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BULLETIN NC. H-11 <br /> r <br /> SIR VELOCITIES <br /> WITH THE DWYER FITOT TUBE <br /> AIR VELOCITY <br /> The total pressure of an air streonr flooring in a duet is tete sura of tate static or bursting pressure aseerred <br /> wpm" tate sadewalls of the duct and the impact or velocity pressure of the moving air. Threegh the use of a <br /> PIT*? tube connected diffrtentially to o manometer, the velocity pressure alone is indicated and the Cor- <br /> responding air velocity determined. <br /> For accuracy of plus or minus 2:,as in laboratory appiicotloasr extreme care is required and the following <br /> precautions should be observed: <br /> 1. Duct diameter A" or greater. NOR <br /> 2. Meka an accurate traverse per sketch at <br /> right, calculate the velocities and ay. I I <br /> *rag* the readings. i ' . 1 . . • 1 <br /> 3. Proviae smooth, straight duct sections `r t ' ' ' <br /> -. <br /> a asrnimum of 8}5 aiarneters in length '• <br /> upstream and 1% asarnaters down. Z <br /> stream from in& Pitot tube. "'"K' G:..= •,•�_� <br /> A. Provide an egg crate type straightener <br /> upstream from+ the prrat tube. <br /> king an air velocity chack select a 104011011 as suggested above, Conhect tubing leads from bout petit <br /> connections to tete manometer and insure in The duct with the tip directed into the eir It, M. If the <br /> moinent0ter shows a minus indicaTion reverse the tubes. Wvtls a direct reading manometer,air velocities will <br /> now be shown in feet per errriute. in other types, The monometer will read velocity pressure in 'Aches of <br /> crater and the certesponeang velocity will be found from the curves in this bulletin. If circumstances do <br /> not permit an accurdt0 traverse, canter The Pitot tubo in tate dud, dittermone the center velocity and stolte. <br /> ply by a facTar of .9 for the oPproattrnate average vrl0cit7`- Field tosts run in this monner show'd be ac• <br /> curiae within plus or minus 5'd.. <br /> Tore velacity indicated is for dry air of 70oF., 29.9" Barometric Pressure ons a resulting density of .075:/ <br /> Cu. ft. For ort at a temperature atltor than 700F. refer to the carves in this 21611110tut. For other variations <br /> from these conditions, corrections may b+ basod upon the fellowenq data: <br /> Air Velocity— 1096.2 N <br /> D <br /> where Pvsvehmarr presswe in ntdtes of water <br /> D a A►r density in R'cw. h <br /> Au Donsrrr— 1.325 s T <br /> T <br /> where Pi —8aromemc Pre wre ie irtdtes of mercury <br /> T—Absdute Ternporature (indicate0 temperawro 'F <br /> Pius 4601 <br /> Flow to cu. ft. per nein. =Ower area in square feet a[ our v,Necity in ft. <br /> per Mon. <br /> AIR VELOCITY STAINLESS STEEL <br /> C.L&-CULATOR PITOT TUBES <br /> CowMawaa ..ri.a,r� Lrate/ Tout e..r...n.J U tory cr <br /> : <br /> woo *or 40001610y earreatod aiC..wt -wed I.i�r.ww own. <br /> ..r co.oofts"a of tewtperf Me.304 ate s+ <br /> rr• Ma }—aaYry. Es.ltt.- <br /> ` • Ice a S hoal. I n a it 4ro'•-^ <br /> •tsorv$ sAAw davtit at -w- <br /> txe Rett1 a I a+ 1 a 1��.sY�a C st i C Y- _ <br /> Si T 16"ons. ..�. AMMcoon,Q I atlt7.M1 ler ?r r f i 1 N} <br /> ...,r earpw ee.i. ASHRAE 00alha w <br /> io 000 w 20.000 FPM. �. <br /> �.. rv....auw milt a.K. prat _ Stites 12' to 60 lava. <br /> caro ILr - me" or 6-mod ftoY"t.of s <br />