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Bulletin F-AFG

Series AFG Averaging Flow Grid Specifications - Installation and Operating Instructions

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SECTION A-A SCALE 2:1

A

ØA

B

A

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.

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.

CONSTRUCTION The AFG Flow Grid tubes are stainless, steel, PVC, Polyurethane, acetyl plastics, and neoprene rubber.

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:

The output connectors are 1/4" diameter and are intended for use with plastic tube.

1. Allow at least 3.5 diameters (3.5D) of duct upstream from 1D bends and minor obstructions.

The AFG Flow Grids must not be used in air temperatures above 176ºF (80ºC).

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.

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A.

Phone: 219/879-8000 Fax: 219/872-9057

www.dwyer-inst.com e-mail: info@dwyer-inst.com

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