Page 355 - Boiler_Operators_Handbook,_Second_Edition
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                                                                            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.
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