Dwyer Instruments Series MAFS Averaging Flow Sensor Users Manual
Series MAFS Averaging Flow Sensor
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Specications - Installation and Operating Instructions
Bulletin F-MAFS
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The Series MAFS Averaging Flow Sensor uses evenly distributed total and static
pressure measuring points to deliver an accurate measurement of ows in a duct.
The Air Flow Measuring Probe can be completely installed from outside of the duct
making it very easy to install. With its lightweight and durable construction in addition
to its ease of installation, this product lends itself to being used in the HVAC industry.
These air ow measuring probes may be ordered to t into either round or rectangular
duct installations.
INSTALLATION
When you unpack the Series MAFS Averaging Flow Sensor ensure that there is no
visible damage from shipping. Inspect each sensing point on the probes to ensure
that they are not lled with debris from shipping. If there is obvious shipping damage,
the probe must be replaced prior to use in order to avoid inaccurate measurements.
Please contact Dwyer Instruments, Inc. if it is necessary to replace your air ow
measurement probe.
Location - The sensor should be installed in the owing line with as much straight run
upstream as possible. A rule of thumb is to allow 10 - 15 diameters upstream and 5
downstream. The table below lists recommended up and down piping.
CALCULATING VELOCITY
Pv
Air Velocity = 1096.2 (C
where:
v = Sensed pressure difference (velocity pressure) in inches of water column
P
D = Air density in lbs/ft
C
p = Pitot tube coefcient: See specications for K-factor vs. size
Air Density = 1.325 X
B = Barometric pressure in inches of mercury
P
T = Absolute Temperature (Indicated Temperature in °F plus 460)
p)
D
3
(dry air = .075)
PB
T
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SPECIFICATIONS
Service: Clean air.
Wetted Materials: Aluminum AA6063.
Accuracy: 0 to 9000 FPM (45.7 m/s); ±2% FS, ±3% FS for 6˝ (160 mm) and 48˝
(1200 mm) length models.
K-Factor: 0.81, 0.80 for 6˝ (160 mm) and 48˝ (1200 mm) lengths, 4˝ (100 mm)
length = 0.82.
Max. Temperature: 400°F (204°C); Gasket: -31 to 230°F (-35 to 110°C).
Minimum Design Flow: 400 fpm (2.03 m/sec).
Maximum Design Flow: 12,000 fpm (60.96 m/sec).
Process Connections: 1/4˝ barb.
Straight Run Requirements: 5 diameters or longest side dimensions.
RECTANGULAR DUCT MODELS
Determining Probe Number and Placement for Rectangular Ducts
1. To determine the number of probes you need please consult the chart below.
Short Duct
Dimension
Number of
Probes
2. In order to determine where to place your probes, divide the short duct dimension
by number of probes.
3. Divide the result by two and this will be the distance from the top edge of the duct
to the rst probe location.
4. The next probe will be placed two times the resulting distance from step two from
the rst probe. So, if the rst probe was placed 4˝ from the top edge of the duct,
your next probe would be placed 8” from the rst probe, or 12˝ from the top of the
duct.
5. Continue this pattern until you have determined all probe locations.
Example: You have a duct with a 24˝ short side, and upon consulting the chart
determined that you needed 3 probes for this size duct.
24 / 3 = 8
8 / 2 = 4
APPROX.
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THREADED
STUD
12˝ - 23˝ (<305
mm - 585 mm)
L
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24˝ - 35˝ (610
mm - 889 mm)
2
DWYER INSTRUMENTS, INC.
Therefore, the rst probe is placed 4˝ from the top of the duct.
The second probe is placed 4˝ + 8˝ = 12˝ from the top of the duct.
The third probe is placed 4˝ + (2 x 8˝) = 20˝ from the top of the duct.
LONG SIDE ≥
SHOR
4˝
[100]
24˝
T
[610]
SIDE
Figure 1: View illustration of probe placement example.
Please note that all probes should be installed vertically and running parallel to
each other if installed in a rectangular duct.
RECTANGULAR DUCT PROBE INSTALLATION
1. See drawing for proper opening to cut for insertion. Cut a hole at locations
calculated above in side of duct. Drill a 5/16˝ hole on opposite side of duct. Remove
o-ring, hex and acorn nuts.
2. Place silicon bead around holes.
3. Slide MAFS into holes and screw the included four self drilling screws into duct to
attach MAFS. On far end, re-attach o-ring, hex and acorn nuts.
4. Connect 3/16˝ I.D. tubing to barb ttings on MAFS.
5. Check all ttings and tubing connections for leaks using a leak detector.
6. Tee all high and low ports into one high and one low line and connect to transmitter
or gage.
7. The devices should be checked occasionally for build-up of dirt of debris common
in an HVAC system.
12˝
[305]
20˝
[508]
MAFS
MAFS
MAFS
24˝
[610]
ROUND DUCT PROBE INSTALLATION
1. See drawing for proper opening to cut for insertion. Cut a hole at locations
calculated above in side of duct. Drill a 5/16˝ hole on opposite side of duct. Remove
o-ring, hex and acorn nuts.
2. Place silicon bead around holes.
3. Slide MAFS into holes and screw four self drilling screws into duct to attach MAFS.
On far end, re-attach o-ring, hex and acorn nuts.
4. Connect 3/16˝ I.D. tubing to barb ttings on MAFS.
5. Check all ttings and tubing connections for leaks using a leak detector.
6. Tee all high and low ports into one high and one low line and connect to transmitter
or gage.
7. The devices should be checked occasionally for build-up of dirt or debris common
in an HVAC system.
CALIBRATION
Sometimes eld calibration may be required if the probe is installed in a bad location
i.e. immediately downstream of an elbow. In order to calibrate, you must either perform
a traverse of the duct or a sum of the air registers and compare this with the MAFS
output. Then, you must make the correction to the effective area in the computer to
make up for the error.
MAINTENANCE/REPAIR
Upon nal installation of the Series MAFS, no routine maintenance is required. The
Series MAFS is not eld serviceable and should be returned if repair is needed. Field
repair should not be attempted and may void warranty.
WARRANTY/RETURN
Refer to “Terms and Conditions of Sales” in our catalog and on our website. Contact
customer service to receive a Return Goods Authorization number before shipping the
product back for repair. Be sure to include a brief description of the problem plus any
additional application notes.
CIRCULAR DUCT MODELS
Determining Probe Number and Location for Round Ducts
1. Note that in round ducts only two probes are needed. The quantity of probes
needed does not depend on size of the duct.
2. Locate probes 90 degrees apart. See Figure 2 for an example.
M
A
90°
F
S
MAFS
Figure 2: Cross-sectional view of probe placement in a round duct
Printed in U.S.A. 11/18 FR# 444019-00 Rev. 2©Copyright 2018 Dwyer Instruments, Inc.
DWYER INSTRUMENTS, INC.
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