=80. Steam Pumps and Pumping Engines.=—The direct-acting steam pump, one type of which is shown in Fig. 63, is adapted to pumping sewage the character of which will not corrode or clog the valves. In this form of pump it is necessary to utilize the steam at full pressure throughout the entire length of the stroke, which results in high steam consumption. A flywheel permits the use of steam expansively during a part of the stroke, thus increasing the economy of operation. Other devices used for the same purpose are known as compensators. They are not in general use. Steam engines are classified in many different ways, for example; according to the type of valve gear, as, plain slide valve, Corliss, Lentz, etc.; or according to the number of steam expansions, as, simple, compound, triple-expansion, etc.; or according to the efficiency of the machine as low duty or high duty; or as [Illustration: FIG. 63.—Section of Duplex Piston Steam Pump. Courtesy, The John H. McGowan Co. ] STEAM END 2 Steam cylinder and housing combined. 8 Steam piston head. 9 Steam piston follower. 10 Steam piston inside ring. 11 Steam piston outside ring (2). 12 Steam cylinder head. 14 Steam chest. 16 Steam chest cover. 17 Steam slide valve. 18 Steam valve rod. 20 Steam valve rod, pin and nut. 22 Steam valve rod, collar and set screw. 23 Steam valve rod, stuffing box. 24 Steam valve rod, stuffing box, nut and gland. 38 Piston rod. 47 Piston rod stuffing box. 48 Piston rod, stuffing box, nut and gland. 49 Valve gear stand. 51 Long valve crank and shaft. 52 Short valve crank and shaft. PUMP END 115 Pump body. 127 Brass liner. 129 Water piston head. 130 Water piston follower. 137 Cylinder head. 139 Valve plate. 140 Cap. 152 Suction flange. 161 Discharge flange. 162 Valve seat, suction or discharge. 163 Valve, suction or discharge. 164 Suction valve spring. 167 Discharge valve spring. 168 Valve plate, suction or discharge. 169 Valve stem, suction or discharge. STEAM END 55 Crank pin. 56 Valve rod link. 61 Long rocker arm. 62 Short rocker arm. 63 Rocker arm wiper. 69 Cross head. condensing or non-condensing, etc. Throttling engines or automatic engines refer to the method of control of the steam by the governor. In throttling engines the governor controls the amount of opening of the throttle valve, in automatic engines the governor controls the position of the cut-off.