US Patent 11753905 Downhole tool actuator with viscous fluid clearance paths

A flow tube is axially moveable within an actuator body between a first axial position and a second axial position for actuating a downhole tool, such as for closing a subsurface safety valve. The flow tube includes an interior flow bore for conveying fluids from the tubing string through the actuator body. An external flow tube profile defined on the flow tube includes an upper shoulder for engagement with a wiper in the first axial position, a lower shoulder for engagement with the wiper in the second axial position, and a clearance path between the upper and lower shoulders for allowing viscous flow past the wiper when the flow tube is moved between the first and second axial positions.