Abstract: A method of draining oil from a transmission housing, of an oil-injected screw compressor comprising a compressor housing containing rotor means and a transmission housing. A shaft of the compressor extends into the transmission housing from the compressor housing and the transmission housing is underslung relative to the compression housing. The first portion of the compressor intake stroke, or rotation, is prevented from being filled with intake gas such that a depression is created. Said depression is applied via a bore to a sump portion of the transmission housing, so that the absolute pressure differential between the sump and the suction portion of the rotor means draws oil out of the sump and into the rotor spaces. A compressor employing this method of draining oil is also described.

Abstract: A compressor comprises one or more stages each including an impeller mounted for rotation on a shaft and rotatable in an impeller housing. A transmission is drivingly connected to the shaft and a bearing is provided supporting the shaft. Lubrication means are provided for the bearing which provide a continuous lubricant seal around the shaft between the shaft and the bearing to prevent air leaking through the bearing. A chamber is located between the impeller housing and the bearing for collecting excess lubricant and has an outlet for draining lubricant.

Abstract: Hydraulically powered percussive apparatus for breaking rock, drilling etc. in which a combined spool valve and hammer reciprocates in the bore of a cylinder structure. A high pressure fluid inlet leads to the bore and a low pressure outlet leads from the bore. A fluid flow passage communicates with the bore at two axially spaced locations. As the hammer reciprocates, it cyclically connects, via the bore, the inlet to the passage and the outlet to the passage. Pressures in the inlet and outlet fluctuate between fairly narrow limits whereas the pressure in the passage fluctuates between a pressure approximating inlet pressure and a pressure approximating outlet pressure. The hammer has two operating faces. The first of these is exposed to the relatively steady inlet pressure and the second is subjected to the widely varying pressure in the passage.

Abstract: A reciprocating hydraulic motor, for example for a rotary percussive drilling head, includes a piston and cylinder having a piston face exposed to the pressure in a compression chamber which is connected through ports controlled by the piston to a supply pressure at one end portion of its stroke, and to exhaust at an opposite end portion of the stroke, while between these end portions of the stroke is a compression/expansion travel during which the compression chamber is closed and the liquid in it alternately expands over a higher range of pressure and is compressed over a lower range of pressure.For returning the piston, in the direction in which liquid is compressed, one of two opposed faces of the piston is exposed to the pressure in a biasing chamber which communicates permanently with a constant pressure supply while the other communicates with the compression chamber.

Abstract: In a rotary piston machine the main rotary piston makes sealing engagement with at least one end wall of the main rotor bore and at least one inlet port is provided in that end wall and is located within the compass of the cylindrical portion of the main rotary piston, the main rotary piston is cut-away to open the inlet port to the working spaces of the machine, which are defined by the main and auxiliary rotor bores, the outer peripheries of the rotary pistons and the end walls of the housing, in order to induce working fluid into such spaces.

Abstract: A down-the-hole pneumatic drill in which the reciprocating hammer-piston slides over a ported tubular structure mounted centrally in the cylinder of the drill body and providing two longitudinal passages through which passes all the pressure air required below the piston. The tubular structure comprises an outer tube having a close-fitting inner tube within it, the inner tube being formed in its wall with a longitudinal indentation closed at the lower end, one of the passages being defined by the indentation and the wall of the outer tube and the other passage being defined by the interior of the inner tube. The tubular structure is provided with ports controlled by the sliding hammer-piston, certain of these ports being formed by registering holes in portions of the walls of the inner and outer tubes which lie in contact with one another.

Abstract: A drilling machine has a drill carriage pivotally mounted on the upper end of a jib whose lower end is pivoted to a support structure. To maintain the drill carriage in parallelism as the jib pivots, two hydraulically interconnected hydraulic jacks are provided, namely a slave jack pivotally connected between the jib and support structure to form a first triangle with its corners at the pivot point of the jib and the two pivot connections of the jack; and a follower jack pivotally connected between the jib and the drill carriage to form a second triangle with corners at the drill carriage pivot point and the two pivot connections of the follower jack. These two triangles are similar triangles.

Abstract: A centrifugal compressor has at least one stage with its own impeller shaft, an inlet and an outlet for gas, and an epicyclic gear train for driving the impeller shaft. The epicyclic gear train comprises three members, a sun gear, a ring gear and a carrier on which a series of planet gears are mounted in mesh with the sun and ring gears. Means is provided for connecting a power input to one of the members of the epicyclic gear train, and means is provided connecting a second of the members to the impeller shaft. Means are provided for controlling the rotational speed of the third of the members to vary the speed of the impeller shaft of the compressor, and actuating means are provided for actuating the control means in response to the pressure of the compressed gas at the outlet.

Abstract: A centrifugal compressor has at least one stage with its own impeller shaft and a gear train for driving the impeller shaft. The gear train includes a plurality of meshing parallel shaft gears comprising two input gears either of which can receive drive from a prime mover. The ratio of the number of teeth of the input gears is such that the relative shaft speeds of the input gears are 5n: 6N where n is 1 or 2 and N is 1 or 2.

Abstract: A rotary piston machine is provided in which the, or each, auxiliary rotary piston has a portion projecting axially beyond at least one end face of the main rotary piston, and in which a transfer port is provided in an end wall of the main rotor bore leading to the part of the auxiliary rotor bore containing said projecting portion of the auxiliary rotary piston and a discharge port is provided leading from said part of the auxiliary rotor bore at a position spaced from the transfer port, said projecting part of the auxiliary rotary piston providing a rotary valve for opening and closing communication between the transfer port and the discharge port at the required times during the rotational cycle of the machine.