sembly. Table 32 in the N&V manual explains
(3) Where steel springs are used, unhoused
these category designations.
stable steel springs are preferred. If housed or en-
(b) If the engine must be located closer than
closed springs must be used, special attention must
the distances listed above, for the indicated catego-
be given to the alignment of the mounts so that
ries, the skid-type base should be mounted on
they do not tilt or bind in any direction within their
ribbed or waffle-pattern neoprene pads. The pads
housings. Further, there should be some visual
should be made up of at least three layers of mate-
means to check the spring mount in its final loca-
rial having a total thickness of about 1 in. (para
tion to be certain that binding or tilting does not
36d(l) above). Pipes, ducts, and conduit to the
take place.
engine-generator set should either contain flexible
e. Special situations. The recommendations giv-
connections or be supported: from resilient hangers
en in paragraph 36 will provide adequate cover-
for a distance of at least 25 ft. from the assembly.
age for most typical equipment installations. How-
The engine manufacturer must approve the isola-
ever, general rules cannot cover all marginal and
tion mounting of the assembly.
complex variations. For unusual installations or
(2) "On-site-assembled" generators (over
unfamiliar conditions, it is advisable to have the as-
about 5 MW).
sistance of a vibration or acoustical consultant ex-
(a) No vibration isolation of the assembly is
perienced with this equipment. Vibration problems
required if there is no category 1 area within 400
are sometimes quite complex and unpredictable.
ft., or no category 2 or 3 area within 200 ft., or no
category 4 or 5 area within 100 ft. of the engine as-
37. Vibration isolation of turbine engines.
sembly. Even greater distances are desirable.
Typically, the smaller gas turbine engine-
(b) If the engine must be located closer than
generator sets (under about 5 MW) are mounted,
the distances listed above, for the indicated catego-
transported, and installed as complete assemblies
ries, special concern must be given to the installa-
on steel-frame "skid-like" structures, and the large
tion; and an agreeable design must be devised and
gas turbine systems (over about 5 MW) are in-
approved by both the engine manufacturer and a
stalled at the site on long, stiff steel-beam bases,
vibration engineer or acoustics consultant. Such a
which in turn rest on concrete footings or concrete
design requires detailed knowledge about the spe-
mats, The turbine speeds are very high (typically
cific engine and engine base involved and cannot be
3600 to 6000 rpm, some up to 25,000 rpm), and the
covered by generalizations in this manual.
alignment of turbine, gear, and generator is criti-
Upper-floor location.
b.
cal. The absence of rotary unbalance at these
(1) Skid-mounted, engine-generators (under
speeds is mandatory; hence, there is little or no vi-
about 5 MW). These installations should be vibra-
b r a t i o n compared to the vibration of a
tion isolated in accordance with table 911 in the
reciprocating engine. The steel beams of the large
N&V manual. If gas turbine engines are used to
turbine engine assemblies require their concrete
d r i v e other types of equipment, such as
footings for additional longitudinal stiffness and
reciprocating or centrifugal refrigeration or gas
system alignment, so steel springs are n o t
compressors, the recommendations of tables 93 or
recommended as point supports along the steel
95 (whichever is most nearly applicable) of the
beams unless the manufacturer specifically pro-
N&V manual should be used.
poses such mounts for critical installations. In-
(2) "On-site-assembled" generators (over
stead, it is suggested that the engines be separated
about 5 MW). These units should not be installed
from any critical areas by adequate distance. Dis-
on upper floor locations without the assistance of a
tance requirements set by the airborne noise prob-
vibration or acoustics specialist.
lem will probably assure the adequate distances
needed for vibration control. For these same rea-
38. Vibration isolation of auxiliary
sons, the large units (above about 5 MW) should
equipment.
not be installed in upper-floor locations. The fol-
Ventilating fans, cooling towers, pumps, and com-
lowing recommendations apply to turbine engine
pressors may also be involved with an engine-
installations.
generator system. Vibration isolation of this auxil-
a. On-grade locations.
iary equipment should be in accordance with
(1) "Skid-mounted" engine-generators (under
chapter 9 of the N&V manual.
about 5 MW).
(a) No vibration isolation of the assembly is
3-9. Use of hearing protection devices.
required if there is no category 1 area within 200
Personnel working in engine-generator rooms are
ft., or no category 2 or 3 area within 100 ft., or no
exposed to hazardous noise levels as defined by
category 4 or 5 area within 50 ft. of the engine as-
3-15
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