US Patent 11746509 Backflow prevention device

A backflow prevention device includes a piston received in a device passage between an inlet port and outlet port. A relief port can fluidly communicate with a middle segment of the device passage. The piston is movable between a normal flow position in which the piston blocks fluid communication between the relief port and the middle segment of the device passage and a backflow position in which the piston allows fluid communication between the relief port and the middle segment of the device passage. The piston can move to the normal position in response to normal flow through the device passage from the inlet port toward the outlet port and configured to move to the backflow position in response to greater pressure in the middle segment than in the inlet port.