Chromatography Forum

I've been having pressure problems with our Waters hplc (pump = 616). This started a few weeks ago, and manifested as a complete pressure drop when one of the pump heads was moving out. Did the check valve tests, and the pump with the pressure drop failed. Replaced check valves. Now that pump head passes, but the other side fails. Ok, well these CVs haven't been replaced in ages. Replace those check valves. Now both sides pass check valve test.

This did not solve the pressure problems however. Replaced pump seals. Didn't solve the problem either.

Interestingly, each pump head independently seems to pump just fine and can sustain accurate flow rates, even through the system (but bypassing column). However, when both pump heads are connected to the outlet manifold, only one will pump (i.e. solvent flows out only when one piston is moving out).

I've checked and rechecked for loose/leaking inlet and outlet connections, and even taken apart the pressure transducer/outlet manifold. Solvents are degassed HPLC grade.

At this point I'm out of ideas. Any thoughts?

Thanks for any help.

Maybe an issue with the pressure transducer? I seem to have a vauge memory of something like this many years ago and that was the issue.