VIBRATION CONTROL LIMITED
For more than 20 years Vibration Control Ltd. has been supplying Embelton’s customised system design solutions to eliminate noise and vibration disturbance in mechanical and architectural situations.
The most obvious example of structure-borne vibration is that which is generated by mechanical equipment, such as fans, pumps and chillers. If left unchecked this will spread through a building. Our products actively isolate disturbance at the source by supporting the vibrating equipment on resilient mountings, such as springs or rubber which are designed to deflect under equipment weight.
At Vibration Control Ltd. we also supplies products to exclude externally induced vibration from sensitive spaces (passive isolation). Examples include isolation of critical environments such as operating theatres, research laboratories, recording studios and auditoriums where vibration may interfere with the room’s function. Less critical applications include the isolation of ceilings and walls in multi-tenanted developments to prevent sound from transmitting to adjacent apartments.
IMPORTANCE OF STATIC DEFLECTION
Isolation of vibration is accomplished by supporting the equipment on resilient mounting elements such as springs or rubber, which compress under the equipment weight. Generally, the degree of isolation achieved is directly related to the amount of compression (static deflection) of the mount. The greater the static deflection which can be achieved (without compressing to solid), the better the vibration isolation.
EFFECTIVENESS OF ISOLATION
The effectiveness of any isolation system is usually expressed in terms of its isolation efficiency. This is defined as the percentage of the total vibratory force which is absorbed by the isolators.
To estimate the isolation efficiency of a simple spring system use the given values of static deflection and disturbing frequency in the graph below.
For rubber isolators, use the values of dynamic natural frequency instead of static deflection.
However, the following must also be taken into account:
• Equipment type and operating weight
• Magnitude and nature of the vibratory forces
• Restrictions on equipment motion (see Inertia Blocks)
• Location of equipment within the structure.
For example, an isolation efficiency of 80% is probably satisfactory for a 5kW machine located in the basement, but totally inadequate for a 100kW machine installed on a flexible upper level floor adjacent to office or residential accommodation. In this case an isolation efficiency close to 97% would be required. The Isolator Selection Guide summarises the important theoretical relationship between disturbing frequency, static deflection and the installed environment, offering a guide to the correct mount to be selected.
We can provide detailed technical assistance on the use of Embelton isolators in specific applications. Facilities are available to develop new or modified systems to resolve unusual or difficult vibration isolation problems. Please contact us for more information or a catalogue.
ISOLATION EFFICIENCY CHART
This chart illustrates the theoretical relationship between isolation efficiency, disturbing frequency and static deflection (or dynamic natural frequency) for a simple isolation system on a rigid foundation. It is grouped into zones suggesting isolation efficiency ranges appropriate to different applications.
To use the chart, determine the lowest RPM of the equipment (this will be the disturbing frequency).
Move vertically to intersect the diagonal line corresponding to the required isolation percentage.
Then, for rubber and pad mount selection, move horizontally left to find the dynamic natural frequency.
For spring mounted systems move right to find the required static deflection of the mounting.
ISOLATION SELECTION GUIDE
This chart provides a selection guide for isolator type according to given values of operating speed and suggested levels of isolation efficiency in certain operating locations.
For each isolation efficiency two values are given, one for basement or on-grade installations, the other for upper level installations where some allowance is made for flexibility of the supporting structure.
For rubber and pad mounts, the values have been corrected for average rubber hardness to approximate selections based on dynamic natural frequency (please refer to the Isolation Efficiency Chart on page 10).
This chart is meant as a general guide only and selections should be made based on the properties listed in the Datasheets.