Chromatography Forum

When my system's injector is on mainpass mode, there is a leak on the needle seat and the pressure fluctuates during the injection process and the run pressures are low. Peaks are broad and injection spike occurs at 6 minutes.

On bypass mode, the leak stops with normal run pressure and peak shape. When the instrument runs with ADVR checked, the problems are resolved. I just installed a new needle seat, and I am still seeing the problems. I looked at the rotor/stator and they appear to be intact and clean. The system was PM’d 5 months ago with a new rotor and stator. We are getting by with ADVR mode; however, I’m concerned that we will have problems with carryover in the long term.

Can someone offer a suggestion to fix the problem or further troubleshoot this?

Thanks,
Denise

Where exactly is the leak? Is it between the needle seat and needle? If so, replace both the needle and the seat (perhaps a damaged needle). If the leak is elsewhere please describe in more detail. For example, I have seen leaks at the SS union connecting the needle to the loop.

... and sometimes the screw clamp thing that holds the needle in place (it does up on a hexagonal bit at the top) comes loose. If so, it will never manage to hold the needle firmly in the needle seal.

We had a similar problem. Replacement of the seat didn't help, and neither did replacement of the needle. Apparently, needle and seat were a bit misaligned, and only after running the appropriate procedure through diagnostic software (I don't know about the details, but I can contact the repair person if needed) the leak ceased.

We had a similar problem. Replacement of the seat didn't help, and neither did replacement of the needle. Apparently, needle and seat were a bit misaligned, and only after running the appropriate procedure through diagnostic software (I don't know about the details, but I can contact the repair person if needed) the leak ceased.

Whenever the needle is changed it must be aligned with the seat. To do this, simply lower the needle in steps using the software (needle replacement in "maintenance" menu I believe) until it is just above the hole in the seat. Then carefully bend the needle so it will hit the center of the hole in the seat when fully lowered. Make sure to look at the alignment from several angles then finally lower it into to the seat to check the final alignment. It's easier than it sounds.