Chromatography Forum

Hi all,

I have a system (Waters 2695) which keeps going over pressure when I go to inject a sample/Standard. The pressure is fine when the mobile phase is just going through the HPLC and the column. The engineer was out a couple of days ago to replace a seal pack on the injector and this is the first time we have used it since. The funny thing is it was working fine for about 20 injections before this problem occured.

The error message is accumulator over pressure. Anybody any idea what could be causing this before I contact the engineer again.

Thanks in advance

Is your sample precipitating in your mobile phase and plugging things?

We run this method all time and it doesnt give this problem.
I disconnected after the inline filter and carryout a test injection
just to see if it would inject and it did.

I'm not sure of the plumbing with a Waters system, but a lot of the 6 port injectors have a grooved disk that rotates to change flow direction during an injection. I have seen problems with these grooves getting clogged. If you have an injection loop it could be clogged. If you have a spare injector you might want to try swapping it out to see if the problem is fixed.
Good luck.

Would be worth while having an acid wash completed on the system, also do acid injections. Recommend at least 50 injections and then when the system is running Water you need to do water injections. Your getting a pressure build up in the system somewhere, by doing the acid wash it may fix the issue. Otherwise the seal pack and high pressure valves need to be rebuild/Replaced.

Accum over pressure is the fault, but a pressure rise is in the system is the issue. Try the above at least, acid wash can take a few hours but is highly recommended in this case.

Regards,
Bull76

Hi
Acid is a good idea, use 10% HNO3. I have also seen problem, when you use non preslide caps on your vials, the seal meterial from the cap vil go in to the injection-port. If acid cant fix it, you could try to reverse the flow through the injection valve, and might flush it out.

hi
the alliance (2695) has no six-port valve or similar, so there can't be the problem.
The injector/sample loop is built somehow different.

The error message you've gotten guides you where to look first.
Seems that there is something wrong/plugged just near (or even inside) the accumulator. Otherwise I would expect just a "normal" high pressure shutdown.

To compensate the compressability of the solvents, the accumulator's controller measures the force needed to pump against the system pressure, which is sensed just after the accum outlet and compares theses two values.

If I remember correctly we had such an event once (unfortunately I can't remember the cause, yet).

To bring the pump to work again, I guess you need to shutdown the system and open the purge valve before you power on again, so that the piston can move and initialize itself without any restriction.
If error still exists, it's likely that there is a problem with the accumulator drive itself.

Maybe try to rebuild the piston's head and seals and inspect the plunger. Maybe there is some particles in there (debries from whatever... eg. GPV, primary seals...?). Maybe also have a look at the inline filter.

Any update on this issue for us?

The Waters Engineer was called and the issue was resolved there was a problem with the seal pack he used to correct the leak.