A vibration isolator works by providing a resilient (soft) support between the vibrating source and receptor. If the surface that supports the vibration isolator is also relatively soft, this acts as a compound system. This means the vibration isolator no longer provides the single resilient connection or the expected level of vibration isolation, because a proportion of the vibrational energy is now transmitted to the relatively soft supporting structure.
The layer isolator along the edge of the unit (under the folded channel) is 12mm thick. The folded channel is the same height as the rolled steel box section under the middle of the unit. This means that the base frame of the unit is deflecting by about 12mm (as the slab is fairly level) between these two sections (because the base frame is a folded steel section, not a structural support). With a more suitable framework, there would be a gap between the rolled steel section and ground.
The base does not incorporate suitable supports for the compressors, so the compressors were ‘supported’ on a floor that deflected excessively and resulted in pipework fracturing due to excessive vibration. Although not a pretty installation, our troubleshooting was the most cost-effective way to resolve the problem. The VertiMounts were installed on load spreaders to reduce the deflection in the supporting structure, with the compressors being supported from rolled steel angle brackets between the VertiMounts. This technique avoided the need to reposition or even disconnect the compressors.