Amazon.com : Pawfly Aquarium Air Control Valves for 3/16" ID Airline Tubing Single Way Plastic Air Flow Controllers Regulators Adjustable Blue Hose Connectors Air Pump Accessories for Fish Tanks, 10 Pack :
Double Orifice Kinetic Air Valve VF-017 | ALRECO
Butterfly Valves double-offset
Automatic Air Valves ARV-1A double effect - Unirain
Unique Mixproof valves | Double seat valves | Alfa Laval