Abstract: In order to prevent contamination of a fluid source and to ensure drainage of a sill cock or the like, a detachable check valve back flow preventer for installation between a fluid inlet line and a fluid outlet line is provided. A housing with means for fastening the device to a fluid inlet line at one end of the housing and for connecting a fluid outlet line at the other end of the housing is provided. The housing has a central cavity within the housing. An inlet line drain valve is located within the housing between the central cavity and the fluid inlet line to provide for the drainage of fluid from the fluid inlet line to the fluid outlet line end of the housing when the fluid outlet line is not connected to the back flow preventer. A second valve is located within the housing between the central cavity and the fluid inlet line to control flow of fluids between the fluid inlet line and the central cavity.

Abstract: A self-draining hose connection vacuum breaker and backflow preventer having a flexible annular diaphragm and a coacting seat disc movable relative thereto which, together, function to prevent backflow through the device and with the annular diaphragm coacting with atmospheric vents to provide a vacuum break and fluid drain. A movable piston has two different positions, dependent upon whether or not a hose is connected to the device, with the piston mounting the seat disc for movement therewith and relative thereto whereby the seat disc and annular diaphragm coact to prevent backflow when a hose is attached to the device, but the seat disc is positioned to permit flow through a central opening of the annular diaphragm when a hose is removed from the device to prevent trapped water in a source valve, such as a faucet or the like, which could result in either pipe and/or valve rupture resulting from freezing or retention of stagnant water which could result in bacterial growth.