Chromatography Forum

Hi guys,

I'm having a strange issue with the gradient proportioning valve (GPV) in a Waters 2695. Basically, when the valve is set to open it doesn't allow solvent to flow (e.g. to perform a dry prime). The problem occurs for all four solvent channeld.

I have checked the flow path both before and after the GPV without discovering any problems. In fact, if the solvent stream is connected directly from the degasser to the pump (bypassing the GPV) the system runs completely fine, so there can be no issue with e.g. the check valves or any blockages.

So I thought I'd narrowed the problem down to the valve, and sourced a replacement one. However, now that I've replaced the valve the problem remains exactly the same. I guess there is some problem with the circuit board that controls the GPV maybe?

Does anyone have any suggestions as to what the problem might be, or how I can further diagnose it?

Thanks very much,

Pete

Can you hear the solenoids opening and closing if you set it for 25% of each solvent at a reasonable flow rate or during a wet prime?

If so and you have no flow, check the line going from the center of the GPV to the right-hand check valve holder. It may be clogged or the flat ferrule on the GPV end may be fouled up.

Hi DR,

Thanks for your response.

All solvent lines are clear - currently we are running the system isocratically using the line you mention (the one normally going from GPV to 1st check valve) connected to the degasser. I have made sure solvent can pass through all 4 input lines to the GPV too, by pulling solvent through them manually with a syringe.

When I do a dry prime I can hear the solenoid when I switch to channel B, but weirdly not for any of the others. However, despite this I cannot get solvent to flow regardless of which channel is set to open (including B).

Cheers

It seems ,the voltage feeding the valve is absent ,or very low.

You may check the voltage and the fuses .

Hi Uzman,

I checked the fuses, which were fine, but looked a little closer at the PCB and have found some water damage which looks like it could be the culprit:



I've brought it to our electronics workshop so hopefully they can replace the corroded components...

Fingers crossed we can fix it, but at least now we've got an idea where the problem originates.

PS if anyone has the circuit diagram for a 2695 solvent management PCB it'd be extremely useful!