Pressure changes when injecting

[KarenJ]

We are seeing quite a bit of pressure fluctuation after each injection on our HPLC. For the first several minutes after each injection the pressure fluctuates about +- 10 bar and then it stabilizes. As we were troubleshooting and rinsing the instrument we noticed that the pressure increases about 100 bar if we change the injector valve from the inject position to the load position. This does not occur on our other instrument of the same brand.

Can anyone tell me what would be a normal fluctuation in pressure as the injector valve is changed? Does any one have any ideas on how to fix this? We've tried doing sample loop and buffer loop rinses with water and whole system rinses with IPA.

Thanks very much for any suggestions.

[tom jupille]

A *100 bar* pressure difference between the load and inject!??? Something is plugged somewhere. The most likely location is in the loop (or connections to the loop).

Also, Many (if not most) injection valves today use either "make before break" plumbing or a pressure bypass. Since you are seeing this on only one instrument (I'm assuming they all use the same model valve), there might be a blockage in that part of the plumbing.

If this were my problem, I'd start by changing the loop. If that doesn't help, replace the valve with a service spare (or, if you don't have a spare, swap with the injection valve from another system; if the problem follows the valve, then it will have to be replaced in any case).