Dwyer FLST User Manual
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FLST SPECIFICATION GUIDE
1. Provide where indicated and/or scheduled airflow traverse elements
capable of continuously monitoring the fan or duct air volumes they serve.
2. Each element shall be designed and built to comply with, and provide
results in accordance with, accepted practice for duct system traversing as
defined in the ASHRAE Handbook of Fundamentals, AMCA publication
#203, as well as the Industrial Ventilation Handbook. The number of sens-
ing ports on each element, and the quantity of elements utilized at each
installation, shall comply with ASHRAE Standard #111 for equal area duct
traversing.
3. Each airflow measuring element shall contain multiple total and static
pressure sensing ports placed along the leading edge of the cylinder. The
static pressure chamber shall incorporate dual offset static taps on oppos-
ing sides of the averaging chamber, so as to be insensitive to flow angle
variations of as much as ±20 degrees in the approaching airstream.
4. The airflow traverse elements shall be capable of producing steady, non-
pulsating signals of true total and static pressure, with an accuracy of 2%
of actual flow for operating velocities as low as 100 feet per minute (fpm).
Signal amplifying sensors requiring flow correction (K factors) for field cali-
bration are not acceptable.
5. The airflow traverse elements shall not induce a measurable pressure
drop, greater than 0.18 inch at 4,000 fpm. The units sound level within the
duct shall not be amplified, nor shall additional sound be generated.
6. The probes shall be manifolded together in a 16 gauge galvanized steel
duct section with 90 degree undrilled flanges, fabricated to the duct size,
and shall contain multiple airflow traverse elements interconnected as here-
in before described.
7. Where primary flow elements are located outside of the manufacturer’s
published installation guidelines the manufacturer shall be consulted, and
approve of any special configurations, such as air equalizers and/or addi-
tional and strategically placed measuring points, as may be required.
8. Where the stations are installed in insulated ducts, the airflow passage
of the station shall be the same size as the inside airflow dimension of the
duct. Station flanges shall be sized to facilitate matching connecting duct-
work.
Installation Considerations
1. Primary flow elements shall be installed in strict accordance with the
manufactures published requirements and with ASME guidelines affecting
non-standard approach conditions. These elements serve as the primary
signals for the airflow systems; it shall be the responsibility of the contrac-
tor to verify correct installation to assure that accurate primary signals are
obtained.
2. An identification label shall be placed on each unit casing listing model
number, size, area, and specified airflow capacity.
FLST RESISTANCE to AIRFLOW
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