Control Device for Precisely Regulating Flow of Air or Other Gas at low Rates
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W. H. McKINNEY, Koppers Co., Inc., Oil City, Pa. I-2 N RUNNING such tests as that for 2,000 8,000 2 oxidation of inhibited steam-turbine w K 1: oils (Am. SOC.Testing Materials, D 943) 6.000 a and the Swift stability test [Oil & Soap Y Y a a 22, 101-107 (1945); King, A. E., Rosw 1,000 4,000 2 n chen, H. L., Irwin, W. H., Ibid., 10,204207 (1933)) it is necessary to control the 2,000 flow of oxygen or air, respectively, a t fairly low rates for periods of time up to 0 2 months. This generally proves to be a 0 0.002 0.004 0.006 0.000 0.010 tedious task when using the normal SAMPLE VOLUME. M L . laboratory-type, single-stage, pressurereduction valve and flowmeter system. Figure 3. Effect of sample sizes on peak measurements A simple device can be easily fabricated which will provide a constant Column. 2 meters, Perkin-Elmer B, 50" C. Flow rate. 120 ml. per minute (1 atm., room temperature) flow of gas over periods of several Sample. n-Hexane months with very little attention. The heart of this device is an orifice nipple, shown in detail in the figure. This device is fabricated by soldering a 12-inch length of tubing, 0.01 inch in inside diameter, into a 1/4-inch extra peak heights were found to be A0.897, sample size itself. Here, goo linearity strong brass nipple. If a number of of the peak height. This is regarded as is found between sample size and peak these are to be used from one header, area. Broadening of the peak with highly satisfactory. Volatile liquids they should be matched to the tolerincrease in sample size results in a such as Zmethylbutane (isopentane) ances desired. This can be done readnonlinear peak height relationship. have been introduced equally well. ily by using a wet test meter to check To test the precision in the introducFor quantitative work, peak heights each nipple as it is made. The nipple tion of gas samples, propane was chosen. may be used with sample size held can be used to control flow rates over a It was introduced 27 times using a pipet constant. If areas under peaks are fairly wide range. It mill deliver apof 0.4ml. capacity. The column condiused, any size of sample can be chosen. proximately 13 liters per hour a t 30 tions were essentially the same as those pounds per square inch gage and 3 liters above. In this case the 95% conLITERATURE CITED per hour a t 7 pounds per square inch fidence limits for the measured peak heights were found to be =k0.78%,. gage. If rates lo-xer than 2 to 3 liters (1) Bradford, B. W., Harvey, D., Chalkper hour are required, a longer length linearity. Figure 2 shows that a lev. D. E.. J . Inst. Petroleum 41. 80of capillary tubing should be employed good linear relationship exists between 8 "(iQ55).' rather than pressures lorn-er than 5 concentration and peak height if the (2) Fredericks, E. M., Brooks. F. R., pounds per square inch gage. ANAL.CHEM.28, 297 (1956). size of the total sample remains con(3) Lichtenfels, D. H., Fleck, S. 8., The figure below shows how this stant. These data were obtained by Burow, F. H., Ibid., 27, 1510 device can be used to provide the flow using binary blends of n-hexane and (1955): of 3 liters per hour required by the cyclohexane. (4) Ray, N. H., J. A p p l . Chem. (London) turbine oil oxidation test. The use of 4 , 21, 82 (1954). Figure 3 s h o w the actual effect of two-stage pressure reduction with the orifice nipple manifold pressure carefully controlled is an essential part of this system. 10,000
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+ Flow control device for tank oxygen Brass nipple, '/4 inch, extra strong, 0.540-inch O.D. X 0.302inch I.D. B . 12 inches (approximately 20 turns) of 0.010-inch I.D. brass or copper capillary tubing (use '/s-inch mandrel for winding tubing) C. Silver solder D. Bore nipple to suit disk E. Brass disk, 6/16 inch O.D. X '/I6 inch I.D. X '/le inch thick F. '/a-inch American Standard pipe, threaded both ends G. Gas pressure reducing valve H. Low-pressure manifold, 7 pounds/sq. inch I. Shutoff volve J. Orifice nipple K . Line to test apparatus L. Cylinder pressure regulator, adjust to 15 pounds/sq. inch
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ANALYTICAL CHEMISTRY
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