0. 0. Pritchard
and 0. H. Miller University of California lSanta Barbara1 Goleta
I
I
Safety Device for Vacuum Diffusion Pumps
Mercury or oil diffusion pumps in any vacuum system are dependent on a steady stream of coolant water for safe and efficient operation. Any interruption of the flow of water can be used to activate safety devices for the control of the diffusion pump heater.'-4 A commercial devices which operates on a diaphragm principle is commonly used to protect s~ectrophotometershut can also he used for electrically Gated -pumps. The device described herein is one that can be assembled easilv and is fullv automatic in that the heat, source is reactivat,ed if the flow of coolant water is resumed. If the diffusion pump is heated with a Bunsen burner, a suitable arrangement is shown in the figure. A is a 100-ml round-bottom flask. B is solid glass rod, supporting the glass attachment C. D is a short piece of glass tubing which pivots on a fixed metal rod E. P i s a 250-ml beaker, drawn off as shown, and the outlet to the drain is so regulated that the bulb A floats close to the top of the beaker with a suitable rate of flow of water from the outlet of the condenser of the diffusion pump. The gas flow to the Bunsen burner in normal opcration passes through bulb C. The small pool of mercury in C stays a t the right hand end when the arm BCB has a downward cant. If the water supply from t,he diffusion pump diminishes, the level in the beaker drops, and so does A and the arm BCB. This causes the mercury to run to the left hand end of C which covers the mouth of the small exit tube and cuts off Work supported by National Science Foundation. 1 STEEL,C.. SMITH.R. F., AND SUMMERS, B., J . Sci. Inst?., 34, 125 (i957j. 2 HOUGHTON, G., J . Sei. Instr., 33, 199 (1956) 3 GREEN. G.W . J Sei.Imtr. 35. 147 119581. cROA,'A.J., J. Sei.Instr., 25, 386 (1948). 5 Shnr-fla, automatic interlock, Hays Mfg. Co., Erie, Penna.
the gas supply (the gas pressure is insufficient to blow mercury into the room). A small pilot light (insufficient t,o heat the pump) mounted next to the Bnnsen burner relights t,he gas flame if the water supply should be resumed, when A rises to its former level, and the gas has free passage through C as the mercury returns to its former posit,ion. The mercury in C is covered with a layer of oil to prevent carrying harmful vapor into the room. If the diffusion pump is heated electrically, the arm BGB is mounted horizontally (in place of BCB) so that
the mercury covers the bottom of G and is part of the' circuit. When the wat,er supply fails and A falls, the mercury runs to the left end of G and breaks the circuit. If the water supply is resumed, the circuit is reactivated when G reaches its horizontal position. The device is somewhat sensitive to set up, but once: the flow of water is correct,ly adjusted it provides trouble-free operation. As an additional precaution, the beaker F is mounted directly over the drain in case a sudden upsurge in water pressure causes overflow.
Volume 38, Number 10, October 1961
/
525
