Fig. 134.-Water Cooling System Employed on Packard Motor Cars Showing Arrangement of Components, Including Circulating Pump, Radiator and Cooling Fan.

either of the spur gear or centrifugal style. On marine motors the plunger pump is very widely used because it must lift water instead of merely circulating it from one member to another.

Q. Describe construction and action of centrifugal pump.

A. A typical centrifugal pump is shown at Fig. 135. This consists of a cast bronze casing, having a water inlet concentric with and surrounding the impeller shaft and an outlet extending from a point on its periphery; an impeller or paddle wheel carried by suitable bearings in pump case and pump cover. The impeller is revolved at fairly high speed by mechanical connection with some

Fig. 135.-Parts of Centrifugal Water Pump.

moving part of the motor and as it revolves in the casing it forces the water entering through the inlet at the center of the impeller outwardly by centrifugal force and discharges the water from the outlet in the pump periphery. The pump intake is invariably connected to the lower portion of the radiator where the water is coolest, and the discharge or outlet is joined to the manifold connecting the lower portion of the water jackets.

Q. Outline construction and action of gear pump.

A. The gear form of circulating pump is clearly shown at Fig.

136. This consists of two spur gears that are a fairly tight fit in the pump casing, one of these being keyed to a shaft that serves as a driver while the other revolves idly on a stud fastened to the pump case. As the gears are in mesh no water can pass between them and as they rotate small volumes of water are imprisoned in the spaces between the teeth and are forced from the inlet opening around the side of the casing and are discharged through the outlet pipe.

Fig. 136.—Diagram Outlining Action of Typical Gear Pump. All parts of water circulating pumps are preferably made of bronze because this metal is not as much affected by water and does not corrode or otherwise deteriorate as rapidly as the ferrous materials steel and iron. The gear form of pump is driven by positive mechanical connection in just the same way as the centrifugal type and is utilized in the same manner.

B

Q. How is the heated water from the engine cooled?

A. After the water has become heated by contact with the hot cylinder and combustion chamber walls it is discharged to the top of a cooling device termed a "radiator" by which it is exposed to a large metal surface which absorbs the surplus heat and which, in turn, is kept cool by currents of air passing through the spaces between the water tubes. Two typical radiators are outlined at Fig. 137, that at A being a form intended for application at the front end of the chassis, while the form at B is fitted at the rear of the motor and immediately in front of the dash separating the engine compartment from the body portion.

Q. How do radiators differ in form?

A. The main difference in radiators is in the formation of the water passages. In some types the water is made to flow through tubes of small diameter which spread it out in thin sheets, whereas in others tubes of greater volume are employed and the water is allowed to flow through in larger quantities. The form which divides the water into numerous small streams must be used in connection with a circulating pump of some type while that offering larger water passages can be utilized in connection with engines cooled by the thermo-syphon system.

Q. What type is the more efficient?

A. The type in which the water is divided into many small streams is the most generally used on account of its greater efficiency. Because of the narrow water passages the tubing may have a large area exposed to the influence of the cooling currents of air, and the heat is more easily extracted from a small body of water than from a larger amount.

Q. What are the disadvantages of narrow water passages? A. It is more difficult for the water to flow through narrow passages as shown at Fig. 139, because of the resistance offered by the walls of the cooling tubes. Then again, it is easier for the small passages to become constricted with scale or impurities in the water and circulation is thus impeded. The forms of cooling tubes shown at Fig. 140 A and B when assembled together form what is known as a honeycomb cooler on account of its appearance. As will be