Anti-vibration mounts isolate fan vibration from the building; spring and rubber types suit different frequency ranges.
Spring vs Rubber
Spring mounts use steel coils and are effective at low frequencies, where rubber would be too stiff, making them the choice for heavy fans with low running speeds and for installations where structure-borne noise must be kept very low.
Isolation is judged by transmissibility, the fraction of the fan's vibration that reaches the structure, and the goal is to drive that fraction low by separating the forcing and natural frequencies. A well-chosen mount can cut transmitted vibration by an order of magnitude compared with a rigid, bolted-down set.
The mount rating must cover the full weight including the motor and any inertia base, with margin so the static load sits in the mount's designed range; a mount loaded past its rating bottoms out and transmits instead of isolates. Multiple mounts share the load, so each is selected for its actual share, not the total divided casually.
Frequency is the heart of the choice: a 1,450 rpm fan forces near 24 Hz, and a spring mount with a natural frequency a fraction of that isolates well, while a rubber mount suits a higher-speed or lighter unit where spring travel would be excessive. The mismatch between the two frequencies, not the brand, decides the result.
Even perfect mounts fail if the duct or pipe is rigid, because a hard connection bridges the gap and carries vibration straight into the building. Flexible connectors across the isolation gap are part of the same design, and both are checked at commissioning so the isolation the calculation promised is what the plant actually gets.
The company's 80,000 m² production site builds fans under ISO 9001:2015 with CCC certification, and its engineers respond to selection enquiries within 24 hours to specify mount type, deflection, and inertia base against the fan speed and the structure's noise limit on the project.
The mount's own natural frequency is confirmed, not taken from the catalogue, because the actual load including motor and base sets the deflection and thus the isolation; a mount that looked right on paper can sit at the wrong ratio once the real weight is on it. The inertia base is grouted and levelled so the set is stable, and the isolated assembly is checked for resonance at the running speed before the unit is accepted, because isolation claimed but not verified is just a heavier installation.
Rubber and elastomer mounts suit higher frequencies and lighter loads; they are compact, damped, and simple but have a limited temperature and chemical range, and they age under oil, sunlight, and ozone exposure over time.
The isolation depends on the ratio between the mount's natural frequency and the fan's forcing frequency; the greater the separation, the more vibration is blocked from the structure, which is the core principle behind any isolation design.
Static deflection sets the natural frequency: a larger deflection gives a lower natural frequency and better isolation, which is why spring mounts with more travel isolate better than a stiff rubber block of the same load rating.
Sizing and Details
Each mount must carry its share of the total weight with some margin, so the rated load per mount should comfortably exceed the static load it sees, avoiding bottoming or excessive compression that would stiffen the mount and ruin the isolation.
The fan's running speed gives the forcing frequency; for a 1,450 rpm motor that is about 24 Hz, and the mount natural frequency should be well below this, often a fraction of it, for good isolation and to keep the transmissibility low.
An inertia base, a heavy concrete or steel frame under the fan, lowers the system natural frequency and stabilises a tall or top-heavy unit, improving both isolation and handling during installation and any future relocation of the equipment.
Piping and duct connections must stay flexible, because a rigid duct bridges the isolation and transmits vibration straight back into the building regardless of the mounts, undoing the careful work spent on selecting and placing the isolators.
| Item | Specification | Note |
|---|---|---|
| Spring mount | low freq | Heavy, slow fans |
| Rubber mount | high freq | Light, compact |
| Deflection | larger=better | Lower natural f |
| Forcing f | ~24 Hz | At 1,450 rpm |
| Inertia base | lowers f | Stabilises |
| Flex connect | required | No bridge |
Selection Checklist
- Pick spring mounts for heavy, low-speed fans; rubber for light, high-frequency.
- Rate each mount above its static load with margin.
- Keep mount natural frequency well below the forcing frequency.
- Add an inertia base for tall or top-heavy units.
- Use flexible duct and pipe connections across the isolation gap.
- Verify the deflection gives the isolation the spec requires.
About the Manufacturer
Keruite Air Conditioning Group, headquartered in Dezhou, Shandong, has more than 30 years of HVAC manufacturing experience and operates an 80,000 m² production site with its own performance testing laboratory. Products are built under ISO 9001:2015 quality management and carry CCC certification, and are supplied to customers in over 50 countries.
Our engineers respond to selection enquiries within 24 hours and can provide project-specific sizing, performance curves, and documentation to support specification and procurement.