The light copper shells for light pressure, not reinforced, a r e collapsible under partial vacuum, and frequently do collapse when the supply is being drained, on account of the delivery failing to admit air to take the place of the water. Cop per shells are also much more likely to rupture under strain than iron or steel shells. Take, for instance, a house with copper storage cylinder, with hot fire and in extremely hot water, as on wash-day; then, if the pressure is suddenly reduced by opening a faucet or otherwise, and the temperature is far above the boiling point of the water under the remaining pressure, the tendency is for the whole volume of water to turn instantly to steam. This has happened with disastrous effect in more than one instance, the copper shell being ripped and spread out almost in a plane.
Rumbling noise is frequently heard in any type of reservoir. Water being heated throughout, or perhaps only at some points in the stove, to above the boiling point corresponding to the pressure, steam bubbles form in the hottest places and crowd the water-back into the main or into the air-chambers to make room for themselves. It is the concussion caused by the collapse of these bubbles forming and condensing in rapid succession, that creates the rumbling noise. This condition sometimes results from a brisk fire when the reservoir water is not overheated, and is due to air-traps in the connection, or constriction by incrustation or otherwise. Rumbling under this condition is a cause for prompt investigation.
The means of heating may be a cast back or front, or a hand made pipe coil in the firebox. Air-traps favoring the formation of steam are occasioned by wrong inclination of the connection, by reduction of its diameter in the horizontal part, or by the upper hole of a cast back being tapped below the top of the water cavity. The bottom of a reservoir is below the firebox level when placed on the regular stand. When it is desirable to connect a reservoir with two water-backs, one in the kitchen range for regular service and another in a laundry stove in the cellar, the plan of connecting them seen in Fig. 79 is proper. In this case, either stove may be used sepa rately, or both together, as occasion . demands. The sediment cock of the upper reservoir may be handy to draw from at times; but the lower one will be found to collect most of the sediment, and should be opened quite frequently to cleanse the water-back and con nections.
In laundries, public bathrooms, etc., where a large amount of hot water is used, it is necessary to have a larger storage tank and a heater with more heating surface than can be obtained in the ordinary range water-back. Fig. 80 shows an arrangement for this purpose, using the horizontal type of storage tank. The tank may be of gal vanized wrought iron or steel, any size desired, and is usually sus pended from the ceiling by means of heavy iron stirrups. The heaters used are similar to those employed for hot-water house warming. The simplest method of making the connections is indicated in the illustration. If the supply is from a street service, or there are faucets
on the storage tank supply below the hot storage reservoir level, making it possible for the tank to become empty through those faucets or failure of the street supply, there should be a check-valve in the cold-water connection.
The capacity of the heater and tank employed will depend upon the amount of water used. In some cases a large storage reser voir and a comparatively small heater are preferable, and in others the reverse is more desirable.
The required grate surface of the heater may be computed as follows:—First determine or assume the number of gallons to be heated per hour, and the required rise in temperature. Reduce gallons to pounds by multiplying by 8.3, and multiply the result by the rise in temperature to obtain the number of thermal units. Assuming a combustion of five pounds of coal per square foot of grate, and an efficiency of 8,000 thermal units per pound of coal, we have the formula: Grate surface in sq. ft. m Gal. per hour X 8.3 X Rise in temp.
5 X 8,000 Example. How many square feet of grate surface will be required to raise the temperature of 200 gallons of water per hour from 40 degrees to 180 degrees? Substituting values in the above formula, we have: 200 X 8.3X (180 — 40) 5.8 square feet. 5 X 8,000 In computing the amount of water required for bathtubs, it is customary to allow from 20 to 30 gallons per tub, and to consider that the tub may be used three or four times per hour as a maximum during the morning. This will vary a good deal, depending upon the character of the building. The above figures are based on apartment hotel practice.
Storage cylinders or reservoirs for hot water are often called boilers, but will henceforth be referred to as reservoirs. A stove or range connection is essentially described as follows: The sediment pipe should terminate in a faucet at the lowest point in the bottom connection, which connection should rise continuously from the lowest point to the bottom hole in the heater. No direct connection should ever be made between the water supply pipes and the drain. Even if such a connection is above the trap of a fixture, there is some danger that foul liquids or gases may penetrate for some distance into the supply pipes and thus afford a possibility of contamination of the water supply. The upper connection should rise continuously from the upper hole of the heater to the hole in the side of the reservoir; or, if preferred, in order to get hot water instantly after the fire begins, the upper connection may rise and connect into the main hot service over the reservoir. The circulation will be the same; but in general, connecting at the hole in the side gives best results, though in this case the first portion of water heated mingles with the balance in the upper end of the reservoir, and the following portions in succession, so that no hot water can be obtained until all the water above the side hole is warmed. The bottom hole serves for emptying, cleansing, and circulation to the stove.