INFICON HAPSITE ER Chemical Identification System - Manual (Page 547)

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HAPSITE ER Operating Manual
B.1.1.2 Diluting the Gas On Site
The comments above, concerning hardware, relate as well to the case of dilution
systems. Guidelines to verify acceptable performance of suitable dynamic gas
mixing/dilution systems are suggested in the Federal Register (vol. 59, No. 148,
Aug. 3, 1994 Proposed Rules, 40 CFR Part 51 Method 205),
Systems conforming to the Method 205 suggestions are available commercially
from Environics
3
(Series 2014 Computerized VOC Gas Dilution System) and
Alltech 4 (GB-2 Gas Blender).
The materials in the flow stream must be inert to the VOC compounds to be used,
and heat-traced to prevent condensation and accumulation of any VOC's in the
flow channels. A good gas mixing system minimizes future outlay in certified
cylinder gas standard mixes. This allows a lab to require only the cylinders at the
highest calibration concentration levels. Lower concentrations (by as much as a
factor of 1000) can be prepared by serial dilution (with VOC-free Nitrogen or air) of
these cylinder mixes to the desired calibration levels with the gas mixing system.
This is probably the most economic route for labs which must frequently do multi
concentration re-calibrations for known VOC mixtures.
B.1.2 Correct Delivery of the Mix to the Inlet of the HAPSITE
The HAPSITE is designed to draw in samples which are at atmospheric pressure.
Internal Standards gas is mixed with the sample in a ratio which is dependent on
the flow rate of the sample gas and the suction of the pump.
WARNING
Connecting the inlet of the Hand Control Unit to a sample
at a pressure above or below atmospheric will cause the
mixing ratio of the Internal Standards to be incorrect, so
the resultant calibration will be invalid.
There are two basic approaches to assuring that the calibration mix is at
atmospheric pressure: a free flow of gas or capture of the gas mixture in an inert
sample bag.
3.Environics: (203) 429-5040
4.Alltech: (800) 255-8324