Av-Tek's 5331 and 5341 Ductile Iron combination air valve will exhaust air when the pipeline is filling, exhaust air when the pipe is under pressure and allow air in under vacuum pressure. These 3" and 4" flanged valves are NSF 61/372 certified and in stock!
This valve will protect your water system from getting contaminated with it's integral drain. This drain on the exhaust line ensures no water will ever be sucked back into the system after it has exhausted out. No other manufacture has this feature.