In the Laboratory edited by
Cost-Effective Teacher
Harold H. Harris University of Missouri—St. Louis St. Louis, MO 63121
Deionized Water Watchdog Gregory J. Edens Department of Chemistry and Biochemistry, Long Island University, Brooklyn, NY 11201;
[email protected] We use a deionizer (Barnstead) attached to a dedicated faucet to produce the deionized water used in our teaching labs and research. The deionized water flows through tubing, through the cap of, and into a 5-gal carboy equipped with spigot for storage and dispensing. Filling the carboy is inconvenient because of the need to turn off the valve when the carboy is full. Posted notes imposed a sense of restriction on us and floods occurred if we forgot to turn off the valve. We were able to solve this irritating problem for under $100 with a solenoid valve and a timer switch. The device reported here requires less electronics knowledge than the electronic circuit for automatic shut-off of a water still reported by Stock (1). This device will work with other deionizers. The 3-way solenoid valve, 120 VAC, 60 Hz (Cole Parmer) had fittings of 1兾4-in. NPT(F). In the deactivated (power off ) state, city water was connected to the first (closed) port (Figure 1). The always-open port was blocked with a plug. The third port, which communicates with the first port in the activated (power on) state (Figure 1), was connected to the ion exchange column. Thus the power-off setting corresponds to the closed-valve condition. Connections to the solenoid valve were made with 1兾4in. copper tubing and the appropriate fittings. Tygon tubing with tubing clamps completed the connection to the barbed fitting on the manual valve, which was then left open. Alternatively, one could use pipe fittings to connect the solenoid valve directly to the water supply pipe. The timer switch was a 60-min spring-wound timer (Intermatic, available at home improvement centers). The switch was mounted in a utility box with 1兾2-in. knockouts that mounted directly on the solenoid valve. A 2-wire electrical cord was clamped in a second knockout of the utility box and plugged into an electrical outlet. Water flows only when the timer is on a nonzero time setting. Provided that the dial on the timer is turned past the 10-min mark, it will power off after the set time, and water stops flowing after the elapsed time. We have found that 60 min is adequate to fill the 5-gal carboy.
www.JCE.DivCHED.org
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activated state
timer switch 0 45
from city water
15 30
solenoid valve
120 VAC
to 120 VAC outlet
plug to DI column
deactivated state
timer switch 0 45
from city water
15 30
solenoid valve
0 VAC
to 120 VAC outlet
plug to DI column
Figure 1. Schematic of the activated and deactivated states of the timed shut-off system.
The conductivity meter of the deionizer can be operated any time the water is flowing to check the integrity of the deionized water. We have nicknamed the device the “Deionized Water Watchdog”. This watchdog guards against floods and allows carefree production of deionized water. Literature Cited 1. Stock, J. T. J. Chem. Educ. 1988, 65, 466.
Vol. 81 No. 6 June 2004
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Journal of Chemical Education
841
