Abstract: For use at the apex of a pipe line adapted for air and water flow, there is a housing extending along a vertical axis and having an axial, bottom opening surrounded by a bottom valve seat and affording communication between the interior of the line and the interior of the housing. A similar axial, top opening surrounded by a top valve seat affords communication between the atmosphere and the interior of the housing. A first ball valve in the bottom portion of the housing can move onto and off of the bottom valve seat to control flow through the bottom opening. A second ball valve in the top portion of the housing can move onto and off of the top valve seat to control flow through the top opening. There are stops to limit the motion of the ball valves away from their respective valve seats. Also, there is a lever pivoted on the housing and extending into the pipe line for movement by liquid flow therein. The lever can dislodge the bottom ball valve from a position on the bottom valve seat.