Abstract: The invention is based on a sieving device with at least one rotary drum unit comprising a plurality of sieving openings, said sieving openings being respectively arranged around a centre point of the sieving openings and being categorized in at least one structure group and at least one further structure group and at least one further structure group, wherein the first structure group the centre points of neighbouring sieving openings are arranged at a first intra-distance to one another, and wherein in the further structure group the centre points of neighbouring sieving openings are arranged at a further intra-distance to one another, wherein the smallest structure distance between a centre point of at least one sieving opening in the at least one first structure group and a nearest situated center point of at least one sieving opening in the at least one further structure group is greater than the first intra-distance.

Abstract: The invention is based on a sieving device with at least one rotary drum unit (14a; 14b) comprising a plurality of sieving openings (42a; 42b), said sieving openings (42a; 42b) being respectively arranged around a centre point of the sieving openings (42a; 42b) and being categorized in at least one first structure group (44a, 44a?, 44a?; 44b, 44b?) and at least one further structure group (46a, 46a?; 46b, 46b?), wherein in the first structure group (44a, 44a?, 44a?; 44b, 44b?) the centre points of neighbouring sieving openings (42a; 42b) are arranged at a first intra-distance (48a; 48b) to one another, and wherein in the further structure group (46a, 46a?; 46b, 46b?) the centre points of neighbouring sieving openings (42a; 42b) are arranged at a further intra-distance (50a; 50b) to one another.

Abstract: In order to support a mud-driven impeller of a down-hole turbogenerator in such a manner as to provide long bearing service life in the hostile conditions down-hole, a bearing sleeve is provided which comprises an outer shell of marine brass and an inner lining of nitrile rubber bonded to the inside surface of the shell. The lining extends axially beyond the end of the shell to form a portion positioned beyond the end of the shell and turned over the end of the shell. This portion comprises radical lands separated by radial grooves, and the radial lands define axial bearing surfaces for cooperating with an axial bearing surface of a bearing member which the bearing sleeve surrounds in use.

Abstract: A down-hole signal transmitter includes an annular impeller mounted on a cylindrical casing and arranged to be driven by the mud flow passing along a drill string. Each of the impeller and the casing incorporates two sets of magnets with their poles arranged axially relative to one another such that axial movement of the impeller in one direction will tend to be resisted by a force of magnetic repulsion acting between the first set of casing magnets and the second set of impeller magnets and axial movement of the impeller in the opposite direction will tend to be resisted by a force of magnetic repulsion acting between the second set of casing magnets and the first set of impeller magnets. In this way the axial thrust due to the fluid flow is largely taken up. Furthermore the magnetic coupling between the magnet sets in such as to enable driving torque to be transmitted by the impeller to a rotary drive member on which the casing magnets are mounted.

Abstract: A down-hole signal transmitter includes an annular impeller mounted on a cylindrical casing and arranged to be driven by the mud flow passing along a drill string, and an annular stator fixed to the casing upstream of the impeller. The stator has blades canted in one sense relative to the mud flow direction, whereas the impeller has blades parallel to the mud flow direction. The stator blades thereby cause the mud flow to impact on the impeller blades at such an angle that a small or negligible thrust results at the impeller bearings. It is therefore possible to insure a long service life for the bearings.