Anti-Vibration Mount Selection Guide: How to Specify the Right Isolator
A surprising number of vibration complaints come not from missing mounts but from the wrong mounts — overloaded, underloaded, or stiff enough to land the machine on resonance. This anti-vibration mount selection guide is built to prevent exactly that.
It is written for engineers and procurement managers who need a repeatable method for selecting vibration mounts that actually isolate, not just fill a bolt hole. After decades of supplying rubber components to industry, we have distilled the process into a sequence you can apply to almost any machine.
Step 1: Define the Load and Its Distribution
Selection starts with weight. You need the total weight of the equipment and, just as importantly, how it is distributed across the mounting points.
A machine with a heavy motor at one end loads its mounts unevenly, and a uniform mount choice will compress unevenly — ruining isolation.
Practical Method
- Find the total operating weight, including fluids and attached pipework where relevant.
- Determine the load at each mounting foot, accounting for the centre of gravity.
- Size each mount to its actual share of the load.
This is the foundation of a correct load-rated vibration mount decision, and skipping it is the single most common error.
Step 2: Identify the Operating Frequency
The machine’s disturbing frequency comes from its running speed.
Convert revolutions per minute to hertz by dividing by 60:
1,500 revolutions per minute ÷ 60 = 25 hertz
You need this number because it sets how soft the mount must be. Lower running speeds demand softer mounts with greater deflection to isolate effectively.
Step 3: Target the Right Natural Frequency and Deflection
Effective machine vibration isolator selection keeps the system’s natural frequency well below the disturbing frequency — a ratio of about 3:1 or better.
In practice, engineers use static deflection as the working proxy: more deflection means a lower natural frequency and better isolation.
A Rough Field Guide
- For typical rotating machinery, aim for the mount to compress a meaningful, specified amount under load, according to the mount’s rated deflection.
- Never select a mount so stiff that it barely deflects — it will sit near resonance and amplify vibration.
- Never overload a mount past its rated capacity — excessive deflection causes early failure.
Correct rubber mount sizing is fundamentally about hitting the right deflection at the actual load.
Step 4: Choose the Load Rating With a Margin
Each mount has a rated load range. Select a mount so the working load sits comfortably within that range — not at the extreme top and not far below the bottom.
Operating near the top of the range risks overload and creep; operating far below it means too little deflection and poor isolation.
A mount loaded to roughly the middle of its rated range usually performs best.
Step 5: Match the Environment
The vibration mount specification must account for what the mount lives in. This drives compound choice:
- Oil or fuel exposure → Nitrile rubber
- Outdoor, ozone and weathering → Neoprene or Ethylene Propylene Diene Monomer rubber
- High temperature → Heat-resistant compounds
- General indoor use → Natural rubber for best damping
An ideal mount in the wrong compound degrades quickly, so treat material as part of the specification, not an afterthought.
You can review compound and configuration options for anti-vibration mounts.
Step 6: Select the Mount Type and Orientation
Different geometries suit different duties:
- Anti-vibration pads for light to medium machines and simple installations.
- Cylindrical or bobbin mounts for general bolt-down machine mounting.
- Conical or bush mounts where loads are directional.
- Spring or spring-rubber mounts for heavy, low-frequency equipment needing large deflection.
Also consider whether the mount sees mainly compression, shear, or a combination, and orient it accordingly — rubber behaves differently in each mode.
Step 7: Consider Durometer (Hardness)
Hardness fine-tunes stiffness. Softer rubber, with a lower Shore A hardness, gives more deflection and better isolation but carries less load. Harder rubber carries more load but isolates less.
Within a chosen mount, durometer is the lever you use to balance load capacity against isolation.
This is the finishing touch in selecting vibration mounts.
A Worked Example
Consider a 400 kilogram compressor on four feet, running at 1,200 revolutions per minute, or 20 hertz, in a clean indoor plant.
Each foot carries roughly 100 kilograms, adjusting for the centre of gravity if needed.
You would choose a mount rated comfortably around 100 kilograms per mounting point, in natural rubber for good damping, with a durometer that delivers enough deflection to put the natural frequency near 6–7 hertz — approximately a 3:1 ratio below 20 hertz.
That combination isolates well while staying clear of resonance.
Change the environment to an oily workshop and the only change is the compound: nitrile rubber instead of natural rubber.
Quick Selection Checklist
To turn this anti-vibration mount selection guide into a desk-side process:
- Total weight and per-point load distribution.
- Operating frequency: revolutions per minute ÷ 60 = hertz.
- Target natural frequency at approximately a 3:1 ratio through appropriate deflection.
- Load rating with the working load near the middle of the rated range.
- Compound matched to the environment.
- Mount type and orientation for the load direction.
- Durometer to balance load against isolation.
Frequently Asked Questions
1. What is the first step in an anti-vibration mount selection guide?
Defining the total weight and how it is distributed across mounting points. Sizing each mount to its actual share of the load is the foundation of correct selection.
2. How do I calculate the operating frequency for selecting vibration mounts?
Divide the machine’s running speed in revolutions per minute by 60 to get the disturbing frequency in hertz.
For example, a 1,500 revolutions per minute machine has a 25 hertz fundamental frequency, which helps determine how soft the mount must be.
3. What load rating should a vibration mount have?
Choose a load-rated vibration mount so the working load sits near the middle of its rated range — not at the top, which risks overload, and not far below, which gives too little deflection for good isolation.
4. How does environment affect vibration mount specification?
The environment drives compound choice: nitrile rubber for oil exposure, neoprene or Ethylene Propylene Diene Monomer rubber for outdoor and ozone exposure, heat-resistant grades for high-temperature environments, and natural rubber for general indoor use where good damping is required.
5. Does mount hardness, or durometer, matter in rubber mount sizing?
Yes. Softer rubber deflects more and isolates better but carries less load, while harder rubber carries more load and isolates less.
Durometer is the lever for balancing load capacity against isolation.
Conclusion
A reliable anti-vibration mount selection guide is really a sequence: load and distribution, operating frequency, target deflection, load rating with margin, environment-matched compound, mount type, and durometer.
Work through it in order and you avoid the two classic failures — resonance from over-stiff mounts and early failure from overloaded mounts.
To match a correctly sized and correctly compounded mount to your machine, explore the UMABOND anti-vibration mount range or contact the UMABOND team for selection support backed by in-house American Society for Testing and Materials testing.