[
Chapter:
Topic:
INSTALLATION
Checking for
Gas
Leaks
J
Once
all
of the appropriate
gas
supply sources and lines have
been
properly
installed, along
with
all
other
GC
columns and connections, the entire system should
be
systematically
pressurized
aod checked for possible leaks. Begin by opening
all
of the compressed
gas
cylinder valves
and
setting exit pressures to the appropriate value for each cylinder regulator. Remember that cylinder
exit pressures should never exceed the required GC pressure settings
by
more
than
20 psi and 80
psi is the maximum pressure that the GC
can
safely haodle.
First check for leaks
in
the lines and connections between the compressed gas cylinder and
the
GC
flow control fluistors. With the system pressurized and the GC power
turned
off, close
eachof the compressed gas cylinder valves one ata time and closely watch the pressure indicator
on the cylinder regulator
to
see
if
pressure decreases.
If
the system is leak: free between these two
points.
the cylinder pessure indicator should not noticeably decrease for at least five minutes.
If
pressure
does
noticably decrease over
this
time
period,
then
it
indicates a significant leak
somewhere between the cylinder output
and
the
GC
fluistor. Any leak, especially with flammable
gases, must be immediately
located
and
repaired. The best way to check
specific connections
for
leaks
is
with a leak check solution
(see
section below on Using
Leak
Check Solution).
If
pressure
test indicates that the system
is
leak free from the cylinder to the
fluistor,
then
proceed
to check the
rest of the carrier
gas
system for leaks.
If
the system
does
have a leak, locate aod repair prior to
proceeding.
Next check for leaks between the fluistor and injection port. Begin by disconnecting the
column from the back sideof the injection port. Next insert some
type
of pressure blocking fitting
on the injection port where the column was attached. A standard Swagelok nut
with
an injection
septum in place of the ferrule
will
work quite well.
Tum
the
GC
power and gas supply back on.
Use the control panel
to
seewhat the
actual
carrier pressure value
is
and
write
itdown. Now
turn
off the carrier
gas
supply at the cylinder onceagain. Wait 5 minutes
and
then use theGCcontrol
panel to view the
actual
carrier pressure once again. H
this
value
has
decreased
in
the 5 minute
time frame and the previous test results were negative, it indicates that there
is
a significant leak
somewhere
in
the interal GC carrier
gas
lines between the fluistor and the injection port. Once
again
immediately
locale
and
repair any leaks using a leak check solution
as
described below.
After
all
of the leaks upstream from the column have
been
eliminated
and
confirmed by the
two
pressure tests described above, properly
attach
your column to the injection
port.
Use leak
check solution to check
all
of the fittings within the column oven for leaks
and
repair aoy that
you
find.
Following
all
the instructions above
will
assure the operator that thesystem is leak free. Any
time fittings arechanged or the GC
is
relocated, the system should
be
rechecked for leaks. Failure
to
properly repair leaks cancause safety risks aswellasoperational malfunctions.
A3
cc
medical
syringe
is
excellent
for
dispeming
leakchcck
solution.
An
eyedropper,
pipette
or
squeeze
boUle may
also
be
used.
Deposit
several
drops
where
" -
fillin8s.
Swagelok
bulkhead
fitting/'
Leak
Checking Solutioo
SRI recommends that a solution of 50% water aod 50% alcohol (methaool, ethanol, or
propanol) be
used
as
a leak check solution. The water-alcohol mixture leaves no residue which could
leak
through
the fittings and cause system contamination. Furthennore,
water,
when usedalone
and.
due to its high surface tension, tends
to
bead
rather thao flow into spaces between the tubing
and
the
connectors where leaks may occur. A leak
will
show
up
as a stream or
froth
of tiny bubbles.
Inspect
aoy leaking fitting for damaged threads
and
reversed, missing, or damaged ferru1es.
