A method of casting a rotor using a cavity and core mold allows a longitudinal slot oriented transversely to the axis of rotation to be finish ground to high precision and tight tolerances by casting the slot to have a wider section which extends from the axis to a radius greater than the radii of the hubs of the rotor, and a narrower section which extends from the wider section to the outer surface of the rotor. The geometrical relation of the slot sections to the hubs as cast permits the grinding step to be performed without forming a leak path in either of the hubs.

A coupling element for connecting a helix-shaped eccentric screw pump rotor to a drive shaft, with a drive shaft receiving portion and a rotor connecting portion arranged at an opposite end of the coupling element from the drive shaft receiving portion, the rotor connecting portion is constituted as a hollow cylinder for receiving a rotor end of the screw pump rotor, wherein the hollow cylinder has at least two inner circumferential surfaces which are complementary to the rotor and have a radius which is fixed with respect to the cross-sectional center of the hollow cylinder.

In a rotary compressor, a lower end plate cover is formed in a shape of a flat plate, and has a through hole that is provided to penetrate in the thickness direction of the lower end plate cover and that communicates with a communication groove. When a sectional area of the communication groove which passes through a center line of a rotation shaft, and is on a section along the rotation shaft direction is S1 [mm.sup.2], an area in which the through hole and the communication groove overlap each other on a plane orthogonal to the rotation shaft is S2 [mm.sup.2], and an excluding capacity of a lower cylinder chamber is V [cc], each of 0.10(S2/V)0.50, and 1.0(S2/S1)7.0 is satisfied.

A stator for use in a positive displacement motor or a progressing cavity pump. The stator comprises an elastomer mix preferably including rubber and a fiber reinforcement. The fiber reinforcement includes a plurality of fibers. The elastomer mix is formed into a stator via an injection molding process. The injection molding process includes a shear flow step in which shear flow is induced in the elastomer mix while the elastomer mix is in an uncured state. The shear flow modifies the orientation of the fibers into an advantageous modified fiber orientation. Shear flow is induced preferably via differential rotation of injection mold assembly elements during the injection molding process. Methods of manufacturing the stator are also disclosed.

A gear pump comprising:a pair of gears (2) able to interact with a fluid crossing the pump (1);a housing seating (3) of said pair of gears (2), said housing seating (3) comprising a rest plane (30) of a shim (4);a delivery conduit (6) which develops from said housing seating (3) and comprising an inlet mouth (60). The inlet mouth (60) of the delivery conduit (6) is at a distance from an intersection (7) between a rest plane (30) of the shim (4) and remaining parts of the housing seating (3).

The present invention is directed to providing a pump capable of achieving improvement of a discharge efficiency. A pump configured to suck and discharge fluid includes a housing, a driving shaft rotatably supported on the housing, and a pump element contained in the housing and configured to be rotated by the driving shaft. The housing contains therein an intake passage into which the fluid delivered from outside the housing is introduced, an intake port configured to guide the fluid from the intake passage to the pump element, a discharge port into which the fluid pressurized by the pump element is introduced, and a discharge passage configured to discharge the fluid delivered from the discharge port to outside the housing. The discharge passage includes a first passage including a beginning portion connected to the discharge port and a termination portion. The first passage extends as far as the termination portion around one straight line. The discharge passage further includes a second passage connected to the termination portion of the first passage and opened to outside the housing. A shape of the first passage in cross section taken along a direction perpendicular to the straight line changes continuously from the beginning portion to the termination portion.

In a stator injection molding centralization technique, a mold core is disposed inside a stator tube, thereby forming an annulus between the stator tube and mold core. The mold core includes a pitch length defined between a first and second lobe tip of the mold core. A centralizing member is positioned in the annulus, which has a length at least as long as the pitch length of the mold core. During the injection molding process, elastomeric material is injected into the annulus behind the centralizing member, which is located adjacent to the injection point. As the elastomer is injected, it displaces the centralizing member ahead of it along the annulus. As the centralizing member moves through the annulus, it supports the mold core, thus preventing the sag effect.

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.

There is provided a liquid feeding type screw compressor that can reduce size and weight and improve vibration insulation and sound insulation. A liquid feeding type screw compressor includes as components: a compressor main body; a motor driving the compressor main body; and a gas-liquid separator separating a liquid from a compressed air discharged from the compressor main body. The motor is arranged above the compressor main body. The gas-liquid separator is arranged below the compressor main body. A compressor main body casing constituting an inner cylindrical space forming a compression operation chamber together with the screw rotor and constituting the contour of the compressor main body and a casing constituting the contour of another component consist of an integrally molded single member.

A cast for producing end plates for a pump assembly, the cast comprising a base portion and a pair of projections, the pair of projections providing material to machine bearing assembly housings for accommodating drive and idler shafts in the pump assembly. Also provided is an inner plate bushing for an end plate in a pump assembly, the inner plate bushing comprising a collar extending from a flange, the collar to be inserted into a mounting recess in the end plate with the flange seating flush with a surface of the end plate, the surface area of an end of the collar being larger than an inner surface of the flange.