Servomex SERVOPRO k2001 User Manual

User Manual SERVOPRO PLASMA Trace N
2
Analyzer
APPENDIX 6
79
THE IMPORTANCE OF REGULATOR PURGING, (AN-01 )
Here are some quick calculations to help you understand why it is so important to have some techniques to
evacuate the air from pressure regulators when replacing calibration cylinders.
For example, let’s take a pure argon cylinder of size 44 (i.e. 6m
3
of gas). On this cylinder there is a double
stage pressure regulator with two pressure gauges, CGA connector, and an outlet isolation valve. Lets
assume that the internal volume of this pressure regulator is 100 CC (±10%). When installing this pressure
regulator on the cylinder, the internal volume is occupied by the atmospheric air i.e. 78.2% N
2
, 20.9% O
2
,
0.9% Ar, moisture, CO
2
, etc.
When the regulator is screwed in place on the pressure regulator, the air still is trapped inside the regulator.
If you open the valve on the cylinder to pressurize the regulator, and there is no or little flow through the
regulator, the air trap inside the regulator will diffuse inside the argon cylinder. The shock caused by the
quick pressure build up inside the regulator helps to speed up the diffusion process.
So, assume no flow (worst case), we have the following situation:
100 CC of air and atmospheric impurities added to 6 m
3
of pure argon (assuming perfect argon i.e. no
impurities at all). This leads to the following calculation:
100 x 10
-6
m
3
(i.e. 100 CC) of Air = 16.66 x 10
-6
6 m
3
argon
So the dilution ratio is 16.66 x 10
-6
and 16.66 x 10
-6
x 78.2% N
2
= 13 ppm of N
2
and
16.66 x 10
-6
x 20.8% O
2
= 3.5 ppm of O
2
So starting from a pure argon cylinder and just by a bad pressure regulator purging procedure, we’ve got an
argon cylinder with 13 ppm of N
2
and 3.5 ppm of O
2
. These impurities will be added to any other impurity
in the cylinder. This situation makes it difficult or even impossible to get accurate calibration In some
cases, we received phone calls from people claiming that the zero cylinder had higher readings than the span
cylinder….
So Be Aware !!!!!

Servomex SERVOPRO k2001 Specifications

General

Brand	Servomex
Model	SERVOPRO k2001
Category	Analytical Instruments
Language	English