Problem with pump pulsations during low pressure mixing

[Margot-1]

I have an Agilent 1100 quaternary pump which has 9-10 bar pressure fluctuations when mixing organic and aqueous on all channels (works fine if mixing aqueous/aqueous or organic/organic). When pumping isocratic the pressure fluctuations are normal (0.5-1 bar) and flow rate is fine. I have replaced the gradient mixing valve and inlet check valve. Any ideas what may be the problem?

[richiekichi]

I've had a similar problem. A thorough clean of the piston housing, replacement piston seals, AIV cartridge, gold seals and caps on the purge valve and outlet ball valve, re-grease the pistons and the problem resolved itself.

[LCbob]

Hi
Do you have a degasser attached?

[Gerhard Kratz]

I'm sure it is a degassing problem. If you have a degasser in use please check if there is a leakage. If no degasser is available please do ultrasonic the solvents before use, flush the solvent bottles with nitrogen or Argon. 9-10 bar fluctuation is too much. Flush your system, without the column, with acetonitrile to purge all airbubbles out. Check flowrate of all solvent valves to be sure that even at low flow rates the flow is constant and correct.
Good luck.
Do you operate at elevated temperatures?

[Consumer Products Guy]

Do you purge ALL FOUR channels daily, even if only two are used? I would, like 5 minutes each channel at 100%, and five minutes each.

[J-FLu]

Follow-up question for Consumer Products Guy:
What is the reason/background for purging the channels not in use every day?

I mean, if your mixing compartment doesn't work right, there could be problems if the unused channels would be filled with air or an inappropiate solvent for the analysis performed.

But what's the point of flushing it daily? That's new to me, so I'm just curious. Can you tell a little more about that?

Best regards
J-FLu

[Consumer Products Guy]

We were told by Hewlett-Packard/Agilent back about 25 years ago with the 1050, before computerization, when we did manual purge (and before their automated purge valves) by unscrewing the line from the head of the column. The setting "PURGE ALL" actually only purged the channels that were set up, like only the "A" and the "B".

Basically some solvent could evaporate in the MCGV (mixing valve) and cause it to operate improperly.

So if you are not currently doing this, I would strongly say to do this. Should I type that in CAPITALS ???

Typical purge for us is 5ml/min, each channel separately, for at least a few minutes. And remember when changing the solvent type, you must clear the old type of solvent out of the dead volume of the vacuum degasser (which could be up to 40 ml per channel in the old 1050 units, and is much less with more-modern units).