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A system for preventing stall in a centrifugal compressor. The compressor includes an impeller rotatably mounted in a housing and a nozzle base plate fixed to the housing adjacent the impeller. The nozzle base plate cooperates with the housing to define a diffuser gap. The base plate includes a plur

A system for preventing stall in a centrifugal compressor. The compressor includes an impeller rotatably mounted in a housing and a nozzle base plate fixed to the housing adjacent the impeller. The nozzle base plate cooperates with the housing to define a diffuser gap. The base plate includes a plurality of mechanism support blocks positioned on the backside of the nozzle base plate. A drive ring, mounted to the support blocks, is rotationally moveable with respect to the support blocks and the nozzle base plate between a first position and a second position. Connected to the drive ring is a diffuser ring that moves in response to movement of the drive ring. Diffuser ring moves between a retracted position that is not within the diffuser gap and an extended position extending into the diffuser gap to constrict the gap opening and reduce the flow of fluid through the diffuser gap. The diffuser ring can be positioned at any location between the retracted and extended position to control the amount of fluid flowing through the diffuser gap.

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1. A diffuser system for a variable capacity centrifugal compressor for compressing a fluid, the compressor having a housing and an impeller, the impeller being rotatably mounted in the housing, the system comprising:a nozzle base plate connected to the housing adjacent the impeller, the nozzle base

1. A diffuser system for a variable capacity centrifugal compressor for compressing a fluid, the compressor having a housing and an impeller, the impeller being rotatably mounted in the housing, the system comprising:a nozzle base plate connected to the housing adjacent the impeller, the nozzle base plate having an elongated surface that cooperates with an opposed interior surface on the housing to define a diffuser gap, the elongated surface of the nozzle base plate having a groove adjacent the diffuser gap; a plurality of support blocks mounted to a back side of the nozzle base plate opposite the diffuser gap; a drive ring rotatably mounted to the support blocks and movable between a first position and a second position, the drive ring including a plurality of cam tracks positioned on a circumference of the drive ring, at least two of the plurality of cam tracks aligned with at least two of the plurality of support blocks; an actuating means attached to the drive ring and movable between a first axial position and a second axial position to move the drive ring between the first position and the second position; a plurality of drive pins, each drive pin extending through a corresponding support block and the nozzle base plate, each drive pin having a first end and a second end opposite the first end, the first end of the drive pin including a cam follower mounted into a cam track on the drive ring and the second end of the drive pin extending through the nozzle base plate into the groove on the surface of the nozzle base plate; a diffuser ring mounted on the second end of each of the plurality of drive pins, the drive pins extending into the groove on the nozzle base plate surface; wherein the rotational movement of the drive ring between a first position and a second position moves the cam followers in the cam track which axially moves the drive pins, the axial movement of the drive pins moves the diffuser ring between a retracted position in which the diffuser ring resides in the groove on the nozzle base plate and an extended position in which the diffuser ring substantially closes the diffuser gap to reduce fluid flow through the diffuser gap. 2. The system of claim 1 wherein each of the plurality of support blocks is aligned with one of the plurality of cam tracks.3. The system of claim 1 wherein three support blocks are mounted to a back side of the nozzle base plate.4. The system of claim 3 wherein the drive ring includes three cam tracks, each cam track being aligned with a support block.5. The system of claim 3 wherein the drive ring includes three cam tracks, each cam track being aligned with a support block.6. The system of claim 1 wherein the nozzle base plate groove has a depth sufficient to receive the diffuser ring when the diffuser ring is in the retracted position so that no portion of the diffuser ring extends outwardly into the diffuser gap.7. The system of claim 1 wherein the plurality of support blocks are mounted to the back side of the nozzle base plate with fastening means.8. The system of claim 7 wherein the fastening means includes threaded fasteners extending into threaded apertures on each of the support blocks and corresponding threaded apertures on the nozzle base plate.9. The system of claim 7 wherein the fastening means includes threaded fasteners extending into threaded apertures on each of the support blocks and corresponding threaded apertures on the nozzle base plate.10. The system of claim 1 wherein the plurality of support blocks are integrally manufactured with the nozzle base plate.11. The system of claim 10 wherein the plurality of support blocks are included as cast elements in a nozzle base plate casting.12. The system of claim 10 wherein the plurality of support blocks are included as cast elements in a nozzle base plate casting.13. The system of claim 1 wherein the drive ring includes a top surface, a bottom surface, an inner circumferential surface extending axially between the top surface and the bottom surface, an outer circumferential surface extending axially between the top surface and the bottom surface, and a circumferential groove extending along at least a portion of the inner circumferential surface, the circumferential groove having a preselected width in the axial direction and a preselected length.14. The system of claim 13 wherein each cam track is fabricated as a groove in the outer circumferential surface, the groove having a preselected width sufficient to receive one of the cam followers and a preselected depth, the groove extending at a preselected angle to an axis of the drive ring.15. The system of claim 14 wherein the preselected angle is between about 5°-45°.16. The system of claim 14 wherein the preselected angle is about 7-14°.17. The system of claim 14 wherein the groove further includes a portion at a first end in a plane parallel to the top surface and a portion at an opposite end in a plane parallel to the bottom surface, these portions accommodating overtravel of one of the cam followers.18. The system of claim 13 further including a plurality of axial bearing assemblies, each axial bearing assembly comprising a support structure, a first means for securing the axial bearing assembly to the support structure, an axial bearing on a shaft extending through the support structure, the axial bearing being rotatable about the shaft, and a second means for securing the axial bearing to the support structure, wherein each axial bearing is positioned in the circumferential groove to resist axial movement of the drive ring as it rotates when the bearing is assembled to the support structure and the support structure is secured to prevent movement of the bearing out of the groove.19. The system of claim 18 wherein the first means of securing the axial bearing assembly to the support structure includes a pair of threaded fasteners extending through apertures in the support structure and into mating threaded apertures in the support block, whereby the support structure is secured to the support block by the fasteners.20. The system of claim 18 wherein the second means of securing the axial bearing to the support structure includes a threaded nut attached to a threaded end of the shaft, the threaded end of the shaft extending through the support structure on a side of the support structure opposite the axial bearing.21. The system of claim 13 further including a radial bearing assembly wherein the radial bearing assembly includes a roller having an inner aperture, at least one flanged bushing installed in the inner aperture of the roller and a shaft for fixedly securing the radial bearing in contact with the inner circumference of the drive ring to counteract radial movement of the drive ring.22. The system of claim 21 wherein the radial bearing assembly includes a pair of flanged bushings.23. The system of claim 21 wherein the at least one flanged bushing includes TEFLON? flanges.24. The system of claim 21 wherein the radial bearing shaft secures the radial bearing to a support block.25. The system of claim 1 wherein the actuating means includes a motor attached to a mechanical actuator having a cylinder linearly movable between a first contracted position and a second extended position, whereby activation of the motor causes linear movement of the mechanical actuator which rotates the drive ring.26. The system of claim 1 wherein the actuating means is a hydraulic actuator having a cylinder linearly movable between a first contracted position and a second extended position, whereby the linear movement of the hydraulic actuator in response to pressure from an applied fluid rotates the drive ring.27. The system of claim 1 wherein the actuating means includes a motor attached to a mechanical actuator having a threaded member, whereby the motor, upon activation, rotates the threaded member which moves the actuator between a first contracted position and a second extended position, whereby the movement of the actuator rotates the drive ring.28. The system of claim 1 further including a sensor positioned within the compressor to sense the presence and absence of a stall condition and to send a signal, a controller in communication with the sensor and the actuating means, the controller sending a signal to the actuating means to position the drive ring and connected diffuser ring in response to the signal received from the sensor.29. The system of claim 28 wherein the sensor is positioned adjacent the impeller.30. The system of claim 1 wherein each of the plurality of support blocks is aligned with one of the plurality of cam tracks.31. The system of claim 1 wherein three support blocks are mounted to a back side of the nozzle base plate.32. The system of claim 1 wherein the nozzle base plate further includes a groove on its elongated surface having a depth sufficient to receive the diffuser ring when the diffuser ring is in the retracted position so that no portion of the diffuser ring extends outwardly into the diffuser gap.33. The system of claim 1 wherein the plurality of support blocks are mounted to the back side of the nozzle base plate with fastening means.34. The system of claim 1 wherein the plurality of support blocks are integrally manufactured with the nozzle base plate.35. The system of claim 1 wherein the drive ring includes a top surface, a bottom surface, an inner circumferential surface extending axially between the top surface and the bottom surface, an outer circumferential surface extending axially between the top surface and the bottom surface, and a circumferential groove extending along at least a portion of the inner circumferential surface, the circumferential groove having a preselected width in the axial direction and a preselected length.36. A system for a variable capacity centrifugal compressor for compressing a fluid, the compressor having a housing and an impeller, the impeller being rotatably mounted in the housing, the system comprising:a nozzle base plate fixed to the housing adjacent the impeller, the nozzle base plate having an elongated surface that cooperates with an opposed interior surface on the housing to define a diffuser gap, the elongated surface of the nozzle base plate having a groove adjacent the diffuser gap; three support blocks positioned concentrically on a back side of the nozzle base plate opposite the diffuser gap about 120° apart; a drive ring mounted substantially out of contact with the support blocks rotationally selectably movable with respect to the support blocks and the nozzle base plate between a first position and a second position, the drive ring a top surface, a bottom surface, an inner circumference extending between the top surface and the bottom surface, an outer circumference extending between the top surface and the bottom surface, the inner circumference including an inner circumferential groove, the drive ring including three cam tracks positioned on the outer circumference of the drive ring about 120° apart, each of the cam tracks aligned with each of the support blocks; an actuator having a motor movable between a first axial position and a second axial position attached to the drive ring to rotate the drive ring from the first position to the second position; three drive pins, one drive pin extending through each of the support blocks and the nozzle base plate, a first end of each drive pin including a cam follower mounted into one of the cam tracks on drive ring and the second end of each drive pin extending through the nozzle base plate into the groove on the surface of the nozzle base plate; three axial bearing assemblies, one axial bearing assembly mounted to each of the support blocks and each axial bearing assembly positioned within the inner circumferential groove of the drive ring to resist axial movement of the drive ring as it rotates; three radial bearing assemblies, one radial bearing assembly mounted to each of the support blocks and each radial bearing assembly positioned in contact with an inner circumferential surface to resist radial movement of the drive ring as it rotates; a diffuser ring mounted on the second end of the drive pins extending into the groove on the nozzle base plate; a sensor positioned within the compressor to provide signals indicative of a fluid condition in the compressor; a controller in communication with the sensor and the actuator, the controller sending a signal to the actuator to position the drive ring and connected diffuser ring in response to signals received from the sensor; wherein the motion of the actuator in response to the signal from the controller causes the rotational movement of the drive ring between a first position and a second position, causing axial movement of the drive pins by movement of the cam followers in the cam tracks, which causes movement of diffuser ring between a first position corresponding to a first position of the drive ring and a second position corresponding to a second position of the drive ring to control fluid flow through the diffuser gap and prevent compressor stall. 37. A centrifugal compressor, comprising:a housing; a fluid inlet; an impeller assembly rotatably mounted on a shaft in the housing for compressing fluid introduced through the inlet; a fluid outlet to discharge compressed fluid from the impeller; a nozzle base plate connected to the housing adjacent the impeller, the nozzle base plate having an elongated surface that cooperates with an opposed interior surface on the housing to define a diffuser gap; a plurality of support blocks positioned on a back side of the nozzle base plate opposite the diffuser gap; a drive ring rotatably mounted to the support blocks and movable between a first position and a second position, the drive ring including a plurality of cam tracks positioned on a circumference of the drive ring, at least two of the plurality of cam tracks aligned with at least two of the plurality of support blocks; an actuating means movable in its axial direction attached to the drive ring and movable between a first axial position and a second axial position to move the drive ring between the first position and the second position; a plurality of drive pins, each drive pin extending through a corresponding support block and the nozzle base plate, each drive pin having a first end and a second end opposite the first end, the first end of the drive pin including a cam follower mounted into one of the plurality of cam tracks on the drive ring and the second end of the drive pin extending through the nozzle base plate and protruding from the elongated surface; a diffuser ring mounted on the second end of each of the plurality of drive pins protruding from the nozzle base plate surface; wherein the rotational movement of the drive ring between a first position and a second position moves the cam followers in the cam track which axially moves the drive pins, the axial movement of the drive pins moves the diffuser ring between a retracted position in which the diffuser ring is distal from the opposed interior surface of the housing to increase fluid flow through the diffuser gap and an extended position in which the diffuser ring is proximal to the opposed interior surface of the housing to substantially close the diffuser gap and reduce fluid flow through the diffuser gap.