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340 Boiler Operator’s Handbook
Figure 10-78. Turbine pump impeller
Figure 10-77. Horizontal split case pump
turbine. That’s not the case. A turbine pump is a type
of pump and although they exhibit some characteristics
comparable to a centrifugal pump they differ. The tur-
bine pump grabs the liquid on the outer diameter of the
impeller, spins it around inside the pump and heaves it
out the discharge. A turbine pump impeller looks like
the one in Figure 10-78 with little slots all around the
outside. The fins formed by those slots is what grabs the
liquid and whirls it around inside the pump casing until
it gets to the discharge.
Turbine pumps can produce very high differential
pressures because they act more like a positive displace- Figure 10-79. Turbine pump curve
ment pump than a centrifugal. The typical turbine pump
curve (if you got to see one that showed all conditions Turbine pumps are commonly used as boiler feed
from zero flow) looks like a centrifugal pump curve but pumps, especially on low pressure steam boilers. Their
most of the curves you get look almost like a straight line steep curves permit them to handle the significant varia-
with a steep negative slope (Figure 10-79). Since they tions in boiler pressure without any effect on pump ca-
operate more like a positive displacement pump you pacity. I’ve run into many a plant with centrifugal pumps
should treat them like one. Don’t start a turbine pump that also have curves so steep that their flow isn’t altered
with the discharge valve closed. significantly by changes in boiler operating pressure.