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A fueldraulic metering valve uses pressurized liquid fuel to control flow of gaseous fuel to a jet engine combustion chamber. The valve has a disconnectable body defining a piston chamber and a cavity for an interchangeable venturi nozzle module, both disposed about a stroke axis. A servo valve cont

A fueldraulic metering valve uses pressurized liquid fuel to control flow of gaseous fuel to a jet engine combustion chamber. The valve has a disconnectable body defining a piston chamber and a cavity for an interchangeable venturi nozzle module, both disposed about a stroke axis. A servo valve controls flow of the liquid fuel through the piston chamber and supply and return ports. The liquid fuel drives a piston and pintle assembly to open and close off the throat of the venturi passageway, and thereby control metering of the gaseous fuel, which flow through separate intake and exhaust ports. The gas and liquid fuel are separated by a high temperature seal. The liquid fuel is routed through the piston and a special baffle to dissipate heat transferred to the seal and piston from the hot gaseous fuel. A LVDT position transducer provides feedback to the controller for correcting position error.

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1. A valve actuated by a pressurized drive media for metering a primary media, the valve comprising:a body defining a piston chamber and having a nozzle passageway axially aligned with the piston chamber about a stroke axis, the body having drive media supply and return ports in communication with t

1. A valve actuated by a pressurized drive media for metering a primary media, the valve comprising:a body defining a piston chamber and having a nozzle passageway axially aligned with the piston chamber about a stroke axis, the body having drive media supply and return ports in communication with the piston chamber and primary media intake and exhaust ports in communication with the nozzle passageway, the piston chamber and supply and return ports being isolated from the nozzle passageway and intake and exhaust ports;a pintle extending along the stroke axis has a head sized to close off the nozzle passageway;a piston disposed in the piston chamber along the stroke axis, the piston being coupled to the pintle and having a head responsive to the drive media when pressurized to drive the pintle between an open position in which the primary media intake and exhaust ports are in communication with each other and a closed position in which the pintle head closes off the nozzle passageway such that the intake and exhaust ports are not in communication with each other; anda baffle disposed within the piston chamber so as to direct the drive media in a path adjacent the piston. 2. The valve of claim 1, wherein the primary media is at a higher temperature than the drive media. 3. The valve of claim 2, wherein the drive media is liquid and the primary media is gaseous. 4. The valve of claim 3, wherein the drive media is liquid jet engine fuel. 5. The valve of claim 1, wherein the piston defines a radial passageway leading to an axial cavity open at the head so that drive media can pass through the piston. 6. The valve of claim 5, wherein the baffle has a hollow core and an open end, the baffle being disposed in the piston cavity such that drive media can pass through the radial passageway, between the piston and the baffle and exit the piston through the opening in the piston head. 7. The valve of claim 6, wherein baffle has an external threaded section contacting the piston cavity wall through which the drive media passes. 8. The valve of claim 7, wherein the threaded section defines two helical flow paths. 9. The valve of claim 6, further including a piston guide fixedly disposed about the stroke axis, the piston guide defining an inner diameter against which the piston head slideably seals and an outer annular channel sealed against the piston chamber at one axial end and defining an passageway at an opposite end for drive media to pass to the piston. 10. The valve of claim 9, further comprising a seal separating the drive media from the primary media disposed downstream from the piston guide. 11. The valve of claim 6, further including a position transducer disposed along the stroke axis, the position transducer including a sensing coil fixed with respect to the body and a metallic probe coupled to the piston and movable with respect to the coil within a center of the coil. 12. The valve of claim 11, wherein the position transducer is a linear variable differential transformer. 13. The valve of claim 1, further including a servo valve for controlling flow through the drive media supply and return ports. 14. The valve of claim 1, further including a servo valve and an electronic control unit providing an input signal to the servo valve for controlling flow through the drive media supply and return ports. 15. The valve of claim 14, further including a position transducer disposed along the stroke axis, the position transducer including a sensing coil fixed with respect to the body and a metallic probe coupled to the piston and movable with respect to the coil within a center of the coil. 16. The valve of claim 15, wherein the position transducer provides a feedback signal to the control unit corresponding to the position of the piston for adjusting the input signal supplied to the servo valve in response to the feedback signal. 17. The valve of claim 1, wherein the nozzle passageway is a venturi passageway having a narrowed throat th at can be sealed by the pintle head. 18. The valve of claim 1, wherein the body is defined by a main housing and a removable nozzle body. 19. The valve of claim 18, wherein the nozzle body is secured to the main housing by a threaded collar. 20. The valve of claim 18, wherein the nozzle passageway is an insert module disposed at one end of the nozzle body. 21. The valve of claim 1, further comprising a seal separating the drive media from the primary media disposed downstream from the piston guide. 22. A pressurized liquid driven valve for metering fuel, the valve comprising:a valve body at least in part defining a piston chamber disposed about a stroke axis and having supply and return ports for passing pressurized liquid through the piston chamber;a nozzle body extending from the valve body along the stroke axis in axial alignment with the piston chamber and having intake and exhaust ports for passing fuel through a throat of a venturi passageway;a pintle extending along the stroke axis and having a head sized to close off the throat of the venturi passageway;a piston axially disposed in the piston chamber along the stroke axis, the piston being coupled to the pintle and having a head responsive to the pressurized liquid to drive the pintle along the stroke axis between an open position in which the fuel can pass through the venturi passageway and a closed position in which the pintle head closes off the venturi passageway;a baffle disposed within the piston chamber so as to direct the pressurized liquid in a path adjacent the piston;a seal separating at least a portion of the piston chamber and the supply and return ports from the venturi passageway and the intake and exhaust ports; anda servo valve in communication with the supply and return ports for controlling flow of the pressurized liquid through the piston chamber and thereby control translation direction and speed of the piston. 23. The valve of claim 1, wherein the pressurized liquid is liquid fuel and the fuel is a gaseous fuel at a temperature at least twice that of the liquid fuel. 24. A fueldraulic valve array for metering gaseous fuel, the valve array comprising:a valve body manifold at least in part defining a plurality of piston chambers disposed about parallel stroke axes, the manifold having supply and return ports for passing pressurized liquid fuel through the piston chambers;a plurality of nozzle bodies connected to the manifold and extending along the stroke axes in axial alignment with the piston chambers, the nozzle bodies each having intake and exhaust ports for passing gaseous fuel through a throat of a venturi passageway;a plurality of pintles extending along the stroke axes and having heads sized to close off the throats of the venturi passageways;a plurality of pistons axially disposed in the piston chambers along the stroke axes, the pistons being coupled to the corresponding pintles and having heads responsive to the pressurized liquid fuel to drive the pintles along the stroke axes between open positions in which the gaseous fuel can pass through the venturi passageways and closed positions in which the pintle heads close off the venturi passageways;a plurality of baffles disposed within respective piston chambers so as to direct the pressurized liquid fuel in a spiral path adjacent the pistons;a plurality of seals in the piston chambers separating at least a portion of the piston chamber and the supply and return ports from the venturi passageway and the intake and exhaust ports; anda plurality of servo valves in communication with the supply and return ports for controlling flow of the pressurized liquid fuel through the piston chambers and thereby control translation direction and speed of the pistons.