Theodore D. Perrine
National Institute; of Health Bethesda 14, Maryland
Method for Attaching Glass Water Aspirators to Water Lines
In our experience, metal water aspirators have not been very successful. They are attacked by corrosive substances and in most instances fail to produce a satisfactory vacuum after a short period of use. By contrast, as illustrated in Figure 1, glass aspirators are fast and efficient, usually rapidly attaining a vacuum approaching the vapor pressure of water. The difficulty of attaching them to the water line is their major drawback. Whereas metal pumps may be screwed into a metal fitting, glass pumps must be attached by a length of compressible tubing clamped to the glass neck of the pump.' We have devised a means of screwing glass aspirators to water lines by means of metal pipe bushings. This method is quick, inexpensive, and effective. Moreover,
put dozens of these pumps into service, and have not encountered a single instance of aspirator failure due to breakage or detachment. The method used is illustrated in Figure 2. The water feed tube of the aspiratorZis cut off conveniently near the ring seal and replaced by a piece of 9 mm 0.d. glass tubing approximately 35 mm long. A 1/4-in. X 3/s-in. (nominal iron pipe size) pipe bushing (hex-nut type, preferably of brass) is bored out to '/z-in. i.d. This bushing is slipped over the water feed tube of the aspirator to the position shown in Figure 2. The end of the feed tube is then flared to form a strong shoulder approximately 131/z mm in diameter. It is absolutely essential that this flare be too large to pass through the bushing, and yet be small enough to pass without interference into the pipe fitting to which the aspirator will be attached. A surprising amount of irregularity is permissible in this flare before untoward results are encountered, but if the flare does not pass easily into the female thread of the pipe line, it will inevitably be broken.
Figure 2.
T I M E I N MINUTES
Figure 1. Dynamic test glass versus metal water ospirotorr Evocvotion time for 5-liter glorr Rork through 30 in. of 8/,rin,!bore rubber vacuum tubing.
it has met with the complete approval of our plumbing shops. In the several years since its adoption, we have Joint contribution from the Laboratory of Chemistry, National Institute of Arthritis and Metaholio Diseases. and the Rackv Mountain Laboratory, National Institute of '~llergyand 1;feotious Diseases. National Institutes of Health, U. S. Public Health Service, Department of Health, Education, and Welfare, Bethesda 14, Maryland. 1 The Scientific Glass Apparatus Company offers a large-sized aspirator (Cat. No. 5-4965) which utilizes a piece of Pyrex pipe and pipe flange to effect a solid connection to the water line. a Scientific Glass Apparatus Company Cat. No. 5-4960, or any similar aspirator may he used.
Detoil of pipe bushing onachment.
A sleeve of bore X '/,-in. wall rubber tubingis slipped over the flare, and between the feed tube and the pipe bushing, in such a way that part of the tubing surrounds the flare. Castor oil may be used as a lubricant to facilitate this procedure. The rubber tubing is cut off to a length that will not impede the water flow, and the aspirator is attached to the water line. In use, a certain amount of leakage between seal and bushing is sometimes encountered, especially when the pump is first turned on. Full water pressure usually sufficesto effecta tight seal at this point. We regard a small amount of leakage here as acceptable, since it runs into the drain. Most seals do not show this leakage, and the purist can no doubt eliminate it entirely by carefully making the flare and preparing of the end of the pipe bushing. Since the rubber sleeve cushions the feed tube against the metal bushing, the pump will stand a lateral blow of surprising force without breaking. The pump is free to rotate in the bushing, and the vacuum outlet can be turned to any desired position. Volume 37, Number 9, September 1960 / 481
