Greaseless Gas-Measuring Receiver for Toepler Pump Richard M. Roberts and John J. Madison, Shell Development Co., Emeryville, Calif.
IN work it is often iiecessary to transfer gas by a Toepler pump VACUUM
to a receiver where it can be measured alld for analysis. Apparatus described in the literature is either Or inconvenient to Operate (1-3). A simpler ToePler Pump and gas receiver consists of a gas pipet mounted directly above the Toepler pump with a mercury check valve between pipet and pump to keep the gas in the pipet. The Toepler pump is of conventional design and is provided with three gastight tungsten electrodes which permit automatic operation by means of a relay system actuating .two solenoid valves: one connected to a vacuum line and one to the atmosphere. A needle valve is placed in the line to the atmosphere to control the rate of inflow of air to the mercury pot. The spherical ground glass check valve between the Toepler pump and the pipet is shown in detail in Figure 1. A ring of mercury seals this valve on the downward stroke of the Toepler pump, and the valve does not leak a t differential pressures up to 350 mm. of mercury. A soft iron core is sealed into the stem of -TO
the check valve to lessen buoyancy and to permit raising of the valve with a solenoid if it is desired to pump out the pipet from the system side. The gas pipet consists of four bulbs connected by capillary tubing having calibration marks corresponding to volumes of about 5, 15, 50, 100, and 200 cc. The relay circuit shown in Figure 2 was designed so that the spark generated on breaking contact between mercury and electrode would involve only low (‘ and low amperage (about pa.). gas mixtures were not in the apparatus described here, and a different type of control system is advisable for such mixtures.
‘
When in operation, the mercury level is made to travel up and down between electrodes B and C by the relay system. Starting with the mercury below electrode B or electrode A , the positions of the three relay switches are those shown in Figure 2. Accordingly, solenoid B is actuated and air pressure forces mercury upward. When the mercury makes contact with electrode C, the doublepole relay is actuated, closing the air
System
pressure solenoid valve and opening the vacuum solenoid valve. The mercury then falls, and although contact with electrode c is broken, the lower singlepole relay and the double-pole relay remain actuated and maintain the vacuum during the downward movement of the mercury until contact with electrode B is broken. The pump requires about 30 seconds per cycle. It is operated until most of the gas is transferred to the pipet and the Pressure in the system is low enough (0.1 mm. or less) to allow measurement of pressure on the manometer. Then the relay system is turned off and air is admitted to the mercury pot through a manually operated needle valve from a compressed air line regulated at 10 pounds per square inch gage, raising the mercury level to one of the calibration marks on the pipet. Pressure above atmospheric was usually required to compress gas into uppermost bulb. The height of the mercury in the manometer, above this mark, is noted to determine the pressure of the gas in the pipet. A well-annealed, 1-liter borosilicate glass spherical mercury pot has never failed in service a t 10 pounds per square inch gage. However, a plastic shield should be placed around the mercury pot and Toepler pump for protection in the event of accidental breakage. ACKNOWLEDGMENT
The assistance of M. M. Nottage and the late H. J. Henriques in the construction of the relay control circuit is gratefully acknowledged.
eavy Wall Pyrex
mm.OD, 3 mm ID
a c k l e s s hletdl valve
LITERATURE CITED
(1) Sanderson, R. T., “Vacuum Manipulation of Volatile Compounds,” p. 72, Wiley, New York, 1948.
PlPet with Calibration Marks Betweeii Bulbs
~i~~~~ 2. ~ ~ tcon-~ trol for Toepler pump
Pyrex Envelope wlth Ground Seat
(2) Weaver, E. R., Shepherd, M., J . Am. Chem. SOC.SO, 1829 (1928). (3) A. ~ Williamson, ~ + i T.,~ Rev. Scz. Instr. 3, 782 (1932).
Tungsten EleCtmde
all Check Valve 500 ml. p U ~ e xF l a s k Detail of B ~ I I Check Valve
Tungsten Electrodes
llter Pyrex Flash
Plaster Of P a n s
Figure 1.
Greaseless gas-measuring receiver for Toepler pump VOL. 29, NO. 10, OCTOBER 1957
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