MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

, _1174.3 Jet PumpsA jet pump is a device which uses the kinetic energy of one fluid(i.e., the driving fluid), rather than an impeller, to pump another fluid.Depending on their application, jet pumps are known by several names;injector, jet heat exchanger, ejector, and eductor. The first two utilizea gas (usually steam) to drive another gas or a liquid, while the lattertwo devices utilize a liquid (usually water) to driveanother liquid or agas (Engineering, 1968, and Kneass, 1903). The term, eductor, also appliesto air-lift pumping (Chapter 3) which is a positive displacement methodand should not be confused with the jet principle. Injectors and exchangersare primarily used in conjunction with boilers. Therefore, in irrigationand drainage applications, the use of a “jet pump” usually implies anejector .An ejector utilizes a driving pump * to force the driving water at ahigh pressure into a venturi tube or suction box. There it entrains additionalwater to deliver a discharge of higher volume and lower pressure.This principle can be used in either of the two methods shown in Figure 4.7.For ease of operation and installation in wells, the sequence of Figure4.7b is usually utilized in irrigation and drainage systems. However, itis the design in Figure 4.7a that is often used to add fertilizer toirrigation water. The arrangement of Figure 4.7b can increase the capacityof a centrifugal pump, however, at the expense of total head and efficiency.Although ejector efficiencies rarely reach 40 percent, this is also aneffective way to increase the suction lift capability of a centrifugal* This pump is usually a centrifugal device, however, recent developmentsare incorporating positive displacement pumps--see Walkden, 1967, p. 318-319.