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A valve positioner for controlling a valve closure element is provided. The positioner includes a positioner housing with a plurality of fluid flow passageways in fluid communication with a fluid supply source and the valve closure element. The positioner housing is configured to receive a detachabl

A valve positioner for controlling a valve closure element is provided. The positioner includes a positioner housing with a plurality of fluid flow passageways in fluid communication with a fluid supply source and the valve closure element. The positioner housing is configured to receive a detachable spool manifold assembly. The spool manifold assembly is positioned adjacent the plurality of fluid flow passageways. The spool manifold assembly includes a reciprocally moveable spool configured to selectively port fluid flow from the plurality of fluid flow passageways. The spool manifold assembly includes a diaphragm connected to the spool via a flexible shaft. The diaphragm is in fluid communication with a transducer for receiving a fluid causing the diaphragm to expand or contract and thereby displacing the spool. The flexible shaft is radially elastic in order to minimize axial backlash between the diaphragm and the spool. The flexible shaft configuration minimizes the spool stroke.

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1. A spool manifold assembly, comprising: a manifold housing having a plurality of fluid flow passageways for receiving and exhausting fluid;a spool disposed and reciprocally movable within the manifold housing, the spool defining a longitudinal axis and being configured to slide axially along the l

1. A spool manifold assembly, comprising: a manifold housing having a plurality of fluid flow passageways for receiving and exhausting fluid;a spool disposed and reciprocally movable within the manifold housing, the spool defining a longitudinal axis and being configured to slide axially along the longitudinal axis to selectively port fluid to the plurality of fluid flow passageways:a diaphragm operatively coupled to the spool and configured to displace the spool in accordance with a pressure level exerted on the diaphragm; anda flexible shaft having a first end rigidly attached to the spool and a second end rigidly attached to the diaphragm, the flexible shaft extending between the spool and the diaphragm along the longitudinal axis and defining a radially elastic and axially rigid joint therebetween. 2. A spool manifold assembly, comprising: a manifold housing having a plurality of fluid flow passageways for receiving and exhausting fluid;a spool disposed and reciprocally movable within the manifold housing, the spool defining a longitudinal axis and being configured to slide axially along the longitudinal axis to selectively port fluid to the plurality of fluid flow passageways;a diaphragm operatively coupled to the spool and configured to displace the spool in accordance with a pressure level exerted on the diaphragm; anda flexible shaft connected to and extending between the spool and the diaphragm along the longitudinal axis, the flexible shaft being adapted to transmit a bidirectional motive force from the diaphragm to the spool. 3. The spool manifold assembly of claim 2, further comprising a biasing spring disposed about the flexible shaft between the diaphragm and the spool, the biasing spring being operative to normally bias the spool to a prescribed position. 4. A spool manifold assembly comprising: a manifold housing having a plurality of fluid flow passageways for receiving and exhausting fluid;a tubular sleeve disposed within the manifold housing, the sleeve defining a plurality of apertures for receiving fluid from the fluid flow passageways;a spool disposed within the sleeve, the spool defining a longitudinal axis and being configured to slide axially along the longitudinal axis to port fluid to the plurality of fluid flow passageways via the plurality of apertures;a flexible shaft extending along the longitudinal axis, the flexible shaft having a first end coupled to the spool and a second end coupled to a diaphragm which is operatively coupled to and configured to exert a bidirectional motive force on the spool via the flexible shaft in response to a pressure change associated with the diaphragm; anda biasing spring disposed about the flexible shaft between the diaphragm and the spool, the biasing spring being operative to normally bias the spool to a prescribed position. 5. The spool manifold assembly of claim 4, wherein the spool includes a bore extending axially therein along the longitudinal axis, the bore being configured to partially receive the flexible shaft. 6. The spool manifold assembly of claim 4, wherein a portion of the flexible shaft is disposed within an elongate sleeve which is sized and configured to minimize lateral displacement of the flexible shaft when a compressive force is exerted thereon. 7. The spool manifold assembly of claim 1, wherein the first end of the flexible shaft and the second end of the flexible shaft each define an axially rigid joint. 8. The spool manifold assembly of claim 1, wherein the flexible shaft is radially elastic. 9. The spool manifold assembly of claim 4, wherein the spool is selectively moveable between a neutral position and an unbalanced position, and is operative to prevent the flow of fluid from the fluid flow passageways to an actuator when in the neutral position, the biasing spring normally biasing the spool to the unbalanced position. 10. The spool manifold assembly of claim 9, wherein the spool is configured to allow the flow of fluid from at least one of the fluid flow passageways to the actuator when in the unbalanced position. 11. The spool manifold assembly of claim 10, further in combination with a valve positioner comprising: a positioner housing having a plurality of fluid flow passageways disposed therein; anda positioner microprocessor disposed within the positioner housing, the positioner microprocessor being configured to receive an input signal representative of a position of the actuator;the spool manifold assembly being cooperatively engaged to the positioner housing such that the fluid flow passageways of the manifold housing communicate with corresponding ones of the fluid flow passageways of the positioner housing, the spool being operative to selectively port fluid flow from the fluid flow passageways of the manifold and positioner housings to the actuator, with the diaphragm being disposed within the positioner housing and the positioner further including a transducer in fluid communication with the diaphragm, the transducer being in electrical communication with the positioner microprocessor and configured to receive a pneumatic signal which is operative to regulate the fluid supplied to the diaphragm for displacing the spool. 12. The spool manifold assembly of claim 11, wherein the plurality of fluid flow passageways of the positioner housing are each of a gradually decreasing width as they extend toward corresponding ones of the fluid flow passageways of the spool manifold assembly. 13. The spool manifold assembly of claim 11, wherein the valve positioner further comprises a software interface in communication with the positioner microprocessor and adapted to accept inputs of a plurality of desired variables for the positioner microprocessor to generate a pneumatic signal. 14. The spool manifold assembly or claim 11, further comprising dual exhaust ports disposed within the positioner housing adjacent the fluid flow passageways thereof, the dual exhaust ports being configured to exhaust fluid from the positioner housing. 15. The spool manifold assembly of claim 14, wherein each of the exhaust ports is enclosed by a flexible diaphragm. 16. The spool manifold assembly of claim 11, wherein the positioner microprocessor comprises a set of control algorithms which are operative to compare the input signal to the actuator position and generate a pneumatic signal. 17. The spool manifold assembly of claim 16, wherein the valve positioner further comprises a feedback mechanism coupled to the actuator. 18. The spool manifold assembly of claim 17, wherein the feedback mechanism of the valve positioner comprises: a shaft for absorbing a load generated by the actuator; anda sensor mounted elastically and independent from the shall, the sensor being configured so as not to absorb any load generated by the actuator. 19. The spool manifold assembly of claim 18, wherein the feedback mechanism is in electrical communication with the positioner microprocessor, the feedback mechanism being operative to generate a feedback signal representative of a pressure change within the actuator. 20. The spool manifold assembly of claim 19, wherein the positioner microprocessor is operative to process the feedback signal received from the feedback mechanism using the set of control algorithms to generate an updated pneumatic signal.