Flexible connectors are important because they can prevent stresses due to expansion and contraction, isolate against the transfer of noise and vibration, and allow for minor misalignment. In the past, buildings were constructed with heavier materials and were more forgiving to vibration. Now, more lightweight building materials are used which makes the buildings more susceptible to transmit and resonate vibration. Additionally, with office space being more valuable, mechanical systems are often located in smaller areas near occupants which increases the probability of complaints. This tight office space sometimes necessitates the equipment be located in the area between the suspended ceiling and the floor above, resulting in a greater risk of vibration transmission to the floor above.
The problem with not specifying the type of dampener to use is that one size does not fit all; there are many different types with different uses at differing costs. Some of the different types of vibration dampening devices include:
- Open steel spring isolators: These provide high efficiencies, are often adjustable, and have a long maintenance-free life. These are the most common isolators used in the commercial industry. The springs are fastened to an integral cup/base plate or welded to the spring mounting base plate and compression plate for stability.
- Restrained spring isolators: These are open steel springs which incorporate built-in restraints to prevent outdoor equipment from too much sway due to wind load.
- Elastomeric pads: These are typically used with very high-speed equipment or electrical equipment (transformers, etc.) and less critical installations.
- Spring and elastomeric hangers: These are used for isolating suspended equipment, piping and ductwork. They consist of a steel box, coil spring, spring retainers and elastomeric element.
- Wire ropes: These isolators are made up of helical, stranded-wire rope held with metal retaining bars. This design provides excellent shock and vibration isolation in a multiple range of applications.
- Air springs: These have high efficiency and are adjustable. They have long life, but require a constant compressed air source and maintenance. Somewhat problematic without a reliable compressor system.
- Flexible connectors: These provide piping flexibility to protect equipment from strain due to misalignment or thermal movement of piping. They can also help attenuate noise and vibration.
- Flexible canvas and elastomeric duct connections: These are along the same lines of flexible connectors and are used at fan and AHU discharge and intake.
- Rubber Mounts: These consist of a steel top plate and base plate completely embedded in oil-resistant neoprene. The neoprene mountings are furnished with a tapped hole in the center which enables the equipment to be bolted securely to the rubber mount.
- Thrust restraints: These are installed in pairs to resist reaction forces caused by air pressure. Thrust restraints are recommended where thrust exceeds approximately 10% of equipment weight and should be selected with the same deflection requirements as spring isolators.
With all of these options available for vibration dampening, one would not want to leave which type to be employed up to the contractor. Not all dampeners are created equal and cheaper is not necessarily better. Knowing which type of vibration dampener the designer of record called for and having it clearly documented on the drawings will provide the Owner with a building they will be happy with, assist during construction inspections, as well as assist during post installation inspections.