Abstract: A speed sensitive pressure regulator system includes a diaphragm of resilient flexible material positioned within a housing and forming an actuating chamber therein. A valve is associated with a passage and is movable between a first position at which fluid pressure in the actuating chamber is substantially equal to the fluid pressure in the passage and a second position at which the fluid pressure in the actuating chamber is less than the fluid pressure in the passage. The valve is connected to the diaphragm in a manner sufficient for biasing the valve toward the second position in response to pressurized fluid in contact with the diaphragm. A flyweight assembly is associated with the valve and is of a construction sufficient for moving the valve to its first position in response to rotation of the flyweight assembly above a preselected speed and for permitting the valve to move to the second position in response to a decrease in the rotational speed of the flyweight assembly below the preselected speed.