34 of 120
MVA 02 rev 5 - December 2017
CAUTION:
Fan operation within a very broad range of operating speeds may lead to increased vibration
in correspondence with a specific resonance frequency of the system of which the fan is only a
single component.
Avoid working at speeds coinciding with structural resonance frequencies, and if this is not
possible, modify some variable that can change the resonance frequency of the system, for
example by using vibration dampers of a different type.
If the rotation direction of a fan must be inverted, or if it must be restarted, this must be done only when the
impeller is in the rest position (total standstill).
CAUTION:
Inverting the fan rotation direction or starting it with the impeller turning in the opposite
direction may cause breakage of the blades and/or the impeller hub, with the risk of ejection of
metal parts.
The replacement of moving parts with non-original spare parts may be the cause of different operating
conditions with respect to the original design condition (e.g. AISI 304 stainless steel, AISI 316L stainless
steel or Corten).
CAUTION:
Respect the maximum speeds indicated in the catalogue for the applicable temperature. For
transmission shafts in stainless steel, these speeds must be reduced by 20%. Comply with the
information given on the transmission specifications document supplied with the fan.
Operation at a speed significantly lower than up to 40% of nominal speed (unless otherwise specified by
FVI
)
may affect the cooling of the motor and bearings, with possible malfunctions due to higher temperatures. For
electrical components, the user and installer are advised to provide adequate protection for the drive system
or motor, with the use of heat detection capsules if possible, and also using a servo-ventilated motor if
necessary.
Resonance phenomena in the structure must be avoided. These may emerge at specific rotation speeds,
and may cause damage to the structure.
CAUTION:
Resonance phenomena at low frequencies may cause damage to the structure.
3.8.6
Noise emission risks
FVI
designs its fans dedicating attention to the elimination of the noise that they generate. Nevertheless,
during normal operation fans act as a sound source.
The spectrum of frequencies of acoustic emission depends on the dimensional and structural characteristics
of the fan, and also on its application of use (rotation speed, fluid moved, etc).
FVI
, in collaboration with TUV, has measured the acoustic emissions of its fans in its own test laboratory in
accordance with the EN ISO 3744
– EN ISO 3746 – ISO 13347 standards.
Tests were conducted with fans similar to those to which this manual refers, and relative values of acoustic
power and pressure are shown in Chart 3-3, Chart 3-4, Chart 3-5, and Chart 3-6.