Classification Pumps

Overview

Engineering reference data for Classification Pumps in pumps.

Key Formulas

Pump Power

$P = \frac{Q \cdot H \cdot \rho \cdot g}{\eta}$

Hydraulic power / efficiency.

NPSH Available

$NPSH_a = \frac{P_s}{\rho g} + \frac{v_s^2}{2g} - \frac{P_v}{\rho g}$

Net Positive Suction Head available.

Affinity Laws

$Q \propto n, \quad H \propto n^2, \quad P \propto n^3$

Flow, head, power vs speed.

Variables

Pump Selection Criteria

When choosing between centrifugal and positive displacement pumps, several key performance characteristics differ significantly:

Flow Rate and Pressure Behavior

• Centrifugal Pumps: Flow rate varies with system pressure/head.
• Positive Displacement Pumps: Delivers nearly constant flow regardless of system pressure/head. Generally achieve higher pressures.

Viscosity Effects

• Centrifugal Pumps: Flow decreases as viscosity increases; become inefficient at even modest viscosities.
• Positive Displacement Pumps: Flow (volumetric efficiency) increases with viscosity as liquid fills internal clearances. Better suited for high-viscosity applications.

Mechanical Efficiency & System Response

• Centrifugal Pumps: Flow rate is highly sensitive to changes in system head/pressure.
• Positive Displacement Pumps: Flow rate is largely unaffected by changes in system head/pressure.

Net Positive Suction Head (NPSH)

• Centrifugal Pumps: Required NPSH is a function of flow rate, which is determined by pressure.
• Positive Displacement Pumps: Required NPSH is a function of flow rate, which is determined by speed. NPSH can be reduced by lowering pump speed.

Pump Type Classifications

Centrifugal Pump Types

• End suction pumps
• In-line pumps
• Double suction pumps
• Vertical multistage pumps
• Horizontal multistage pumps
• Submersible pumps
• Self-priming pumps
• Axial-flow pumps
• Regenerative pumps

Positive Displacement Pump Types

• Reciprocating: Piston, plunger, diaphragm
• Power: Power pumps
• Steam: Steam pumps
• Rotary: Gear, lobe, screw, vane, regenerative (peripheral), progressive cavity

References

• Original Source