Chromatography Forum

I need some advice. My Agilent G1311A quaternary pump has some fluctuations in pressure....the pressure varies in an interval of 3-4bars uncontrolled. i tried changing the purge valve because it had some fittings that were overused but that didn't help.
For example, the pressure varies between 42-46bars (with more or less regularity) for a system were it's usually between 45-46bars.
Any ideas?
Thanks

I'm not really sure what it is called but the round circular stainless steel head just to the right of your gradient valve (MCGV) that has the tubing that runs from the outlet valve into it is some sort of pressure drum/pulse dampener. It is not a listed part in the manual and it has been a few years since I have had to replace one but changing it did solve my problem (which sounds exactly like what you are having). A call to Agilent will probably help you out. Another thing to check for is to make sure you do not have a bunch of air coming from your degasser into the pump but chances are you already have checked for this and don't.

Purge ALL four channels independently for 5 minutes each at 5 ml/min, routinely. Even if you only use two channels.

First of all, thanks for your replies.
I have already checked for air, purged the channels, flushed the whole system, stuff like that.
This is why i figured it must be one of the seals or something.
We have called Agilent, and they'll be comming this week. I'll have them look at it, and if you want i can post the results, so if in the future anyone has problems, i can help.
Regards,
Leni

Hopefully just the seals. Please let us know how it turns out.

Pressure fluctuations are typically caused on this unit by:

bad outlet valve
bad active inlet valve and/or cartridge
pump seals/pistons
improper purge
improper degassing
fluctuating/malfunctioning multi-channel gradient valve (even if running isocratic)

The last item can be bypassed, or all four leads put into one pre-mixed reservoir, lines purged, then check pump.

Pressure fluctuations are typically caused on this unit by:

bad outlet valve
bad active inlet valve and/or cartridge
pump seals/pistons
improper purge
improper degassing
fluctuating/malfunctioning multi-channel gradient valve (even if running isocratic)

The last item can be bypassed, or all four leads put into one pre-mixed reservoir, lines purged, then check pump.

Add to that the filter frits on the solvent lines. Especially problematic is any that sit in aqueous solutions. If algae grows on the frit it will have problems pulling solvent through and cause many problems that seem to come from nowhere(know this too well from personal experience). Also make sure no algae has managed to grow in the degasser, it can give you fits too, and very difficult to get rid of.

Pressure fluctuations are typically caused on this unit by:

bad outlet valve
bad active inlet valve and/or cartridge
pump seals/pistons
improper purge
improper degassing
fluctuating/malfunctioning multi-channel gradient valve (even if running isocratic)

The last item can be bypassed, or all four leads put into one pre-mixed reservoir, lines purged, then check pump.

Active inlet valve cartridge was bad...changed it...problem solved.Thanks for all the great advice guys, i really appreciate it.
Regards,
Leni