A rotor for a mud motor includes a core having a first outer shape, and a shell positioned around the core, the shell having a second outer shape that is different from the first outer shape, the second outer shape defining one or more lobes and one or more cavities that are configured to engage a bore of a stator during rotation of the rotor relative to the stator. A thickness of the shell varies as proceeding around the core, from a non-zero minimum thickness to a maximum thickness.

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.

A scroll compressor and a method for assembling a scroll compressor are provided. The scroll compressor may include a casing including a rotational shaft, a main frame coupled to an inside of the casing, a first scroll that revolves due to rotation of the rotational shaft, the first scroll being supported by the main frame, and a second scroll disposed on or at a side of the first scroll to define a plurality of compression chambers together with the first scroll. The second scroll may include a head plate including a wrap, and at least one coupling guide that extends from the head plate. The at least one coupling guide may include a first reference pin coupling hole, into which a reference pin may be inserted, and a guide hole, into which a coupling member may be inserted.

A reduced noise screw expander is described, which comprises a main rotor and a gate rotor each having an N profile. The rotors are designed so that the torque on the gate rotor caused by pressure forces is in the same direction as the torque on the gate rotor caused by frictional drag forces. A method of designing a screw machine exhibiting reduced noise is also described. The screw machine has two or more rotors having an N profile, and the method involves determining a ratio r/r.sub.1, where r is the main rotor addendum and r.sub.1 is the radius of the rack round side, and ensuring that this ratio is greater than 1.1 where the screw machine is to be a screw compressor or less than or equal to 1.1 where the screw machine is to be a screw expander.

A stator casing of an eccentric screw pump with an elastomer stator inner part including a plurality of shell-like casing segments and a production method for such a stator casing, with which the outlay for maintenance work can be reduced. According to the invention, casing segments adjacent in the longitudinal direction of the stator casing are disposed offset with respect to one another around the longitudinal axis of the stator casing, wherein each casing segment includes connection means and at least four casing segments engage with one another and form a composite. For the production of the stator casing, the casing segments are acted upon by an axial force component as a result of clamping, wherein the casing segments engage with one another, as a result of which a radial force component is generated and the composite is formed.

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 stator for a mud motor and methods for manufacturing and using the same, of which one such method includes obtaining a mud motor having a stator made at least partially from a rubber. At least a portion of the rubber is cured by at most about 90%. The method also includes deploying the mud motor into a well as part of a drill string. The rubber is not further cured prior to deploying the mud motor into the well. The method further includes generating torque using the mud motor by pumping a mud through the stator.

A compressor having a lower frame and a method of manufacturing the same are disclosed. The compressor may include a cylindrical shell, a rotational shaft rotatably mounted in the cylindrical shell, a rotor and a stator that rotates the rotational shaft, a compression device driven by the rotational shaft, a lower bearing configured to rotatably support one side of the rotational shaft, a lower frame configured to support the lower bearing, the lower frame being configured to be press-fitted into a lower end portion of the cylindrical shell, and a base configured to seal the lower end portion of the cylindrical shell. The lower frame may include a main body configured to be press-fitted onto an inner circumferential surface of the cylindrical shell and a flange that extends from the main body, the flange being configured to limit a press-fit depth by contacting the lower end portion of the cylindrical shell.