Center Of Gravity; Lateral Rates And Stability - Firestone EMDG198 User Manual

AIRMOUNT
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.
Height 48"
Width 46"
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).
VIBRATION ISOLATION
®

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:
Length 50"
Height
9.5 inch (design height)
8.5 inch
7.5 inch
Notice that the #22 becomes unstable in the horizontal or lateral
direction when moving down only two inches from design height.
Lateral Rate Vertical Rate
325 lbs/in 1,373 lb/in
212 lbs —
Unstable —
23