A self-acting pressure activated drain valve includes at least one inlet configured to receive a fluid. A drainage passage delivers the fluid to at least one outlet where the fluid is expelled. The self-acting pressure activated drain valve further includes a flexible diaphragm configured to operate in an open position and a closed position based on a pressure. The flexible diaphragm is normally biased in the open position such that fluid is delivered from the at least one inlet to the at least one outlet via the drainage passage. The pressure, however, initiates the closed position such that air is prevented from flowing through the drainage passage.