Chromatography Forum

Hi All, i wonder if you can shed some light on my problem

I used an agilent 1100 system. I have noticed that when i purge my lines/ or even just have everything switched off. The pressure is still saying 8 bar. I have no idea where this back pressure is coming from. I have replaced the frit and gold seal on the purge valve. Flushed the lines through with IPA thouroughly. But can not work out where this blockage is (although as it says 8 bar with everything switched off, perhaps this is more of an electrical fault? im hoping it isnt as there is no way as far as i am aware of recalibration it.

Other things i have noticed which may be relevant. When i close the purge valve, i run line A (water) and line B (ACN) at 0.6ml/min. I notice that the flow rate is fluctuating at times obviously causing the pressure to fluctuate..

I tried running the leak/pressure test but always get failed at the end.

Hope you guys can help me.

Regards
James

Hi

First off yes it sounds like a pressure problem with a constant signal of 8bar. I wouldn't worry about it, just monitor it to make sure it is not steadily rising over a short period of time.; If so you will need a new pressure damper ( the solid state sensor is on the back ).

Your other problem sounds like a check valve failure, run the leak test again and either report to us which plateau is failing or check the manual.

Hope this helps

ıt sounds like a check valve problem. maybe you wıll change active inlet valve catridge, active inlet valve or outlet valve also damper can failed.
on the other hand you run a leak test ( in location of blank nut; on pump, autosampler and coloumn compartment.) check the results of three location.
I think the problem reason is check valve.

with the 8 bars pressure, maybe the pressure check is in offset and you need to reset it
with a check valve problem and a failing pressure test you cannot have a left over 8 bars pressure left over in the system
and yes the other problem sounds like a check valve problem which is more serious i think then the 8 bars left over

Hi

1.If yu see continuous pressure of 8 bar then is the pressure sensor problem, please remove capillary from teh purge valve and try purging so that you can isolate the block from other modules, still if you see then u need to change the Dampner(Pressure sensor)

2.Pressure fluctuation mainly comes because of bubble from Degasser coming in to pump or the Check valves(Either Acive inlet valve cartridge or the Out let ball valve)Try sonicate temin organic solvent and fix them back All the best

A few comments to address your two questions:

The observed system back-pressure reading of "8 bars" with no flow and the Prime Purge Valve open is most likely not a problem at all. If you have a fresh clean PTFE frit installed and the valve has been thoroughly cleaned, then what you are witnessing is normal age related offset of the pressure transducer. You will just have to make note that your new 'zero' is 8 bars for this system. Unfortunately, Agilent did NOT provide a simple means to adjust the transducer back to zero. Any adjustments made to the sensor may through off the entire calibration range so best leave it alone. If it bothers you, another option is to purchase a new or used pressure dampener (w/ transducer), then install it. This may restore the zero back to zero again.

Fluctuating "flow" rate: Several possible causes, but we really need more info.

The back-pressure you are operating at may be too low to prevent cavitation or check valve operation (normal operation of an HPLC pump usually requires at least 40-bars of back pressure. This will depend on the pump type, mobile phase, flow rate and tubing dimensions).

Your PTFE frit may be clogged (replace every MONTH with a new one!).

Your mobile phase pickup filters may be clogged (replace with new ones).

You may have a worn out and leaking MCGV. Flush the valve with pure IPA, all channels, one-by-one.

Not properly degassing your mobile phase. Make sure you are using a clean, fully serviced HPLC vacuum degasser module to degas solution on ALL channels. Poor quality degassing will result in poor quality flow rates and many pump issues. *We see many clients using broken vacuum degasser modules for years without realizing that the degasser module is not only NOT degassing their mobile phase, but also contaminating the entire flow path of their HPLC system!

"Diagnosing & Troubleshooting HPLC Pressure Fluctuation Problems (Unstable Baseline) "; https://hplctips.blogspot.com/2014/01/d ... -hplc.html