| 摘要 |
A metering body for a chemical injection system comprises a free piston having a pair of mechanically-actuated poppet valves which may individually open to permit fluid to pass from one side of the free piston to the other. The free piston slides within a cylinder having cylinder heads at opposing ends. Input/output ports are provided in the cylinder heads. In a preferred embodiment, the poppet valves have actuators that extend beyond the opposing faces of the free piston. If one face of the piston moves to within a predetermined distance of a cylinder head, the actuator contacts the cylinder head and further movement of the piston causes the corresponding poppet valve to open, permitting fluid to flow through the piston. In this way, a fault-tolerant system may be implemented. If a power interruption or other failure of the controller occurs, the system will continue to supply fluid at the most recently selected flow rate. When power is restored (or the fault is corrected), the controller causes a valve to reverse the flow of fluid through the metering body and the spring-loaded poppet valve will close as the free piston moves away from the cylinder head. |
