11 ways you may be using your gas detection tubes incorrectly

Ever send someone out to collect samples with a gas detection pump and tubes that may not have received proper training? Ever have a time where you received inaccurate data? What did that mean for you? Believe it or not, there are still many people who do not use gas detection tubes properly. Ron Roberson, CIH at Sensidyne had a list of ways that detection tubes have been used incorrectly.

gas-detector-tubes1) Using tubes past their expiration date: As the chemical deteriorates, it will affect the stain length, and alter the accuracy. Then at some point it will no longer react at all.

2) Tubes used backwards: Most tubes will only work in one direction, due to multiple internal layers. They incorporate a directional arrow which must be pointed toward the pump.

3) Improperly storing tubes: If tubes are allowed to get hot in storage, or they are left exposed to the sun, they may not respond properly, due to advanced aging.

4) Storing tubes in freezers: Detector tubes will last longer refrigerated, and some part numbers require refrigerated storage. Refrigeration temperatures should be in the range of 5 to 10 degrees C or about 40 to 50 degrees F. Tubes should never be frozen, due to the different materials contracting at different rates. The plastic end plugs that hold the chemical in place, will often contract more than the glass, when frozen. The end plugs can then become loose when the tubes are handled frozen, and the chemical contents also become loose, thereby rendering the calibration void.

5) Too many pump strokes: People often try to obtain a lower range by adding pump strokes and correcting the reading for the new sample volume. The limitation is in the tube’s pre-layer, which is often designed to remove water vapor. The chemical in the tube is coated onto silica gel crystals. If the pre-layer is over-loaded then humidity enters the analyzer layer, and it can cause the chemical to separate from the silica gel crystals.  This potential exists in most tubes. Always consult the supplier before adding strokes beyond the limit given in the instruction sheet.

6) Mixing brands of tube and pump: This can cause the tube to operate at a different flow rate than it did when calibrated, and that will change the stain length and the accuracy. Some mixes also leak, and bias the sample low when part of the sample misses the tube.

7) A leaking pump: The tube fits into the pump by means of a tapered rubber inlet. When it wears out the pump can leak. Similarly the piston gasket can wear (in piston pumps) and the sealing gaskets can wear in bellows pumps. All brands specify a quick field leak check, and it should be done daily.

8) Using ampoule tubes without first breaking the ampoules: Some specialty tubes include a glass ampoule with liquid inside that is required to activate the tube. If the glass ampoule is not broken and the liquid not distributed, those types of tubes won’t respond properly.

9) Worn out return springs in a bellows pump: This will cause the flow rate to slow down, which affects stain length and accuracy.

10) Partial strokes: If a bellows pump is not squeezed completely flat with each stroke, the air sample will be smaller than intended, and the tube will read low.

11) Incorrectly assembled dual tubes: Some tubes require two tubes to be connected in series to work. In these cases both sections must be used, and the tubes must be assembled in the correct order. Otherwise they do not respond correctly.

RAECO LIC LLC has a full line of Sensidyne pumps and tubes available.

RAECO LIC LLC is the authorized Sensidyne representative  in the Midwest United States


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