128. Hot-water System (Cylinder Form).
Figs. 128 and 129 show two distinct forms of apparatus, both of which are at present in general use, and both of which even now nearly equally share the public favour, although No. 1 is the more modern and has been proved to be practically superior to No. 2, and is now nearly exclusively adopted by most firms who profess this work.
No. 1 is known as the cylinder system, and consists of a cylinder (a square tank is sometimes used where the pressure of water is light, tanks costing much less than cylinders of the same capacity) which is placed at the nearest position to, but above the level of the boiler. Two pipes connect the boiler with the cylinder, the upper pipe a is termed the “flow,” and is carried from the upper surface of the boiler to about 9 in. up the nearest side of the cylinder as shown, and the lower pipe b, known as the “return,” is carried from a lower position in the cylinder, under the “flow,” to within about 3 in. from the bottom of the boiler, either through the top, as shown, or entering at the back or side.
From the highest point in the cylinder is carried a pipe c, called the “rising main,” by the nearest or most convenient route to above the level of the cold-water cistern, and terminates either by being carried through the roof (as shown) or by being turned over the top of the cistern referred to (as shown in dotted lines). This pipe, when the apparatus is in use, is charged with water to a little above the level of the cold water in the cistern, and the pipe is open at the top end to admit of the free escape of steam, and on that account is sometimes called the expansion pipe; from this pipe is, or should be carried all the draw-off services to the various points at which they are required. In event of this rising main being carried to a considerable distance or height, it should be “returned” from any convenient point below the cold cistern (as shown in dotted lines at d); this will cause the water to circulate in this upper service and avoid the annoyance and waste caused by drawing sometimes a large quantity of cold water (which lies stagnant in single pipes) before the hot water is obtained. When this “return” is effected, the service is known as the “secondary flow and return.”
129. Hot-water System (Old Form).
Another good use to which the return can be put is in event of any draw-off services being unusually long, as that shown at m to the dressing-room in the illustration, the return can be connected as shown in dotted lines, and will bring about the same good results as explained in “returning” the rising main.
The supply of cold water to the apparatus is either brought by a direct and distinct service from the cistern, or is branched from the nearest existing cold service, but in the latter case the existing service must be of good size, for reasons that will be explained later on. The cold supply should be provided with a stop tap f, which is found most convenient if placed near the cylinder, as it can then be used by workmen or others without their having to traverse the house, but this tap should have a loose key or handle, which should be kept by some responsible person to prevent its being interfered with by any one ignorant of its use. There should be also a tap provided at a convenient point, say g, to empty the cylinder when the boiler requires to be cleaned or any repairs effected, and this tap should have a loose key for the reasons before stated.
The chief advantage of this system is safety, the cook or user being unable to empty the cylinder, consequently should the water supply fail, the fire can be lighted in the usual way without risk, as in ordinary use it would take several days to boil away or evaporate the contents of the cylinder and boiler.