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Contents
. . . . . . . . . . . . ~ : - . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.6 Pump system analysis 44
3.6.1 Example 1 45
3.6.2 Example 2 47
3.6.3 Example 3-A 49
3.6.4 Example 3-B 51
3.6.5 System curve revisited 51

4 Suction Conditions 53
4.1 General 53
4.2 Vapor pressure 53
4.3 Cavitation 53
4.4 Net positive suction head 55
4.4.1 NPSH required by the pump 56
4.4.1.1 Increase the eye area of the impeller 57
4.4.1.2 Install a suction inducer 57
4.4.1.3 Use a double suction impeller 57
4.4.1.4 Use a slower speed pump 57
4.4.1.5 Use lower capacity pumps 57
4.4.1.6 Use a boosterpump 58
4.4.2 NPSH available from the system 58
4.4.2.1 Static head (Hs) 59
4.4.2.2 Surface pressure (Ha) 59
4.4.2.3 Vapor pressure (Hvp) 59
4.4.2.4 Friction losses (Hf) 60
4.4.2.5 Sample NPSHA calculation 61
4.5 Suction specific speed 62
4.6 Confusing conditions 63
4.6.1 Suction recirculation 63
4.6.2 Discharge recirculation 63
4.6.3 Air entrainment 63
4.7 Similarities and differences 65
4.8 Priming 66
4.8.1 Self-priming pump layout 67
4.8.2 Centrifugal pump with priming tank 68
4.8.3 Air ejector system 68
4.9 Submergence 68

Pump selection and purchasing 71
5.1 Pump selection factors 71
5.1.1 Operational experience 72
5.1.2 End user data sheets 73
5.2 System operating considerations 73

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