Vibration isolation, though simple in concept, can be quite complex in practice. The rule-of-thumb is that an isolation medium needs to have a natural frequency, under gravitational load, at least 1/3 lower than the disturbing vibration created by an energized system (Note: This is usually a Mechanical or Electrical piece of equipment but could be one of many other sources such as an aerobics class jogging-in-place in unison, as but one example).
Here is another example:
A simple belt driven fan on ‘face value’ may appear to be very straight forward but the pulley ratio between the drive (motor) and the Driven component (fan) may be something like 3:1. If one isolates for the 1800rpm of the motor, instead of the 600rpm of the fan, not only will one fail to reduce the vibration induced noise created by this fan but, in fact, run the risk of amplifying the problem due to having the isolators in resonance with one of the predominant driving frequencies of the equipment. Further, the fan assembly may have the heavy motor towards one corner, side or end of the equipment assembly and using the same capacity isolator may well exceed the rated capacity of some isolators and significantly under-load others. Though counter-intuitive, the least compressed isolator dictates the overall isolation efficiency of the isolation system and, hence, could exacerbate the situation rather than resolve it. Then again, with many projects located on or near the West Coast of Canada, Seismic Restraint codes need to be met without interfering with the day-to-day vibration isolation that has been effected.
This adds, yet again, another dimension that needs to be considered in the selection of the appropriate isolation medium/product.
The team at Vibra-Sonic Control has been working with engineers and building contractors on projects requiring vibration isolation for more than 40 years.