Another advantage gained by this system is that the cylinder being in such a warm situation, much less heat is lost by radiation, and by its being nearer to the boiler the circulation is effected more rapidly; and there are several other minor advantages to be gained by it, which, however, are not of sufficient importance to warrant detail here. The cold supply pipe h leads from the cistern i to the cylinder k; l is the boiler; m are draw-off service pipes with taps n in the various apartments where needed.
Fig. 129 is commonly known as the “high” or the “old” system. This consists of a square or rectangular tank a, which performs the function of a reservoir for the hot water in the same way as a cylinder, but instead of being situated near the boiler b, it is fixed somewhere above the highest draw-off service, but of course below the cold cistern c; it is commonly found in the roof or attic in proximity to the cistern, but these are cold and bad situations for it; it is more often found in the bathroom, enclosed in a casing or cupboard, which is thereby made an efficient airing closet, and serves somewhat to prevent loss of heat referred to before (and hereafter), and the presence of the tank in the bathroom, although occupying considerable space, is a source of warmth, no mean advantage in winter.
The tank a is connected with the boiler b by “flow” and “return” pipes d e, the same as the cylinder, but they are necessarily much longer; the draw-off services f are, or should be, all connected to the “flow” pipe d as shown, as the water in this pipe is the first to become heated as the water circulates or “flows” from the boiler to the tank; and an expansion pipe g (not called a rising main in this instance) is carried from the highest point in the tank a to above the level of the cold supply c, as in the cylinder system. There is no need to return this expansion pipe, but an unusually long draw-off service can and should be returned for the reasons before explained, and the method is to connect and carry the draw-off service from the flow pipe in the usual way and return it into the return pipe at a lower point, somewhat after the manner shown at h. Obviously the run or course of all pipes has to be adapted to circumstances, but it can be taken as an invariable rule that in correctly executed work “flow” pipes never descend and “return” pipes never ascend, but this will be more fully explained later on. In speaking of circulating pipes, the “flow” is recognised as running from boiler to tank (or cylinder), and the “return” from tank to boiler.
The cold-water supply i is carried and connected to the tank a in the same manner as to a cylinder, and provided with a stop tap k to save the necessity of plugging the pipe where it leaves the cold-water cistern.
The chief advantage of this system is obtaining hot water a little quicker (but in less quantity) from the time the fire is lighted, than in the cylinder system, as it can be drawn almost immediately it leaves the boiler; but as good results in this respect can be attained with the cylinder if the directions subsequently given are attended to; another advantage in this system is that it can be erected at less expense than the other, and the tank costs but little more than half the price of a cylinder. These advantages are more than counterbalanced by the disadvantages, viz. the easy means of exhausting the apparatus of water if the supply fails, the longer period occupied in obtaining a body of hot water, and the necessarily cold or cool situations of the tank and pipes, so causing loss of heat by radiation, &c.
A few lines may be here devoted to explaining the cause of circulation, which the generality of householders are totally unacquainted with. For the reader to fully understand the subject, he must first know that water is composed of extremely minute particles (molecules), quite invisible to the eye, which have the property of gliding over, under, around, to and from each other, as circumstances dictate, in we may say a perfectly free manner, almost entirely without friction or resistance. When the apparatus is charged and the fire lighted, the particles nearest the fire become heated and expanded, and are, bulk for bulk, rendered lighter than their fellows, and consequently rise to the top of the boiler; finding an outlet there they rise up into this, and continue to rise until they reach the highest limit, which in No. 2 system is the top of the tank, and in No. 1 system, the top of the cylinder, unless the rising main is “returned,” in which case it will be where this “return” commences. Immediately the expanded particles leave the heated surface of the boiler, other cold particles descend into their place and are heated and expand to follow their predecessors, and so it continues as long as there is heat applied to the boiler. The circulation is really a continuous stream of expanded (heated) particles of water ascending the flow pipe, and a corresponding stream of cold or cooler particles descending the return pipe, a natural and very simple means of automatically transporting the hot water from the heating chamber (boiler) to the reservoir (tank) and automatically providing a supply of cold water to be heated in its turn.
The specific gravity of water at the boiling point, compared with water at the freezing point, is as 21 to 20, i.e. 20 gal. of very cold water will balance 21 gal. of very hot water.
The following are the few general rules to be observed for the efficient, economic, and safe working of either description of apparatus.
Commencing at the boiler, it is very necessary that the flue under this be quite cleared of cinders and ash once daily, and the length of the flue should be ascertained, as they differ considerably, and many instances occur where these flues are scrupulously cleaned but only in half or three-fourths their length, and very quickly the accumulation at the end of the flue becomes hard and solid, and an inexperienced person would then consider it to be the wall which forms the boundary at the back of these flues; this stoppage of course effectually prevents the water heating as it should do. Another cause of the water failing to heat quickly is omitting to have the interior of the boiler cleared of the incrustation or deposit (commonly known as fur) that accumulates more or less according to circumstances that will be fully described later on; when this inner coating attains a moderate thickness it very naturally retards the heat in passing from the fire to the water, especially as it is a poor conductor. There is, however, a more important reason why this incrustation should be removed regularly, and that is, when the boiler is coated to a certain thickness (which coating is more or less porous according to the district) it prevents the water coming in contact with the iron, and the boiler plate, however thick, is soon destroyed the same as if it contained no water at all, or to use a more familiar illustration, the same as a kettle would be “burnt” if left on the fire without having any water in it; this is a serious result from the costly nature of the repair.
The general form of incrustation is caused by the lime or chalk (bicarbonate of lime generally) held in solution, being separated from the water and precipitated; this precipitation commences at a moderately low temperature and gradually increases as the temperature rises, and the whole (excepting a very small quantity) is deposited when the water boils. The incrustation varies very much in quantity according to the district, as before stated; it is generally what is known as hard water that has the greatest percentage of this depositable matter; in some favoured districts the water is so soft that no appreciable deposit occurs, whilst in others it is not safe to leave the boiler longer than a month without cleansing to keep it in good order. There is also a variation according to whether the water boils much or otherwise, therefore the only reliable plan is to have a good workman in after a certain period, and he can then decide whether the amount of incrustation is too great or whether it might be permitted to go longer, and how long.