US Patent 10513977 Adjustable snap action passive inline air valve

A valve assembly includes a piston housing inside a flow duct between an inlet and an outlet so as to form an annular flow passage between the flow duct and the piston housing. The piston housing is axially aligned with a center axis of the flow duct. A piston is inside the piston housing and is configured to extend downstream of the piston housing in a closed position. A spring biases the piston to the open position. A fluid chamber is between the piston and an upstream end of the piston housing. A control opening extends through the upstream end of the piston housing and fluidically communicates with the flow duct and the fluid chamber. A control piston and a control spring are inside the piston housing. The control spring biases the control piston toward a first position that obstructs the control opening.