Check valves, sometimes referred to as “one way valves” or “non-return valves” are common components found in air management systems. These SMC check valves are generally used on each supply line from the tank to the manifold in order to prevent back-flow from your air springs in the event that your air tank were to depressurize. Great to have for doing maintenance on your tank / management when you want your car to be at a raised height to save your back.