Laserfiche WebLink
• The vapor sample is then <br /> P infected into an FID (Flame Ionizing <br /> Detector) chromatograph and the resulting chromatogram compared <br /> to standard chromatograms of known TFH (Total Fuel Hydrocarbons, <br /> gasoline) and BTEX (benzene, toluene, ethylbenzene, and xylenes) <br /> concentrations. <br /> FLOW RATES <br /> Flow rates are measured at the site by use of orifice plates . A <br /> one inch orifice is placed in line for each well and two one inch <br /> orifices in parallel are used to measure the total flow. <br /> An orifice plate restricts the flca of air across it . This <br /> restriction causes a pressure drop across the orifice By <br /> measuring the resulting pressure change across the orifice it is <br /> possible to calculate the air flow rate. <br /> The flow rate is calculated by the pressure drop (millimeters <br /> (mm) water) across a square edge orifice plate . <br /> Ve = CK sgr(P) Q = AVe <br /> Where. <br /> Ve= velocity in feet per minute (fpm) <br /> C = Orifice Coefficient = 0 . 65 (for orifice used) <br /> K = Constant = 794 6 mm water <br /> P = Pressure differential across the orifice <br /> Q = Flow rate in cubic feet per minute (CFM) <br /> A = Area orifice in square feet . 1" = 0 . 00545 ft2 <br /> Q = A X 0 65 X 794 6 X sqr (P) <br /> page 4 of R604 , 06/06/94 <br />