High-Vacuum Valves

In laboratory vacuum installations, ground-in stopcocks—glass and metal—are widely used. They provide a good vacuum, are simple in design, and are convenient in operation. However, they have the substantial drawback that they cannot be used in installations with high gas evolution, where high pumping speeds and, consequently, large pipelines are employed.

Recently, with the development of vacuum technology and the increasing complexity of the tasks set before it, metal valves have replaced stopcocks.

One of these valves is described in the article under review*). It reliably shuts off large pipelines and makes it possible to carry out the necessary manipulations in the system being evacuated without stopping the diffusion pumps. This is important because oil diffusion pumps do not allow air to be admitted while they are in a heated state. In order to prevent the oil from burning, they must be cooled each time before admitting air.

The valve described is used by the authors in work with a mass spectrograph, with which samples were analyzed. In the absence of a valve, changing samples would require a great deal of time for cooling and subsequent evacuation of the system (for oil pumps have a rather considerable starting period, during which the oil gradually warms up to the operating temperature).

With the aid of the valve, placed between the pumps and the rest of the vacuum installation, it proved possible to isolate the diffusion pumps, which continued to operate the entire time while replacement was being carried out—

) A. Loeckenvitz, D. Hughens, L. Lipson and G. Olewin, The Rev. of Sci. Instr. 19*, 4 (1948).

of the specimen. The operation of the valve is clearly shown in the drawing, which represents its cross section.

In this position the valve is open and a high vacuum exists in the system.

In order to admit air into the apparatus, it is first necessary, by turning the handwheel \(H\), to advance the stem \(V\) until its tooth seats in the groove with the rubber ring \(G_2\). In this way the diffusion pumps will be isolated from the rest of the vacuum system. Air is admitted by the cock \(E\) through the opening \(D\) and the slot \(F\). After air has been admitted, the specimen in the spectrograph is replaced and the system is evacuated through the same opening \(D\) by an auxiliary pump to a pressure of \(10^{-2}\)—\(10^{-3}\) mm of mercury. Then the stem \(V\) is withdrawn back to its original position, until the tooth of the stem seats in the groove with the rubber ring \(G_1\). Now the entire left-hand part of the valve with the opening \(D\) and the auxiliary pump is isolated from the main vacuum system, and the diffusion pumps evacuate it to a high vacuum. The dimensions of the parts are not specified in the article, since they are determined by the conditions of the problem—the dimensions of the apparatus itself. Only the dimensions of the sealing rubber rings are mentioned. Thus, rings \(G_1\) and \(G_2\) had diameter \(D \simeq 25\) mm with rubber thickness \(d \simeq 3\) mm, while ring \(G_3\) had \(D \simeq 50\) mm and \(d \simeq 5\) mm.

For systems with a pressure equal to \(7 \cdot 10^{-6}\) mm Hg and even \(3 \cdot 10^{-6}\) mm Hg, the valve provided reliable sealing.

V. Fedorov