Pumps running in series

Let's begin by viewing an arrangement of pumps running in series, followed by the development of the series curve (Figure 8-28).

Series pumps theoretically offer twice the pressure at the same flow (Figure 8-29). The second pump takes the discharge head of the first

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Figure 8-28

PUMP CURVE A or B

SERIES PUMPS PROVIDE 2 TIMES PRESSURE AT SAME FLOW

PUMP CURVES A AND B IN SERIES

SERIES PUMPS PROVIDE 2 TIMES PRESSURE AT SAME FLOW

PUMP CURVES A AND B IN SERIES

Figure 8-29

pump and jacks up the head again. However, because the system design includes 4 'T' connections, 6 valves, and at least 6 pipe elbows right at the pumps, the actual pressure is not quite doubled because the Hf is significant through the arrangement. The same tips that apply to pumps in parallel, also apply to pumps in series. Depending on the profile of the system curve, one solo pump running in a series arrangement may be running to the left of its BEP or even at shut-off head. If it is running at shut-off head, you don't really have the option of running one solo pump. Use double mechanical seals. It will be necessary to identify and trace the elements of the TDH, and match the TDH to the curve of the pumps running in series.

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