MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

88of 3000 gpm or 5000 psig. Depending on such variables as material, size,and design, rotary pumps-- such as some of the more common designs shownin Figure 3.48-- may range in price anywhere from $50 to $14,000 (Hollandand Chapman, 1966).The two rotary pumps which are capable of handling abrasive fluidsare the single helical-screw and the flexible impeller designs. Asshown in Figure 3.26, the helical I rotor pump consists of a helical-shapedrotor which turns inside a molded rubber stator which has a similar innershape. As the rotor turns, it traps water along the stator walls and"squeezes" it toward the discharge outlet. Helical pumps are commonlyused in a horizontal position and close-coupled to an electric motor forpumping from shallow wells, i.e., they have NPSHR limitations just likeany other pump. Deep-well helical pumps are capable of heads up to about1000 ft. Between these two types of helical pumps, they cover a range ofdischarges from 5-75 gpm. Close-coupled units may vary in price fromabout $100 to $2000, including motor, while the vertical units will varywith horsepower, at a slightly lower rate than vertical turbine pumps(see Section 4.2.6).The flexible-impeller or -rotor pump utilizes a flexible, paddle-wheel-like rotor to trap and lift water, as shown in Figure 3.27. Because of theflexible impeller, this pump --unlike most rotary pumps--can operate againsta closed discharge without building up damaging pressures. However, sincethe flexible vanes stay in contact with the casing, high friction lossesoccur which lower efficiency. Also,, at high pressures, these vanes tendto slip, creating leakag e losses within the casing, Most flexible impellerpumps are in the $20 to $600 range. They can be made to handle from 0.5 to100 gpm and with heads up to about 110 ft.