Model2000
Serie
s
DewPrime
Dew
Point
Hygrometers
-----------Installatio
n
Procedures-----------
2.13.3 Flow Gauges
(with
valves
)
Stainless
Steel and
Brooks Sho-Rate
"50"
No
.
Glass 1350-V,
or
-
equivalent
.
Glass,
range
0.2-4.5 SCFH
Brass and Lucite
Brooks-:Mite
No
.
2001V,
0.1-4.5 SCFH
2.13.4 Sample Tubing and Recommended
Fittings
Stainless Steel
,
1/4 in. Flare
or
Swagelok
Teflon(orKel-F) 1/4 in. Swagelok
StabilizedPolyproplylc:ne, Swagelok
1/4
in.
2.14 PRESSURE MEASUREMENTS
The
dew point
temperature
of a gas is a
measure
of
the
absolute
moisture
content of
the
gas, at
a
given
pressure,
regardles
s
of the
temperature
of thegas.Most conversion
tables for
dew
point (or frost point),to parts-per-million,
grains-per-pound
,
etc.
,
are
made
at
atmospheric
pressure
(14
.
7
psia or 1.03
.kglcm
2
;
therefore,
i
f
accurate
absolute
moisture
content
measurements
are to be
converted
to
atmosphc:ric-pressure-reference
d
values,thepressure
must
be
known.
If
dew
points are to be
measured
at
sample
operating
pressure
s
other
than
atmospheric
,
the
hygrometer
Sensor
should be fitted with
an
appropriate
pressure
gauge
.
(A
dew
point pressure
conversion
chart
is
shown in
the
appendix, BasicHmnidity Definitions.)
2.15 CLEANING THE SAMPLING SYSTEM
Most types of metal tubing
contain
oil
deposits
on
the
interior
walls
due to
the
manu&cturing
process.
This
residue
must
be
removed
before
puttingthe
lines
into
service
in
a
gas
sampling
system.
Trichloroethylene
or
similar
degreasing
solvent
ca
n
be
used
to
clea
n
individual
line
s
an
d components
before
assembly,
with a
final
flushin
g
after
assembly.The
lines
shouldbe purged
dry
with air
or
nitroge
n
before
beingplaced into
service.
In
additio
n to
the
initial
installation,
the
process
itself
may
constintte
a
source
of
coummination,
and,in many
applications,these are
volatile
hydrocarbons
.
An
excel-
lent
fluid
for pmging
and
cleaniDg
the
instrument
8nd!or
the
sample
linesisFreon114.This
is
a
suitable
solvent
since it is
capable
ofholdiug
many
hydrocarbonsin
solution
,
anditis
highly
volatile,nontoxic,nonexplo-
sive,readily
available
,
andwillnot
attack
comi:non
sampling
material
s
.
2.16 SAMPLE FLOW
RATE
When
setting
sample
flo
w
rates at other than
1
atmo-
sphere
(1.03
kglcm
2
or
14.7
psia
),
or
when
gase
s
other
thanair are
ilivolv
us
e
Figures
2-3 and 2-4 to convert
the indicated
sample
flo
w ratereading to
the
actual
flow
rate.
Figure
2-3
gives
the
actua
l
flow
rate of air at pressures
othe
r
than
1
atmosphete
(14.7
psia
)
.
For example,the
actual
flo
w rate of air at 30
psia
is 3.3
SCFH whe
n
the
sample
flo
w rate
reading
is
2
.
3
SCFH.
Figure
2-4
gives
the
actua
l
flo
w rate
of
six different
gases
.
The
actual
flo
w rate of
helium,
for
example
,
when
the
sample
flo
w rate
indicates
1.2
SCFH
is 3.3
SCFH
(
at
1
atmosphere).
When
gas
pressures
other
than
1
atmo-
sphere
are
used
,
use
Figure
2·3to
convert
the
"actual"
flow rate reading
obtained
from
Figure 2-4
to the
true
flow
rate
.
Using
30
psia,
rather
than1
atmosphere
in
the
helimn
gas
example
above,
apply the
3.3
scm
"actual"
flo
w
rate
obtained
from
Figure
2-3 as the Flow
Gauge
Reading
on
Figure
2-4,
andread
4.8
SCFH
as the
actual
flow rate of
helium
at 30 psia.
2-6
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