Dwyer FLST User Manual

Bulletin F-FLST

Series FLST Duct Mounted Airflow Measurement Station

Specifications - Installation and Operating Instructions

TOTAL PRESSURE

(T.P.) TAKEOFF

STATIC PRESSURE

(S.P.) TAKEOFF

TOTAL PRESSURE
(T.P.) TAKEOFF

TOTAL PRESSURE

(T.P.) TAKEOFF

STATIC PRESSURE

(S.P.) TAKEOFF

(L)

(L + 2.5˝)

.25˝ RADIUS
BEADED EDGE (TYP)

STATIC PRESSURE

(S.P.) TAKEOFF

(L=5˝)

AIRFLOW

AIRFLOW

(F)

DIMENSIONS

CIRCULAR FLANGE
STATION

(D)

SIZE “D”

8˝ - 15˝
16˝ - 44˝
45˝ - 72˝
73˝ & OVER

FLANGE
THICKNESS

.064˝
.064˝
.188˝
.188˝

FLANGE
SIZE “F”

1˝
1-1/2˝
1-1/2˝
2˝

CASING
LENGTH “L”

6˝
6˝
10˝
12˝

OVAL FLANGE (OPTIONAL)

CASING

FLANGE
SIZE “F”

1-1/2˝
2˝

FLANGE
SIZE

1-1/2˝
1-1/2˝

LENGTH “L”

6˝
8˝

STATION
WIDTH “W”

UP TO 44˝
OVER 44˝
NOTE: All oval flow stations without flange have a

casing length of 5˝.

(W)

(F)

RECTANGULAR FLANGE

FLANGE
THICKNESS

.064˝
.188˝

STATION SIZE
“H” OR “W”

8˝ - 72˝

(H)

73˝ & OVER

The Series FLST Airflow Measurement Station consists of single or
multiple airflow elements, factory mounted and pre-piped in a casing
designed for flanged connection to the ductwork. Standard materials con­sist of a G90 galvanized casing and 6063-T5 anodized aluminum flow sen­sors, suitable for most HVAC applications.

The airflow averaging element, utilized in the FLST, is a head type device,
which generates a differential (velocity) pressure signal similar to the orifice,
venturi, and other head producing primary elements. The FLST is con­structed so that strategically located sensing ports (based on duct size)
continually sample the total and static pressures, when inserted normal to
flow. The total pressures sensed by the upstream ports are continually
averaged within the element in an isolated chamber. The static sensing
ports (located where the influence of the velocity head is zero) are averaged
in a second isolation chamber. Multiple elements are manifolded together
for connection to a differential measurement device (gage, transmitter, etc.)
for flow measurement and indication purposes.

SPECIFICATIONS
Accuracy: Within 2% of actual flow when installed in accordance with

published recommendations.

Velocity Range: 100 to 10,000 fpm (0.51 to 51 m/s).
Wetted Material: Elements 6063-T5 anodized aluminum; Casings 16 ga

G90 galvanized steel.
Temperature Limits: Galvanized Casings and Aluminum Elements
350°F (177°C) continuous operation (in air) 400°F (204°C) intermittent
operation (in air).

Humidity: All Airflow Stations 0 to 100% non condensing.
Process Connections: 1/4˝ compression fittings.

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]

Circular Flange Dimensions

Station
Size

6˝ - 15˝
16˝ - 44˝
45˝ - 72˝
73˝ & Over

Circular Stations

Standard circular airflow measuring stations include a 16 gage galvanized
casing with attached 90° connecting flanges as listed above.

Flange
Thickness

0.064˝

0.064˝

0.188˝

0.188˝

Flange
Size

1˝
1-1/2˝
1-1/2˝
2˝

Casing
Length “L”

6˝
6˝
10˝
12˝

Oval Flange Dimensions (Optional)
Station
Size

Up to 48˝
Over 48˝

Oval Stations

Standard oval airflow measuring stations include a 18 gage galvanized
casing, 5 inches long between beads with 1-1/4 inch connecting sleeve
on each end (7-1/2 inch overall length). Actual O.D. dimensions are 1/4
inch less than specified duct I.D. dimensions.

Flange
Thickness

0.064˝

0.188˝

Flange
Size

1-1/2˝
1-1/2˝

Casing
Length “L”

6˝
8˝

Rectangular Flange Dimensions

Station Size

8˝ - 72˝
73˝ & Over

Rectangular Stations

Standard rectangular airflow measuring stations include a 16 gage galva­nized casing, 5 inches long, with formed integral 90° connecting flanges
as listed above.

Flange Size

1-1/2˝
2˝

ELBOWS

INSTALLATION

The elements may be installed in any duct configuration. However, the
accuracy of the installation is dependent on the flow conditions in the
duct. The minimum installation requirements for the elements based upon
a uniform velocity profile approaching the duct disturbance for flow rates
less than 2,500 fpm are shown below. Add one duct diameter to the
installation requirements shown below for each additional flow rate of
1000 fpm. These are not ideal locations. It is always best to locate the ele­ments as far as possible from all duct disturbances, with upstream distur­bances being the most critical consideration.

TRANSITIONS

Notes:

Round Ducts:
D = Duct diameter

Rectangular Ducts:

D = 4HW

π

H = Duct height
W = Duct width