Vibration Pads, Mounts & Hangers
Technical Information
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Basics of... Vibration Pads, Mounts & Hangers
Deflection
The More the Better
Deflection is the change in an isolator′sunloaded to loaded height. The deflectiondetermines how well the isolator works. Moredeflection means less vibration transmission. Asoft, yielding support is better than a stiff one.There are three classes of vibration isolatorsbased on deflection:
1. Pads act mostly as noise breaks. Theyinterrupt hard surface-to-surface contact andreduce high frequency vibration.
2. Neoprene mounts and hangers deflect moreand are the first step in true vibration control.
3. Spring isolators have the greatest deflectionfor maximum vibration reduction.
Location
Sensitive Structural Supports Require Greater Deflections
The location of your equipment in the building is the main deciding factor in selecting neoprenemounts or springs. Neoprene mountings are satisfactory under equipment on a very stiffsupport structure such as a ground supported concrete slab. On upper building levels where thestructure can be very susceptible to vibration, springs are necessary.
The key to proper isolator selection in upper levels is to make sure isolator deflection is muchgreater than floor deflection.
If equipment is running below 1200 RPM, springs are recommended regardless of location. (Theimportance of location is the same for isolating suspended equipment.)
Selection
To select the proper isolation for mechanical equipment you need to ask:
1. Is slowest equipment SPEED ABOVE 1200 RPM?
If NO, use spring mountings. If YES, see 2.
2. Is equipment LOCATED on a RIGID concrete building structure or a FLEXIBLE VIBRATION SENSITIVE structure?
If RIGID, use "double deflection" neoprene or springs. If FLEXIBLE, use springs only.
The key is to select isolators that are "softer" than the supporting building structure. Ideally isolator deflection should be more than three times greater than the deflection or "sag" of the support.
3.What is the equipment′s "corner weight" or weight at each mounting point?
The load rating of each spring or rubber mounting must be matched with the portion of the equipment′s weight at the corners or mounting points. Equipmentcorner weights usually differ and require the use of mountings with different load capacities. Oversized mountings may be used, but can reduce vibrationcontrol. Select mountings with load capacities equal to or slightly greater than the portion of the equipment weight they are to support.
Regardless of the above, your experience in isolating a particular piece of equipment is more important than all the theory. If you used a class of product where you got good results before, use itagain. In many cases, pads provide enough relief to satisfy a problem just because they are a cushion between a steel leg and a concrete floor. Pad performance can always be improved bystacking them with 16 gage plates between layers.
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