Fig. 486.—See page [210].
The engraving, Fig. [487], shows Root’s rotary pump. This has two impellers which are geared together and each turn at equal speeds towards one another at the top. The engraving, Fig. [488], also shows a Root pump with two impellers each having three wings or lobes. The pump proper consists of half circles, AA, with air chambers, DD, cast with them, the head plates, B, carrying the bearings, and the revolvers, CC, together with shafts, EE. The shafts carry involute gears at each end which keep the lobes of the two impellers in their relative positions, and rotate them. Either shaft may be made the driving shaft and to deliver water, as shown by the arrows in the cross section, the shafts revolve so that the tops move toward one another.—Same as in the preceding case.
Fig. 487.
Fig. 488.
The action of this pump is as follows: the suction pipe on starting, being full of air, the first few revolutions of the pump expel the air until the required vacuum is formed, which allows atmospheric pressure to raise water into the pump. It then flows between the case and the lobes into the space, F, and is carried by the impellers to the discharge edge of the case, point, G, where it enters the discharge pipe. Each succeeding lobe brings up an amount of water equal to spaces, FF, thus delivering the contents of the six at each revolution. The irregular form of the lobes keeps them in contact at the center line, thus preventing the return of water into the suction below.
Heads of water from 10 to 250 feet are successfully handled by this type of pump, with a slip of from 5 to 15 per cent., according to the discharge pressure.