CHAPTER 6
VELOCIS SOLUTIONS @2018
13
Multiple pumps in series and parallel
When the required head is relatively high, several pumps in series combination are used to match system
demand. To maintain harmonious operation of pumps affinity law is developed and represented by
equation applied for fixed impeller diameter:
𝑁
1
𝑁
2
=
𝑞
1
𝑞
2
=
𝐻
1
0.5
𝐻
2
0.5
=
𝑘𝑊
1
1 3
⁄
𝑘𝑊
2
1 3
⁄
Where:
𝑁 −speed
𝑞 − flow rate
𝐻 – head
𝑘𝑊 − power
Subscript (1) and (2) refer to two different condition for the same pump or can be applied to two
different pumps.
If rpm remains constant and impeller diameter is changed, multiply:
1. original capacity by (𝑑
2
𝑑
1
⁄
)
2. original head by (𝑑
2
𝑑
1
⁄
)
2
3. original power by (𝑑
2
𝑑
1
⁄
)
3
This can be used to convert performance expected for an individual pump from a known condition
to a new condition.
Figure 7.10: Performance curve for pumps in series
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