A flowcontrol assembly comprising: a fluid conduit configured to receive flow of a fluid; a flow-control valve positioned in the fluid conduit; a fluid expansion conduit comprising: an inlet defined by the fluid conduit and configured to selectively receive flow of the fluid from the fluid conduit, and an outlet in fluid communication with the fluid conduit downstream of the flow-control valve; and a rotating fluid expander in the fluid expansion conduit configured to expand the fluid and thereby rotate; wherein the fluid expansion conduit comprises a volute which substantially surrounds the rotating fluid expander and supplies flow of the fluid thereto, wherein the flow-control valve comprises a butterfly valve having a throttle plate disposed in the fluid conduit and coupled to a shaft that is rotatable about its longitudinal axis, the flow-control valve being selectively positionable in a first position, in a second position, and in a third position, wherein the fluid conduit includes a sealing wall which the throttle plate engages with a tight fit when the flow-control valve is in the first position such that the throttle plate blocks flow of the fluid through the fluid conduit and the fluid expansion conduit, wherein the inlet to the fluid expansion conduit comprises a hole in the sealing wall at which the throttle plate is out of contact when the flow-control valve is in the second position in which the flow-control valve blocks flow of the fluid through the fluid conduit and at least partially unblocks the inlet to the fluid expansion conduit to thereby allow flow of the fluid through the fluid expansion conduit, and wherein the sealing wall defines a curved profile of substantially the same radius as the throttle plate in order to accommodate rotation of the throttle plate, whereby the throttle plate maintains a tight fit with the sealing wall in the second position, wherein in the third position the throttle plate is rotated past the inlet to the fluid expansion conduit and out of contact with the sealing wall to allow a direct flow of the fluid to pass through the flow-control valve via the fluid conduit without traveling through the fluid expansion conduit. a fluid conduit configured to receive flow of a fluid; a flow-control valve positioned in the fluid conduit; a fluid expansion conduit comprising: an inlet defined by the fluid conduit and configured to selectively receive flow of the fluid from the fluid conduit, and an outlet in fluid communication with the fluid conduit downstream of the flow-control valve; and an inlet defined by the fluid conduit and configured to selectively receive flow of the fluid from the fluid conduit, and an outlet in fluid communication with the fluid conduit downstream of the flow-control valve; and a rotating fluid expander in the fluid expansion conduit configured to expand the fluid and thereby rotate; wherein the fluid expansion conduit comprises a volute which substantially surrounds the rotating fluid expander and supplies flow of the fluid thereto, wherein the flow-control valve comprises a butterfly valve having a throttle plate disposed in the fluid conduit and coupled to a shaft that is rotatable about its longitudinal axis, the flow-control valve being selectively positionable in a first position, in a second position, and in a third position, wherein the fluid conduit includes a sealing wall which the throttle plate engages with a tight fit when the flow-control valve is in the first position such that the throttle plate blocks flow of the fluid through the fluid conduit and the fluid expansion conduit, wherein the inlet to the fluid expansion conduit comprises a hole in the sealing wall at which the throttle plate is out of contact when the flow-control valve is in the second position in which the flow-control valve blocks flow of the fluid through the fluid conduit and at least partially unblocks the inlet to the fluid expansion conduit to thereby allow flow of the fluid through the fluid expansion conduit, and wherein the sealing wall defines a curved profile of substantially the same radius as the throttle plate in order to accommodate rotation of the throttle plate, whereby the throttle plate maintains a tight fit with the sealing wall in the second position, wherein in the third position the throttle plate is rotated past the inlet to the fluid expansion conduit and out of contact with the sealing wall to allow a direct flow of the fluid to pass through the flow-control valve via the fluid conduit without traveling through the fluid expansion conduit.