Primary pump issues

<p>We are relatively new to UPLC, and are not sure how to even classify this problem.  We had a full PM on our BSM in August 2012.  Things were working well until Nov 2012, at which time we had erratic pressures and when running a static decay test primary pump B seemed to be the problem.  We were told by a Waters tech to change the plunger and seals, which we did, and things went well for awhile.  Last week we noticed that retention times were shifting quite a lot, and in running the static decay test/dynamic leak test we can't get primary pump A or B to pass.  The message we get is unable to compress or unable to maintain pressure.  We have tried changing seals again (which seems excessive...should we have to change seals every 2 months?) and this has not helped, same results/messages when running the static decay/dynamic leak test.  We would appreciate any tips, suggestions, etc. as we are at a loss. </p>


  • This sounds similar to a problem I have been experiencing for a year or so.  In fact, I wrote in to this forum about it just after we had our PM in the fall.  What I did to solve the problem was to run the equipment at a high pressure (14000 psi) for a number of hours and then the pump would pass the decay tests.  It seems if the equipment is left idle with a low flow rate after the seals are changed that they don't seat correctly and it takes a high pressure for an extended period of time to get them to do so.  At least that was my experience.  Hope it works for you.

  • Thanks so much for responding.  A question to your reply, how exactly do you run the pump at 14000 psi for a number of hours?  Just by setting a high flow rate and going into waste? Again, we are fairly new to this and I realize my inexperience is showing

  • Choose a column that can handle those high pressures and then ramp up the flow rate gradually until you get to the desired pressure.  I left mine running like that overnight to get the seals to seat properly.  Yours may not take that long.  You might want to do it during the day and monitor it every few hours by doing the decay test.  You should see the numbers improve (even if the test fails) which will indicate that this is working.

    Good luck.

  • rune


    Normally 30 minutes at high pressure should be enough to seat the seals.

    best regards


  • Thanks for your replies.  We changed the plunger/seals on primary A, let it run at 14000 psi for ~30 min, and it is passing well.  We have also changed the plunger seals on primary B and let it run at 14000 psi, we have changed the plunger, seals, and check valve on accumulator B (because one dynamic leak test told us that we had excessive back leakage and was unable to complete accumulator test) , still can't get it to pass a dynamic leak test on the primary (message is unable to compress).  I am at a loss, I would appreciate any other suggestions you might have.  Thanks.

  • rune

    Hi Jennifer

    You say that you have changed the seals on the primary head on the B pump but have you tried changing the check valve ? Since the fault is that the primary head is unable to compress this could indicate that the check valve is not closing properly and is leaking back into the solvent bottle. Also have you tried tightening all fittings on the pump heads. Sometimes a microscopic leak from one of the fittings will cause the leak test to fail.

    best regards


  • lizh


    I think the Primry Inlet CV needs to be swapped - it seems that this is the leak site, I do not see that it was changed? Please let us know.



  • So we received and switched out the cv today, still no luck.  Primary B is still not able to pass the static decay test, and the message is still unable to compress.  Any other suggestions?

  • We are few days after full Acquity-TQD PM. We had similar problem with Primary-A (water solvent) pump to yours. It wasn't able to pass static decay test even after BSM PM (exchange of seals, plumbings, check-valves, mixer...).

    The solution is: exchange Primary pump head + seal-wash housing.

    The reason: corrosion of the pump head and seal-wash housing caused by formic acid.

    We were told, that the problem with Primary pumps occurs when formic or trifluoroacetic acid is routinely used as an addition to mobile phase. The reason is that Primary has to compress solvent in milliseconds to very high pressures and therefore mobile phase can squeeze between the seals (it's not my theory). It is advisable to set Seal wash time in method to 1 minute or shorter (0.5 min) to keep the pumps away from the acidic conditions.

  • Hi guys

    What zablociak has described is very true but on my experience this happens more ofter at the pump head that delivers the organic solvent if acidified with strong organic acids. Under high pressure organic acids are less soluble and so for come out of solution and accumulate at the pump head. When it occurs over long periods they can corrode stainsless steal by forming small channels around the piston chamber. As result when piston compreses, solvent  goes backwards and so for the static decay test fails at all time. If this happens you need to change the pump head module.

    If I can give you an advise that works perfectly well on my system and reduced the instrument down time and maintance cost is at the end of every analystical batch to purge both modules with MeOH/H2O 50/50 for about 4minutes and the problem is very much solved. I would also advice you guys when you dont use the UPLC take an old column and a bottle of MeOH/H2O 50/50 and keep both modules pumping by maintaining the presure to about 8000psi. If you want to reduce solvent waste just recycle solvent. This will keep you instrument functional with seals wet and when ever you will need it will be ready to run samples. Give it a try and if works drink a pint for me

  • Thanks for your helpful accomplish this, couldn't I just put A2 and B2 in a bottle of 50/50 H2O/MeOH and create an inlet method that will run this at the end of every analytical batch (we run A1/B1 for sample analysis).  If this works, I will definitely drink a pint for you!

  • I can confirm the problems with corrosion of the pump head, especially the primary B (we use 0.05% TFA in ACN). We also finally replaced the B pump heads but instead of stainless steel we use the titanium pump heads. These are a bit more expensive, but the pump is running now for a year without problems ... although I am not sure, it looks like titanium is more resistent to corrosion. I hope this may help you.

  • Hi Jennifer,

    This is exactly what I  did. If you can also figure out how to automate and purge the LC at the end of each analytical run with this solvent would help to keep your analytical column free of MeOH/H2O. It definetely worked for me the last 4years that I use routinely these tips.

    Titanium pump heads could be more resistant to corrosion but for sure has clear benefit in reducing ionic interaction between ionic species and stainles steel that are a big killer in a lot of chromatographic separations.

    Let me know if I can be more helpful

  • We have changed out the pumphead and all seems well.  I am wondering how often you all have to do this?  We are now running a 50/50 MeOH water flush at the end, and I hope we can move along without pump issues for awhile!  Thanks for all your help.