The Coil-Drum.—The drum generally consists of a pipe of G in. in diameter and about 4 ft. long, and nipped at both ends. In this drum is placed a coil of copper pipe, which coil is made a part of the hot-water circuit within the car. Steam from the locomotive is admitted to this drum around the copper coil, through which heat is imparted to the water of circula tion. That part of the circuit above this drum becoming relatively lighter than the descend ing column of the hot-water circuit, a movement of the circulating medium is produced, creating a steady flow up through the coil. It is evident that the amount of heat CoM Mopleated to the circulating medium depends upon the surface of the coil and upon its MU ductive power to hat. In order to maintain the water of circulation at or near its boiling point, a pressure of from 10 to 20 lbs. of steam must be carried in the drum. The Sewall drum-system is, perhaps, the most widely used of this type of heater. This drum is placed within the car by the side of the heater, and is connected with the circulating pipes so as to form a branch circuit. around the heater. At the point where the two circuits unite above the drum is placed what is known as a current-director, which is a casting so arranged that. the force of the moving circuit from the drum creates an upward flow through the heater, so as to produce a circulation through the piping in the car. In case this current-director is not used, the drum is apt to produce a short circuit, creating a downward flow through the coil of the heater.
Salt-water nsnally constitutes the circulating medium in this system, which water has a freezing-point of about 10° above zero. When solutions of salt, giving a lower freezing-point, are used, the excess of salt is liable to deposit in the circuit within the coils of the drum and the heater, and so to greatly reduce the effectiveness of the heating apparatus.
The Disk-Drum is a modification of the coil-drum above described. A series of bronze castings made in the form of hollow disks take the place of the coil within the drum. The disks are 12 in. in diameter, and are securely screwed together at their centers. Eight strong studs are east midway between the center and the circumference of each disk. for the purpose of binding its wails together. These studs are necessary to give sufficient strength to withstand the enormous pressure liable to come upon the circulating pipes when tire is used in the heater. All disks are tested at 500 lbs. per sq. in. Five disks are usually em ployed in each drum, althongh seven disks are sometimes used. Each disk is ribbed or cor rugated, and has 2 sq ft, of heating surface, so that the heating surface in each drum varies from 10 to 14 sq. ft., depending upon the number of disks employed. This construction allows a large amount of heating surface to be put into a compact form, and also presents a very small internal resistance to the flow of water through the disks. The drum itself is made of east iron, to which a cast-ii.on head is bolted, Two drums thus constructed are connected with the heating circuit of each car at its lowest point (see Figs. 2 and 3). They are placed so as to form the risers from the cross-over pipes,
and as the two drums discharge into the pipes on different sides of the car, the heat in the ear is evenly distributed It is evident that the joint action of the two drums is to produce the circulation of water in the same direction throngh the pipes. The direction of flow is the same as when fire is used in the heater. Since the water is heated at two points, all the water is heated when it has moved through one half of a complete circuit. Steam is taken into the Arum from the train-pipe, and water of condensation is removed from the drums by means of a trap or trap-valve and is discharged on the ground. A brine of salt and water is generally used as the circulating medium.
The Direct-Steam System.—In this system steam from the locomotive is turned directly into the radiating pipes of the ear, Three pipes If in. in diameter are generally used on each side of the car. The three pipes are joined together at both ends of the car by a three-pipe manifold. A distributing tee is placed near the center of the car, and is connected into the two upper pipes. To this distributing tee a pipe leading from the train-pipe is connected, through which steam is supplied to the heating pipes. A tee is also placed in the lower pipe near the center of the ear, and a drip-pipe is connected from this tee to a casting placed in the train-pipe in which is a bleeder-valve controlling the discharge to the ground. The pipes in the car are graded so that water will flow to the ends of the car in the two upper pipes, and then flow to the (Titter of the ear in the lower and out through the drain-pipe and the bleeder-valve in the train-pipe casting, to the ground. ln the same train-pipe casting is placed the steam-valve which controls the flow of steam to both sides of the ear, and the drip pipes from both sides of the ear are also controlled by the one valve above described. The two vall'N in the train-pipe casting are provided with extended spindles, which terminate in a floor-plate made flush with the level of the floor.
The office of the train-pipe casting above mentioned is to prevent. the drip-pipes from the car from freezing by connecting them into a casting always deriving heat from the train-pipe. This feature, patented by the Consolidated. Car-I lent ing Co., is one of great importance as, by removing possitiility of freezhig the dritio-pipe when the bleeder-valve is closed. it becomes practicable to nearly (dose the bleeder-valve and allow the pipes to till with water of con densation when hut little heat is reipiired. In this way the tierce heat of direct steam can be toned down to meet the requirements of mild weather. in cold weather the bleeder-valve is given FL larger opening, so as to allow the greater part. of the radiating pipes to be filled with steam. This construction furnishes an effective means of adjusting the amount of piping filled with steam to the needs of all kinds of weather.