The 31021 may be used as a source of zero air (air free of CO2 and H2O) for performing a field zero of the AP200 gas analyzer. This is a convenient and inexpensive alternative to a tank or cylinder of zero air. The port labeled Out is connected to the AP200 enclosure’s Zero port using a length of ¼-in. tubing, such as the 15702. This tubing is ordered to length and as a separate item. Two nuts (¼-in. Swagelok) are included with the 31021 for connecting the ¼-in. tubing. The 31021 includes a bracket to attach the unit to a vertical pipe of outer diameter less than 5 cm (2 in.).
When connected to the AP200 system enclosure, the AP200 pump pulls ambient air into the 31021 and through a molecular sieve, which scrubs the air of CO2 and H2O. Over time, the molecular sieve will need to be replaced using two bottles of the 27450. To test whether a sieve needs replacement, the CO2 and H2O concentrations from the Out and Test ports should be compared occasionally. This is done manually by changing the tube connection from the Out port to the Test port. If air from the Test port contains more CO2 or H2O than the Out port, the molecular sieve should be replaced by unscrewing the bottle and replacing the molecular sieve inside.