Ok so no one wants to see the pressure on their HPLC higher than what it should be. In my experience the number one cause of high pressure is a clog in the autosampler. Followed by a clog in the purge valve frit, as the second highest cause of HPLC over pressure. Luckily, there’s an easy way to diagnose whether or not there’s a clog in the autosampler. This technique works on Agilent model HPLCs and Chemstation, not sure about other brands.
Turn the pump on, once you see the high pressure, right-click on the diagram of the autosampler. Select the switch valve to bypass option (see below). See if pressure drops immediately, if so change the needle and needle seat (or backflush).
Note: Older versions of chemstation will only have that option available in the diagnosis tab. I may make a tutorial on the process in the future.
What if the pressure is still high? Try removing the column from the flow path. If that doesn’t help, try removing the autosampler from the flow path. If that doesn’t work, try opening the purge valve. If opening the purge valve does not decrease the pressure, try replacing the purge valve frit.
Pro Tip: When installing a brand new column, make note of the pressure of the system. This is what your pressure baseline is, and will be a good reference in the future when you are not sure if your pressure is where it should be.