Method and apparatus for air flow regulation comprise a vertically oriented conduit, a sail assembly positioned in the conduit and moveable therewithin responsively to air flow through the conduit to regulate rate of air flow through the conduit and to stop air flow through the conduit upon air flow rate through the conduit exceeding a preselected value with a detector for sensing when the sail assembly has stopped air flow thought the conduit as a result of air flow rate exceeding said pre-selected value.