The Duplex. Pump (fig. 8), the best known of its class, moves the steam-valye of each side through purely mechanical means by the piston-rod of the other side. There are many other makes of duplex pumps in which each side mechanically moves the valves of the other.
Figure t ti4) shows the pumping-engine of the Brooklyn (N. Y.) water-works, and Figure 3 (pi. I t5) that at Brunswick, Germany. The pump piston-rods are prolongations of the steam-cylinder piston-rods, and the fly-wheel in each case simply steadies the motion.
Centrifugal Pumps include those devices which have a paddle-wheel or vane-wheel rotating- in a case 114, fig. 2), and which by the repeated rotation of this wheel draws the water in at the centre of th6 ease and throws it by centrifugal action to the periphery of the case, whence it may be taken up tangentially in any direction. In one of the best-known forms the suction-pipe is branched so that the liquid being pumped enters the chamber from each side, and the casing, which fits snugly to the blades of the wheel, is surrounded by a channel having a circular cross-section which increases in diameter from one part of its circumference until it has made a complete revolution, when it is led off at a tangent. The centrif ugal pump requires to be worked at a high speed of rotation, but it is useful for handling large quantities of water which are to be draughted only a short distance and not forced against any great head or pressure. It is well adapted for wrecking purposes, for pumping out dry-docks, etc.
Rotary Pump.—The rotary pump has in its design and construction very much the same principle as is found in a rotary engine (p. 260). In it, by the continuous rotation of one or more winged or toothed pistons in a cylinder or other suitably conforming case, there is formed a partial vac uum, and the water which rushes up to fill this vacuum is swept up and discharged by the rotating wing or wings. There may be one piston which sweeps past the inlet and the discharge opening, or two which are practically gear-wheels with one or more teeth each, these teeth meshing air-tight with each other and with the walls of the chamber or case. Where there are two pistons, instead of there being one wing which sweeps past the inlet and the outlet openings and fits air-tight all around the case there are two; and each during part of the revolution fits the chamber, and during the rest of the revolution fits the other piston.
The Si&by Rotary Pump (pl. 115, fig. r) has two rotating pistons, each of which has three long teeth meshing in three depressions in the other, and six shorter teeth similarly meshing. The three long teeth of each fit snugly against the walls of the casing. The suction is into the casing at a point below the line connecting the two shafts, and the discharge is at a point diametrically opposite. Nearly any rotary pump might be used as rotary motor, and vice versd, although the duty would be low.
The Positive piston Pump 2) has two rotating rollers, each of which is cylindrical, and one of which has a projecting tooth, while the other has a corresponding depression, so that as they are rotated with their peripheries in contact they mesh precisely in the manner of gear-wheels. The tooth or projection of the larger one closely fits the walls of the cylindrical casing, which is intersected by another in which the toothless piston rotates with a snug fit. The suction is central, passing through the toothed cylinder, in which there are screw-propeller-shaped blades. The water, which is drawn in all the revolutions of the toothed cylinder, passes through an opening in the periphery of the latter into the space between it and the casing, and is discharged at a point in the outer casing about where the two cylindrical casings intersect. External gears insure the perfect meshing of the rotating cylinders. In construction there are two of each of these cylinders on one axis, to steady the running and the discharge.
Artesian-well Pump.—Figure 3 (pi. 114) shows in section a vertical bucket-plunger steam-pump for non-flowing artesian wells and for deep driven wells. The "working barrel" or pump-end is a casting of hard brass with a pump-bucket and foot-valve, and is screwed on the lower end of the well piping, through which the pump-rod works. The pump-rod connection between the pump-bucket and the upper plunger is of wood or extra-heavy iron pipe. A special arrangement of the steam-valves makes the up-stroke and the down-stroke uniform. The pump-bucket discharges water on the up-stroke, and the upper plunger on the down-stroke.