Found Y-end QDP80 with "low N2 flow" alarm -> Investigation shows low pump shaft N2 flow due to near zero vapor pressure at LN2 dewar (pump shaft purge utilizes LN2 dewar boil-off which is nominally 10psi N2) -> "Economizer" valve (a.k.a. pressure relief valve) for this dewar has a history of sticking open and closed - see ilog entries from Jan. 2010 -> frost indicates economizer plumbing is flowing -> Turned adjuster screw 1 full turn cw -> will hold-off on continuing pumpdown of Y-end until normal shaft seal protection (flow) can be demonstrated.