Firestone EMDG198 - Manual (Page 23)

23
AIRMOUNT ® VIBRATION ISOLATION
Up to this point, only the weight and disturbing frequency have
been discussed. THERE ARE MANY OTHER IMPORTANT
CONSIDERATIONS:
CENTER OF GRAVITY
An Airmount isolation system is inherently soft (easily deflect-
ed); therefore, precautions must be taken to insure that the
system is stable. First, consider the location of the center of
gravity (c.g.). Ideally, the Airmounts should be located on the
same plane (parallel to the ground) as the center of gravity.
Where this is not possible, follow this guideline: The distance
between the most narrow mounting points should be at least
twice the height of the center of gravity.
In the above example, the most narrow distance between two
Airmounts is 46 inches The height to the c.g. is 48 inches;
therefore, this system does not meet our guideline. Two pos-
sible solutions would be:
1. Increase the base dimensions to meet our guideline by
increasing both the width and length to at least 48 x 2 or
96 inches.
2. Locate the Airmounts at the c.g. as shown above (in the
next column).
LATERAL RATES AND STABILITY
Single and double convoluted air springs SHOULD BE USED
AT THE DESlGN HEIGHTS GIVEN, because that is the point
of maximum lateral rate or stability. The lateral rate
decreases
as the Airmount height decreases. Consider a #22 again at
80 psig:
Notice that the #22 becomes unstable in the horizontal or lateral
direction when moving down only two inches from design height.
Height Lateral Rate Vertical Rate
9.5 inch (design height) 325 lbs/in 1,373 lb/in
8.5 inch 212 lbs —
7.5 inch Unstable —
Height 48"
Width 46"
Length 50"