Multistage pumps

For double suction pumps, using the HI convention, is taken as the total pump flow, although some pubHcations use half-flow, ie, flow per impeller eye. For multistage pumps, the developed head must be taken per stage for the NS calculation. By definition (eq. 9), high head, low flow pumps have low specific speed low head, high flow pumps, such as turbine and propeller pumps, have high specific speed. 

Multistage pumps may be of the volute type (Fig. 10-41), with single- or double-suc tion impehers (Fig. 10-42), or of the diffuser type (Fig. 10-43). They may have horizontahy split casings or, for... 

In-house correlation of pumps should be made using gpm vs. cost with head as a parameter. These should result in step functions, since one size pump with different impellers can serve several flow rates and heads. Different correlations should be made for each type of pump. The price of a vertical multistage pump may be quite different from a horizontal splitcase multistage pump. A sump pump with a 15-ft drive shaft would cost more than a single-stage horizontal pump with the same gpm and head. 

Water above 250° F. Single or double suction. This is usually boiler feed service at high pressures requiring multistage pumps. Closed except for very small capacities... 

Figure 3-56. Viscosity performance correction chart for centrifugal pumps. Note do not extrapolate. For centrifugal pumps only, not for axial or mixed flow. NPSH must be adequate. For Newtonian fluids only. For multistage pumps, use head per stage. (By permission. Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, 13th ed.. Hydraulic Institute, 1975.)...

The validity of the method has not been completely established, although it has been used rather widely in setting approximate values for proper operation [10]. For multistage pumps use only the head per stage in temperature limit bv this method. 

Another centrifugal pump classification is whether the pump is a single-stage pump (the pressure head is developed by a single impeller) or a multistage pump (the pressure head is developed by two or more impellers). 

Radially split multistage pumps, 21 67-68 Radial patternators, 23 194 Radial thrust, 21 83-84 Radial velocity, in hydrocyclones, 22 285... 

NPSHR) The NPSH, iu meters (feet), deterruiued by veu-dor testing with water. NPSHR is measured at the suction flange and corrected to the datum elevation. NPSHR at rated and other capacities is equal to the NPSH that produces a 3 percent head drop (first stage head in multistage pumps) due to cavitation within the pump. 

Note The purchaser may consider the use of variable speed drive capability and/or the use of blank stages (to add impellers in the future) for multistage pumps to meet this requirement. 

The FFT spectra shall include the range of frequm-des from 5 Hz to 2Z times running speed (where Z is the number of impeller vanes in multistage pumps with different impellers, Z is the highest number of impeller vanes in any... 

Note In the case of high-energy pumps (see 2.1.15), and multistage pumps, it may not be feasible to test at shutoff. 

Impellers of multistage pumps shall be individually located along the shaft and positively secured against axial movement in the direction of normal hydraulic thrust. An interference fit is not considered a positive locking method. 

Interstage bushings and thrust-balancing devices on multistage pumps may have the manufacturer s standard clearances, provided these clearances are stated as exceptions to this standard (see 2.6.4.2) in the proposal and are approved by the purchaser. When the manufacturer s standard clearances are based on material combinations exhibiting superior wear characteristics, supporting data shall be included in the proposal. 

Certified rotor balance data for multistage pumps. ... 

Are impellers for multistage pumps to be positively locked against axial movement in the direction opposite to normal hydraulic thrust Yes No... 

NPSH that results in a 3% loss of head (first stage head in a multistage pump) determined by the vendor by testing with water... 

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