US Patent 10267430 Backflow prevention valve

A valve assembly includes an outer housing having a first opening in fluid communication with a first fluid, a second opening in fluid communication with a second fluid, a third opening in fluid communication with a third fluid and a fourth opening in fluid communication with a fourth fluid. The valve assembly includes a piston configured to slide within the outer housing into a first position at which the third opening is blocked from fluid communication with the fourth opening based on a fluid pressure of the first fluid being greater than a fluid pressure of the fourth fluid. The piston is further configured to slide within the outer housing into a second position at which the third opening is in fluid communication with the fourth opening based on the fluid pressure of the second fluid being greater than the fluid pressure of the fourth fluid.