Hi, I've got an Agilent 1200 Binary Pump that sprung a leak last night from the outlet valve on top of one of the pumps. After tightening down on the connections (that didn't fix leak), and then removing the outlet valve to sonicate it (also didn't work), I'm about to order a new outlet valve, but something a little weird just happened. I wanted to store the HPLC column that I had been using when the leak started, so I put 50:50 H2O/MeCN in the buffer reservoir for the pump which wasn't leaking and set the HPLC control to run 100% from the good pump. After a few minutes, I noticed that the outlet valve from the pump which was leaking WHICH I WASN'T USING was still leaking!!!??? So maybe my understanding of the internal plumbing of my HPLC system is a little simple-minded, but if the outlet valve on the pump that isn't being used is leaking, is it possible for the back pressure from the HPLC column is pushing solvent/buffer up through the plumbing for the pump that's not being used until the solvent encounters the non-functioning outlet valve and starts leaking thru?