In this category you'll find an assortment of both control and check valves. Control valves allow you manage the flow of air from your aquarium air pump. You can divide and control the flow of air between different devices including multiple air stones, sponge filters etc. Check valves are small devices that allow water to flow in one direction only. They contain a flapper or small trap door that prevents water from flowing back into your air pump when a power outage occurs. If your air pump is located below the level of the water in your aquarium be sure to add a check valve to the air line tubing coming from your pump.