Chromatography Forum

Hi everyone.
It is annual PQ time for our 1100 system, and during preparation of the instrument I noticed that the quaternary pump cannot pump 2 mL/min at 100 bar. The flow rate and pressure are stable with a restriction capillary at about 50-60 bar with 1 mL/min flow. So 2 mL/min should give roughly 100-120 bar. I see that the pump *tries* to get to 2 mL/min but slows down and retries to go up again (this it what the flow rate indicator in Chromeleon software tells me). Going back to 1 mL/min, everything runs smooth again. 2 mL/min and even 5 or 8 mL/min is OK with upened purge valve. Any idea what could cause this?

Thanks in advance
Jörg

(Btw: The piston seals are new, channels were alle purged before, problem occurs with all four solvent lines)

Update: I narrowed the problem down a bit:

1.64 mL/min with UV detector => fine at 104 bar
1.64 mL/min without UV detector => fine at 84 bar
1.65 mL/min with UV => pump slows down
1.65 mL/min without UV => pump slows down, too

So what is the magic between 1.64 and 1.65 mL/min? The pressure is very unlikely to be the reason.

Hello

I'd recommend:
1.set pressure limit to 400bar (you run it only on 2 ml/min)
2.set "maximum flow gradient" to 100 ml/min (it is in auxiliary setting for pump)

If it won't help perhaps problem is with pump drive.

Regards

Tomasz Kubowicz

1. When was the PTFE purge frit last replaced?

2. What is the pressure when pumping out the waste line (purge valve "on") with an aqueous phase at 5.0 ml/min ? Should be under 10 bar, best if under 2 bar.

3. I assume that you've purged all channels, and maybe I'd try without the inlet frits to try to isolate the issue.

1.) Was replaced in November (Update: Replaced today)
2.) 2.6 bar at 5 mL/min (Update: 1.4 bar with fresh frit)
3.) To do (Update: No difference.)

Hi Jörg,
Happy new year to you and all here in the forum.

Maybe stupid idea - did you measured the flow at 2ml on the outlet using a graduated cylinder and your stop watch?

Good luck
Gerhard

Update:

The "magical limit" between 1.64 and 1.65 mL/min is the point where the MCGV changes the mixing mode (you can hear the opening frequency changes, try at home if you have such a pump). There seemed to be a particle disturbing this high flow rate mixing mode if there is back pressure (don't ask, this is beyound my understanding of what happens inside this device). After removing/reconnecting the tubings and flushing, the pump is up and running again.

Regards, Jörg