Abstract: A system is provided for controlling flow of air and preventing flow of liquid within vent lines connected to, for example, a pipe line or other like piping systems. The system has a first float in a first body and a second float in a second body. The first body has an open flanged top end, a flanged bottom end with an inlet therethrough and an interior wall defining an open interior. The second body also has an open flanged top end arranged to mate with said flanged bottom end of said first body, a bottom end, an interior wall defining an open interior and an inlet into the open interior. In an embodiment, the first body and the second body are identical in size, shape and configuration. A cover is arranged to engage the top end of the first body and it has an outlet formed therethrough. A first seat is secured at the outlet in the cover to define an outlet for the first body. A second seat is secured at the inlet of the first body to define an outlet for the second body.