Installation Instructions
Mechanical Installation
®
4
Determining Torque Loading and Actuator Sizing
Damper torque loadings, used in selecting the correct size
actuator, should be provided by the damper manufacturer.
If this information is not available, the following general
selection guidelines can be used.
Damper Type Torque Loading
Opposed blade, without edge
seals, for non-tight close-off
applications
3 in-lb/sq. ft.
Parallel blade, without edge seals,
for non-tight close-off applications 4 in-lb/sq. ft.
Opposed blade, with edge seals,
for tight close-off applications 5 in-lb/sq. ft.
Parallel blade, with edge seals, for
tight close-off applications 7 in-lb/sq. ft.
The above torque loadings will work for most applications
with 1000 FPM face velocity. For applications between this
criteria and 2500 FPM, the torque loading should be
increased by a multiplier of 1.5. If the application calls for
higher criteria up to 3000 FPM, use a multiplier of 2.0.
General Information
Belimo actuators should be mounted indoors in a dry,
relatively clean environment free from corrosive fumes. If
the actuator is to be mounted outdoors, a protective
enclosure must be used to shield the actuator.
For new construction work, order dampers with extended
shafts. Instruct the installing contractor to allow space for
mounting and service of the Belimo actuator on the shaft.
The damper shaft must extend at least 3 1/2” from the
duct. If the shaft extends less than 3-1/2” or if an
obstruction blocks access, the shaft can be extended with
the AV 8-25 shaft extension accessory or the actuator
may be mounted in its short shaft configuration.
Mechanical Operation
The actuator is mounted directly to a damper shaft up to
1.05” in diameter by means of its universal clamp. A crank
arm and several mounting brackets are available for
applications where the actuator cannot be direct coupled
to the damper shaft. The NFB, NFX series actuators
provide true spring return operation for reliable fail-safe
application and positive close-off on air tight dampers. The
spring return system provides constant torque to the
damper with, and without, power applied to the actuator.
The NFB…-S, NFX…-S versions are provided with two
built-in auxiliary switches. These SPDT switches are
provided for safety interfacing or signaling, for example,
for fan start-up. The switching function at the fail-safe
position is fixed at +10°, the other switch function is
adjustable between +10° to +90°.
Standard Mounting
NOTE: The NFB, NFX…series actuator is shipped
with the manual override adjusted for a +5° position
at the universal clamp (not at full fail-safe, 0°). This
allows for automatic compression of damper blade
seals when the actuator is in use, providing tight
shut-off. This assumes that the damper is to have
tight shut-off at the fail-safe position. If tight close-
off is desired at the opposite direction from fail-safe,
the manual override should be released so the
actuator can go to the full fail-safe position. See the
manual override instructions.
1. Manually move the damper to the fail-safe position
(usually closed). If the shaft rotated counterclockwise
(), this is a CCW installation. If the shaft rotated
clockwise ( ), this is a CW installation. In a CCW
installation, the actuator side marked “CCW” faces out,
while in a CW installation, the side marked “CW” faces
out. All other steps are identical.
2. The actuator is usually shipped with the universal
clamp mounted to the “CCW” side of the actuator. To
test for adequate shaft length, slide the actuator over
the shaft with the side marked “CCW” (or the “CW”
side if this is the side with the clamp). If the shaft
