Page 65 - Centrifugal Pumps Design and Application

48 Centrifugal Pumps: Design and Application

Step 3

Establish next size pump by multiplying each base line BEP by
• GPM x 1,75
• Head x 1,45

Example: Smallest pump on chart has BEP of 86 GPM and 150-ft
head. Thus, BEP for next size pump = 86 x 1.75 = 150 GPM and
150 x 1.45 = 220 ft. Repeat this step for each base line BEP. As can
be seen from the chart, the head of 220 ft now requires a 9-in. impeller,

Step 4

For all additional pump BEP's multiply preceding pump flow by
1.75 and head by 1.45.

The constants 1.75 and 1.45 are recommended for a well-planned per-
formance chart following a number of constant specific speed lines.
There are no gaps between pumps, each performance block can be cov-
ered by normal impeller trim, and there are no overlaps. The chart is also
helpful to the designer. In this example, only six small pumps have to be

Figure 4-2. Recommended performance chart.