Dionex GP50 pressure issue

[Scott_A]

Hi, I’ve just been tasked with getting our IC up and running again after a while of standing. All seemed to be going well, but the pump pressure on the GP50 has steadily gotten worse. It began by fluctuating between 500 and 1500psi and after cleaning every part and checking the seals this has dropped to 0 to 500psi. The on unit diagnostic screen shows the p-points for left and right fluctuating between 20 and 25, but I have no idea if this is good or bad as the manual is annoyingly useless. Any help on getting the pressure stable would be great.

Thanks, Scott

[Alfred88]

Dear Scott:
Just my initial thoughts: First, purge the system of air bubbles. If that does not help, then you may need to replace the seals. Tight seals will help to maintain a steady, high pressure.
When running to check the system (PQ/PV), if the RT's are not consistent, you may need to replace the check valve(s).

[Scott_A]

Alfred

i have purged the system and i am pretty sure that is isnt due to air bubbles. Thought it might be due to the seals but didnt want to start replacing stuff before id checked everything else.

Thanks

[ljc]

After being sure that the eluent(s) are sparged or degassed, things that help with these pumps (basically PEEK clones of the classic Waters pumps) you should:

replace all the check valves because these are often mashed by folks who overtighten the housings when they leak, then they're wrecked...you may have to replace the housings too. After all these are plastic and will flow when they're torqued down too much.

replace the seals. They're cheap so just do it so you're at a baseline.

pressurize the reservoirs; these pumps do best when there is a slight positive pressure on the reservoir(s) feeding the proportioning valve.

When priming the pump, disconnect the injection valve and observe the stream coming out of the tubing: when it is working correctly the stream should be smooth and pulse-free.

Be patient, these pumps can be difficult to get working right but if you are the first one to use them in a long time, assume that the previous users were actually "abusers" and that you need to do a complete overhaul ! Good luck...when they're working as designed they are very good.

[John Guajardo]

If none of ljc's suggestions work, I would also recommend pulling the service tray out a little and observing the pistons to see if one may have decoupled from its magnet.

[Scott_A]

ok thanks for that ljc and John, ill give it a try and hope it gets it all running nicely.

[djaydearz]

Hi Scot, i am having exactly the same problem, did any of the above work?

[joelyue]

Hi,

i am facing the same problem too. Could it be caused by the eluent used? i am using a combination of NaOH and NaCO3 as my eluent and i find that a white substance slowly leaks out of the pump even after i change the seals. Suspect that it is NaOH crystals.

[djaydearz]

, i managed to solve my pressure issue, was just a matter of looking at each individual tubing, to find out where the problem lay, and found out that as it was coming out of the mixing chamber, air was getting in. Replaced seals and tightened check valves (Make sure the bottom 2 check valves have 2 holes facing in the direction of the flow and the 2 top ones have the single holes)