A hydraulic tool includes a stator, a rotor, and a removable coating. At least one of the stator and the rotor comprises a resilient material. The removable coating has a thickness selected to compensate for expected swelling of the resilient material or an expected contraction of a clearance between the rotor and the stator based on thermal expansion. The removable coating is disposed on a surface of at least one of the rotor and the stator, and the removable coating is formulated to be removed during operation of the hydraulic tool. A method of operating a hydraulic tool includes passing a fluid through the hydraulic tool during rotation of the rotor within the stator and removing at least a portion of the removable coating responsive to rotation of the rotor within the stator as a volume of the resilient material increases responsive to contact with the fluid passing through the hydraulic fluid.

Minor diameter enlargements are engineered into a stator in a positive displacement motor (PDM) power section to relieve stator stress concentrations at the lower (downhole) end of the power section in the presence of rotor tilt. The minor diameter enlargements may include one or more contoured stress relief lengths according to various tapered or step functions.

A hydraulic tool includes a stator, a rotor, and a removable coating. At least one of the stator and the rotor comprises a resilient material. The removable coating has a thickness compensate for expected swelling of the resilient material or an expected contraction of a clearance between the rotor and the stator based on thermal expansion. The removable coating is disposed on a surface of at least one of the rotor and the stator, and the removable coating is formulated to be removed during operation of the hydraulic tool. A method of operating a hydraulic tool includes passing a fluid through the hydraulic tool during rotation of the rotor within the stator and removing at least a portion of the removable coating responsive to rotation of the rotor within the stator as a volume of the resilient material increases responsive to contact with the fluid passing through the hydraulic fluid.

A tool (100) for working the internal bore of a tube comprises a motor (10), having a housing with a rotary output; a housing sleeve (14a) and shaft (22); a first bearing housing (16), having a rotatably journalled first spindle (102), mounted on the housing sleeve; and an end sleeve and shaft connected to a tool head. The motor output drives, along a common axis (1), the housing shaft, first bearing spindle, end shaft and tool head. A change mechanism (56,58) is in the tool head to change direction of said drive to transverse said common axis. An output (60) is adapted to receive a tool bit. Gauge means (18,18) is disposed on said tool head and is adapted, in use, to bear against the bore of the tube and maintain the tool head located radially with respect to the tube axis; and support means (24,24) is disposed on one or more of said housing shaft, first bearing housing and end sleeve adapted, in use, to bear against the bore of the tube and support the tool. A long length of tool can work the inside of long tubes.

A stator for a progressive cavity pump or motor includes a stator housing having a longitudinal axis. In addition, the stator includes a stator insert of a material moulded within the housing. The stator housing includes an outer tube having an inner surface. The stator housing also includes a plurality of framework elements disposed on the inner surface of the outer tube. Further, the stator housing includes at least one recess in the inner surface of the outer tube. The conjunction of the framework elements and the at least one recess define a plurality of chambers receiving insert material therein whereby the insert material is mechanically fixed axially, radially and torsionally within the outer tube.

Minor diameter enlargements are engineered into a stator in a positive displacement motor (PDM) power section to relieve stator stress concentrations at the lower (downhole) end of the power section in the presence of rotor tilt. The minor diameter enlargements may include one or more contoured stress relief lengths according to various tapered or step functions.

A downhole fluid motor can include a tubular housing and multiple stator sections. Each of the stator sections has a helical stator profile formed therein. Deformation of the housing secures each respective stator section in the housing. A method of producing a downhole fluid motor can include securing multiple stator sections to each other, each of the stator sections having a stator profile formed therein, and securing the stator sections in a tubular housing. The securing steps can be performed without any welding. The step of the securing the stator sections in the housing can include deforming the housing toward the stator sections.

Minor diameter enlargements are engineered into a stator in a positive displacement motor (PDM) power section to relieve stator stress concentrations at the lower (downhole) end of the power section in the presence of rotor tilt. The stator may be a hybrid construction of heterogenous materials.