Downhole actuator

A downhole device adapted for connection in a tubing string in an oil or gas well, the tubing string having a tubing string axis, the downhole device comprising:

• a body with a body axis co-axial with the tubing string axis;
• a flowpath allowing axial passage of fluid through a bore in the body;
• a closure device for restricting passage of fluid through the flowpath;
• an actuator for actuating the closure device;
• the actuator comprising first and second counterweight devices moveably mounted at different circumferential positions around the axis of the body of the downhole device;
• wherein the counterweight devices are radially movable relative to the body axis from a first position to a second position in response to rotation of the device around the body axis, wherein the counterweight devices are spaced radially further from the body axis in the second position than in the first position, wherein movement of the counterweight devices away from the body axis from the first position to the second position is adapted to at least partially close the closure device and restrict the flowpath through the downhole device;
• wherein the counterweight devices are interconnected by upper and lower sleeves at axially spaced apart locations on the counterweight devices;
• wherein the downhole device includes a balancing mechanism adapted to balance the volume and/or pressure changes within the body of the device between the first and second positions of the counterweight devices;
• and
• wherein the balancing mechanism comprises a piston sealed within an annulus between the bore and the body in fluid communication with the radial chamber adjacent to the counterweight devices, whereby changes in the volume of the radial space adjacent to the counterweight devices as a result of the movement of the counterweight devices between the first and second positions are accommodated by sliding movement of the piston within the annulus.