Patent ID: 7946557

Claim:
An apparatus, comprising: a housing including an inlet operable to allow material to enter the housing and an outlet operable to allow the material to exit the housing; a valve operable to control a flow of the material into the outlet; and an actuator operable to move the valve, the actuator including a resilient member and a stem coupling the valve to an endplate; wherein at least one of the valve and the resilient member has one or more dimensions such that forces applied against the valve and the resilient member by pressures from the material are approximately balanced when the valve is in any of a plurality of positions, the plurality of positions including a most open position and a most closed position; wherein the stem is arranged to pass through a flange, the stem operable to move with respect to the flange, the resilient member positioned between the flange and the endplate; wherein no seal is present where the stem passes through the flange such that at least some of the material that enters the housing enters a portion of the housing containing the resilient member between the stem and the flange; and wherein the forces are approximately balanced only as a function of pressure from the material being applied against the valve and pressure of the material entering the portion of the housing between the stem and the flange being applied against the resilient member.