Spring Isolators vs. Rubber Isolators
Spring vibration isolators and rubber vibration isolators both reduce mechanical vibration and noise, but they are suited to very different applications. Spring isolators use coiled steel springs to achieve high static deflections of 12–50mm, making them the preferred choice for heavy, low-speed equipment such as chillers, large pumps, and cooling towers. Rubber isolators use compressed elastomer to absorb vibrations and are best suited for lighter, higher-frequency equipment such as fan coil units, air handling units, and small pumps. Choosing the wrong type can result in poor isolation performance or resonance — this guide explains the key differences and how to select correctly
Spring Isolators
Spring isolators use precision-wound coiled steel springs to support equipment loads while allowing controlled vertical deflection. Because steel springs have very low damping and can achieve deflections of 12–50mm, they are highly effective at isolating low-frequency vibrations generated by slow-speed, heavy equipment. They are the standard choice for HVAC plant rooms housing chillers, cooling towers, large centrifugal pumps, and air handling units, as well as for power generation equipment including DG sets, generators, and turbines. Spring isolators are available in open (free-standing) and enclosed (housed) configurations, with the enclosed type offering additional protection in outdoor or dusty environments. For applications requiring seismic restraint, spring isolators are available with integrated snubbers that limit movement during an earthquake while preserving normal isolation performance.
Key Benefits:
Durability: Made from high-strength steel wire, spring isolators are virtually impervious to oil, chemicals, and UV exposure that degrade rubber over time. Properly specified spring isolators routinely achieve service lives exceeding 20–25 years with no performance degradation, making them the lower-maintenance choice for critical plant room equipment.
High Performance: Spring isolators can achieve isolation efficiencies of 90–92% for equipment operating at 500 RPM and above, making them the highest-performing standard isolator type for HVAC and MEP applications. They are the specified product type in most hospital, hotel, and data centre acoustic specifications.
Versatility: Spring isolators can be factory-set or field-adjusted to match precise load and deflection requirements. They are available in a wide range of load capacities — from a few kilograms per mount to several tonnes — and can be combined with neoprene pads for additional high-frequency noise attenuation.
Rubber Isolators
Rubber isolators use compressed elastomeric material — typically neoprene or natural rubber — bonded to metal plates to create a compact, self-contained vibration mount. Their natural damping properties make them effective at attenuating high-frequency vibrations and structure-borne noise, though their static deflection is limited to 3–7mm. This makes them the correct choice for equipment operating at higher speeds — typically above 1000 RPM — where the disturbing frequency is sufficiently above the isolator’s natural frequency for effective isolation. Common applications include fan coil units, small inline pumps, split air conditioning units, rooftop package units, electrical control panels, and general MEP equipment in commercial and residential buildings.
Key Benefits:
Flexibility: The elastomeric element in rubber isolators absorbs both vibration and minor structural misalignments, making them tolerant of imperfect installation conditions. Their inherent damping also prevents resonance build-up during equipment start-up and shutdown, which is a common problem with undamped spring isolators on smaller equipment.
Cost-Effectiveness: Rubber isolators are significantly more economical than spring mounts — both in initial product cost and installation time. For large MEP projects with dozens or hundreds of small equipment items, rubber mounts offer a practical and effective solution that keeps within project budgets without sacrificing isolation performance for their intended application.
Ease of Installation: Rubber isolators are lightweight, require no levelling, and are typically bolted directly to the equipment base in minutes. Unlike spring isolators, they require no adjustment after installation, reducing both commissioning time and the risk of incorrect field setup.
Comparison Table:
| Feature | Spring Isolators | Rubber Isolators |
|---|---|---|
| Load Capacity | High | Moderate |
| Vibration Frequency | Low to High | Low to Moderate |
| Durability | Very High | Moderate |
| Cost | Higher | Lower |
| Outdoor Usage | Preferable | UV and oil can protection required |
The choice between spring and rubber isolators depends on your specific requirements, including load, vibration frequency, and budget. To make the best decision, consider the following framework: first, evaluate the weight and size of your equipment to determine the load capacity needed. Next, assess the environment where the isolators will be used. Finally, review your budget constraints and prioritize features that align with your operational goals. By following these steps, you can select the vibration isolator that offers optimal performance for your specific application. For expert guidance, trust RMS Corporation’s decades of experience.
Contact RMS Corporation
Along with your equipment data sheet — operating weight, RPM, and application — and our engineering team will recommend the correct product and quantity.
Frequently Asked Questions
Spring isolators use coiled steel springs to achieve high static deflections of 12–50mm, making them ideal for heavy, low-speed equipment. Rubber isolators use compressed elastomer with deflections of 3–7mm, suited to lighter, higher-frequency equipment. The primary selection factor is the equipment's operating speed in RPM and its static weight at each mount point.
Spring isolators are the correct choice for chillers. Chillers are heavy, low-speed machines — typically operating at 900–1800 RPM for centrifugal types and even lower for screw and absorption types — and generate significant low-frequency vibration that requires the high static deflection only spring isolators can provide. A minimum deflection of 12-25mm is typically specified for chiller applications.
Rubber isolators or rubber hanger mounts are the standard choice for fan coil units. FCUs are lightweight, operate at relatively high fan speeds, and are typically ceiling-suspended — making compact rubber hangers the practical and cost-effective solution. Spring hangers are can also be used as per specifications.
An incorrectly selected isolator can perform significantly worse than no isolator at all. If the isolator's natural frequency is too close to the equipment's disturbing frequency, resonance occurs — amplifying rather than reducing vibration. This is why matching the isolator to the specific equipment operating speed and load is critical. RMS Corporation provides selection support to ensure the correct product is specified every time.
The correct isolator for a generator or DG set depends on its size, operating speed, and installation location. Gensafe Rubber Mounts are the recommended choice — these are purpose-engineered anti-vibration mounts designed specifically for generator sets, providing effective isolation of the characteristically uneven vibrations generated during start-up, load changes, and shutdown cycles. For larger generators or where a lower mounting profile is required, Cushyfoot Mounts offer a robust rubber-to-metal bonded solution that handles higher static loads while maintaining good isolation performance. Where the generator is installed on an upper floor, rooftop, or in a noise-sensitive environment such as a hospital or hotel, Spring Isolators with Viscous Dampers are the preferred specification — the spring element provides high static deflection for effective low-frequency isolation, while the viscous damper controls the resonance transients that occur during generator start-up and shutdown, preventing structural transmission of impact loads into the building fabric.
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