The Air/Vacuum Valve automatically exhausts large volumes of air from the system while it is being filled with the slurry. When the contamination is being emptied, air displaces the fluid and re-enters the pipeline to equalize pressure. It prevents discharge of the medium to keep your work environment clean and safe. When the system is filled and operating, the fluid lifts the ball until it closes the orifice. The orifice will remain closed until the system is emptied. Air may enter the valve and displace the fluid while the system is operating, but the internal pressure will keep the valve tightly shut. The valve will not re-open until the system pressure drops to near atmospheric pressure and the ball is no longer buoyant.