Vibration Specifications Standards For Fans With Alarm
Limits
Fans are defined as:
All non-positive displacement air handling units including
Induced Draft (ID) Fans, Forced Draft (FD) Fans, Overhung
Fans, Centerhung Fans, Centrifugal, Vaneaxial, Tubeaxial,
Blowers, etc.
BALANCING
Permanently attached balancing weighs must be secured by
welding, bolting, pop-riveted, or of a "clip-on"
design.
• If bolted, a hardened bolt must be used in conjunction
with a mechanical locking device (e.g. lock washer or lock
nut).
• Clip-on" balancing weights can only be used
on centrifugal type fans and must be located and attached
on the ID pitch of the blades such that the rotational motion
of the fan creates a positive seating of the "clip-on"
weight against the fan blade.
• Balancing weights and method of attachment must
be stable at fan operating temperature, and of a material
compatible with the parent material of the fan to which
the balancing weight is attached.
NOTE: THE
USE OF STICK ON LEAD WEIGHTS IS NOT ACCEPTABLE
Any parent metal removed to achieve dynamic or static balance
shall be drilled out in a manner which will maintain the
structural integrity of the rotor or sheave.
Access to the fan rotor for field balancing shall be designed
in to the system.
NOTE: It
is recommended that components (rotor, shafts sheave) be
balanced individually and then trim
balanced as a total assembly.
SHAFT TOLERANCE
Fan shaft diameter shall meet bearing manufacturer specifications
for shaft tolerances.
RESONANCE
Natural frequencies of the completely assembled fan unit
shall not be excited at the operating speed. (Running speed
should be at least 25% removed from a natural frequency
of the system.)
LIMITS
New and Rebuilt/Repaired Fans shall conform to the vibration
limits specified when operating at specified system CFM
and Fan Static Pressure.
The frequency range for fan certification shall be from
Fmin = 0.3 X Running Speed of Fan to 60,000 cpm for velocity
and to 120,000 cpm for acceleration.
For fan speeds up to 3600 RPM, the maximum velocity amplitude
(inch/sec-Peak) of vibration at bearing locations in any
direction shall not exceed the Line Amplitude Band Limit
values specified and graphed. When determined in accordance
using the frequency range defined
For fan speeds up to 3600 RPM, the Band-Limited Overall
vibration level of acceleration (g's Peak) at bearing locations
in any direction (as defined in Section 4) shall not exceed
the Band-Limited Overall Amplitude Acceptance Limit values
specified and graphed, when determined in accordance using
the frequency range defined.
Acceptance limits for fans running over 3600 RPM shall
be specified by the purchaser.
Figure 1 Line Amplitude Acceptance Limits
for Fans
Figure 2 Band Limited Overall Amplitude
Acceptance Limits for Fans
OTHER REQUIREMENTS
Variable speed or adjustable sheaves shall not be used
in the final installation.
Drive sheave and driven sheave should differ in size by
20 % or more to avoid "beat" vibration
