Page 80 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 2 .9 Pump Best Practices

Fig 2.9.8 Centrifugal pump performance curve shapes

Flat curves (1 and 2), show little variation in head for all flows
between design point and shut-off
Drooping curve (2), head at shut-off is less than head developed at
some flows between design point to shut-off
Rising curve (1,3,4), head rises continuously as flow decreases
from design point to shut-off
Steep curve (4), large increase between head developed at design
flow and that developed at shut-off
Stable curve (1,3,4), one flow rate for any one head
Unstable curve (2), same head can be developed at more than one
flow rate

Fig 2.9.9 Definition of characteristic curve shape

Increasing head produced by a pump
2 2
D 1 N 1
H 1 = HorH 1 = H
D N
= diameter of changed impeller
where: D 1
D = diameter of existing impeller
H 1 = head in feet changed impeller
H = head in feet existing impeller
N 1 = speed (RPM) changed condition
N = speed (RPM)existingcondition

Fig 2.9.10a The affinity laws Fig 2.9.10b The affinity laws

54