Agilent 1100 Quat pump unstable flow at 2 mL/min - 100 bar

[bunnahabhain]

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.

[kubowicz.tomasz]

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

[Consumer Products Guy]

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.

[bunnahabhain]

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.)

[Gerhard Kratz]

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

[bunnahabhain]

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