TM 5-805-4/AFJMAN 32-1090
cal equipment, floor slab thicknesses of 6 to 10
inertia block. Provision must be made to allow
inches are assumed. For occasional locations of one
positive visual inspection of the spring clearance
or a very few pieces of small high-speed equipment
in its recessed mounting.
(say 1800 rpm or higher) having no reciprocating
(2) When this type of mounting is used for a
action, floor slabs of 4 to 6 inches may be used
pump, the concrete inertia block can be given a
with reasonable expectation of satisfactory results.
T-shape plan, and the pipes to and from the pump
However, for reciprocating-action machines operat-
can be supported rigidly with the pump onto the
ing at the lower speeds (say, under 1200 rpm), any
wings of the T. In this way, the pipe elbows will
floor slab thicknesses reduced from those listed
not be placed under undue stress.
above begin to invite problems. There is no clear
(3) The weight of the inertia block and the
crossover from "acceptable" to "unacceptable" in
static deflection of the mounts shall be in accord-
terms of floor slab thickness, but each reduction in
ance with the recommendations given in the table
thickness increases the probability of later difficul-
for the particular equipment.
ties due to vibration. The thicknesses mentioned
d. Type III mounting assembly. The equipment
here are based on experience with the "acoustics"
or the assembly of equipment should be mounted
of equipment installations. These statements on
on a steel frame that is stiff enough to allow the
thicknesses are in no way intended to represent
entire assembly to be supported on flexible point
structural specifications for a building. "House-
supports without fear of distortion of the frame or
keeping pads" under the equipment are assumed,
misalignment of the equipment. The frame should
but the height of these pads is not to be used in
then be mounted on resilient mounts-steel springs
calculating the thickness of the floor slab.
or neoprene-in-shear mounts or isolation pads, as
(4) The ratio of the weight of the concrete
the static deflection would require. If the equip-
block to the total weight of all the supported
ment frame itself already has adequate stiffness,
equipment (including the weight of any attached
no additional framing is required, and the isola-
filled piping up to the point of the first pipe
tion mounts may be applied directly to the base of
hanger) shall be in accordance with the recommen-
the equipment.
dations given in the paragraph and table for the
(1) The vibration-isolation assembly should
particular equipment requiring this mounting as-
have enough clearance under and all around the
sembly. The inertia block adds stability to the
equipment to prohibit contact with any structural
system and reduces motion of the system in the
part of the building during operation.
vicinity of the driving frequency. For reciprocating
(2) If the equipment has large starting and
machines or for units involving large starting
stopping torques and the isolation mounts have
torques, the inertia block provides much-needed
large static deflections, consideration should be
stability.
given to providing limit stops on the mounts.
(5) The static deflection of the free-standing
Limit stops might also be desired for large deflec-
stable steel springs shall be in accordance with the
tion isolators if the filled and unfilled weights of
recommendations given in the paragraph and ta-
the equipment are very different.
ble for the particular equipment. There shall be
e. Type IV mounting assembly. The equipment
adequate clearance all around the springs to as-
should be mounted on an array of "pad mounts".
sure no contact between any spring and any part
The pads may be of compressed glass fiber or of
of the mounted assembly for any possible align-
multiple layers of ribbed neoprene or waffle-
ment or position of the installed inertia block.
pattern neoprene of sufficient height and of proper
c. Type II mounting assembly. This mount is the
stiffness to support the load while meeting the
same as the Type I mount in all respects except
static deflection recommended in the applicable
that the mounting brackets and the top of the
accompanying tables. Cork, cork-neoprene, or felt
steel springs shall be located as high as practical
pad materials may be used if their stiffness char-
on the concrete inertia block but not necessarily as
acteristics are known and if they can be replaced
high as the vertical center-of-gravity position of
periodically whenever they have become so com-
the assembly, and the clearance between the floor
pacted that they no longer provide adequate isola-
and the concrete block shall be at least 2 inches.
tion.
(1) The floor should be grouted or shimmed to
(1) If necessary, the steel springs can be re-
assure a level base for the equipment and there-
cessed into pockets in the concrete block, but
fore a predictable uniform loading on the isolation
clearances around the springs should be large
enough to assure no contact between any spring
pads.
(2) The pads should be loaded in accordance
and any part of the mounted assembly for any
with the loading rates recommended by the pad
possible alignment or position of the installed
8-5
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