Figure 6-13.—Portable diaphragm pump.

Figure 6-13.—Portable diaphragm pump. pumping heavy and thick liquid long distances away from the pump. The pump is fitted with discharge hose connections, and the ball valves and chambers are designed to prevent fouling by sticks, stones, rags, and so on. The WATER HOG is used for pumping thinner and less viscous liquids; however, it can handle liquids containing sand, gravel, and mud. The discharge outlet from the water hog is open to permit free flow and increased discharge capacity. Thus the liquid is discharged directly at the pump. However, a discharge hose can be fitted to the pump if desired; but, the efficiency is reduced. Both the mud hog and water hog can be of either the simplex or duplex type. Because of the nature of the liquids handled by diaphragm pumps, operator inspection during pump operation becomes particularly important. Make frequent inspections of the suction inlet strainer to prevent accumulation of debris that can reduce suction efficiency. Most diaphragm pump installations also permit easy access to the suction and discharge ball valves. The valve mechanisms can be inspected frequently to detect scoring, fouling, and improper valve seating. Because the diaphragm and ball-check valves are subjected to the corrosive action of such material as sand and gravel they require frequent attention. Therefore, operator maintenance schedules stress a continuing program of inspection and cleaning of these parts. In most cases, it is not practical to repair damaged or worn diaphragms and valves. They should be replaced with new ones; therefore, keep an adequate supply of these parts readily available. The reciprocating pump shown in figure 6-12 is called a single or simplex pump because it has only one liquid cylinder. Simplex pumps are either direct acting or indirect acting. A double or duplex pump is an assembly of two single pumps placed side by side on the same foundation; the two steam cylinders are cast in a single block, and the two liquid cylinders are cast in another block. In a single-acting pump, the liquid is drawn into the liquid cylinder on the first or SUCTION STROKE and is forced out of the cylinder on the return or DISCHARGE STROKE. In a double-acting pump, each stroke serves both to draw in the liquid and to discharge the liquid. As one end of the cylinder is filled, the other end is emptied; on the return stroke, the end that was just emptied is filled and the end that was just filled is emptied. The pump shown in figure 6-12 is double acting, as are most of the reciprocating pumps used in the Navy. (NOTE: Only one of two sets of valves is shown in figure 6-12.) 6-14