July 1998 In scuba diving, the tank is the diver's link to life. When scuba divers use nitrox (air enriched with oxygen), it is essential that they can accurately measure the oxygen level in their tanks to plan their dives. Using the wrong oxygen level at the wrong depth can result in oxygen toxicity or even death. Nitrox Technologies, Inc. (NTI), Petaluma, Calif., manufactures nitrox membrane systems to supply mixed gases for scuba divers. Each NTI system includes an oxygen analyzer that allows the diver to verify the tank's oxygen content. With the standard regulator on a scuba tank set to 140 to 150 psi, NTI needed an accurate, yet cost-effective, flow restrictor to meter gas flow to a rate of 1.5 lpm from the tank to the analyzer. Of course, a needle valve could do this, but tampering or inadvertent changes in the valve setting could alter the floe rate and affect the sampling results. A better solution was a fixed orifice with a 0.005-in diameter, drilled through an artificial ruby by Bird Precision, Waltham, Mass. The relatively inexpensive orifice maintains a precise, consistent flow rate into the oxygen analyzer to assure stability and accuracy.
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