Improved Mercury Float Valve. I. Shapiro, U. S. Xasal Ordnance Test Station, Pasadena, Calif. REQUENTLY
in high-vacuum work it is found necessary to
F keep vapors and gases from coming in contact with the grease used in stopcocks, and in these instsnces the replacement of stopcocks with mercury float valves has proved useful.
and eliminates the use of a separate mercury reservoir in that it incorporates the reservoir,’(volume,18 ml.) in the hollow stopcock barrel. iThis type of float valve bas been in operation for a oonsiderable period of time and its performance has been excellent. The U-tube is 11mm. in outside diameter, with hollow-ground plug with iron core, and is connected t o the reservoir by Zmm. capillary tubing. The stopcock barrel contains three holes, two at the bottom level and one st the top level, so arranged that each hole at the bottom level will be in line with the capillary tube connecting to the U-tube as the hole a t the top level of the barrel coincides with either protruding arm. One arm can be connected directly t o a vacuum pump and the other arm left exposed to the air. Then as the stopcock is turned from one position t o the other, the mercury will either rise or fall in the U-tube. I n the neutral position the mercury level will remain stationary. The mercury can never fall below the bend in the capillary tube and the length of the ground barrel eliminates any danger of air leakage into the higli-Vacuum system. The entire assembly oan be supported by placing a elsmm around the middle of the stoncock. Assembling Multiple-Ji and Ralph Scruby, C Colo. following methou rnermucuupie a s ~ e m ~ u e s 1 are mechanically rugged and withstand flexure indefinitely wit,hout short circuits.
A float valve consists essentially of a pair of grqund-glass plugs in a U-tube arrangement, a mercury reservoir, and a method of controlling t,he flow of mercury from the reservoir to and from the U-tube. As mercury enters the U-tube the plugs float up into position and thus seal off communication between the two arms of the U-tube; then a6 B vacuum is pulled on the mercury reservoir, the mercnry is withdrawn from tho U-tube and the plugs drop to an open position, thus permitting vapors and gases to pass between the two arms. In any arrangement i t is necessary to supply both air and vacuum to the mercury reservoir. In some of the older arrangements an ordinary stopcock (or.ground plug) is placed between the reservoir and the U-tube, and m operation a rubber tubing connected to a vacuum pump is placed over the open end of the reservoir in order to pull a vacuum on the valve, or the open end ofthe reservoir is left untouched in order t o get positive air pressure. When one has a number of these mercury float, valves in a system, operation of the valves by this method becomes very cumbersome. Recently there has appeared on the market ~1 float valve in which a fivo-way stopcock effectively replaces the ordinary stopcock and allorvs air or vacuum to be piped directly to each reservoir and thereby facilitate the manipulation of the float .valves. However, it is possible for all the mercury to drain back i n b the reservoir, thus exposing the grease in the stopcock to the vapors or gases, and the short distance along the ground barrel of the stopcock between the entrance to the U-tube and the end of the stopcock increases the danger of air leaking (especially after long usage) into the high,vacuum system. The float valve described herein circumvents these difficulties
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