Dynamic Leak Test
I need some guidance from Waters or other experienced users. We had the PM done on our system on November 5, 2012. The BSM (and other components) passed all post-performance checks which for the Acquity UPLC BSM (not the I-class) is the static decay test. However, last Friday I stopped flow so that I could put a new column in the column manager and when I started the flow up again the pressure trace for the B pump primary did not look right. It looked like it would try to increase pressure and then fail. I primed a number of times and then did a static decay test but changed the accumulator pressure to 10000 psi as we are currently using the UPLC for size exclusion work that does not get even that high a maximum pressure. It failed that test for the primary. The message was that the primary had excessive leakage with a decay rate of 594 psi/min. I then reduced the accumulator pressure to 5000 psi and the static decay test passed. (The A pump passed at 10000 psi). Today, following the advice Liz Hodgdon gave in an earlier post, I used the dynamic leak test on the B pump. It passed at 6000 psi (leak rate was 4.5 nL/min) but failed at 10000 psi (leak rate was 500.9 nL/min). Thinking that the seals might not have been exercised enough (again as per Liz's excellent post) I ran it at close to 14000 psi for about an hour. I then repeated the Dynamic Leak Test at 10000 psi. Again it failed as the leak rate was 342.3 nL/min. I have two questions:1. Since my pressures will be considerably less than 5000 psi is it okay to continue to use the UPLC for Size Exclusion work?2. This is not the first time we have had the B pump fail the leak tests. The Waters service engineer has replaced check valves, plungers and seals and then replaced the entire pump head earlier this year. The B pump is used for the organic solvent (currently acetonitrile with .05% TFA and .05% FA). I am scrupulous about using filtered solvent and clean bottles. Can anyone suggest a reason why the B pump fails so frequently?