Owner's manual

Series AFG Averaging Flow Grid
Specifications - Installation and Operating Instructions
Bulletin F-AFG
DWYER INSTRUMENTS, INC. Phone: [phone] www.dwyer-inst.com
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: [phone] e-mail: [e-mail]
The Series AFG Flow Grid is an outstandingly simple yet accu-
rate and cost effective alternative to other duct mounted pressure
sensors. Once installed and connected to a suitable measuring
instrument, the device will provide years of trouble free monitoring
of both air and gas flow. Fitting the AFG Flow Grid is simple, with
the unit supplied in kit form to allow both workshop and on-site
installation into a wide range of square and circular ducts.
The AFG Flow Grid is a fundamental pressure-sensing device
designed to transmit a continuous differential pressure signal.
When this output is connected to a suitable measuring instrument
(i.e. manometer, pressure transducer, etc.) it may be used to
determine air velocity and volume flow rate.
HOW THE AFG FLOW GRID WORKS
The AFG Flow Gird consists of two tubes mounted diagonally
across a square or rectangular duct, or diametrically across a
round duct. The tubes are drilled with a series of equi-spaced
holes.
The holes in one tube face directly upstream and sense total pres-
sure, while the pairs of holes in the second tube also face forward
but at an included angle of 79 degrees, sensing static pressure.
The total and (sub) static pressures are averaged along the length
of each tube and provide pressure signals at connectors outside
the duct wall. The pressure differentials across these connectors
constitute the output signal.
CONSTRUCTION
The AFG Flow Grid tubes are stainless, steel, PVC, Polyurethane,
acetyl plastics, and neoprene rubber.
The output connectors are 1/4" diameter and are intended for use
with plastic tube.
The AFG Flow Grids must not be used in air temperatures above
176ºF (80ºC).
SPECIFICATIONS
Service: Monitor air or compatible gas flow.
Wetted Materials: 304 SS, PVC, Polyurethane, acetyl plas-
tics, and neoprene rubber.
Accuracy: ±5%.
Maximum Temperature: 176ºF (80ºC).
Velocity Range: 295.2 ft/min to 5904 ft/min (1.5 to 30 m/sec).
Diameter of Tubes: 5/16˝ (8 mm) or 5/8˝ (16 mm).
Max Duct Diagonal: 60.4˝ (153.4 cm).
Max Duct Diameter: 59.4˝ (150.9 cm).
Process Connections: 5/16˝ barbed.
Weight: AFG-1: 1 lb (454 g); AFG-2: 3 lb (1361 g).
APPLICATIONS
The AFG Flow Grids will give useful and reliable readings in a wide
variety of ‘in duct’ locations often where other flow rate measuring
devices are found to be unsatisfactory.
However, AFG Flow Grids should not be used in conditions of high
humidity or where material of a sticky nature is present in the air
stream, as a build-up of deposits on the pressure tubes or in the
pressure holes will affect calibration. Where a high dust burden is
likely to be encountered, it is advisable to provide access for
cleaning when installing an AFG Flow Grid.
Positioning in Ducts:
The AFG Flow Grids should be positioned in straight lengths of
duct and at right angles to the axis of the duct. The following cri-
teria should be complied with when positioning an AFG Flow Grid:
1. Allow at least 3.5 diameters (3.5D) of duct upstream from 1D
bends and minor obstructions.
2. Major obstructions such as right angled bends and opposed
blade dampers require greater lengths of upstream duct (See the
last page).
3. Allow at least 1D of duct downstream of the AFG Flow Grid
before any change to the duct cross section or obstruction to the
flow. Shorter lengths are likely to increase pressure loss.
SECTION A-A
SCALE 2:1
A
A
B
1/64
[.396]
ØA
1-1/16
[27]
2
[51]
5/32
[2.38]
1-3/16
[30.16]
1-11/16
[42.86]
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