Centrifugal Pumps Operation Tips, Tricks & Noise Level Calculator

1. Introduction

Why are centrifugal pumps noisy ?

The impeller of a centrifugal pump rotates at high angular velocity. Consequently, the vanes of the impeller hit the fluid, generating turbulent vortex shedding, wake interactions with the cutwater (volute tongue), and blade-pass frequency pressure pulsations. This dynamic energy is transmitted as mechanical vibration through the shaft, bearings, pump casing, and attached piping. The surrounding air and resonant pipe walls then radiate these pulsations as acoustic sound pressure waves, creating an industrial noise hazard.

🔊 Centrifugal Pump Noise Level Calculator

Estimate Sound Power Level \(L_{wA}\) and Sound Pressure Level \(L_p\) at distance according to pump type and absorbed power.

2. Noise of a centrifugal pump : step by step calculation

How to estimate what will be the noise emitted by a pump ?

2.1 STEP 1 : Define the type of pump

Different hydraulic designs of centrifugal pumps emit distinct acoustic spectra and total sound power levels. The primary industrial categories defined in acoustic empirical standards include:

• Side channel pump: Self-priming peripheral impellers with high differential pressure across small chambers.
• Single stage volute or ring section pumps with multi impellers: Standard industrial process pumps (ISO 2858 / API 610 single-stage or ring section pumps).
• Multi-stage ring section pump: High pressure boiler feed or reverse osmosis booster pumps with multiple stage diffuser casings.

2.2 STEP 2 : Calculate the absorbed power

The absorbed mechanical power \(P\) delivered by the electric motor to the pump shaft is calculated from the mass flow rate, total developed head, fluid density, and overall pump hydraulic efficiency:

\[P = \frac{\rho \cdot g \cdot Q \cdot H}{3600 \times 1000 \times \eta} \quad [\text{kW}]\]

Where:

• \(\rho\) = Liquid density \((\text{kg/m}^3)\)
• \(g\) = Acceleration due to gravity \((9.81\text{ m/s}^2)\)
• \(Q\) = Volumetric flow rate \((\text{m}^3/\text{h})\)
• \(H\) = Total differential dynamic head \((\text{m liquid column})\)
• \(\eta\) = Pump hydraulic efficiency at the operating point \((-)\)

Refer to the detailed calculation procedure in the dedicated guide: Pump Power Calculation Procedure.

2.3 STEP 3 : Calculate the noise emitted (Sound Power Level \(L_{wA}\))

According to extensive experimental acoustic surveys compiled by pump manufacturer Sihi [Sihi], the total A-weighted sound power level emitted by the pump casing under nominal hydraulic duty is expressed as a logarithmic function of absorbed power:

Type of Pump	Applicable Power Range	Emitted Sound Power Formula (\(L_{wA}\))
Side channel pump	\(2 \text{ kW} \le P \le 40 \text{ kW}\)	\(L_{wA} = 67 + 12.5 \cdot \log_{10}\left(\frac{P}{P_0}\right)\)
Single stage volute or ring section pumps with multi impellers	\(10 \text{ kW} \le P \le 2000 \text{ kW}\)	\(L_{wA} = 66 + 13.5 \cdot \log_{10}\left(\frac{P}{P_0}\right)\)
Multi-stage ring section pump	\(10 \text{ kW} \le P \le 2000 \text{ kW}\)	\(L_{wA} = 78 + 8.5 \cdot \log_{10}\left(\frac{P}{P_0}\right)\)

Where:

• \(L_{wA}\) = A-weighted sound power level in \(\text{dB(A)}\) (referenced to \(10^{-12}\text{ W}\))
• \(P\) = Absorbed pump shaft power in \(\text{kW}\)
• \(P_0\) = Reference power standard = \(1\text{ kW}\)

2.4 STEP 4 : Convert Sound Power Level \(L_{wA}\) to Sound Pressure Level \(L_p\) at Distance

In industrial plant layouts, acoustic sensors or worker ear levels measure the Sound Pressure Level \(L_p\) at a specified distance \(r\) (typically 1 meter). In a semi-free acoustic field over a rigid reflective concrete foundation (hemispherical propagation with directivity factor \(Q = 2\)), the relationship is:

\[L_p(r) = L_{wA} + 10 \cdot \log_{10}\left(\frac{Q}{4 \pi r^2}\right) = L_{wA} - 20 \cdot \log_{10}(r) - 8.0 \quad [\text{dB(A)}]\]

For standard compliance verification at \(r = 1.0\text{ m}\), the sound pressure level on a concrete pad simplifies directly to:

\[L_p(1\text{ m}) \approx L_{wA} - 8.0 \quad [\text{dB(A)}]\]

3. Noise control : reduction for pumps

How to make a pump less noisy ?

3.1 Noise reduction by design

Accurate hydraulic design is the first line of defense. Selecting an oversized pump forces the operating point to the left of the Best Efficiency Point (BEP). Operating in this low-flow zone induces internal hydraulic recirculation at the impeller inlet and discharge tips, creating strong structural vibration and hydrodynamic noise. Best practices include:

• Low Flow Velocity: Size suction and discharge pipe diameters generously to maintain conservative fluid velocities.
• Low Noise Fittings: Install long-radius elbows (\(R \ge 1.5D\)) rather than short-radius fittings, and avoid concentric reducers in horizontal suction lines (use eccentric reducers flat-on-top to eliminate air pockets).
• Structural Damping: Mount the motor-pump skid on a mass-concrete inertial foundation with epoxy grout and vibration-damping neoprene/spring mounts.
• Low Noise Drivers: Standard totally enclosed fan cooled (TEFC) electric motors frequently generate aerodynamic fan whistle. Use low-noise aerodynamic fans, variable speed drives (VFDs) running at lower rpm, or acoustic motor baffles.

Special case of cavitation:

A pump experiencing acoustic cavitation must be addressed immediately. Ensure that the Net Positive Suction Head Available (\(\text{NPSH}_a\)) exceeds the vendor Net Positive Suction Head Required (\(\text{NPSH}_r\)) by at least a 0.6 m to 1.0 m (or 20% to 25%) safety margin under all operating temperatures. Check our detailed guide: NPSH and Cavitation Troubleshooting.

3.2 Noise reduction by insulation

When hydraulic redesign or motor substitution is unfeasible, install acoustic enclosures constructed of mineral wool absorption cores backed by galvanised steel sheeting. Ensure the enclosure provides forced acoustic labyrinth ventilation to prevent motor overheating, along with quick-release access hatches for mechanical seal inspections and vibration monitoring.

4. Field Troubleshooting: Practical Tips & Tricks

Field process engineers encountering pump issues can troubleshoot common symptoms using the following systematic checks:

• Pump Suction Head & Starting NPSH: Always vent air from the pump casing and prime the suction line before starting. Starting a centrifugal pump against an air pocket can cause cavitation-like hammer, dry seal running, and severe vibration.
• Measuring Motor Amperage: High running amps indicate operation too far right on the H-Q curve (excessive flow and motor overload), high specific gravity liquid, or mechanical binding. Low amps with zero flow indicates internal air-lock, closed isolation valves, or backward impeller rotation.
• Direction of Rotation: Three-phase electric motors can easily run in reverse if wiring polarity is switched. A centrifugal pump rotating backwards will still pump liquid, but with significantly reduced head (typically 30–50% of nominal) and an abnormally loud hydraulic drone. Verify the motor rotation arrow prior to coupling the shaft.
• Hot Motor Casing: A hot motor casing can result from excessive ambient temperature, high start/stop cycle frequency, clogged cooling air cowls, low voltage causing elevated current, or improper coupling alignment transmitting axial thrust into the motor bearings.
• Energy Savings & Extended Seal Life: Throttling a discharge control valve wastes significant electrical energy across the valve and shifts the pump into the noisy recirculation zone. Trimming the impeller diameter or implementing a Variable Frequency Drive (VFD) saves energy while slashing acoustic pressure and bearing loads.

5. Manufacturers & References

For specialized acoustic specifications, low-noise impellers, or certified noise emission guarantees, consult certified pump vendors:

• Flowserve, Sulzer, and KSB: Industrial single-stage and heavy multi-stage API 610 / ISO process pumps with full acoustic documentation.
• Sterling Sihi (Flowserve Sihi): Side channel liquid pumps, multi-stage pumps, and liquid ring vacuum machinery.
• Grosclaude: Chemical centrifugal pump equipment.

Note: MyEngineeringTools has no commercial affiliation with the companies referenced.

Acoustic Bibliography & References:

[Sihi] Basic Principles for the Design of Centrifugal Pumps Installations, Sterling Sihi GmbH, 2003.
[ISO 3744 / 3746] Acoustics — Determination of sound power levels and sound energy levels of noise sources using sound pressure.
[API 610] Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries, American Petroleum Institute.