Abstract: A method for manufacturing a side housing of a rotary piston engine including the steps of forming a flame sprayed layer on the rotor sliding portion of the inner surface thereof and forming an anodized layer on a portion of the inner surface with the exception of the rotor sliding portion so as to eliminate a jamming of whetstone employed for an abrading process.

Abstract: A rotor housing for a rotary piston engine having improved gas sealing property between the inner surface and apex seals mounted on a rotor. The rotor housing has an inner surface applied with a hard layer such as chrome plating. The portions of the hard layer surrounding openings of plug holes at the inner surface side are formed with softened areas having lower hardness than the apex seals. The softened areas can be made by a high-energy beam such as a laser beam. Should portions surrounding the openings of the plug holes be thermally deformed to project inward and scratch the apex seals, the projected portions formed of the softened areas will be worn before the apex seals. Hence, uneven wearing of the apex seals can be avoided, which prevents degradation of the gas sealing property and consequently prevents drop in the compression pressure in the working chambers.

Abstract: A gear pump or motor comprises a pair of gears intermeshing with each other, a case body accommodating the pair of gears, and a hard layer formed on an inner surface of the case body. The hard layer is made of a material to be as hard as not to be cut by tooth tips of the pair of gears. The hard layer may be a ceramic coating or a composite coating layer which performs a grinding like operation on the tooth tips.

Abstract: A method for manufacturing an apex seal for a rotary piston engine comprising steps of preparing an apex seal blank made of ceramic material, and applying a high energy heating radiation to the sliding surface of the apex seal blank to form a roughened and porous structure on the surface portion of the apex seal blank. The high energy heating radiation is desirably applied to the apex seal blank under a non-oxidizing atmosphere so that an oxidization of the components of the ceramic material can be prevented.

Abstract: There is disclosed a rotor housing for a rotary piston engine which is designed particularly for high output power wherein the rotor housing inner wall surface is required to possess heat and wear resistant properties, improved affinity to lubricant oil, resistance to uneven wear which may cause chatter marks and scratches, oil retaining property, and less harmfulness to the apex seal. The rotor housing is formed at the inner wall surface with a porous Cr-Mo plating containing 0.50 to 0.90% in weight of Mo.

Abstract: The present invention relates to an apparatus and a method for finishing engine cylinder walls and reconditioning used engine cylinders. The invention also provides engine cylinders having a multilayer coating of a base layer, a steel layer and a layer of a tetrafluoroethylene fluorocarbon polymer, i.e., a "Teflon" wear surface.

Abstract: A Roots-type rotary fluid machine having resin-coated rotors fluid-tightly accomodated in a chamber formed in a housing structure which consists of a generally cup-shaped main housing body having a bore closed at its one end and open the other end, and a covering member which closes the open end of the bore in the housing body. The housing body includes a fillet portion which bridges an inner flat surface defining the bottom of the bore and facing one end face of each rotor, and an inner peripheral surface defining the periphery of the bore and facing the outer peripheral surface of each rotor. The fillet portion is formed along a line of intersection of extensions of the inner flat surface and the inner peripheral surface of the housing body, and inwardly into the bore from this line of intersection. The fillet portion has a generally triangular shape in cross section taken in a direction perpendicular to the above line of intersection.

Abstract: A housing mantle or casing produced in a compact construction for a rotary piston engine with a trochoidal-shaped dual-arc mantle runway or raceway and sealing strips arranged in corners of a triangular piston rotating upon an eccentric of an eccentric shaft so that the sealing strips slide along the mantle runway. A layer of steel forming the mantle runway and an outer layer of aluminum alloy is cast around the layer of steel. The layer or band of steel forming the runway has openings with radially outwardly bent-open edges which are cast of filled-out with cast metal forming the outer layer as far as to a plane which coincides with a base plane of the steel layer or band forming the mantle runway.

Abstract: A composite material suitable for use as an abradable seal is described. The seal comprises a high temperature stable fiber reinforced glass or glass-ceramic matrix base having at least one layer of abradable ceramic material, plasma sprayed or bonded to it. The ceramic abradable layer has a working temperature up to at least 3000.degree. F. (1648.degree. C.) and is oxidatively stable. The abradable seal has particular utility in a gas turbine engine.

Abstract: A pair of dry-sealed screw rotors for compressors which includes rotor tooth profiles in which an inter-tooth gap at a profile point on male and female rotor of a normal temperature is determined by an amount of interference due to thermal expansion caused during the operation of the compressors and an amount of minimum safety clearance necessary for the operation. The inter-tooth gap is further determined by a total thickness of seal coatings applied to the peripheral surfaces of the rotors at a profile point at which the thus determined gap is smaller than the total thickness of seal coatings. With the thus shaped rotor teeth, a most preferable seal line is achieved so as to produce an improved compression efficiency.

Abstract: A method for manufacturing an apex seal for rotary piston engines, comprising steps of providing a substrate made of an iron based material and having a portion wherein a sliding surface is provided, spraying the portion of the substrate with a molten-state Co-Mo-Si type intermetallic compound to form a coating of the compound, heating the coating of the compound by applying electron beams or laser beams to thereby make the intermetal compound dispersed in the substrate, heating the substrate to 580.degree. to 780.degree. C. to anneal it and machining the substrate into a configuration of the apex seal. The apex seal made in accordance with this method is also disclosed.

Abstract: A gear pump and motor is provided having increased life and efficiency as a result of improved wiping action of the gear teeth on the inner periphery of the pump chamber. This is accomplished by providing a non-smooth surface layer of a dissimilar metal such as a carbide on the tip ends of the teeth.

Abstract: A rotor for a rotary compressor having a metal central portion integral with two opposite end portions that are fiber-reinforced metal matrix composites having a matrix metal common to the central portion. Such rotors may be made by pressing inorganic fibers to form the end portions of the rotor, arranging the end portions in an opposing relationship in a mold to form the central portion between the end portions. Molten metal is placed into the mold such that it infiltrates the porous end portions while forming the central portion. Solidification of the metal forms fiber-reinforced metal-matrix composite end portions integral with the central portion.

Abstract: A gear mechanism, of the Moineau type, having an outer gear member with a helical inner surface. The motor also has a helical inner gear member within the outer member. A resilient sleeve is located between the inner and outer gear members, and has helical inner and outer surfaces. The inner gear member has one less helical thread than the inner surface of the resilient sleeve. The outer surface of the resilient sleeve is similar to, but rotationally offset from, the inner surface of the resilient sleeve.

Abstract: A scroll type fluid displacement apparatus is disclosed which includes a pair of scrolls each having a circular end plate and a spiral element extending from one end surface of the circular end plate. The pair of scrolls are maintained at an angular and radial offset so that both spiral elements interfit to form a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The fluid pockets are moved by relative orbital motion of the pair of scrolls. At least one of the circular end plates is provided with an anti-wear plate covering the end surface thereof in the area on which an axial end surface of the opposing spiral element slidably contacts. The circular end plate has a depressed portion at the center portion thereof to define an axial clearance between the anti-wear plate and the central portion of the end plate.

Abstract: A rotor for rotary piston engines having flanks coated with coatings of a modified fluorine resin. The modified fluorine resin is prepared with a fluorine resin, such as tetrafluoroethylene resin, and a binder resin, such as epoxy resin. The coating layer is formed by applying the modified resin to the flank surface of the rotor and drying it at a low temperature to have the resin adhered to the flanks. The coating is heat-resistant and has an anti-peel-off property. The coating is softened during engine operation so that it can catch deposits of unburnt residual substances. The rotor is therefore effective to prevent carbon lock.

Abstract: The present invention is directed to an apparatus useful for measuring the flow of an abrasive fluid. The present invention comprises a rotary metering device particularly useful for the measurement of oil well production fluids including sand and other abrasive materials. The present invention comprises a rotary metering device for repetitively producing a measuring chamber by the shuttle movement of a plurality of symmetrically disposed blades through slots in a rotor body into and out of a fluid flow channel between the rotor body and its housing. The rotor body of the present invention includes slots having surfaces comprised of a highly wear resistant metal, preferably having a hardness between about 40 and about 70 on the Rockwell C hardness scale to increase the service life of the meter.

Abstract: A sliding member having a number of oil retaining pores is manufactured by forming a hard plating layer on a metal base, forming a masking resist film on the hard plating layer by exposure to light and development, forming a number of pores in the hard plating layer by effecting electrolytic etching at a current density of 50 to 600 A/dm.sup.2, dissolving said masking resist film and removing the same, and forming a hard ceramic film on the hard plating layer by vapor phase plating.

Abstract: A vane type rotary compressor comprising a housing having a cylindrical inner wall surface, a rotatable sleeve disposed in the housing for rotation about its own longitudinal axis, a rotor disposed in the sleeve for rotation about its own longitudinal axis, which is offset from the longitudinal axis of the sleeve, and a plurality of vanes carried by the rotor to extend in radial directions and maintained in contact with the inner surface of the sleeve to divide the interior of the sleeve into a plurality of working chambers. The rotatable sleeve is made of an Si-Al type alloy containing 12 to 25% by weight of Si. The sleeve is age hardened and provided with an anodic oxidation coating. A further coating of wear resistant resin may be provided on the outer surface of the sleeve.

Abstract: A process for the production of valve seat rings by powder metallurgy wherein molybdenum disulfide in the range of about 0.5% to 1.5% by weight is added to a powder mixture containing 0.8% to 1.5% by weight graphite, 1.0% to 4% by weight lead, 0.5% to 5% by weight nickel, 1.2% to 1.8% by weight molybdenum, 9.6% to 14.4% by weight cobalt, and the remainder iron. The resulting powder mixture is pressed into valve seat rings at a pressing force between 40 and 60 and preferably 50 KN/cm.sup.2. The rings are then sintered in a neutral atmosphere at a temperature of 1100.degree. C. to 1200.degree. C., finally compressed at a pressing force above 120 KN/cm.sup.2 and heat-treated if required. The resulting valve seat rings have greatly improved wear properties when used in internal combustion engines using lead-free gasoline.

Abstract: A scroll-type fluid machine having a stationary scroll member and an orbiting scroll member each of which includes a disc-like end plate and a spiral wrap extending axially from one side of the end plate, with the wraps of the scroll members meshing with each other to define therebetween closed compression chambers. The orbiting scroll member is disposed between the end plate of the stationary scroll member and a frame of the machine with a back clearance between the other side of the end plate of the orbiting scroll member side thereof and the opposing surface of the frame. The orbiting scroll member is driven to make an orbiting movement with respect to the stationary scroll member so that the compression chambers are progressively moved towards the center of the scroll members while decreasing their volumes, to thereby suck a fluid through a suction port in the stationary scroll member and compress the same to discharge the compressed fluid through a discharge port formed in the stationary scroll member.

Abstract: A rotor housing for rotary piston engines has an inner wall formed with a first layer of chromium plating, and a second layer of nickel-fluorine resin composite plating formed on the first layer. The second layer of composite plating includes 9 to 40 vol. % of fluorine resin particles dispersed in nickel matrix and has a thickness of 5 to 25 microns.

Abstract: In a vane pump having a casing, an annular rotor rotatably disposed in the casing, a plurality of vanes longitudinally movably carried by the rotor, and a cam ring eccentrically disposed about the rotor with its cylindrical inner surface slidably contacting with the leading ends of the vanes, the cam ring having at the diametrically opposed portions thereof inlet and outlet ports which face in the same direction, there is proposed a measure in which a groove is formed in the cam ring near the inlet port and faces in the same direction as the inlet and outlet ports, and in which the groove is connected to the outlet port for balancing the cam ring.

Abstract: The pump has a casing, bearing members having portions for radial and axial mounting situated in the casing, at least one displacement element having journals rotatably received in the bearing members, a drive shaft extending from outside into the casing and sealed with respect to the casing by a sealing ring and drivably connected to one of the journals. At least the surfaces of each displacement element, of the journals, of the further elements and of the portion of the shaft inside the sealing ring are plasma-nitrided and the portions for axially mounting the journals are coated with a ceramic material. Also the portion of the shaft inside the sealing ring and the journals may be encased by a ceramic material.

Abstract: In a vane type compressor, in which a plurality of radial vanes are supported on a compressor shaft and extended through a rotary piston, each vane is formed of two wall portions spaced from each other and two ring portions receiving bearings for supporting the vanes on the shaft. The wall portions and the ring portions of each vane are formed as a one-piece element which may be produced by stamping-out and bending a sheet metal. A supporting structure of kernels of aluminum disposed in a honeycomb manner is inserted between two wall portions of each vane.

Abstract: A scroll-type fluid displacement apparatus is disclosed having a pair of scroll members each comprising an end plate and a spiral wrap extending from one side of the end plate. The spiral wraps interfit at an angular and radial offset to make a plurality of line contacts to define at least one pair of sealed-off fluid pockets. At least one of the scroll members has a discharge port or fluid hole near the center of the spiral element and is provided with an anti-wear plate on its end surface facing the other scroll member. The anti-wear plate is an involute plate that covers substantially the area of the end surface of the end plate on which the spiral wrap of the other scroll member makes contact during the orbital motion of the orbiting scroll member. The radially inner end of the anti-wear plate is spaced from the discharge port to avoid blocking the discharge flow or covering the discharge port. Therefore, the undesirable vibration of the anti-wear plate by fluid flowing through the port is avoided.

Abstract: The rotors (M, F) each have a conical outer profile and a constant pitch diameter, the rotors being mounted in opposition in the housing (1) with their axes (2, 3) parallel and their pitch diameters tangent (4). The grooves (5) of the female rotor (F) have a radial depth, in relation to the pitch diameter, which varies in inverse proportion to the outside diameter of the female rotor (F), and which, more specifically, have a circular cross-section the radius of which increases progressively in the direction of reduction of the outside diameter of the female rotor, the center of these radii remaining on the pitch diameter. The rotors are produced advantageously by molding a plastic or by casting a light alloy.

Abstract: A blade for a pump means of the type comprising a rotor rotatably supported within a housing with its center line being eccentrically disposed with respect thereto and a number of blades each shiftably received in respective radial slots formed in the rotor is disclosed. The base body of the blade is constituted from a solid lubricating material such as graphite and only its axial end surfaces are covered by layers of a synthetic resin which has excellent wear resistance, excellent heat resistance, and a low coefficient of friction.

Abstract: A rotary compressor comprises a rotor, a cylinder having an inner surface slidably contacting the rotor at one or more portions thereof, side plates disposed on both sides of the cylinder for supporting a rotor driving shaft, and axial insert type discharge valves disposed inside the cylinder. The cylinder includes an inner cylinder having an inner surface slidably contacting the rotor, and an outer cylinder surrounding the whole of the outer periphery of the inner cylinder.

Abstract: A vane pump having a cylindrical drum which revolves in a fixed housing part about an axis extending eccentrically to the housing part. The cylindrical drum drives at least one vane which is rotatably supported in the center of the fixed housing part so that the vane passes through an opening in the wall of the cylindrical drum to the inner surface of the housing part. Spring parts are disposed as sealing elements in the vicinity of the opening and are secured on each side of the vane on the cylindrical drum. At a distance from the fastening location, lip sections bent outward in convex fashion toward the vane so that the spring parts press against the respective associated outer faces of the vane for forming a seal, and also for centering the vane inside the opening when the pump is shut off.

Abstract: A scroll type fluid displacement apparatus having a pair of interfitting, relatively orbiting scroll members which define a plurality of moving fluid pockets. A fluid passage through the end plate of one of the scroll members has an elongated shape to reduce contact of the axial end of the other scroll member with the edge of the fluid passage, thereby reducing wear and improving volumetric efficiency.

Abstract: In a cam ring of a vane pump having a contoured bore whole wall is constantly and slidingly engaged by the radially outermost ends of vanes during rotation of a rotor, a radially inner part of the cam ring including the wall of the contoured bore is formed of sintered alloy while a radially outer part surrounding the inner part is formed of a material which prevents working fluid from oozing out therethrough. The outer part comprises a moulding of plastics, a die casting or a piece blanked from a steel sheet.

Abstract: The compressor, with rotating assemblies of low inertia, and of compact construction, comprises, housed in a housing, two hollow rotors (5, 6), for example out of plastic material, fixed respectively on a front shaft member (20, 21) journalled in a front bulkhead (26) and each supported at the rear by a rear bearing assembly (11) fixed to a rear end wall (2) of the housing and entirely contained within the internal space (7, 7) in the rotor. The drive is provided by the female rotor (6). The inner surfaces of the housing and the outer surfaces of the rotor threads are coated with an overthickened layer of an erodable coating material containing particles of a dry lubricant material.

Abstract: In a scroll fluid compressor including orbiting and stationary scroll members having end plates and wraps in vortical form in upstanding positions on the end plates meshing with each other to define therebetween spaces for compressing a fluid introduced through an inlet line and discharging the compressed fluid through an outlet line, flat plates in vortical form having surface finishes of higher precision than the end plates are placed in valleys between the outer wraps and the inner wraps of the scroll members to enable the wrap of the orbiting scroll member to move in orbiting movement while having the forward ends of the wraps in sliding contact with the surfaces of the flat plates in vortical form.

Abstract: The embodiment depicted comprises a pair of coacting rotors, in a rotary compressor, having interengaging lobes and grooves, the rotors being journaled in intersecting bores in a housing. The circumferential surfaces, and end walls of the bores are polymer-layered, and the rotors carry abrasive to machine the polymer to define an optimum clearance for rotor rotation within the bores, and in coaction together. Each rotor is polymer-coated and abrasive particles are borne in the polymer on the outer edges of the lobes and in discrete radial patterns on the rotor sides. The method defines the polymer-coating and abrasive particles-deposition steps.

Abstract: A pivoted vane rotary pump especially for pumping food-stuff and abrasive material comprises a split housing in which a hub is rotatable, with an annular channel formed between the outer periphery of the hub and the inner periphery of the housing. Pivoted vanes on the hub are rotatable about radial axes between a position in which they are crosswise of a transport portion of the channel between an intake and a discharge and a position in which they move edgewise in a restricted sealing portion of the channel between the discharge and the intake. The housing is lined with elastomeric plastic material which is vulcanized to metal housing parts of pumps for handling foodstuff or corrosive media, or is vulcanized to metal carrier plates removably secured to housing parts of pumps for handling abrasive media. The pump can be easily disassembled for cleaning and for servicing, including replacement of the plastic lining of pumps for abrasive media.

Abstract: In a vane compressor, a liner formed of iron or an alloy thereof is disposed along the endless camming inner peripheral surface of the cylinder forming part of the pump housing. The liner has at least one break extending thereacross and has its whole surface elastically permanently urging the cylinder in the radially outward directions. The use of the liner permits forming the rotor and the cylinder of aluminum or an alloy thereof. Preferably, the cylinder has its camming inner peripheral surface formed with a pair of elongate recesses extending parallel with the axis of the rotor and diametrically symmetrically arranged. The recesses are supplied with pumped compression fluid. The liner is partially urged by the rotor and located in the above recesses to maintain fluid tightness between the suction side and the discharge side in the pump housing.

Abstract: A fuel supply unit including a pump rotor and electromotor in which the elements forming the pump rotor are constructed from a non-friction creating or low wearing material.

Abstract: An injection unit intended to inject, for example, rubber into a mold comprises in principle two driven cog-wheels, which are located each in a hollow space in the unit housing and mesh with each other, and which in an injection chamber located in direct connection to the engagement zone of the cog-wheels subjects material fed-in to a high pressure, so that the material is pressed out of the injection chamber to a mold.

Abstract: A rotary machine has a plurality of rotors rolling over one another and defining therebetween and end covers at least one working chamber, and at least one sealing plate at at least one side of the rotors and arranged so that an opposite side of the sealing plate communicates with the working cavity and the working medium flowing to the opposite side of the sealing plate presses the latter against one end face of the rotors. Insert members of bearing have conical surfaces receiving the shaft and can turn about their axes to compensate for wear.

Abstract: A sliding vane compressor for use in refrigeration systems includes a rotatable hollow shaft, a cylindrical compressor rotor which surrounds the shaft, end covers enclosing the compressor rotor and a pair of vanes disposed within the rotor to compress a working medium entering the rotor. The compressor rotor and end covers have end faces in a contact area therebetween. At at least one of end faces of either rotor or end cover, a number of spirally-shaped grooves are formed curved in the direction of rotation of the rotor shaft. These grooves extend from the periphery of the respective end face toward the center thereof but short of said center to produce a flow preventing leakage of the working medium between the low pressure region and the high pressure region in the compressor.

Abstract: Metal/ceramic abradable seals of the type used in jet aircraft are improved by using a substrate which is able to deform during cooling from the brazing temperature and then rendering the substrate rigid after the cool down.

Abstract: A rotary positive displacement pump of the pin roller type comprising a pump housing made of aluminum having a pump chamber with the inner periphery being cylindrical, which is fixed between a pump base and a pump case, a rotor eccentrically located within the pump chamber and driven by a motor, a plurality of rollers made of synthetic resin which is inserted in clearance grooves formed on the outer periphery of the rotor, wherein a centrifugal force generated when the rotor rotates moves the rollers toward the inner wall of the pump housing thereby to form a pump operation space.

Abstract: A compressor-expander having a vaned rotor in which the vanes rotate about an axis which is canted with respect to the rotor axis. The housing of the device has a disc-shaped main cavity having adjacent hub recesses which are concentrically spherical. The cavity is in the form of a doubly truncated sphere canted with respect to the shaft axis. The rotor has a central spherical portion for mating with the recesses and includes an integral Saturn-like ring extending to the outer wall of the cavity to divide the cavity into first and second complementary sides of annular wedge shape. The vanes occupy radially extending slots in the rotor and serve to separate each side into successive chambers which vary cyclically in volume as the shaft rotates without requiring the vanes to bodily reciprocate either radially or axially. Each side is provided with inlet and outlet ports.

Abstract: Hydraulic equipment useful as a pump or motor intended for applications where hydraulic fluid is exposed to contamination by abrasive particulate material is disclosed. Leakage paths from the high pressure chamber in a gear pump or motor are provided with inserts of an abrasion and erosion resistant material at points where wear from abrasives in the hydraulic fluid is aggravated. In particular, the bearing surfaces of the pressure loaded side plates are provided with an insert of abrasion and erosion resistant material in the mesh region of the teeth. Erosion and abrasion resistant rings are located on the side plates in the region surrounding the openings for the shafts and extending interiorly of the tooth root circle to the journal bearings.Also disclosed are radial sealing shoes which are supported by the side plates and are radially urged into sealing relationship with the tips of the teeth by the pressure existing at the high pressure side of the gears.

Abstract: In a displacement machine operating according to the spiral principle and having two displacement elements presenting respective axially interengaging sprial-shaped walls, and drive means connected between the elements to produce a relative translatory circular movement therebetween, an elastic suspension is provided to support at least one of the displacement elements for permitting elastic movement between the elements in a plane perpendicular to the axis of translatory circular movement.In such a displacement machine, whether or not the elastic suspension is provided, the walls of the displacement elements are preferably made, at least at the surfaces contacting one another, of respectively different materials presenting a low mutual coefficient of friction.

Abstract: A pneumatic rotary motor comprising a body to which is secured a bracer bushing closed by a cover. A deformable bushing is freely housed within the bracer bushing and is interposed between the cover and the casing. The bushing has a bore and two opposed longitudinal circular recesses extending from the bore. Two intermeshed rotary gears extend longitudinally in the bushing and are centered in a respective recess, the gears teeth sealably contacting the internal bushing along the circular recesses. The gears have shafts respectively supported for rotation in the cover and the casing and form opposed working chambers on either side of the recesses and in communication with openings provided in the cover for the intake and exhaust of a fluid. Screws, or the like, are mounted in the bracer bushing for abutting against the internal bushing to produce deformation thereof at the recesses for effecting sealed contact with the teeth of the gears.

Abstract: A rotary fluid pump having a rotor with carbon vanes disposed in a rotor chamber. A cylindrical aluminum sleeve is force fitted into a mating arrangement with the inner peripheral surface of the rotor housing. The aluminum sleeve reduces the friction between the housing and the vanes. The sleeve may be of the same axial length or shorter than the rotor housing. If it is equal end seal plates are employed to provide the necessary expansion gap or end washers are employed at the housing to increase the effective axial length.

Abstract: An improved vane compressor is provided which employs a rotor comprising: a hollow boss element into which a rotary shaft is force fitted; at least two pairs of lateral plates formed upright on a peripheral surface of said boss element; and a peripheral element fitted between opposed ones of the lateral plates of adjacent pairs; wherein said boss element and said lateral plates are made of a metal having a sufficient mechanical strength, and said peripheral element is made of a material which has a smaller specific gravity than that of said metal and has a coefficient of friction small enough to keep sliding contact faces of parts facing said rotor in the pump section of the compressor from undergoing substantial abrasion.

Abstract: A sliding vane compressor has a housing and a rotor mounted in the housing. The rotor has axial endfaces which are juxtaposed with respective housing surfaces from which they must be kept at a predetermined spacing. This spacing is obtained by mounting in open recesses of the axial rotor endfaces respective elements of a material having a higher coefficient of thermal expansion than the material of the rotor itself. As the compressor comes up to operating temperatures the resulting thermal expansion of these elements causes them to protrude beyond the axial rotor endfaces by a distance corresponding to the desired spacing.