Chromatography Forum

Hallo,
We have a fairly new (purchased 2008) Beckman System Gold (model 126) HPLC, on which we run (for the most part) 0.1M phosphate buffer (pH 6) on pump A and HPLC-grade MeOH pump B (all solvents pre-filtered). We have been changing the inlet + outlet check filters every 3-5 months, because of occasional high back-pressure during the method run; however, recently we noticed that the pump pressure would gradually increase at the end of the run to at least 200 bar (2.9 kPsi) and simultaneously flow from pump A would stop. So we tried introducing a water wash at the end of the method (which is when we would usually see this problem), and that seemed to help matters, but only in that it decreased the frequency with which this problem occurred. We changed out the high-pressure seal a couple of times as well, and after the last change we have noticed that our actual flow does not match the set flow-rate. We've been in touch with Beckman and they suggested we do a sequential high-pressure check to rule out the inlet and outlet check valve cartridges, but we still have not been able to find a cause or solution for our problem. ANY input at this point would be helpful!
Thanks.

You might want to tee in a separate pressure gauge immediately downstream from the pump. If that pressure matches what the pump is telling you, then there is some downstream blockage. If the pressure gauge reads a significantly lower pressure than what the pump is indicating, then you either have a blockage somewhere inside the pump, or else you have an electronic problem (transducer failure?).

I don't have any hands-on experience with that pump, but in general terms trace the plumbing backward and replace any in-line filters as well as the check valves (it's always good to have a spare set handy in any case!). If the problem persists, then its and electronic problem and probably not a user-serviceable issue.

I have worked on many brands and models of HPLC pumps over many years and find that replacing check valves that often is very strange. I would start by removing the column and check the flow rate without it, and the back pressure without it. It should be theoretically ZERO, but more likely to read something, but under a couple of hundred PSI.
If that is good, it's the column,or a column guard that's creating the back pressure. Worth trying at least.
Good luck,
\

Hallo,
We have a fairly new (purchased 2008) Beckman System Gold (model 126) HPLC, on which we run (for the most part) 0.1M phosphate buffer (pH 6) on pump A and HPLC-grade MeOH pump B (all solvents pre-filtered). We have been changing the inlet + outlet check filters every 3-5 months, because of occasional high back-pressure during the method run; however, recently we noticed that the pump pressure would gradually increase at the end of the run to at least 200 bar (2.9 kPsi) and simultaneously flow from pump A would stop. So we tried introducing a water wash at the end of the method (which is when we would usually see this problem), and that seemed to help matters, but only in that it decreased the frequency with which this problem occurred. We changed out the high-pressure seal a couple of times as well, and after the last change we have noticed that our actual flow does not match the set flow-rate. We've been in touch with Beckman and they suggested we do a sequential high-pressure check to rule out the inlet and outlet check valve cartridges, but we still have not been able to find a cause or solution for our problem. ANY input at this point would be helpful!
Thanks.

Hi all

This is Beckman tech support and both Tom and remesquaddie are right. Determination of pressure problems downstream from the pump is first and foremost the primary step in troubleshooting. Once the pressure problem is isolated to the pump, then fixing the problem can begin. The inline solvent filter or the inlet check valve are usually to blame for low pressure or flow rate problems (and occasionally that tubing going from the prime port to the inlet check valve). Always remove the inline solvent filter first and flush with HPLC grade water before each run (as you saw this helped out well). Phosphate buffer is notorious for precipitating out with high concentrations of organics or miscible organics (like MeOH) so its best to put a water pump wash into your shutdown method to avoid salt crystal buildup in the lines. This is what is causing the problem if the pump still shows high pressure once removed from the system. High salt can scratch the piston as well causing irreparable damage to the pump and you would need to replace the filter. Also check pressure and flow rate one pump at a time starting with Pump A. Call us if there is anything further