Chromatography Forum

Yesterday I was doing some preventative maintenance on an Agilent 1100 system. I replaced the frit in the purge valve and the pump seals as per usual. When I started up the instrument again, I was getting abnormally high pressure that would fluctuate between 100-120 bar when running through a union. I disassembled the pump several times thinking that maybe there was a leak some where or perhaps something was being blocked but that didn't help. From here, I decided to disconnect lines one at a time starting from the union moving backwards to the pump and may have isolated the problem to the injection valve. I replaced the isolation seal, rotor seal, and stator head but none of that seemed to be causing my issue. At this point, I'm completely lost. Please help and thanks in advance

I decided to disconnect lines one at a time starting from the union moving backwards to the pump and may have isolated the problem to the injection valve. I replaced the isolation seal, rotor seal, and stator head but none of that seemed to be causing my issue. At this point, I'm completely lost. Please help and thanks in advance

If you have very little backpressure entering the ALS valve, but high pressure when all connected, then you HAVE isolated it to the ALS valve.

So you need to dig in deeper, like see if there's high backpressure when the inlet line is connected to the freestanding stainless steel stator cover, etc. The solvent path goes through the cover, the seal, the tiny channels in the vespel seal, then out. If there's backpressure then something is blocked.

You could use maintenance positions to set to "bypass" and see if pressure is still high or drops.

I took off the stator cover and let it flow through there and pressure was fine so its definitely something deeper. None of the seals seem to be out of place and they're all brand new. Assuming I did the same bypass you're talking about, the pressure remained high but the ripple increased significantly. What could be causing that?

It seems the needle and/or needle seat tubing blocked.

Would the needle seat tubing have an effect on the pressure even if I'm not injecting anything?

Edit: Quick update. When I moved the needle out of the seat the pressure did drop significantly, but it goes back up once the needle moves back. It also seems like the problem is moving down the instrument. Now I'm having pressure issues around the flow cell. Could there just be something clogging the tubing that is slowly being pushed out?

Hello

Please do as below:
1.disconnect capillary between purge valve and autosampler valve - if pressure is low (for flow 1ml/min) there is no blockage in pump
2.connect capillary to autosampler valve and disconect capillary between needle seat and autosampler valve (port 5 as I remember). Set flow to 1ml/min - in mainpass position you should see your solvent flowing from needle seat capillary - if pressure is high you have blockage in needle/needle seat. Switch valve to bypass position and now your solvent is going from port 1 (from pump) to port 6 (to the column compartment). If you have blockage in needle/needle seat you will observe pressure drops to normal range. That confirms blockage.
Then replace needle/needle seat or remove needle seat and sonicate it for 10 min in hot water (optionally connect needle seat to purge valve and try to backflush it).

I hope it helps

Regards

Tomasz Kubowicz

Yesterday I was doing some preventative maintenance on an Agilent 1100 system. I replaced the frit in the purge valve and the pump seals as per usual. When I started up the instrument again, I was getting abnormally high pressure that would fluctuate between 100-120 bar when running through a union. I disassembled the pump several times thinking that maybe there was a leak some where or perhaps something was being blocked but that didn't help. From here, I decided to disconnect lines one at a time starting from the union moving backwards to the pump and may have isolated the problem to the injection valve. I replaced the isolation seal, rotor seal, and stator head but none of that seemed to be causing my issue. At this point, I'm completely lost. Please help and thanks in advance

As others have said, the needle and/or the needle seat are blocked. You can make large volume injections such as 50 to 80 uL with hot water in a sample vial. Also IPA injections might help to dissolve any solids/crystals. Anyway, in future, always start troubleshooting from the detector to the pump rather than pump to detector. Remove one tubing connection at a time and note the pressure change.