(3) Each steel spring should rest on a block of
engine speed and power combination, although it
ribbed or waffle-pattern neoprene pads, as de-
would still be beneficial if used. All other recom-
scribed in d(l) below.
mendations of (2) above apply to the installation. If
( 4 ) The structure floor supporting a
the concrete block is eliminated, a substantial
reciprocating engine assembly should be at least
housekeeping pad should be provided under the en-
10-in. thick and made of dense concrete (140 to 150
gine assembly, and the engine assembly should be
3
lb/ft. ). Where possible, the engine should be lo-
mounted on a steel frame that is stiff enough to
permit use of individual steel spring isolators un-
cated over primary or secondary beams supporting
the structure slab.
der the steel frame without introducing equipment
(5) Proper airborne noise control must be pro-
misalignment.
vided between the engine room and all nearby
c. Upper-floor location. It is strongly suggested
occupied areas, as discussed in chapter 5 of the
that no reciprocating engine assembly remounted
N&V manual.
on any upper floor location of a wood-frame build-
d. Other general recommendations. The follow-
ing and that no reciprocating engine over 600 hp or
ing general recommendations apply to all engine in-
under 1200 rpm be installed on an upper floor of a
stallations requiring vibration isolation.
steel or concrete building. If an engine rated under
(1) Ribbed or waffle-pattern neoprene pads
600 hp and operating above 1200 rpm is installed in
should be made up of three or four layers of the
an upper floor location in a building containing cat-
material, giving a total thickness of approximately
egory. 15 occupancy areas (table 32 of the N&V
manual), the following suggestions should be
1 in. of neoprene. The area of the pads should be
such as to provide the surface loading recom-
applied.
mended by the pad manufacturer. For critical loca-
(1) The entire engine assembly should be
tions, provision should be made to permit replace-
mounted rigidly to a concrete inertia block having a
ment of the pads after about 25 years, as the pad
weight at least 3 times the total weight of the sup-
material may deteriorate by that time. An arrange-
ported load. The concrete inertia block may be
ment for providing layers of neoprene pads under a
eliminated, if desired, for any engine of less than
100 hp that is located two or more floors away from
spring base is seen in figure 91 of the N&V
manual.
a category 1 or 2 area, or that is not located direct-
ly over a category 3 area. If a concrete inertia
(2) For an isolated engine assembly, there
should be no structural, rigid connections between
block is used, it should be thick enough to assure
the engine assembly and the building proper. This
stiffness and good alignment to the entire assem-
includes piping, conduit, and ducts to and from the
bly. Its area should be at least as large as the over-
all area of the equipment that it supports. If the
assembly.
(a) A long bellows-type thermal expansion
engine drives a refrigeration compressor that is
joint in the exhaust piping meets this requirement,
connected directly to its evaporator and condenser
as does a flexible connection in the inlet-air ducting
cylinders, all this equipment should be mounted to-
to the engine.
gether onto the same concrete block. The bottom of
(b) Piping to the engine assembly may con-
the inertia block should rest at least 4 in. above the
tain long flexible connections (length at least 6
top of the housekeeping pad or the structure slab.
times the outside diameter of the piping) that are
If a Type 5 floating-floor slab is involved (para 55e
not short-circuited by steel bars that bridge the
of the N&V manual), this 4-in. air space under the
flanges of the flexible connections; or piping may
concrete inertia block should be covered with 2-in. -
be used without flexible connections, if the piping
thick low-cost glass fiber or mineral wool. The en-
is supported on vibration isolation hangers or
gine assembly is not to be mounted on the floating-
floor slab. If a concrete inertia block is not used, a
mounts for a distance along the pipe of at least 200
pipe diameters. The vibration isolation hangers
substantial housekeeping pad should be provided
should have a static deflection of at least one-half
under the engine assembly, and the engine assem-
the static deflection of the mounts that support the
bly should be mounted on a rigid steel frame that is
engine base. If steel springs are used in the pipe
stiff enough to be supported off the floor on indi-
hangers, neoprene or compressed glass fiber pads
vidual steel spring isolators without introducing
should be in series with the springs.
stability or alignment problems.
(2) The concrete inertia block or the stiff steel
should either contain a 6-ft. length of braided, flex-
frame of (1) above should be supported off the
ible conductor across the vibration isolation joint,
structure floor slab with steel spring vibration iso-
lation mounts having minimum 2-in. static deflec-
or be supported from resilient hangers for a dis-
--
tance of about 50 ft. from the isolated assembly.
tion under load.
3-14
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