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Pumps Parallel Serial

Reference data and engineering information about pumps parallel serial for pumps applications.

pumpsparallelserial

Overview

Engineering reference data for Pumps Parallel Serial in pumps.

Key Formulas

Pump Power

P=Q⋅H⋅ρ⋅gηP = \frac{Q \cdot H \cdot \rho \cdot g}{\eta}

Hydraulic power / efficiency.

NPSH Available

NPSHa=Psρg+vs22g−PvρgNPSH_a = \frac{P_s}{\rho g} + \frac{v_s^2}{2g} - \frac{P_v}{\rho g}

Net Positive Suction Head available.

Affinity Laws

Q∝n,H∝n2,P∝n3Q \propto n, \quad H \propto n^2, \quad P \propto n^3

Flow, head, power vs speed.

Variables

SymbolDescriptionUnit
PPPowerW
QQFlow ratem³/s
HHHeadm
η\etaEfficiency—
nnRotational speedRPM

Operational Behavior

When pumps are arranged in series or parallel, the actual operating point differs from the theoretical addition point due to system resistance.

Series Operation

  • Ideal: For two identical pumps in series, head at a given flow rate doubles (moving from point 1 to point 2 on the curve).
  • Practical: The operating point moves along the system resistance curve from the single-pump operation point (1) to the combined operation point (3).
  • For two identical pumps at point 3, each pump operates at half the total head but the full system flow rate.

Parallel Operation

  • Ideal: For two identical pumps in parallel, flow rate at a given head doubles (moving from point 1 to point 2 on the curve).
  • Practical: The operating point moves along the system resistance curve from the single-pump operation point (1) to the combined operation point (3).
  • For two identical pumps at point 3, each pump operates at the total system head but at half the total flow rate.

Failure Scenario: If one pump in either a parallel or series arrangement stops, the operating point will move back along the system curve towards point 1 (single-pump operation), resulting in decreased head and flow rate.

Parallel Operation Requirements

For stable parallel operation of centrifugal pumps, the following should be considered:

  • Matching Shut-Off Heads: The zero-flow or "shut valve" heads of the pumps must be compatible.
  • Avoid Unstable Curves: Pump performance curves that are not continuously rising (i.e., have a peak or drooping characteristic) can lead to unstable operation and hunting.
  • Preferred Curve Shape: Steeper pump curves are generally preferred for parallel operation as they provide more predictable flow distribution.

References

Source: engineeringtoolbox.com