INFICON HAPSITE Smart Plus Chemical Identification System - Manual (Page 574)

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HAPSITE Smart Plus Operating Manual
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.
B.1.2.1 Free Flow of Gas
The free flow of gas from the regulator of a pressure cylinder is reduced to
atmospheric pressure when the impedance to flow is small. This can be achieved
by placing a sampling tee at the point where the line becomes large in diameter.
The connection of the HAPSITE sample probe inlet should be at right angles to the
direction of gas flow with 1/8" stainless steel Swagelok fittings.
WARNING
The excess vent flow (overflow) from this sampling tee
(in the gas flow direction) should exit through stainless
steel fittings of at least 1/4" size and a short vent line to a
fume hood or other exhaust system.
The smaller "leg" of the sampling tee is coupled to the HAPSITE. The total flow to
the sampling tee should be approximately 1 liter/min. to allow sufficient excess over
the HAPSITE sampling flow rate which is approximately 200 cc/min. and to prevent
external air from being drawn back into the vent "leg" of the sampling tee which
would alter the concentrations delivered from the cylinder or mixer.
B.1.2.2 Inert Sample Bag
Ultra clean Tedlar sample bags, dedicated to a given VOC compound
mix/concentration level, will be the most economic option for regular calibration
(more than once a week) and eliminates the waste of certified gas mix out of the
sampling tee vent. The dedicated Tedlar bag can be filled directly from the
associated gas cylinder or gas mixing system effluent.
WARNING
Regulate the gas delivery to avoid overfilling the bag. The
bags are not designed to be pressurized.
Alternatively, a bag can be filled by delivery of a set volume of the diluent gas (via
a mass flow meter), then adding a set volume of the certified cylinder VOC gas mix,
followed by mixing to homogeneity in the bag to obtain the proper dilution. A 12-liter
Tedlar bag will allow about 60 HAPSITE samplings of the contents between refills.
The use of properly filled Tedlar bags inherently assures that the gaseous contents
are at atmospheric pressure for sampling. A properly filled Tedlar bag will have
plenty of flex left in the bag walls so that the bag can be easily kneaded to mix the