Why Use an Elastomeric Coupling for Vibration Damping?

Every motor-driven machine produces torsional vibration. The motor produces cyclic torque ripple at the electrical supply frequency and its harmonics. The pump or compressor produces pressure pulsations that appear as torsional excitation. The VSD, if fitted, produces switching frequency components in the motor torque. On a rigid drivetrain, all of these torsional excitations pass unattenuated from the motor through the coupling to the driven machine and into the structural supports ¡ª generating vibration, noise, and accelerated bearing and seal wear. An elastomeric coupling placed in the torque path changes this fundamentally: it inserts a compliant element that absorbs and dissipates torsional energy before it can propagate through the drivetrain. The F-type flexible tyre coupling and the NM elastomeric coupling are the two products from Ever Power’s range most commonly specified specifically for their vibration damping characteristics.

Flexible elastomeric coupling motor pump vibration damping orange

The Physics of Elastomeric Vibration Isolation

An elastomeric coupling acts as a torsional spring-and-damper system between the motor and driven machine. Its torsional stiffness (kt) determines the frequency at which the coupling-load system resonates. Its damping ratio (¦Æ) ¡ª determined by the hysteretic energy dissipation in the elastomeric material ¡ª determines how much vibration is absorbed versus transmitted at any excitation frequency.

At excitation frequencies well below the system natural frequency, the coupling transmits most of the excitation torque through its stiff spring behaviour. At the natural frequency, resonant amplification occurs ¡ª vibration is amplified rather than reduced. Above the natural frequency, in the isolation region, the elastomeric element’s compliance prevents the excitation torque from being transmitted to the driven machine, and the damping dissipates the absorbed energy as heat in the elastomeric material. For most industrial pump and fan drives, the operating speed and excitation frequencies fall comfortably in this isolation region.

Damping Performance by Elastomer Grade

Elastomer Grade Shore Hardness Torsional Stiffness Damping Ratio (¦Æ) Best Application
Natural Rubber (NR) 45¨C55A Very low High (0.10¨C0.15) Maximum isolation ¡ª reciprocating pumps, compressors
Polyurethane (PU) Soft 80A Low Medium-high (0.08¨C0.12) High misalignment + good damping ¡ª fan drives, flexible bases
Polyurethane (PU) Standard 92A Medium Medium (0.05¨C0.09) General pump and fan drives ¡ª most common specification
Polyurethane (PU) Hard 98A High Low-medium (0.03¨C0.06) VSD drives, high torsional stiffness required
Hytrel (Thermoplastic) 55D Medium-low Low (0.02¨C0.04) High temperature, chemical resistant ¡ª limited damping
Flexible flange coupling 125mm PCD elastomeric vibration isolation

Real-World Applications Where Elastomeric Damping Matters Most

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HVAC Pump and Fan Drives in Buildings

Building occupants are sensitive to low-frequency vibration and noise from mechanical services. Elastomeric tyre couplings on HVAC pump and fan drives reduce structure-borne noise transmission to occupied spaces ¡ª a standard specification in commercial building mechanical services design.

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Reciprocating Compressor Drives

Reciprocating compressors produce torque pulsation at the compressor stroke frequency ¡ª typically 10¨C25 Hz for a 4-cylinder unit at 600 RPM. This frequency is close to the torsional natural frequency of many standard drivetrains. A soft elastomeric coupling is the most accessible intervention to detune the system from resonance.

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Precision Manufacturing Equipment

Machine tools and measurement equipment mounted in the same building as large motors experience floor-transmitted vibration that affects measurement accuracy. Elastomeric couplings on the large drive systems reduce the source vibration level.

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Marine Engine-to-Pump Drives

Marine diesel engines produce torsional excitation at their firing frequency. A soft elastomeric coupling between the engine and pump prevents resonance at any engine speed in the operating range and protects pump bearings from the engine’s vibration signature.

Elastomeric Coupling vs Vibration Isolating Mount ¡ª Which to Prioritise?

Elastomeric coupling and anti-vibration mount are complementary interventions, not alternatives. The coupling reduces torsional vibration transmitted through the shaft connection. The anti-vibration mount reduces lateral and vertical vibration transmitted through the baseplate to the building structure. On a pump drive where both bearing vibration and structure-borne noise are concerns, fitting both produces the best result. If only one can be specified, the elastomeric coupling typically provides the greater improvement in rotating machinery bearing life, while the anti-vibration mount provides the greater improvement in structure-borne noise isolation.

Frequently Asked Questions

How much vibration can an elastomeric coupling reduce?+
The vibration reduction achievable with an elastomeric coupling depends on the excitation frequency relative to the coupling’s torsional natural frequency. At excitation frequencies well above the coupling’s torsional natural frequency ¡ª as is the case for most motor and pump vibration relative to standard elastomeric couplings ¡ª vibration isolation efficiency of 50¨C80% is achievable. In practical terms, replacing a rigid or gear coupling with an elastomeric tyre coupling on a pump drive typically reduces motor bearing vibration amplitude by 40¨C70%, which corresponds to a bearing life increase of 3¨C5 times.
Does elastomeric coupling hardness affect vibration damping?+
Yes, directly. Softer elastomers (80A Shore) have lower torsional stiffness, which lowers the coupling’s torsional natural frequency and improves vibration isolation for most industrial excitation frequencies. Harder elastomers (98A Shore) have higher stiffness, which raises the natural frequency and reduces isolation effectiveness. For maximum vibration damping on a pump or fan drive, specify the softest elastomer grade that still provides the required torque capacity ¡ª this is usually 80A or 92A Shore for standard centrifugal pump drives.
Can an elastomeric coupling reduce structure-borne noise in a building?+
An elastomeric coupling provides torsional isolation ¡ª it reduces the torsional vibration transmitted from the motor to the driven machine and vice versa. It does not directly reduce lateral vibration at the bearing housings (radial vibration from imbalance or misalignment). To reduce structure-borne noise transmission through the building, the motor and pump should also be mounted on anti-vibration mounts. The elastomeric coupling complements the anti-vibration mount by reducing the internal excitation force, making the mounts more effective.
Does a flexible elastomeric coupling reduce noise as well as vibration?+
Yes, but through vibration reduction rather than acoustic damping. Airborne noise from a pump or motor drive is generated by vibration of the structural surfaces ¡ª motor casing, pump casing, pipework, and baseplate. By reducing the torsional vibration transmitted through the coupling, an elastomeric coupling reduces the excitation of these radiating surfaces, which lowers the radiated sound level. In commercial building HVAC applications, switching from rigid to elastomeric couplings on fan and pump drives is a common noise reduction measure.
What is the natural frequency of an elastomeric coupling?+
The torsional natural frequency of a coupling-load system is: fn = (1/2¦Ð) ¡Á ¡Ì(kt / J), where kt is the coupling torsional stiffness in Nm/rad and J is the total rotational inertia of the driven mass in kg¡¤m2. For most industrial pump drives with standard 92A polyurethane F-type tyre couplings, the torsional natural frequency falls in the range 5¨C25 Hz. Motor-generated torsional excitation frequencies (from 6-pole motors at 1,000 RPM to 2-pole motors at 3,000 RPM) are typically well above this range, placing the coupling in the vibration isolation region of its frequency response.

Need Expert Coupling Advice?

Our engineering team in Condell Park NSW is ready to help ¡ª free of charge.

Ever Power Flange Couplings Australia Ltd.27 Harley Crescent, Condell Park NSW 2201  | +61 29708 3322  | [email protected]