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sr y r i� V I all n V. AIR VELOCITIES WITH THE DWYER PITOT TUBE • AIR VELOCITY The total pressure of an air stream flowing in a duct is the sum of the static or bursting pressure exerted upon tate sidewads of the duct and the impact or velocity pressure of the moving air Througn the use of a pitot tube connected differentially to a manometer, the velocity pressure alone is indicated and the cor- responding air velocity determined For accuracy of plus or minus 2&a',as in laboratory applications, extreme care is required and the following precautions should be ooserved I Duct diameter 4" or greater 2 Make an accurate traverse Der sKetch at right calculate the velocities ona av- erage the readings 3 'rovide smooth straight duct sections �f r a minimum at 8'2 diameters in length uosrream and P2 diameters down- stream rrom the picot tube 4 Proviae an egg crate type straightener upstream tram the pitot tube In malting an air velocity check select a location as suggested above, connect tubing locos from both pitat 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 oe shown in feet per minute In other types, the manometer will read velocity pressure in inches of water ana the carresoonaing velocity will be round from the curves in this bulletin If circumstances ao not permit an accurate traverse, center he pitot tube in the duct, determine the center velocity and mustF- ply by a factor of 9 for the approximate average velocity Field tests run in this manner should be ac. curate within plus or minus 5-5% The velocity indicated is for dry air at 70OF: , 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 nosed upon the fallowing data Air Veiocity= 1096 2 Ii p where Pv=veiocity pressure in inches of water D=Atr density in ;t/cu ft Air Density= i 325 x 7B where PS =Barometric Pressure in inches of mercury T=Absolute Temperature (indicates temperature 'F plus 460) Flow In cu ft per min =Duct area in square feet it air velocity in ft per min AIR VELOCITY STAINLESS STEEL CALCULATOR PiTOT TUBES Computes veiociry bases r Teat eont,rthea unity co on air density corrected - eFF,uanr one lifetime ten ions tore and For cane creo ra ti imi-of terrioero- struetion or No 304 stain d l a u less sleet Inch graau- i ` nates t e gCom C u Orions %new 4eath or in latrans Raanngeel s from 01 section for tra,,er sin to 10 -*for cb.resoono. Camolies ww,n, AMCA oma ng to 400 to t0 000 FP44 ASHRAE soecnicarions Furn,snea with each alrot Sites IZ to 00 'Ong tube Wdk Hans or fi xea mount.m q ypes PnnteG in U S A 8 gZ C wngm 1492 Dwver Insirumems Inc D W Y E R INSTRUMENTS, INC. T�e�4��tsis�s-S000 P 0 BOX 373 • MICHIGAN CITY, INDIANA 46360, USA Fax 219AM-9057