=134. The Construction of the Fan in Common Use.= A motor turns the fan. There is a regulator on some fans, so that they can be run at different rates of speed. Oil cups are important parts of fans. When a new fan is purchased, these cups are full of oil. The oil will last for many months, but if an old fan heats and sparks while being run, have an electrician examine it to see if all the parts are in order and there is a supply of oil. Figs. 64, 65 and 66 show types of fans in common use. [Illustration: FIG. 66. Movable electric fan.] [Illustration: FIG. 67. Stove ventilator.] =135. Ventilator.= A hood (Fig. 67) with a pipe leading into the chimney, placed over a cook stove, will conduct hot air and steam up the chimney. This is due to the fact that warm air rises and cold air comes in to take its place. An open skylight over a cook stove, also, makes an excellent ventilator and cooling device for kitchens. QUESTIONS FOR PART IV 1. How may refrigerators be judged for efficiency? 2. What are the essentials of a good refrigerator? 3. How is an iceless refrigerator cooled? Under what conditions is it useful? 4. What may be the matter with an electric fan when it heats and sparks? PART V WATER SUPPLY AND SEWAGE DISPOSAL. CHAPTER XIX PUMPS AND WATER FILTERS =136. Suction Pumps.= A pump is a device for lifting water. The pumps in common use work on the principle that water which is under the pressure of air will rise to fill a vacuum or a partial vacuum. The pump is composed of a combination of valves and a piston for forcing the air out of the pipe to allow the water from below to be forced into it. A valve catches the water as it starts to flow back. The weight of the water holds the valve closed. An outlet above the piston permits the water to flow into a tank or sink when the piston is again lifted to make a new vacuum and draw more water (Fig. 68). =137. Care of Pumps.= The leather or material forming the piston must be kept moist, or it will shrink and leak. When it becomes worn and old, it must be renewed. It is not a difficult task to put new packing on a small suction pump. To do this, remove the pin attaching the piston to the handle. Lift out the piston, unscrew the bolt which holds the leather packing in place; put on the new packing, and replace the bolt, piston and pin. Always pump with a regular, even stroke--a jerky one tends to wear the working parts of the pump. The cylinder and pipe containing water must not be allowed to freeze. There is usually a plug in the pipe which may be removed to let out the water when there is danger of freezing. A cracked cylinder or pipe will leak air and not raise water. [Illustration: FIG. 68. Suction pump.] [Illustration: FIG. 69. Force pump.] Keep the bearings for the handle well oiled. When the pump gets old, the cylinder becomes worn and leaks. It can sometimes be replaced with a new cylinder, or more packing must be put on the piston.