centrifugal pump in series and parallel​

Centrifugal Pumps in Series and Parallel

Centrifugal pumps can be connected in series or parallel to meet specific flow and pressure requirements in industrial and commercial applications.

1. Pumps in Series

Connection: The discharge of the first pump feeds into the suction of the second pump.

Characteristics:

✔ Total Head (Pressure) increases (almost additive).
✔ Flow rate remains the same as a single pump.

Performance Curve (Series Operation):

• The head (H) at a given flow rate (Q) is the sum of the individual pump heads.

• The flow rate remains unchanged compared to a single pump.

Equation:

$${\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}<span\; style="font-size:\; 18px;">+</span>\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">n</span>}}$$Htotal=H1+H2+...+Hn$${\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}<span\; style="font-size:\; 18px;">=</span>\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">n</span>}}$$Qtotal=Q1=Q2=...=Qn

Applications:

• Booster pumping systems

• High-pressure applications (e.g., multi-stage pumps)

• Pipeline pumping where long-distance pressure is needed

Example:

If two identical pumps each provide 50 m head at 100 m³/h, in series:

• Total head = 50 + 50 = 100 m

• Flow rate remains 100 m³/h

2. Pumps in Parallel

Connection: Multiple pumps share the same suction and discharge lines.

Characteristics:

✔ Flow rate increases (nearly additive for identical pumps).
✔ Head remains the same as a single pump (if pumps are identical).

Performance Curve (Parallel Operation):

• The flow rate (Q) at a given head (H) is the sum of individual pump flows.

• The head remains the same as a single pump (if pumps are identical).

Equation:

$${\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}<span\; style="font-size:\; 18px;">+</span>\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}<span\; style="font-size:\; 18px;">+</span>{\mathrm{<span\; style="font-size:\; 18px;">Q</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">n</span>}}$$Qtotal=Q1+Q2+...+Qn$${\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">o</span>}\mathrm{<span\; style="font-size:\; 18px;">t</span>}\mathrm{<span\; style="font-size:\; 18px;">a</span>}\mathrm{<span\; style="font-size:\; 18px;">l</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">1</span>}}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">2</span>}}<span\; style="font-size:\; 18px;">=</span>\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}\mathrm{<span\; style="font-size:\; 18px;">.</span>}<span\; style="font-size:\; 18px;">=</span>{\mathrm{<span\; style="font-size:\; 18px;">H</span>}}_{\mathrm{<span\; style="font-size:\; 18px;">n</span>}}\text{<span style="font-size: 18px;">(if pumps are identical)</span>}$$Htotal=H1=H2=...=Hn(if pumps are identical)

Applications:

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

• Variable demand systems (one pump runs at low demand, multiple at peak)

• Cooling water circulation

Example:

If two identical pumps each provide 50 m head at 100 m³/h, in parallel:

• Total flow = 100 + 100 = 200 m³/h

• Head remains 50 m

Comparison Table (Series vs. Parallel)

Key Considerations

• Matching Pumps: For best performance, pumps should have similar characteristics.

• System Curve: The combined pump curve must intersect the system curve at the desired operating point.

• Cavitation Risk: In series, the second pump may experience higher suction pressure issues.

• Control Strategy: Parallel pumps often use variable speed drives (VSDs) to optimize efficiency.

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