US Patent 6857444 Flow-actuated trapped-pressure unloader valve

The invention recites an unloader valve operable to direct a flow of fluid. The valve includes a housing having a bypass opening, an inlet opening, an outlet opening and an internal chamber between the inlet opening and the outlet opening. A shuttle valve is disposed within the internal chamber and is movable between a first position wherein the flow of fluid is substantially directed to the bypass opening and a second position wherein the flow of fluid is directed to the outlet opening. The shuttle valve includes an internal flow path having a venturi therein. A biasing member biases the shuttle valve in the first position.