hplcnewuser1 wrote:
thanks everyone. I am able to narrow it down now. I Turned off the system and when I unscrewed the thin plastic tube, from multichanel mixing valve into the pump, I saw mobile phase flow coming through.
That means you have fluid flowing down to the pump. That is good.
Now the problem can be at the Active Inlet valve on the bottom of the pump, the pump seals, or the outlet check valve screwed into the top of the pump.
Attach the thin line to the pump, and remove the waste line coming from the purge valve, turn on the pump at 1ml/min, open the purge valve and use something to pull a suction on the little outlet stem on the purge valve. If you can pull flow through there, then nothing is clogged and the Active inlet valve is opening. If you can't pull any liquid through then possibly the Active Inlet Valve solenoid is not opening or the valve is clogged.
If you can pull liquid through there, attach a column and close the valve slowly. If pressure builds up then it just needed priming. If pressure does not build up then the active inlet valve is not closing. If pressure build but falls again with the rhythm of the pump, then the outlet check valve is not closing and allowing the pressure to flow back into the pump head as the piston returns.