Dynamic Leak Test

<p>I need some guidance from Waters or other experienced users. </p><p></p><p>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). </p><p></p><p>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. </p><p></p><p>I have two questions:</p><p></p><p>1.  Since my pressures will be considerably less than 5000 psi is it okay to continue to use the UPLC for Size Exclusion work?</p><p>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?</p>