Page 127 - Fluid mechanics, heat transfer, and mass transfer

PUMPS 105

FIGURE 5.5 Open, semiopen, and enclosed impellers.

& Semienclosed: Used for general purpose. For higher & Impractical to use on most vertical pumps and for
heads. Have open vane tips at entrance to break up mixed flow or axial flow impellers.
suspended solid particles and prevent clogging. & Compared to single-suction impellers, double-suc-
& Enclosed: Used for higher heads and higher pressure tion impellers are less compact, have two stuffing
applications. Higher efficiencies because liquid flow boxestomaintain,lessflexibleinpipingarrangement,
is close to radial conditions with minimum lateral handle solids poorly and less resistant to abrasion,
movement. NPSH requirements are lowest. corrosive, high temperatures, and expensive.
. What type of impeller is used for pumping water from a & Figure 5.6 shows a double-suction centrifugal pump.
sump/pit?
& Open impeller as water pumping from sumps/pits
involves contamination with solid particles and any
other type creates deposits on internal surfaces and it
would be difficult to clean them.
. What is meant by a double-suction impeller for a
centrifugal pump? What are its merits and limitations?
& Fluid enters from both sides of the impeller eye.
& Useful for high flows.
& Lowers suction specific speed and maintain hydrau-
lic balance. This lessens NPSH requirements and
reduces thrust bearing loads.
& Used in many horizontal services with more than two
stages to avoid a high-pressure seal. FIGURE 5.6 Double suction to a centrifugal pump.