Design of a Fail-safe Vacuum Line I t is a common laboratory practice to continually out-gas an experimental line by consE.por* v-cuum stant operation of the adjacent vacuum pump. Inevitably a power shut down will occur: cain- TWO^^^ S"''"o'd"""r I . ~ ~ ~ ~ ~ . ~ u I cidentally oil from the pump will be drawn up into the system, requiring considerable time and effort t o refurbish. During the design of such a line for studies with active nitrogen' a feature of general applicability was incorporated to prevent inadvertent "suck-back" of oil in the event of power failure. A two-way miniature solenoid valve2 was installed in a tee between the vacuum pump and the "down-stream" stopcock of the experimental line (figure). Power faila 9""' ure de-energizes the solenoid-opening a small vent. Air bleeding into the system brings the 7 7 i ,,-;,-~line to atmospheric pressure, thereby excluding the oil. Subsequently the line can be re-outgassed in a fairly short time in comparison to that required to remove the oil. During normal operation, the energized solenoid is closed and pressure down to 2 p can be obtained. Inert gas may be introduced instead of air, if required. The technique described will also prevent mercury back-up in similar systems.
$?
' NSF Grant GY-8643. Miniature Solenoid Valve: Two-way, normally open, general purpose valve, Type V51-%a in. orifice diameter, '14 in. NPT, Catslog No. V51DB2200; assembled with Viton plunger for extended service use in energized stage, Catalog No. V5-1499Y. Skinner Electric Valve Division, Skinner Precision Industries, Ine., New Britain, Connecticut 06050. Distributor: Silliter-Holden. Inc., 433 New Park Avenue, Hartford, Connecticut. Central Connecticut S t a t e College New Britain, 06050
Herbert Slotnick
Volume 53,Number 1, January 1976 / 59
