New Design of Vacuum Pressure Regulator FLOYD TODD
Todd Scientific Company, Springfield,Pa. for vacuum pressure regulator to maintain N EED vmous .developed vacua aocurately and with a high degree of sensia
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tivity in the range of 0.1 to 50 mm. of mercury pressure. A number of types of pressure regulstors reported in the literature ( 1 4 0 ) were studied. Some regulators were tedious to operate; some would drift; while others would fluctuate in pressure when the systems evolved moisture or other noncondensahle vapors during vacuum fractionations and other chemical vacuum processes.
The regulator consists essentially of an o u k r cyiiiiur~ctlrr y r e x tube, t, which serves as the reservoir for holding either mercury or butyl phthalate. The larger upper half of the inner concentric tube is a safety trap, e, which prevents any bquid in the reservoir from escaping if a back pressure is developed. The annular clearance hetween the safety trap and the outer reservoir is 2 mm. The smaller lower half of the inner tube is marked with a line, 1, approximately 50 mm. above the lover orifice, o, which is slightly flared in order to have maximum sensitivity. Two circular baffle plates, b, are an integral part of the inner,glass tube and have an annular clearance of 2 mm. The sensitivity of the regulator is increased by the use of these baffles, which reduce the turbulence in the reservoir caused by air or other gases passing under the liquid. The safety trap and larger outer tube me connected a t the top by a glass ring seal through which the trap opens into the arm connected to the apparatus. Tho other arm opens only into the outer tube and is connected directly to the vacuum pump. These two arms are carefully placed in line wlth each other and perpendicular t,o the loneit.udina1 axis of the reservoir tube.
te ahout 2 years for several types of laboratory vacuum operations. The regulator also serves as a leak detector the amount of leakage, if any, is visually detectable hecause d l air or other gases must pass under the liquid before entering the pump. Mercury or butyl phthalate may be used, depending on the range and sensitivity of pressure control desired. The compact, singlepiece Pyrex construction eliminates the possibility of leakage or of failure in operation. KOelectrical appliances or other aocessories me needed. The glass part of the regulator is mounted in a metal housing which can be readily clamped in any convenient position by its support rod. The vertical micrometer control screw has a high mechanical advantage which easily permits precise control. A stopcock allows the regulator to be by-passed when not needed. VACUUM PRESSURE REGULATOR
Figure 1shows the regulator mounted in position ready for use.
A diagram is shown in Figure 2.
Glass journals on these side arms support the glass part of the regulator in a central position in its metal housing. A stopcock, shown in Figure 1, connects one arm of the regulator and the outer chamher of the reservoir tube. A constriction, c, 1 mm. in diameter, in one of the side arms prevents the liquid in the reservoir from being blown out in the event that the vacuum is suddenly released m any part of the system. This constriction also maintains smooth operation by removing fluctuations in the head, h. The control knob, k, on the micrometer screw, s, has a m e chanical advantage of approximately 100 which enables the regulator to be easily controlled with precision. The scrcw, 28 threads per inch, passes through a threaded hole in the top of the metal housing, and contacts the tilting arm, a, which is attached at a 45" angle to the regulator. This housing is made of a sturdy single-piece aluminum alloy with a rem horizontal support rod which enables the regulator to he clamped in any convenient position. 1248
1249
V O L U M E 20, N O . 1 2 , D E C E M B E R 1 9 4 8 T a b l e I.
Effect of Rates of Air Leakage on Pressure Maintenance a t 10 Mm. of Mercury
Rate of Air Leakage .WE./Xin.
Pressure Deviations" Mm.
Hg
0.00 0.00 0.00 0.01
0
20
40 60 80
0.02 0.03
100 120 140
0.05
0.08
0.15
160
180 0.24 a Pressure deviations were measured with a butyl phthalate gage which could be read with an accuracy of t0.01 mm. of H g .
OPERATION
The amount of mercury or butyl phthalate (about 20 ml.) used in the regulator is not critical. However, the upper level of the liquid shown by I should be several millimeters below the safety trap, e (Figure 2). The height of the liquid, h, above o will determine the maximum pressure a t which the regulator can be used. The regulator is removed from the metal housing and readily filled simply by immersing the pump arm of the regulator in the liquid to be used, and applying gentle suction to the other arm until the desired amount of liquid is obtained. When filling with butyl phthalate, care should be taken to keep it from obstructing the side-arm constriction, c, or sluggish pressure control will result. The glass part is replaced in the housing, mhich is then clamped in a vertical position. The pressure, which is controlled by the regulator, may be measured by an ordinary mercury manometer or a more sensitive butyl phthalate gage. The regulator is connected to the apparatus and to the pump by no! less than 15-cm. lengths of flexible rubber suction tubing in order to allow the regulator to be tilted through a 90" angle. When the tubing is attached (using lubricant), it is twisted slightly to make a press gently against s. When the system is ready for evacuation, it is important that the stopcock on the regulator be in an open position before the exhaust pump is started. This stopcock is used for by-passing the bulk of the air around the regulator and thereby prevents excessive turbulence of the liquid within the regulator during the evacuation process. After the pressure reaches a few millimeters above the final pressure to be maintained, the stopcock is closed for the remainder of the vacuum operation. The head, h, which is the difference in pressure between the t\vo side arms on the regulator, is controlled to any desired pressure simply by tilting the regulator by means of s. The true pressure as measured by a manometer is the 'sum of h and evacuation pump pressure. The regulator can be moved with precision through any angle from a vertical position with maximum pressure to a horizontal position with zero pressure. After the vacuum operation is completed, the stopcock must be opened before air is slowly ad-
13. 2-Methylnaphthalene
T
HE compound 2-methylnaphthalene is very unusual in that it possesses almost no tendency to crystallize with plane faces. The orthopinacoid face, 100,is always present, but under no simple laboratory conditions is it possible to obtain other faces. The crystals used for the present study were prepared from fusion or by sublimation (Figure 1). There is no evidence for polymorphism in these studies.
CRYSTAL MORPHOLOGY (determined by W. McCrone). Crystal System. Rlonoclinic.
mitted to the evacuated stystem. If this is not done, some of the liquid in the regulator may be forced through the safety trap into the system. The efficiency of the regulator in handling air leaks or evolved gases is illustrated by Table I. The table shows that this regulator, using a Cenco Hyvac pump, maintained relatively stable pressure control even when exaggerated air leaks mere intentionally allowed. The use of a larger pump showed that these deviations of pressure from 10 mm. were due to. the fact that the exaggerated rates of air leakage began to exceed the exhausting capacity of the Hyvac pump, and not to the incapacity of the regulator. The many vacuum conditions under which this new design of vacuum pressure regulator can be readily used suggest a wide field of application where sensitivity, stability, and ease of precise pressure control are essential. The absence of any moving mechanical parts during the operation of this regulator practically eliminates the possibility of fouling, loss of sensitivity, or wear. LITER4TURE CITED (1) (2) (3) (4)
(5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30)
Bachman, G. B., IND. ESG.CHEM., ANAL.ED.,7, 201 (1935). Bailey, -4.J.,Ibid., 15, 283 (1943). Bruun, J. H., Ibid., 11, 628 (1939). Caldwell, M .J.. and Barham, H. N., Ibid., 14, 485 (1942). Central Scientific Co., Catalog No. 94610. Cox, H. L., IND.ESG. CHEM., h i v k r , . ED.,1, 7 (1929). Dalin, G. A., Ibid., 15, 731 (1943). Douslin, D. R., and Wells, W. S., Ibid., 16, 40 (1944). Ellis, L. M., Jr., Ibid., 4, 318 (1932). Emerson, R. L., and Woodward, R. B., Ibid., 9 , 347 (1937) Ferguson, B., Jr., Ibid., 14, 164 (1942). Ferry, C. W., Ibid., 10, 647 (1938). Gilmont, R., and Othmer, D. F., I b i d . , 15, 641 (1943). Huntress, E. H., and Hershberg, E. B., Ibid., 5, 144 (1933).
Ibid., 5 , 3 4 4 (1933). Jacobs, G. T.,I b i d . , 7 , 70 (1935). Lewis, F. M . , I b i d . , 13, 418 (1941). Liebig, G. F., Jr.,Ibid., 6, 156 (1934). Melville, H. J., J . Chem. Soc., 1931, 2509. Munch. R. H., J . Chem. Education, 9, 1275 (1932.) Nen-man, hl. S., IXD. ESG. CHEM., ASAI. ED.,12, 274 (1940). O'Gorman, J. M., Ibid., 19, 506 (1947). Palkin, S., I b i d . , 7 , 436 (1935). Palkin, S., and Nelson, 0 . A , , Zbid., 6, 386 (1934). Schierholtz,0. J., Ibid.. 7, 284 (1935). Spadaro, J. J., et al.. Ibid.. 18, 214 (1946). Sunier, A. A , and White, C. M.,I b i d . , 3, 259 (1931). Thelin, J. H., I b i d . , 13, 908 (1941). Todd, F., U. S. Patent 2,419,042 (-1pril 15, 1947). Warner, B. R., IND. ENG.CHEM., A N ~ LEn. . 15, 637 (1943).
RECEIVED September 2,1947.
Form and Habit. Rounded crystals, no definite form or habit by ordinary crystallization methods from the common organic solvents. Groth reports tablets by sublimation with the forms orthopinacoid, (100); and clinodomes (011). Interfacial Angles (P7lar). 110 A 110 = 76'28'. Beta lo3" l6 * Twinning Plane. Shows plastic deformation with mechanical ttvinning. Cleavage. lOO(1). X-RAYDIFFRACTION DATA(determined bv 2). Cell Dimensions. a = 18.6A; b = 5.98; c = 7.80. Formula Weights per Cell. 4. Formula Weight. 131. Density. 1.088; -1.10 (2). "
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