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HOW TO HANDLE GAS SAMPLES

by Philip L. Hanst - PHanst5609@aol.com
 

Gas samples are conveniently moved in plastic bags. They are also conveniently moved through vacuum cleaner hose. 

Gas bags with special quick-connect fittings can be purchased, but they are needlessly expensive. A kitchen bag works just as well, and costs almost nothing. It is important that the bag be dry and contaminant-free. This always seems to be true of kitchen bags.

The easiest way to fill an air bag is by the "wind-sock" method. Open the bag and swing it laterally. Then close it with its tie or its zipper. Transfer of a bagged air sample to an absorption cell requires an outlet on the bag. This can be a small length of plastic tubing that is taped into the corner of the bag. The tubing can be closed off with a clamp or a stopper.

Air may be removed from a cell by a laboratory vacuum pump. The bagged air will then flow directly into the evacuated cell. If the cell has gas in it, rather than vacuum, the bagged air can be forced in by squeezing the bag.

A small blower will cause a gas sample to move continuously through an absorption cell. The air can be conducted to and from the cell by vacuum cleaner hose. The blower needs to be on the output side of the cell, so that the air sample is analyzed before it encounters the blower. On the input side of the cell, the gas sample can be diluted with air or nitrogen by having a "Y" tube with one arm leading to the gas source and the other arm leading to the source of diluent gas. The mixing ratio can be controlled by a ball valve in the sample arm of the "Y". The mixing ratio can be derived from the measurement of a known component of the sample such as CO₂. 

Infrared Analysis, Inc. recommends the following sources for the gas handling components:

(1) Gas handling bags..............................................grocery store

(2) Vacuum cleaner hose and plastic tubing...........hardware outlets

(3) Air moving fans or blowers...........................electronic stores

(4) Ball valves....................................................hardware stores

(5) Vacuum pumps..................................scientific supply houses