Re: HP 5890 II EPC Problem
Drew Spencer
You don't mention this, but have you leak checked everything?
Also, how erratic is erratic? More than 0.01 ml/min flow?
When I've experienced this in the past (flows that bounce around) and
found it mostly related to pressure leakage at the ferrules connecting
the column to the transfer line or inlet. We had the same symptoms as
the components expanded during the run causing things to seal up more
completely than when cold. The ferrule/nut at the ms transfer line has
proven to be the culprit for us in most cases. I've also seen leaks
either at the weldment shell (liner o-ring or septum) or the inlet
ferrule after repeated heating and cooling. We recently replaced the
standard xfer line nut with one of Restek's no-vent setups and have been
very pleased with how well it keeps things sealed not to mention the
convenience of being able to switch columns without having to fully vent.
There could be something flaky with the EPC controller card on the GC
but I'd look there last.
Good Luck,
Drew Spencer
Ray Siegener wrote:
} Hi all,
} I have a 5890 series II GC with EPC connected to a 5971 MS. A 30m
} RTX-5 column is installed. I am observing erratic EPC pressure
} readings at sttings below 10 PSI (I need 6.8 psi to get 1ml/min at 35C
} starting temp). When I turn the purge valve off, the pressure reaches
} 6.8 and holds steady. There also seems to be a temperature component
} to this in that the EPC will remain steady at < 100C but fluctuates
} over 100 C. I have already installed a new mass flow controller, new
} proportional valve, cleaned the split and septum purge lines, and
} swapped out the solenoid for one from a working instrument. Any
} additional suggestions will be appreciated.
} rs
}
grober
used graphitised vespel ferrules. This often recommended for GC/MS rather
than pure graphite ferrules. While I would recommend graphitised vespel at
the mass spec end of the column I found that pure graphite ferrules gave the
most reliable seal at the inlet end. Just use care when installing the
column and break off a short length ~3 cms after you have threaded the end
of the column thro the new ferrule- you should use a new ferrule every
install! good luck.
Ain
}
}Hi all,
}I have a 5890 series II GC with EPC connected to a 5971 MS. A 30m
}RTX-5 column is installed. I am observing erratic EPC pressure
}readings at sttings below 10 PSI (I need 6.8 psi to get 1ml/min at 35C
}starting temp). When I turn the purge valve off, the pressure reaches
}6.8 and holds steady. There also seems to be a temperature component
}to this in that the EPC will remain steady at < 100C but fluctuates
}over 100 C. I have already installed a new mass flow controller, new
}proportional valve, cleaned the split and septum purge lines, and
}swapped out the solenoid for one from a working instrument. Any
}additional suggestions will be appreciated.
}rs
Hi All
According to my handy Hewlett-Packard flow/pressure calculator
(FlowCalc2.07), a 30 m column with a carrier gas (He assumed) flow of 1
ml/min at 35 C and 6.8 psi head pressure and vacuum at outlet would have
an ID of 0.25mm. Is this correct?
A couple of clues: higher flow with purge valve on and >100 C both
cause instability problems.
EPC's have some limitations to complement their benefits. They can need
10-20 psi pressure differential to regulate properly . At 100 C you would
need 10-11 psi column head pressure to obtain 1ml/min carrier flow. This
means that you may need up to 30 psi to your EPC. Is your purge valve
flow reducing the available pressure to the EPC? Excessive purge flow or
massive leak or insufficient EPC pressure (is the EPC line plugged?) may
cause these problems.
Some EPC's also do not work at very low column head pressures (1-3 +
psi).
"When I turn the purge valve off, the pressure reaches 6.8 and holds
steady" Are you suggesting the pressure buildup is gradual?
Is this a new problem? Has the instrument ever worked in this
configuration?
Ain Raitsakas
Senior Analyst
Instrumentation Laboratory
Lakehead University
Thunder Bay, ON
Canada P7B 5E1
Ray Siegener
Ray Siegener <rsie...@metaenv.com> wrote in message news:<c9l0hd$5e4$1...@news-int2.gatech.edu>...
} Hi all,
} I have a 5890 series II GC with EPC connected to a 5971 MS. A 30m
} RTX-5 column is installed. I am observing erratic EPC pressure
} readings at sttings below 10 PSI (I need 6.8 psi to get 1ml/min at 35C
} starting temp). When I turn the purge valve off, the pressure reaches
} 6.8 and holds steady. There also seems to be a temperature component
} to this in that the EPC will remain steady at < 100C but fluctuates
} over 100 C. I have already installed a new mass flow controller, new
} proportional valve, cleaned the split and septum purge lines, and
} swapped out the solenoid for one from a working instrument. Any
} additional suggestions will be appreciated.
} rs
Apparently this problem was caused by a bad injection port; it may be
either due to bad seal between the injection port and the large column
reducing nut, or some sort of problem with the weldment on the
injection port itself. Anyway, after replacing every valve in the
inlet system, as well as swapping out an entire EPC assembly with that
from a different instrument, I decidied to replace the injection port.
As suggested by Andy Yakuboff (THanks Andy!) there must have been
some problem with the old shell as the pressure has behaved
appropriately since then, and we are back to running samples. It is
interesting to note that the instrument DID Pass a pressure test
(Twice!)with the old shell, which confounded the troubleshooting
prossess.
Thanks again to Andy and everyone else who responded.
rs