Strange behaviour of Primary Pump

<p><span>Hi all,</span></p><p></p><p><span>currently, our UPLC-system is working quite well, but today I recognized a very strange behaviour of the Primary Pump A. </span></p><p></p><p><span>For details see the attached picture.</span></p><p></p><p><span>Anyone seen this problem before? What is it? What can I do?</span></p>


  • Hello:

    Our engineers indicate that your plot (thank you - highly doagnostic) is a leaking accumulator check valve, as it is so obviously periodic. Probably a defect on the ball. And will need to be replaced.


  • Hello again,

    I have replaced all check valves, and it took me quite a while until I passed the dynamic leak and static decay test...

    And now this:

    Nothing changed!

    Could this also be a reason for noisy baseline?

  • Hello,

    Now I have more questions, normally the decay test would display some test data and result following a pass or fail. If possible can you note the display message following the decay test. It would help us to understand what direction to take for troubleshooting. Additionally, what mobile phases are being used on the pump side that is failing?

    Thank you,


  • Hello,

    please find attached the failed and passed test results of the static decay test.

    Eluent A is H2O/ACN 8:2 (V/V), Eluent B is H2O/ACN 1:9 (V/V).

  • Sorry, I have to split this in two messages - too many pictures.

    I've ignored the "problem" and started my samples yesterday. They worked quite well.

    The flowrate is 1.0 mL/min now.

    The plot of the primary pump looks nice, until it is zoomed.

    For your information: The other plot was with a flowrate of 0.1 mL/min

  • Hello:

    Based on your latest data - the pressure trace you show here now is normal. We believe that the previous trace was most likely caused by the plunger seals not pressurized up yet, (that was my fault I should have asked that question, not our experts)!. The other thing that I missed was that the system pressure was only 25 PSI and at that pressure the accumulator check valves would not seal very well. Running the leak tests is one of the ways that we recommend that they "break-in" the seals. So I think that you are in good shape now. Do you have a formal protocol, which you use when changing the seals?

    Best regards,


  • Liz,

    thanks for your answer. That sounds nice to me!

    We have a formal protocol for the maintainance of the whole pump.

    All necessary parts are replaced and system tests have to be performed.

    One more word about check valves:

    We have changed the check valves on our system nearly a dozen times now, as they are blocking so often, whatever the reason might be.

    I think it is a good idea, to ultrasonicate and flush the valves with MeOH before the installation.

    Best regards

  • Hello Again:

    We are very concerned that your CV’s are failing so quickly. I would like to understand why. We decided that your issue last time was the accumulator – is this always the case? Usually, are the blocking CV's on the Primary CV (PCV), Accumulator CV (ACV), or Both?

    We critically clean our CV’s so sonication prior to installation is not a traditional approach; our mfg cleaning process is designed to make this unnecessary.

    Thank you


  • Hello Liz,

    the blocking of the CV's happens on both Primary and Accumulator and on both A and B pump. Accumulator happens more often.

    A Waters engineer told us, our acetonitrile would be the problem. But I don't think so. We buy the very best quality we can get. And be banned all salty buffers, as they seem to block the valves, too. We already considered to change the whole pump...

  • Hello:

    This is extremely unusual, I do think that we need to troubleshoot, it is also interesting that your detector is problematic, is there some root casue for the contamination?. Please contact me directly and we can get your local support personnel in contact with you asap. ([email protected])

    Best regards,


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