The Alfa Laval LKUV-2 Air-relief Valve is an air-relief valve with a free moving polypropylene ball, which is lighter than water. The polypropylene ball alternates between two seats depending on pressure conditions on the inlet.
When the pressure on the inlet increases, the ball is forced off the lower valve seat and moves to the upper seat, thereby closing the valve against the atmosphere. If air enters the system, the pressure is reduced, thereby moving the ball away from upper seat and venting excess air to the atmosphere. If there is no pressure or vacuum in the system, the ball alternates to lower position thereby closing the valve.