Pressure fluctuations
Posted: Sat Oct 07, 2017 12:29 pm
We are entering an Agilent 1100 HPLC into service. All new capillaries have been used through the system. The vacuum degasser had the vacuum tubes replaced. The pump was rebuilt with new seals in the pistons, inlet, outlet, and purge valves. The auto sampler analytical head assembly and injection valve assembly were also rebuilt. The system passes pressure tests. Despite these efforts, there are still pressure fluctuations to be seen. Most difficult is that these pressure fluctuations are not constant. There are periods where the pressure runs stable (~+/-1%) but then vary by 50%. The analysis is to be isocratic with 85% Acetonitrile and 15% Water so changes in composition are not responsible. The auto sampler was bypassed and the same fluctuations can be seen. This is a quaternary pump system and purging each leg for over 20 minutes each does not have a consistent impact.
The most significant impact to the stability of the system was replacing the vacuum tubes which makes this component an area of interest. According to the documentation the pump impedance is to be in the KOhm range which it is, 33 KOhm was measured. The operating voltage of the pump is 24V without any tolerance, but the voltage measured by the controller is only 22.4V. Not wanting to drop hundreds of dollars on a new controller, we are looking for some advice form this forum. Any help is appreciated.
The most significant impact to the stability of the system was replacing the vacuum tubes which makes this component an area of interest. According to the documentation the pump impedance is to be in the KOhm range which it is, 33 KOhm was measured. The operating voltage of the pump is 24V without any tolerance, but the voltage measured by the controller is only 22.4V. Not wanting to drop hundreds of dollars on a new controller, we are looking for some advice form this forum. Any help is appreciated.