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A variable orifice assembly includes a housing defining a flow orifice therethrough and configured to be connected in fluid communication between two pipes of a particle conveyance system. The assembly includes a plurality of blades pivotally mounted to the housing to pivot between a retracted posit

A variable orifice assembly includes a housing defining a flow orifice therethrough and configured to be connected in fluid communication between two pipes of a particle conveyance system. The assembly includes a plurality of blades pivotally mounted to the housing to pivot between a retracted position and an extended position. Each blade includes a gas path edge. In the retracted position, the gas path edges of the blades conform to the flow orifice. In the extended position, the blades extend inward from the flow orifice wherein the gas path edge of each blade is spaced apart from the other blades.

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1. A variable orifice assembly comprising: a housing defining a flow orifice therethrough and configured to be connected in fluid communication between two pipes of a particle conveyance system; anda plurality of blades pivotally mounted the housing to pivot between a retracted position and an exten

1. A variable orifice assembly comprising: a housing defining a flow orifice therethrough and configured to be connected in fluid communication between two pipes of a particle conveyance system; anda plurality of blades pivotally mounted the housing to pivot between a retracted position and an extended position, each blade including a gas path edge, wherein in the retracted position the gas path edges of the blades conform to the flow orifice, and in the extended position, the blades extend inward from the flow orifice wherein the gas path edge of each blade is spaced apart from the other blades, wherein the housing includes an axially spaced apart pair of housing rings joined together by a plurality of spacers therebetween, wherein the spacer includes a limiter that contacts the blades to limit travel of the blades to prevent the blades meeting or contacting one another within the flow orifice, wherein the limiter is configured to prevent a free end of each blade opposite a respective pivot point of the blade from reaching, meeting, or crossing a centerline of the orifice passing through the respective pivot point. 2. An assembly as recited in claim 1, wherein the spacers are circumferentially spaced apart from one another, alternating circumferentially with the blades. 3. An assembly as recited in claim 1, wherein the blades are pivotally mounted axially between the housing rings. 4. An assembly as recited in claim 3, wherein each blade is pivotally mounted axially between the housing rings by a respective pivot pin passing axially through each of the housing rings and the respective blade. 5. An assembly as recited in claim 4, wherein the pivot pins are mounted to remain stationary relative to the housing rings. 6. An assembly as recited in claim 1, wherein the spacers are mounted to be stationary relative to the housing rings. 7. An assembly as recited in claim 1, wherein the gas path edge of each blade is curved along a circular arc. 8. An assembly as recited in claim 7, wherein the circular arc has a diameter substantially equal to that of the flow orifice. 9. An assembly as recited in claim 8, wherein in the retracted position, the gas path edge of each blade is substantially flush with the flow orifice. 10. An assembly as recited in claim 1, wherein each blade includes a respective actuator operatively connecting the blade to the housing to move the blade independent of the other blades. 11. An assembly as recited in claim 1, further comprising a linkage operatively connecting the blades together for synchronized actuation of the blades. 12. An assembly as recited in claim 1, wherein the housing includes an outer ring having a respective access opening proximate each respective blade. 13. An assembly as recited in claim 1, wherein the blades together have a maximum extent into the flow orifice in the fully extended position that blocks up to 50% of the flow area of the flow orifice. 14. A particulate piping system comprising: a first pipe configured for conducting a mixed flow of particulate and gas therethrough in an axial direction;a second pipe configured for conducting a mixed flow of particulate and gas therethrough in the axial direction; anda variable orifice assembly including: a housing mounted to connect the first and second pipes for fluid communication from the first pipe to the second pipe, the housing defining a flow orifice therethrough; anda plurality of blades pivotally mounted the housing to pivot between a retracted position and an extended position, each blade including a gas path edge, wherein in the retracted position the gas path edges of the blades conform to the flow orifice, and in the extended position, the blades extend inward from the flow orifice wherein the gas path edge of each blade is spaced apart from the other blades, wherein the housing includes an axially spaced apart pair of housing rings joined together by a plurality of spacers therebetween, wherein the spacer includes a limiter that contacts the blades to limit travel of the blades to prevent the blades meeting or contacting one another within the flow orifice, wherein the limiter is configured to prevent a free end of each blade opposite a respective pivot point of the blade from reaching, meeting, or crossing a centerline of the orifice passing through the respective pivot point. 15. A system as recited in claim 14, wherein the first and second pipes each have an inner diameter that is equal to the diameter of the flow orifice of the variable orifice assembly. 16. A system as recited in claim 14, wherein each of the housing rings is mounted to a respective one of the first and second pipes. 17. A system as recited in claim 16, wherein each housing ring is welded to a respective one of the first and second pipes.