Hi! I am in need of the manual of instructions of a HPLC Pump Waters Model 590. It displays high pressure all the time and I want to know what is happening.
You should first try this: remove the hplc column and see if the flow is smooth and there is no pressure upto the point where it enters the column. Then connect the inlet and outlet ends with a tube and check again if the flow is smooth (there may be a small back pressure). If you see high pressure, then the line is blocked. You need to change the HPLC tubing. Please don't try to open the pump itself. It is very tricky to put it back even with the manual.
By "display high pressure all the time", does this include when the pump is stopped? If so, something is wring with the pump electronics.
Otherwise, there is most likely a clog someplace. Remove the column (which may be the cause of the high pressure) and replace with a union. You may track it by loosening fittings starting at the pump. After seeing the pressure drop, tighten the fitting and move to the next fitting until you no longer see a pressure drop. The clog is someplace between the fitting where the pressure fails to drop, and the last fitting that allowed a pressure drop when loosened.