopped by incrustation, and on that account it should be of good size and should be cleared, if necessary, every time the boiler is opened for cleaning. Safety valves should always be fixed in sight so that they can be tested whenever desired. The working principle of a spring safety valve (which has general preference just now) is, firstly, a brass sealing which closes the opening leading to the boiler and is held in position by a spring and central pin, and the whole works in a strong brass case which is perforated with several good-sized holes; when the valve is fixed, the workman can and does set the spring (generally by a screw-down cap at top) so that it withstands about 3 or 4 lb. more pressure than the boiler is subjected to by the pressure of water; when by any reason an undue pressure is exerted inside the boiler it causes the seating to rise, and the steam and some water escape into the brass case and through the holes above referred to, and the boiler is relieved. The noise occasioned by this escape is _very_ plainly heard, and notice is thus drawn, but the fire need not be extinguished.

It would be a desirable feature if every boiler fixed (except open ones) was provided with a valve, as it is purchasing freedom from risk at a low price (a few shillings only).

There is a common cause of complaint and annoyance in having at some taps to draw off a quantity of cold water that lies stagnant in the service pipe before the hot water can be obtained from the circulation; this is caused by the draw-off service being a long and single pipe, and can be only remedied by “returning” it something after the manner shown in the illustrations, and so cause the water to circulate along it; this trouble is not only a source of annoyance but a practical loss also, as for every quantity of hot water drawn a certain quantity is left in the service to get cold, and this happens every time the tap is used, excepting such taps as are in constant use, and the water only remains stationary 2 or 3 minutes, but this in domestic purposes only applies to the scullery service at certain hours in the day.

It may have come to many people’s notice that when some lever-handle taps are shut a noise and jarring in the pipe ensues; this is caused by the sudden stoppage of the flow of water when the pressure is considerable; when the vertical pressure is say 50 or 60 ft. (height of cistern above the tap) and the tap is opened, the water rushes out and gains a strong momentum; by turning the handle or lever of the tap the stoppage is so sudden that a shock is sustained almost the same as an object falling from a height being suddenly stopped by coming in contact with the ground; this concussion and noise is not only unpleasant but does harm, which is quickly noticeable with light lead pipe, which is either stretched or has protuberances formed upon it, and a continuance of the shocks or really blows will then cause it to split; it will be therefore commonly found that screw-down taps are used with lead pipe where any pressure exists, and the screw-down tap would meet with more favour but for an objectionable feature, which is the number of times it has to be screwed or unscrewed to shut and open it; but there are now made screw-down taps that open or shut with one turn, and these no doubt will come into more general use if found practically good and when the patent expires.

Retarded circulations arise from a variety of causes, amongst which may be mentioned incapacity of the boiler for the work, caused by the boiler not having sufficient heating surface; this is shown by the whole apparatus becoming fully charged with hot water late in the day after several hours firing; the only remedy is to reduce the work the boiler has to do or change the boiler itself. Another cause is by pipes being dipped or trapped. The flow pipe having an inclination or dip downwards, which causes the circulation to become air-locked, this causes noises in the pipes and shakings as the steam is passing or trying to expel the air; this air is eventually expelled, but occurs again when the apparatus is emptied and recharged in boiler cleaning, repairing, &c.; to remedy this the pipes must be traced up and the defect so discovered. Another cause is by incrustation in the pipes; this can be noticed by its gradual growth, also incrustation in boiler, but if boiler is kept clear as referred to earlier in the chapter, the pipes will keep in very fair order. The only remedy for furred pipes is to take them out and by heating and striking to dislodge the deposit; this costs as much almost as renewing the service; with care in regular cleaning it will not occur. Obstructions either stationary or floating are sometimes found in the pipes and retard circulation; these are generally caused by the workmen failing to look through the tubes before fixing them, or the obstruction may be in the form of sediment in rural districts, &c.; the only efficient remedy that can be suggested is to engage the services of an experienced hot-water fitter in any of the cases mentioned, as it lies beyond the power of the householder to remedy them.

There are a number of errors commonly found in apparatus that has been fitted up by those somewhat wanting in experience, such as connecting draw-offs from the return pipe in No. 2 system; result is that the whole of the water in the tank having to be heated before any hot water finds its way down the return pipe, it is naturally a considerable time after the fire is lighted before hot water can be obtained from the tap; connecting draw-offs direct from the tank, result nearly as bad as connecting from the return; dipping or trapping the flow pipe, causing circulation to become air-locked as before mentioned; connecting the cold supply to the tank or cylinder without forming a syphon (inverted) in the pipe, so permitting hot water to find its way up into the cold-water cistern: result, loss of heat and water lukewarm which should be cold; placing tank and pipes in very cold situations, causing serious loss of heat, as before explained. Another common error, or piece of bad work, is connecting or screwing the flow pipe through the top of the boiler so that it projects through the inner surface, as Fig. 130. Now when the apparatus is finished it is, of course, before being charged with water, full of air; when the water flows in, it expels the air as it fills, but it cannot expel the stratum of air existing between the lower edge of the flow pipe and the top of the boiler; this is not noticeable when the water is cold, but when heat is applied and steam is generated, the steam naturally wants to expand into this space, but at the same time the air has no desire to be evicted, so a struggle ensues, and the steam is eventually the victor; but the struggle is fierce, and can be heard and felt in every part of a building of moderate size. The trouble does not end here, for when the position is gained, the steam has to pass away, when it has gained sufficient strength to force its way back through the water and up the flow pipe, and this is an unpleasant experience. Exactly the same result is obtained if the rising main is screwed too far through the top of cylinder or the expansion too far through the top of tank--an air or steam chamber is formed in either case; these pipes should be quite flush with or above the inner surface of the receptacles they are screwed into. There is no more annoying or alarm-producing error than this.

Still another error is in running the circulating pipes up a casing containing other pipes without felting the former, or even without separating them; the result of placing a hot pipe against a cold one for several feet is obvious, and if a hot pipe is placed against a soil (w.c.) pipe, the result is offensive; these errors are commonly found. There are numberless minor errors to be met with; to enumerate all would occupy much space and be of no real use to the reader. Errors are not uncommon things in this work, and some of them are of so extraordinary a nature as scarcely to be creditable. An objectionable feature in an old apparatus is the small supply or feed cistern fixed at the side of the tank, but this is now almost totally in disuse, for it has at last dawned upon some one that it is quite unnecessary; this feed cistern must have a ball valve or cock, and, this is where the mischief lies, no reliance can be placed on a ball valve or cock of any description; they are commonly a source of never-ending trouble. We give this description, as there are some people who still persist in the use of this secondary cistern.

Discoloured water is sometimes caused by the rust that is naturally created in new work, and lasts but a short time, as the pipes get covered internally with a very thin coating of lime, which then prevents the water coming in contact with the metal of the pipe.

Water is discoloured to a greater or less extent if it is permitted to boil very hard, as this agitates any loose sediment that is lying in the tank, and the boiling is much like churning the water.

The water in the tank or cylinder should not be permitted to boil, as it creates an unpleasant noise, and is a certain strain upon the work, and answers no good purpose; it can be stopped by drawing a quantity of water off, so causing cold to flow in, but the remedy is to keep the boiler flue closed by the damper; if this does not prevent the overheating of the water, there is the possibility that the flue is out of order, or “leaks.” This can be tested by closing all the dampers when fire is in working order, which in the ordinary way would cause all the smoke to be discharged into the room; if this is not the cause, there must be an improper exit for the smoke and heat, and a loss is of course being sustained.

Coils and hot-water pipes for heating a small conservatory or chamber are sometimes connected with the circulating service, or direct by a distinct service from the boiler, but there are no especial rules to be observed in using these, as there are only stop-cocks to be turned on or off as the requirements demand.

It may now be useful to give a few hints to those having a new apparatus fitted.

There is a rather old saying to the effect that the “best is the cheapest”: this especially applies to hot-water work. It would be waste of time and space to enumerate the evils of cheap work of this description, as the list would be a very long one. The best plan is to apply to a good firm (not necessarily a large one) who makes somewhat a specialty of this branch (generally boiler or stove manufacturers, or good plumbers and builders). They will provide an estimate of cost with _detailed_ specification free of charge if the distance is not great. The object of a _detailed_ specification is, as probably the reader guesses, to know exactly what size, strength, quality, &c., of boiler, cylinder, or tank; pipes, iron and lead; cocks, &c., &c., that are to be used; and before finally deciding, the purchaser should insist upon the efficiency of the apparatus being _guaranteed_. Boilers are of many various shapes and sizes, but the best form has been proved to be that with a good flue or heating surface underneath, so as to present as much bottom or under surface as possible to the flame and heat; the best surface is easily determined by any one, by applying the heat to the top of a kettle, and afterwards applying it at the bottom, and noting the difference in results; there are many other perhaps better forms of boilers made for heating purposes; but it must be remembered that the boiler for hot-water supply must not be of complicated form inside, but must be quite clear, offering every facility for removing the incrusted deposit. Fig. 131 shows the common form of boiler used in kitchen ranges; the size must be governed by the capacity of the range itself, but it should have as great a width and length as possible, to increase the bottom surface; and the flue should be as large as the size of fire will possibly permit. A most important point is to see that the boiler has a large manhole _easily accessible_.

Experience has proved that the best material from which these boilers should be constructed is wrought iron or copper; the wrought iron should be of 5/16 in. or ⅜ in. substance, and copper can be of a little less substance except the front where the external wear and tear takes place (chiefly by the poker). The principal of these remarks apply to independent boilers also, which, however, are generally set in brickwork and are of larger capacity and strength in proportion. Fig. 132 represents a more powerful form of boiler for domestic purposes, and is found a very rapid heating and efficient shape, in instances where a large number of draw-offs are in use, or a coil or heating pipes are in connection. Care should be taken to avoid boilers with narrow water-ways where the heat is applied; there are occasionally made boilers with 2 projecting horns or cheeks which occupy the place of the fire-bricks in the range firebox; these narrow parts, which are subjected to almost the most intense heat, will fur up solid and crack in 6 months with London water. The advantages of a copper boiler are quicker heating, greater durability, and greater expansion and contraction, which prevents the incrustation adhering to the surface so firmly as it does inside an iron boiler; and although a copper boiler is of greater first cost, yet when worn out it is of almost sufficient value to purchase a new iron one.

These boilers are recognised by several names, viz. “high pressure,” “Bath,” and “circulating,” &c., boilers. The first term is generally known.

Cast-iron high-pressure boilers have now gone almost entirely into disuse on account of the unsatisfactory results experienced.

Safety valves have been generally treated of in an earlier part of this chapter, but it might be impressed upon the reader that the valve should be as near as possible or directly in the boiler; they are sometimes put in the circulating pipes or in the cylinder or tank, but this is away from the seat of danger; it would be a rarity to hear of a cylinder or tank exploding.

The reason that cylinders are used when the No. 1 system is adopted, and tanks with No. 2 system, is that the cylindrical shape is better adapted to bear the greater pressure; otherwise a tank would answer as well to all intents and purposes; to show the pressure-resisting strength, a tank of ⅛ in. plate is tested and warranted to bear 5 lb. pressure to the square inch. This is equal to the cistern being 10 ft. above the tank, whereas a ⅛ in. plate cylinder is tested and warranted to bear 25 lb. pressure to the square inch, equal to 50 ft. In speaking of pressure by feet this alludes to the _vertical_ height between the cylinder or tank and the cold cistern; it does not matter what size pipe connects them. A cylinder or tank can generally be depended upon to bear a little greater pressure than they are tested to. There are 3 or 4 strengths made to meet the various requirements, and the makers’ lists show what pressure they are tested to in lb., and every lb. can be calculated as equal to 2 ft. of vertical pipe.

The general sizes of tanks and cylinders for domestic purposes vary from 30 to 60 gal. according to requirements; the disadvantage of too large a tank is the time taken in heating its contents and completing the circulation, and in some instances the space it occupies; tanks of 100 gal. capacity are sometimes fixed in residences where there are only 4 or 5 taps (hot water). This is much too large for any but large mansions or for business purposes; for say 5 taps, including bath, a 50 gal. tank or cylinder will be found large enough and will admit of 3 baths in succession about 1 hour after lighting the fire.

The pipes or tubes commonly used are iron steam tube, galvanised iron steam tube, iron gas tube, or barrel, and lead pipe; the two latter, though commonly found, should be avoided as being totally unsuitable for this work. Gas barrel is sometimes used on cheap work and in small speculative property, and answers well, when no real work is put upon it; but no respectable firm would undertake to use it, as satisfactory results cannot be relied upon except under very favourable circumstances.

Steam tube, commonly known as “red steam” tube on account of its colour externally, is much like gas barrel, but especially strong for engineering purposes, and the utmost reliance can be put in it. Galvanised steam is the same quality tube, but galvanised to prevent rust; this is much liked, and is absolutely necessary in some districts where unprotected iron rusts at an alarming rate; but care should be exercised to see that it is galvanised _inside_ as well as out; preference, however, is on the side of the “red steam” as it is considered that the tube is deteriorated in strength by the process of galvanising.

Galvanised iron boilers are sometimes used, but the same remarks apply as are given respecting galvanised pipes.

The best size of tube for ordinary domestic purposes is 1¼ in. internal diameter for the circulation and 1 in. for the major portion of the draw-off services; ¾ in. may be used for minor purposes, as lavatory draw-off, &c. There are, however, many apparatuses being fitted at the present moment with 1 in. circulation and ¾ and ½ in. draw-offs, and even ¾ in. circulations are to be met with; but the advantage of a good-sized pipe is the freer flow of water when taps are opened, and most important its less liability of being stopped or rendered unfit for use by incrustation; 1¼ in. tube has fully 30 per cent. more inner surface than 1 in., so that it would take a third longer time to get a ¼ in. coating of deposit in a 1¼ in. tube than it would in a 1 in., and when this thickness has accumulated, the 1 in. tube requires renewing, whereas the 1¼ in. is fit for still further service, so that it can be calculated that 1¼ in. tube will last about double as long as 1 in. so far as incrustation is concerned, and this incrustation, as the reader now knows, is an important element requiring every consideration in almost all districts.

When _circulating_ pipes have to be carried round angles, bends (which are nearly a segment of a circle) should be used invariably, and not elbows, unless absolutely necessary in rare instances. A bend permits the water to circulate round the angle much more freely than an elbow, as the turn in the latter is abrupt, and tends to check the circulation; this only applies to the circulating pipes; it should also be seen that connecting-pieces known as “connectors” are inserted at intervals where they will be of practical use, as they permit of a piece of pipe being removed without disconnecting the whole service, as is so often necessary for a small repair or inspection. A connector is a piece of the tube with the socket so arranged that it performs the function of a union.