Pump problem

Basic questions from students; resources for projects and reports.

8 posts Page 1 of 1
Hello,
I have a problem in the pump of hplc agilant 1100 series pump. I had a sudden increase in the pressure then pump stopped while sequence running. The method was 60 water to 40 ACN.
I realized that another student in my group has provided water (not fresh and setting for a long time in bottles) as mobile phase by mistake.
Since then we cleaned the system and pressure was fine as MeOH or ACN is running but when we inject water, we got rise in the pressure again (high pressure) especially if the water percentage exceeds 50%. We have changed this channel for water and the problem still exists.
I am seeking your help to fix this problem
Than you so much in advance
Regards
It is perfectly normal for mixtures of water and polar organic solvents like MeOH or ACN to generate a higher back pressure. The viscosity of those mixtures can be higher than the viscosity of either of the pure solvents; they are very much non-ideal mixtures in that respect.

The question is "is the pressure with a given mixture/column/flow now higher than it was before the incident?". If it is, then there is a blockage somewhere in the system. If "stale" water was used, there is fair chance that it had some microbial contamination, so the places to look would be wherever there is a frit or filter in the system:
- column inlet: try back-flushing the column (check with the manufacturer to make sure it's OK; most columns can be back-flushed without problems, but there *are* exceptions)
- any in-line filters: change the filter elements

It's unlikely to be a valve or transfer line; blockages in those places generally result in "total" loss of flow.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Thank you so much for your reply. I did back flush the column and still the problem there. I removed the column and collected the waste right from the pump and still have the noticeable high pressure. What would have been damaged in the pump? I would be grateful if you could guide me through that.
Regards
It has to be somewhere between the pump head and the outlet. Most likely suspects are the outlet check valve "seive" or the frit in the purge valve.
Agililent has a nice set of service videos:
https://www.chem.agilent.com/cag/cabu/lcvideoindex.asp
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374
Thank you so much, I will change the valve and inlet valve cartridge then the seals if it appears damaged after pump head examination. I will keep you posted.
Your help is well appreciated
Regards
tom jupille wrote:
It has to be somewhere between the pump head and the outlet. Most likely suspects are the outlet check valve "seive" or the frit in the purge valve.
Agililent has a nice set of service videos:
https://www.chem.agilent.com/cag/cabu/lcvideoindex.asp


Exactly. I doubt that there was any damage.

Typically, work your way backward until you find where there is no pressure blockage.

With an aqueous phase, pumping at 5ml/min through the purge outlet, pressure should be well under 10 bar, typically under 2 bar. Replace that purge frit as pressure approaches 10 psi. And like Tom posted, if the inlet frit in the bottle is clogged, cannot suck fluid.
Tom's right in his suggestions (as always).
I definitely wouldn't start with pump-seals and check valves. Changing to 100% water should not have caused any harm to any part of the instrument. If the water was elderly and had some microbial growth then it could start to block the little filter in the purge valve, but if it's bad enough to do this in a matter of an hour or two, then you would also see a lot of greeny-yellowy mess on the inlet filter in the bottle itself.
Partial increases in back-pressure aren't typical of check-valve or pump-seal problems. Outlet check-valves, if they get stuck closed, cause total loss of flow and infinite back-pressure, not a gradual rise with changing gradient conditions (with the exception that some designs get stuck more often in 100% ACN than other solvent compositions). Inlet check-valves, if stuck shut, mean that at best the pump is sucking a vacuum and re-filling it, which tends to look like low rather than high pressure. Pump seal problems never cause increased pressure (in my experience, so far); they cause puddles, wandering retention times, and ultimately missing peaks.

What I have noticed is that often we tend not to remember what our system looks like, until it goes wrong - sometimes quite a small mistake just tips it over the edge, when in fact it's been going wrong for a long while - or a minor change exposes an existing problem. I suspect that running slightly dirty water for an hour or two was the straw that broke the camel's back, but the camel was probably already close to breaking-point.
Just hold the stepani you will get the same.
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