Centrifugal pump series and parallel connection

Centrifugal pumps can be connected in series or parallel to meet specific flow and pressure requirements in a system. Here’s how each configuration works:

1. Series Connection

• Purpose: Increases head (pressure) while keeping flow rate approximately the same.

• How it works:

• The discharge of the first pump feeds into the suction of the second pump.

• The total head is the sum of the individual pump heads at a given flow rate.

• The flow rate remains similar to that of a single pump (slightly less due to increased losses).

• Applications:

• High-pressure systems (e.g., boiler feed pumps, long-distance pipelines).

• When system resistance is too high for a single pump.

• Characteristics:

• Head: ${\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}$Htotal=H1+H2

• Flow rate: ${\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">\approx </span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">\approx </span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}$Qtotal≈Q1≈Q2

2. Parallel Connection

• Purpose: Increases flow rate while keeping head approximately the same.

• How it works:

• Both pumps take suction from the same source and discharge into a common header.

• The total flow is the sum of individual pump flows at a given head.

• The head remains similar to that of a single pump (slightly higher due to increased system resistance).

• Applications:

• High-flow systems (e.g., cooling water circulation, irrigation).

• When one pump cannot meet the required flow demand.

• Characteristics:

• Flow rate: ${\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}$Qtotal=Q1+Q2

• Head: ${\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">\approx </span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">\approx </span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}$Htotal≈H1≈H2

Key Considerations

• Matching Pumps:

• For series, pumps should have similar flow rates to avoid overloading.

• For parallel, pumps should have similar head curves to prevent one pump from dominating.

• System Curve:

• Series operation shifts the head curve upward.

• Parallel operation shifts the flow curve to the right.

• Efficiency:

• Ensure pumps operate near their Best Efficiency Point (BEP) to avoid cavitation or excessive wear.

Comparison Table

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