Having explained as briefly as possible the principles on which the system is founded, the writer will now describe the details of the heater itself.
In Figs. 1 and 2 are shown an elevation and a vertical section of the heater. The cast-iron base, A, is divided into two parts by the diaphragm, B. The exhaust steam enters at C, passes up the larger tubes, D, which are fastened into the upper shell of the casting, returns by the smaller tubes, E, which are inside the others, and passes away by the passage, F. The inner tube only serves for discharge. It will be seen at once that this arrangement, while securing great heating surface in a small space, at the same time leaves freedom for expansion and contraction, without producing strains. The free area for passage of steam is arranged to be one and a half times that of the exhaust pipe, so that there is no possible danger of back pressure. The wrought iron shell, G, connecting the stand, A, with the dome, H, is made strong enough to withstand the full boiler pressure. An ordinary casing, J, of wood or other material prevents loss by radiation of heat. The cold water from the pump passes into the heater through the injector arrangement, K, and coming in contact with the tubes, D, is heated; it then rises to the coil, L, which is supplied with steam from the boiler, and thus becomes further heated, attaining there a temperature of from 250° to 270° F., according to the pressure in the boiler.
This high temperature causes the separation of the dissolved salts; and on the way to the boiler the water passes through the filter, M, becoming thereby freed from all precipitated matter before passing away to the boiler at N. The purpose of the injector, K, and the pipe passing from O to K, is to cause a continual passage of air or steam from the upper part of the dome to the lower part of the heater, so that any precipitate carried up in froth may be again returned to the under side of the filter, in order more effectually to separate it, before any chance occurs of its passing into the boiler.
FIG. 1.--Elevation. FIG. 2.--Vertical Section
The filter consists of wood charcoal in the lower half and bone black above firmly held between two perforated plates, as shown. After the heater has been in use for from three to ten hours, according to the nature of the water used, it is necessary to blow out the heater, in order to clear the filter from deposit. To do this, the cock at R is opened, and the water is discharged by the pressure from the boiler. The steam is allowed to pass through the heater for some little time, in order to clear the filter completely. After this operation, all is ready to commence work again. By this means the filter remains fit for use for months without change of the charcoal.
Where a jet condenser is used, either of two plans may be adopted. One plan takes the feed-water from the hot well and passes the exhaust from the feed pumps through the heater, using at the same time an increased amount of coil for the live steam. By this means a temperature of water is attained high enough to cause deposition, and at the same time to produce decomposition of the oil brought over from the cylinders. The other plan places the heater in the line of exhaust from the engine to the condenser, also using a larger amount of coil. Both these methods work well. The writer sometimes uses the steam from the coil to work the feed pump; or, if the heater stands high enough, it is only necessary to make a connection with the boiler, when the water formed by the condensation of the steam runs back to the boiler, and thus the coil is kept constantly at the necessary temperature.
In adapting the heater to locomotives, we were met with the difficulty of want of space to put a heater sufficiently large to handle the extremely large amount of water evaporated on a locomotive worked up to its full capacity, being from 1,500 to 2,500 gallons per hour, or from five hundred to one thousand h.p. We designed various forms of heaters and tried them, but have finally decided on the one shown in the engraving, Fig. 3, which consists of a lap welded tube, 13 inches internal diameter, 12 feet long, with a cast-iron head which is divided into two compartments or chambers by a diaphragm. Into this head are screwed 60 tubes, one inch outside diameter and 12 feet long, which are of seamless brass. These are the heating tubes, within which are internal tubes for circulation only, which are screwed into the diaphragm and extend to within a very short distance of the end of the heating tube. The exhaust steam for heating is taken equally from both sides of the locomotive by tapping a two-inch nipple with a cup shaped extension on it in such a way as to catch a portion of the exhaust without interfering with the free escape of the steam for the blast, and without any back pressure, as it relieves the back pressure as much as it condenses.
The pipe from one side of the engine is connected with the chamber into which the heating tubes are screwed, and is in direct communication with them. The pipe from the other side is connected with the chamber into which the circulating tubes are screwed. The beat of the exhaust, working, as it does, on the quarters, causes a constant sawing or backward and forward circulation of steam without any discharge, and only the condensation is carried off.
The water is brought from the pump and discharged into the lower side of the heater well forward, and passes around the heating tubes to the end, when it is discharged into a pipe that carries it forward, either direct to the check or into the purifier, which is located between the frames under the boiler, and consists of a chamber in which are arranged a live steam coil and a filter above the coil. The water coming in contact with the coil, its temperature is increased from the temperature of the exhaust, 210°, to about 250° Fahr., which causes the separation of the lime salts as before described, and it then passes through the filter and direct to the boiler from above the filter, which is cleansed by blowing back through it as before described.
One of these heaters lately tested showed a saving in coal of 22 per cent, and an increase of evaporation of 1.09 pounds of water per pound of coal.--Franklin Journal.