Dwyer FAFM User Manual
Bulletin AV-1-FAFM
Series FAFM Fan Inlet Air Flow Measuring Probe
Specifications - Installation and Operating Instructions
A
A
A
FAFM-D-xxxx
FAFM-S-xxxx
7/8
[22.23]
INLET FLOW VIEW SECTION A-A
L
3-1/8
[79.38]
APPLICATION DIAGRAM
12
[304.80]
3-5/8
[92.20]
MODEL FAFM-D
The Model FAFM Fan Inlet Air Flow Measuring Probes use
evenly distributed total and static pressure measuring points to
deliver an accurate measurement of flows in a fan inlet. The Air
Flow Measuring Probes can be completely installed from outside
of the fan making it ideal for when proper duct locations are
unavailable. With its lightweight and durable construction in
addition to its ease of installation, this product lends itself to being
used in the HVAC industry.
B
D
1
[25.40]
1/16
[1.63]
5/16
[7.70]
MOUNTING PLATES TO
BE BENT TO FIT INLET
Ø3/8
[9.53]
L
A
B
INLET FLOW VIEW
APPLICATION DIAGRAM
4
[101.60]
L = Fan Inlet Dia.
MOUNTING PLATES TO
BE BENT TO FIT INLET
MODEL FAFM-D
SECTION B-B
1/16
[1.98]
R3/16
[4.76]
SPECIFICA T IONS
Wetted Materials: Aluminum with clear anodized finish.
Accuracy: ±2% (Note: Field Calibration May Be Required).
Max. Temperature: 400ºF (204ºC).
Minimum Design Flow: 400 fpm (2.03 m/sec).
Maximum Design Flow: 12,000 fpm (60.96 m/sec).
Process Connections: 1/4˝ NPT female.
D
3/4
[19.05]
There are two versions of the model FAFM fan inlet air flow probes
to choose from depending on the depth of the fan inlet.
INSTALLATION
For fan inlets with depth less than 3-1/2˝ (8.89 cm): Please
order a fan inlet probe with an “S” suffix. This probe has a
diameter of .375˝ (.95 cm). It employs one total flow measuring
tube and one static measuring tube. Each probe is covered with
an extruded aluminum anodized coat. Each measuring tube has
multiple sensing points.
When you unpack the Model FAFM Fan Inlet Air Flow
Measurement Probe ensure that there is no visible damage from
shipping. Inspect each sensing point on the probes to ensure that
they are not filled with debris from shipping. If there is obvious
shipping damage, the probe must be replaced prior to use to
avoid inaccurate measurements. Please contact Dwyer
Instruments, Inc. if it is necessary to replace your air flow
For fan inlets with depth greater than 3-1/2˝ (8.89 cm):
measurement probe.
Please order a fan inlet probe with a “D” suffix. This probe has a
diameter of 3-1/2˝ (8.89 cm). It employs extruded aluminum
anodized coated probes with both total and static sensors on
each tube.
DWYER INSTRUMENTS, INC.
Please note that Model FAFM Fan Inlet Air Flow Measurement
Probes should be installed in portion of the fan inlet with the
smallest diameter.
Phone: 219/879-8000 www.dwyer-inst.com
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: 219/872-9057 e-mail: info@dwyer-inst.com
These units are meant to be installed running parallel to each other
as shown in figures 1 and 2.
Figure 1
To install the Model FAFM Fan Inlet Air Flow Measuring Probe
please refer to the following instructions:
1. Drill a minimum of two (2) holes into mounting plates.
2. Slide Model FAFM Fan Inlet Air Flow Measuring Probe Halves
into smallest diameter of the fan inlet.
3. Once in the smallest inlet diameter, push the probe to the
outside of the smallest inlet diameter and screw or rivet into
place using a minimum of two (2) screws or rivets per FAFM
half.
Note: The FAFM Air Flow Measurement Probe should be installed
with the holes in all probes visible from the outside of the fan.
4. Tee the two high and low connections to create one high and
one low output signal.
5. For double inlet fans tee all of the high and low connections to
create one high and one low output signal.
6. Connect the high and low outputs to a differential measurement
device such as a differential pressure transmitter.
CALIBRA TION
Sometimes field calibration may be required if the probe is installed
in a bad location i.e. immediately downstream of an elbow. In or der
to calibrate, you must either perform a traverse of the duct or a
sum of the air registers and compare this with the FAFM output.
Then, you must make the correction to the effective area in the
computer to make up for the error.
Figure 2
To determine how far apart the two halves of the FAFM should be
placed, consult the chart below.
Fan Inlet Diameter
6"-9" (10.16 cm-22.86 cm)
10"-14" (25.4 cm-35.56 cm)
15"-20" (38.1 cm-50.8 cm)
21"-24" (53.34 cm-60.96 cm)
25" (63.5 cm) and up
Probe Separation
3" (7.62 cm)
4” (10.16 cm)
5" (12.7 cm)
6" (15.24 cm)
8” (20.32 cm)
MAINTENANCE
Upon final installation, the device should be checked once a year
for a build up of dirt or debris that can be common in an HVAC
system. Also check the mounting stability once a year. Other than
this no routine maintenance is required. The FAFM model is not
field serviceable and should be returned if repair is needed (field
repair should not be attempted and may void warranty). Be sure
to include a brief description of the problem plus any relevant
application notes. Contact customer service to receive a return
goods authorization number.
©Copyright 2008 Dwyer Instruments, Inc. Printed in U.S.A. 9/08 FR# R1-443658-00
DWYER INSTRUMENTS, INC.
Phone: 219/879-8000 www.dwyer-inst.com
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: 219/872-9057 e-mail: info@dwyer-inst.com
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