Chromatography Forum

We have a 5890 series II with a split/spitless capillary inlet. My understanding is that if I set the Purge Valve to OFF, there shouldn't be any flow coming out of the inlet vent. Instead there should be extra flow coming from the septum purge vent. That doesn't seem to be the case. All that happens when I switch the purge valve off is that the flow drops a tiny bit for an instant, then returns to where it was. When I turn it back on, the flow jumps for an instant, then back to where it was. (I'm not sure what the actual flow is, the meter I'm using is for air and reads 100 ml/min, but the carrier gas is helium). Injection port is around 8 psi usually and the flowrate is 20ml/min. But the same thing happens even when I fiddle with those settings.

I'm suspecting one of the flow restrictors / switches in the linked picture, but I'm not sure which one and I'm not even sure what they are all called - let alone if I can reorder one. Any suggestions?

My attempt at understanding how the plumbing works:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

Thanks!
Mike

I believe on those you always have a flow at the split vent no matter if the valve is on or off. The pressure regulator maintains the proper head pressure on the inlet, but excess carrier flows to the split vent either through the inlet and out the split line when open, or diverted and out the split vent when closed.

It is just how the regulator works since it is backpressure and not forepressure. A backpressure regulator is placed after the inlet, so when in splitless operation it is still "after" the inlet, just diverted at the "top"

gas >---->--- Inlet --->---> diverter-->--regulator in splitless mode

gas >--->--- inlet --->---> split vent --->---> regulator in split mode.