HPLC pump flow rate problems

[Margot-1]

I have an Agilent 1100 quaternary pump with a flow rate problem. The flow rate tests low ~0.7-0.8 mL/min when set at 1.0 mL/min. This was tested at the end of a column in a 10 mL grad cylinder after 10 minutes. The column pressure was ~220 bar and steadily rose to ~270 bar with 1:1 ACN:H2O mobile phase. Each of four channels (ABCD) tested the same. The pump has new check valve cartridges (inlet & outlet), a new purge valve filter and a new gradient mixing valve. I did not replace the active inlet valve that holds the inlet cartridge yet. The flow rate tests fine with a coil of peek tubing (without a column) at 1.0 mL/min at ~40 bar or at 5 mL/min at 170 bar. We had similar low flow rate results with a brand new column. Any ideas?

[WillyOne]

Perhaps, only perhaps, the problem is at piston seal level.
You say that without column flow seems OK, but under pressure the flow goes down.
Or the check valves that you changed aren't working properly or you have a loss of pressure at the piston seals.
but before that, it can be a good idea to look for leaks across the system.
I don't know what column you are using but 270 bar for a 1ml 50:50 ACN/water seems a lot.
I'm using a Prostar system from Varian, when I surpass 200 bar, I found leaks everywhere.

[Consumer Products Guy]

Margot - I'm assuming that there are no visible leaks because you would've found the leak already.

But what if the purge valve is leaking and that leakage is hidden because there is a waste tube on it? Pull off that waste tube and see if any droplets appear at the outlet as the unit is pumping, may have a bad purge valve with a "hidden" leak.

Ask me how I know this !!!

[Margot-1]

I forgot to mention that preventative maintenance was just performed and hence the piston seals are also new. The peak to peak pressure pulsation was typical at 0.5 bar.

I just ramped flow to 1 mL/min and pressure was ~240 bar with 3 micron particle size column. I pulled the wide bore tubing off of the prime purge valve exit line and it is leaking a bit. We replaced with a new purge valve and it is working. Seems there should be a replaceable seal inside the purge valve but I don't see one listed in manual.

Thanks Consumer Products Guy!

[sepscientologist]

There is a polypro/gold seal in the purge valve. It goes over the frit that you replaced.
Or, if it wasn't there then you know why it was leaking.

[Margot-1]

The gold seal was also new. It looks like there is another tiny seal in the body of the handle that is turned to open and close the purge valve. Since it was leaking out the waste port on the purge valve it seems that it is this small seal rather than the gold seal.

[LCbob]

Hi

Unfortunately you have cannot replace the little ball and seat inside the purge valve and thus have to replace the whole unit. The unit wears overtime but can fail early if ppl overtighten it, this can be very common.
When I run the leak and pressure test I always remove the tubing to the purge valve to make sure there is no leak there.

[Margot-1]

Thanks LCbob. Yes I've had a hard time convincing people that they do not need to overtighten the purge valve in the closed position. Good idea about pulling the purge waste line during pressure tests. The failure to include a pressure test as part of our preventative maintenance is a mistake I plan to fix.

[woolab]

Hello,
I have a pump pressure/flow rate problem with agilent 1100 binary pump. I found a similar post here and quite similar problem that with lower pressure (45 bar with 60%ACN/Water) than usual (83bar) and only 70% flow rate (0.7ml for 5 min with 0.2 ml/min setting). But without column it flows 100%. We have no visible leak anywhere.
So we changed outlet check value, active inlet cartridege, and pump seal - but still no success.
One thing we noticed is that with one pump pressure got lower 55 to 45, then the other pump also got lower to the same.
Any suggestion?
I would appreciate any help on this.

I have an Agilent 1100 quaternary pump with a flow rate problem. The flow rate tests low ~0.7-0.8 mL/min when set at 1.0 mL/min. This was tested at the end of a column in a 10 mL grad cylinder after 10 minutes. The column pressure was ~220 bar and steadily rose to ~270 bar with 1:1 ACN:H2O mobile phase. Each of four channels (ABCD) tested the same. The pump has new check valve cartridges (inlet & outlet), a new purge valve filter and a new gradient mixing valve. I did not replace the active inlet valve that holds the inlet cartridge yet. The flow rate tests fine with a coil of peek tubing (without a column) at 1.0 mL/min at ~40 bar or at 5 mL/min at 170 bar. We had similar low flow rate results with a brand new column. Any ideas?