When using the Acetonitrile (HPLC grade) (100% Pump B) for long time, there is pressure variation in Pump A & B.
Now I solving this problem by ultra sonication of Pumb B filter.
Is the variation in pressure due to pulsation? If so I would say you have an air bubble.
Can you paste a screenshot? I agree with David, but it could also be a leaky pump or seal. Did you check for any leak?
It could be the check valves.
Maybe you could try new ones to check if the problem is still there after replacement.
You could also remove the old ones from the pump and wash them in MeOH/H2O 50/50 (and sonicate).
Try to identify and isolate the conditions where you have these pressure variations.
If you sonicate the filter and the problem is resolved then you should also consider to filter AND degas your mobile phase (especially if you don't have an online degaser)
Do you use a Shimadzu HPLC? If it's the case, the reason is the gem ball in check valve will become sticky in pure acetonitrile. That's a design flaw present in Shimadzu HPLC of some old model (maybe also in some other brands). The resolution is to take apart the check valve and ultrasonicate it by MeOH/water. Or use a 90% acetonitrile instead of pure one.
I agree with Lin-Lin Chen that problem (if this is the problem in the present case) could happen with many other systems tough.
I link an interesting article about this issue
http://www.chromatographyonline.com/lcgc/article/articleDetail.jsp?id=524647&sk=&date=&pageID=3
I found the same problems described by Lin-Lin Chem. My solution was to pass isopropanol though the pump. To avoid problems with the column I open the purge.
The use of an inline HPLC vacuum degassing system will minimize this problem. A properly functioning degasser will remove most of the dissolved gas from your mobile phase before it goes into the pump heads. This will result in less cavitation, lower noise, better reproducibility and better signal quality. If you do not have access to an inline vacuum degasser, continuous sparging of your mobile phase bottles with ultra pure helium will also work very well.
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