583 Pump case protecting ring. 567 Labyrinth packing. 583 Labyrinth packing. 600 Pump case cover. 692 Impeller key. 815 Bearing bracket, outer. 815–1 Bearing bracket, inner. [Illustration: FIG. 51.—Types of Centrifugal Pumps. ] [Illustration: FIG. 52.—Section of a Multi-Stage Centrifugal Pump. Courtesy DeLaval Steam Turbine Co. ] Reciprocating pumps are generally driven by steam and are either direct-acting, or of the crank-and-fly-wheel type. Power pumps are reciprocating machines which may be driven by any form of motor, to which they are connected by belt, chain or shaft. A Deming triplex power pump is shown in Fig. 53. Power pumps can be used only where the character of the sewage will not clog the valves nor corrode the pump. A direct-acting steam pump is one in which the steam and water cylinders are in the same straight line and the steam is used at full boiler pressure throughout the full length of the stroke. The crank-and-fly-wheel type of pumping engine permits the use of steam expansively during a part of the stroke, the energy stored in the flywheel carrying the machine through the remainder of the stroke. Reciprocating pumps are sometimes classified as plunger pumps and piston pumps. In the action of a plunger pump the water is expelled from the water cylinder, by the action of a plunger which only partly fills the water cylinder, as shown in Figs. 54 and 55. In a piston pump the water is expelled from the water cylinder by the action of a piston which completely fills the water cylinder, as shown in Fig. 63, which illustrates a direct-acting piston pump. [Illustration: FIG. 53.—Triplex Power Pump. Courtesy, The Deming Co. ] Plungers are better than pistons for pumping sewage as the wear between the pistons and the inside face of the cylinder soon reduces the efficiency of the pump. Outside packed plungers are better than the inside packed type because the packing can be taken up without stopping the pump and the leakage from the pump is visible at all times. Outside packed pumps are more expensive in first cost, but are easier to maintain and have a longer life than piston pumps. [Illustration: FIG. 54.—Water End of Inside Center-Packed Plunger Pump. ]