Dwyer 160 User Manual

Series 160 Stainless Steel Pitot Tubes

Specifications - Installation and Operating Instructions

Bulletin H-11

The total pressure of an air stream flowing in a duct is the sum of
the static or bursting pressure exerted upon the sidewalls of the
duct and the impact or velocity pressure of the moving air. Through
the use of a pitot tube connected differentially to a manometer, the
velocity pressure alone is indicated and the corresponding air
velocity determined.

For accuracy of plus or minus 2%, as in laboratory applications,
extreme care is required and the following precautions should be
observed:

1. Duct diameter to be 30 times pitot tube diameter, or
greater.

2. Make an accurate traverse per sketch at
right, calculate the velocities and average
the readings.

3. Provide smooth, straight duct sections
a minimum of 8 1/2 diameters in length
upstream and 1 1/2 diameters down­stream from the pitot tube.

4. Provide an egg crate type straightener
upstream from the pitot tube.

In making an air velocity check select a location as suggested
above, connect tubing leads from both pitot tube connections to
the manometer and insert in the duct with the tip directed into the
air stream. If the manometer shows a minus indication reverse the
tubes. With a direct reading manometer, air velocities will now be
shown in feet per minute. In other types, the manometer will read
velocity pressure in inches of water and the corresponding velocity
will be found from the curves in this bulletin. If circumstances do
not permit an accurate traverse, center the pitot tube in the duct,
determine the center velocity and multiply by a factor of .9 for the
approximate average velocity. Field tests run in this manner should
be accurate within plus or minus 5%.
The velocity indicated is for dry air at 70°F., 29.9˝ Barometric
Pressure and a resulting density of .075#/cu. ft. For air at a
temperature other than 70°F. refer to the curves in this bulletin. For
other variations from these conditions, corrections may be based
upon the following data:

Air Velocity = 1096.2

√

Pv

D

where Pv = velocity pressure in inches of water
D = Air density in #/cu. ft.

B

Air Density = 1.325 x

P

T

where P

B

= Barometric Pressure in inches of mercury
T = Absolute Temperature (indicated temperature °F plus 460)
Flow in cu. ft. per min. = Duct area in square feet x air velocity in
ft. per min.

AIR VELOCITY
CALCULATOR

Computes velocity based on
air density corrected for
conditions of temperature and
pressure. Eliminates tedious
calculations. Ranges from .01
to 10˝ water corresponding to
400 to 20,000 FPM.
Furnished with each pitot
tube.

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

STAINLESS STEEL PITOT
TUBES

Test confirmed unity coefficient
and lifetime construction of No.
304 stainless steel. Inch
graduations show depth of
insertion for traversing. Model 160
is designed to meet ASME “Fluid
Meters” 6th Ed, ANSI/AMCA 210­99, ANSI/ASHRAE 51-1999, and
British Standard 1042. Sizes 12˝
to 60˝ long. Hand or fixed
mounting types.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: [phone] e-mail: [e-mail]

AIR VELOCITY IN FEET PER MINUTE

GAGE READING WITH PITOT TUBE (VELOCITY PRESSURE) IN INCHES OF WATER

AIR VELOCITY IN FEET PER MINUTE

GAGE READING WITH PITOT TUBE (VELOCITY PRESSURE) IN INCHES OF WATER

©Copyright 2005 Dwyer Instruments, Inc. Printed in U.S.A.8/05 FR# 440226-00 Rev. 8

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]