German to English Tech/Engineering Mechanics / Mech Engineering

This is from the operating instructions for an Überströmventil intended to protect tanks and pipes from excessive pressure. The context sentence is "Beim Anlüften seitlich zum oder hinter dem Ventil stehen". A later sentence in the same text says "Nicht anlüftbar" which has already been translated as "not liftable" - that seems wrong to me. The inspection activities during commissioning include "Wenn vorhanden, Betätigung der Anlüftung". Another bit of context says "Fremdkörper durch kurzes Anlüften entfernen". Any ideas?