Milford S. Brown and Glen F. Bailey Western Regional Research Center ~ ~ r i c u i u rResearch al Service US. Department of Agriculture Berkeley. California 94710
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Coolant Recirculation System Conserves Water
I n t h e laboratory, water i s often u s e d for cooling a n d t h e n
dimmed of in t h e nearest drain without reuse. Althouzh - some a p p a r a t u s m a y require the low temperature of running water, o t h e r svstems m a v b e a b l e t o o p e r a t e satisfactorilv at t e m peratures slightly above ambient. Rising water cost and droueht-caused local shortage h a v e led to wider u s e in this laboratory of a recirculating cooling system for spectrophot o m e t e r lamps. O n e of these systems h a s o p e r a t e d for a n u m b e r of years on a wheeled s t a n d that c a n b e moved away from water a n d d r a i n piping. The primary need is for a means to ensure that water is circulating hefore power is applied to the lamp, and that the power will be turned off if circulation ceases. Small submersed centrifugal Dumas, such as those used in laboratorv water baths. were used t ~ c i r ~ u l water a ~ e at the rate specitied by the instrument manufarrurer. emus st these p u m p may nut supply the pressure required to actuate the pressure safety w i w h originally insmllrd, n water flow monitoring swireh wns installed. This was constructed by hanging a cup on a snap-action switch (Microswitch or equivalent) fitted with an arm extension. Water returning from the lamp t o the reservoir pours into the cup, which is susoended iust above the water surface. The switch arm extenrion iength icndjusted sothat a j t h e r u p fills,therwitrhcloaes to appi, powrr ru the lnmp, and opens tu shut u i i the lnmp d the cup empties more than haif-way. Adrain hole in rhe h u t t u m d t h e r u p is adjusted so that return water flow must exceed the rated lamp ewling requirement to maintain the switch closed. The figure shows a typical power circuit for one or two water-cooled lamps, plus alamp without cooling. The main power switch turnson the measuring and recording circuits immediately. Switching on a water-cooled lamp starts only the pump. When the water cup actuates its switch, power is applied t o the lamp. Some modifications of the original circuit may he required. For example, the Cary 14 for which this system was first used had double pole switches for the lamp power supplies. The two poles had been wired in parallel, hut were separated to provide independent circuits for the p u p and lamp. The double pole pump and lamp switches are required only if the pump must operate with more than one lamp. In the circuit of the figure, the single pole water-cup-operated switch m be used. It may also be convenient in this circuit, or necessary in other circuits, to use the douhle pole switch that is also shown. Careful study of the circuit diagram and actual wiring of the instrument t o he modified should precede any work, so that the fewest possible changes are made. In the Carv 15 modified recently. the water Dressare switch areceded the lamp power supply switch. Merely replacing the pressure switch with the water-cup-operated switch would have made opera~~~
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514 1 Journal of Chemical Education
Block diaaam oftmica1 circuit. Shaded owtions were ad&. ,~ '. s~ecxroohcmmeter . . ellner double or ringle pole water swntch as req-rw For .narumenlswith only one water-coo ea lamp, delete ponm ulthin oroken i ne, use smgle po e 01 UY switch to turn on pump and power supply. Interlocks are used in same instruments to prevent turning an lamp and detector in same compartment. ~
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tion impossible. The pump wouldnot have started until the cup had been depressed, but there would have been no water to depress the cup if the pumpdid not operate. Therefore theorder of the switches in the circuit had to he reversed. The water-cup-operated sw~tchwas placed in a small metal box that could be held on a stand with a lahoratory apparatus clamp. The lamp power supply chassis, which is separate in this instrument, was fitted with a receptacle for the pump motor. Three conductor cables were used so that the pump motor and switch box muld be grounded. Water wascirculated from a 30 X 50 X 20-em stainlesssteel reservoir. The water temperature was recorded a t intervals during two days of continuous 8-hr operation. With the surface of the bath open, the temperature rme about 8% by the end of the day. Covering the bath caused an additional temperature increase of 2'C during the second half of the dav. Therefore it is sueeested that a cover. if desired to keea will prevent salt accumulation. Reference t o a company andlor product named by the department is only for purposes of information end does not imply approval or recommendation of the product t o the exclusion of others which may also be suitable.
