Agilent 1100 pump pressure and flow variable

[venuzz]

I got a problem with my old agilent 1100 quartenary pump, when I set the flow from 1 ml/min to 2 ml/min for isocratic running 80% ACN in water the pump pressure will fluctuate about 30 bar pressure. But when I set the flow form 2.25 ml/min to 2.75 ml/min the pump pressure and the flow will fluctuate. But when I set the flow to 3.0 ml/min anything will ok no more fluctuation. But the problem will occur again when I reduce the flow. When the pressure and flow fluctuate, the pump will have noise that unusual.
I have change the piston and seal, but it still dont worked. Could somebody help me to solve this problem? please.

[DR]

Replace the check valves.

[Consumer Products Guy]

I got a problem with my old agilent 1100 quartenary pump. I have change the piston and seal, but it still dont worked. Could somebody help me to solve this problem? please.

Did you purge ALL FOUR channels, even though you may only be using two? That's very important !!! I'm assuming all four of your solvents are degassed properly.

Did you run the Agilent flowtest, to see the pressure profile and see if it would pressure like at 390 bar? Did you change both pistons and seals?
One could swap out the active inlet valve cartridge and the ouleck check valve with new ONE AT A TIME, to see if one of those is at fault, but swap back to the previous way if that change did not help (the better, worse, or same theory).

[venuzz]

Thanks for your advice,
After 2 day trial, it seems that the problem is not at the active inlet valve catridge or the outlet check valve. but looks like the problem occur at the mixing chamber gradient valve for the line A. I try using the other line when the pressure and flow problem occur, and soon the problem got solved. but when i changed it back to line A the same problem exist again.
I have contact our agilent technical engineer, may be they would come to visit in this week and check it over again.

[ksharp]

If it is your MCGV, a replacement costs about $1500, but it only takes 15 minutes to remove and clean one of the valves. The MCGV removal is described in the pump manual (page 124 of Agilent document G1311-90003), but that's as far as Agilent will take you. I have written a short cleaning procedure based on my own experience: http://www.scribd.com/doc/50872871/Cleaning-the-MCGV. It is not official, not edited or vetted in any way, so don't hold me responsible if you kill your MCGV...but having said that, it seems to work just fine. And I just wrote it today - now THAT is a weird coincidence!