The water leaves the tank by a pipe attached near the bottom and branches to supply each fixture, to which the water is to be conducted. In the drawing, the pipe may be traced from the point where it leaves the tank to the various fixtures. The cold-water pipe terminates at the range boiler, for at that point the hot-water system begins. The range boiler is connected by two pipes to the water heater in the kitchen range. The water heater is a part of the fire-box of the kitchen range and so long as the fire is kept burning, water is heated and stored in the range boiler. Where the house is furnace-heated, the furnace fire is sometimes utilized for heating the water by use of a coil of pipe above the fire and which may take the place of the range heater. Various other means are also employed for heating the water as described under range boilers. In Fig. 145 is shown a nearer view of a pressure tank with the pump attached. The pump is in this case identical in its action to the one shown in Fig. 132, but differs slightly in mechanical design. The drawing shows the gage-glass G, for indicating the height of water; the pressure gage P, which indicates the pressure to which the water is subjected; the attachment of the supply pipe S, and the delivery pipe D. The water tap T is provided to draw off the water when the tank is to be emptied.

In operation, the air in the pressure tank furnishes the force which sends the water through the pipes to the various points, and forces it through the taps at the desired rate. If for any reason the air in the tank escapes, the propelling force is destroyed. This may occur by reason of absorption of the air by the water, due to the pressure to which it is subjected; or to small air leaks that may develop in the joints, which allow the air to escape. To overcome the possibility of these occurrences, arrangement is made whereby air may be pumped into the tank by the same pump as that which supplies the water. In this way, the air is introduced with the water, which bubbles up through it to the surface. If at any time the pressure in the tank is lost, it may be replaced by pumping air alone into the tank.

Fig. 145. - The pressure tank complete, wtih the pump and gages as used for domestic water supply.