Abstract: A screw pump includes a pump housing in which a pump spindle is rotatably mounted with the involvement of a hydrostatic thrust bearing for absorbing the axial thrust which is produced at the spindle during operation, the hydrostatic thrust bearing being formed by a housing-fixed bearing surface, against which an end-face, spindle-fixed bearing surface of the pump spindle is indirectly supported, by virtue of the fact that the housing-fixed bearing surface and the spindle-fixed bearing surface form a bearing gap therebetween, which bearing gap is fed, in its central region, with a pressure fluid which flows out through the bearing gap in the radial direction, preferably into the intake region, and the hydrostatic pressure of which counteracts the axial thrust.

Abstract: A screw spindle pump having a spindle housing, in which a drive spindle and at least one running spindle which meshes therewith are received in spindle bores, an outer housing which encloses the spindle housing, and a cover component which is placed axially onto the outer housing and on which both an axial fluid inlet port and a lateral fluid outlet port are provided, wherein the fluid inlet port communicates with a fluid inlet of the spindle housing and the fluid outlet port communicates with a fluid outlet of the spindle housing, wherein the cover component is fastenable to the outer housing in a plurality of marked rotational positions with a first pitch, and wherein the spindle housing is fastenable to the cover component and/or in the outer housing in a plurality of marked rotational positions with a second, smaller pitch.

Abstract: The present disclosure relates to a cooling module in which a plurality of cooling water outlets through which cooling water is discharged are formed in an outer housing, an inner housing into which a first screw and a second screw are inserted inside the outer housing, and a communication hole formed in the inner housing communicates with a plurality of cooling water outlets, in which a cooling module or a cooling water system including a plurality cooling water outlets formed in one screw pump is simple, reduces the number of parts, and simplifies a package.

Abstract: A screw spindle pump, including a housing and a drive spindle accommodated therein and at least one running spindle which meshes with the latter and which has in each case two terminal end surfaces. A stop surface is provided axially adjacent to at least one end surface of the running spindle, wherein the running spindle is accommodated displaceably with an axial clearance perpendicular to the stop surfaces.

Abstract: A multi-channel, rotary, progressing cavity pump comprising a housing having an outer wall defined by overlapping cylindrical chambers, a first end wall defining an inlet port, and a second end wall defining an outlet port, said inlet and outlet ports communicating with each chamber; meshed, lobed rotors disposed within said housing and comprising a plurality of lobes having first and second axially-facing end surfaces, said surfaces defining a twist angle, and each lobe defining a helix angle; each rotor being disposed in one chamber of said housing so that a lobe apex sealingly engages the outer wall defined by its associated chamber, and said surfaces sealingly engage said end walls; whereby, when said rotors are rotated in the same direction in unison, (i) an axial progressing cavity is created between said rotors, and (ii) a plurality of peripheral progressing cavities are created between said rotors and said housing.

Abstract: A multi-rotor screw compressor includes a housing, a sun rotor, and first and second planet rotors. The first planet rotor intermeshes with the sun rotor to define a first compression pair. The second planet rotor intermeshes with the sun rotor to define a second compression pair. The first and second compression pairs are rotatably mounted in the housing. The housing includes a first port, a portion of which is in communication with the first compression pair, and a second port, a portion of which is in communication with the second compression pair. The portions of the first and second ports which communicate with the first and second compression pairs have a different geometry for offsetting pulsations in a working fluid flowing through the ports.

Abstract: Rotor for a screw compressor includes a rotor body (2) and a shaft (6), whereby said shaft extends at least with a part into or through a central or approximately central axial bored hole or passage (5) in the rotor body (2). The shaft (6) has a stretch element (7), whereby the rotor body (2) or at least a part thereof is held on the shaft (6) by means of tension elements (11 and 12) which are locked or can be locked axially with respect to the shaft and which are connected with each other by means of the stretch element (7).

Abstract: The invention relates to a pump, a pump system and a method for pumping a medium. The pump for pumping medium comprises an inlet, an outlet, a drivable spindle and at least two follower spindles, wherein the drivable spindle and the at least two follower spindles are provided at a mutual angle to each other.

Abstract: Disclosed herein is a single screw gas compressor having a housing including a cylindrical bore, a primary and secondary gate rotors mounted for rotation in the housing, each gate rotor having a plurality of gear teeth, a main rotor rotatably mounted in the bore and having a plurality of grooves and a plurality of threads, wherein each groove meshingly engages at least one of the gear teeth from each gate rotor, a primary economizer port in communication with the cylindrical bore, and a secondary economizer port in communication with the cylindrical bore.

Abstract: Designs for multiple segment lobe pumps are shown. The designs include pumps using rotors having two lobes to a plurality of lobes and segments that include two segments to a plurality of segments. Designs for both vertical or straight walled conventional lobed rotors as well as helical lobe rotors are shown. The designs are applicable to a variety of rotors and number of segments. In one particular case the designs enable a three lobe helical pump.

Abstract: A screw compressor comprises a first meshing body and a second meshing body. The first meshing body has plural helical flutes disposed around a first rotating shaft. The second meshing body has plural projections or lobes disposed around a second rotating shaft. At least one of the projections or lobes is arranged non-uniformly with respect to the other projections or lobes in a circumferential direction of the second rotating shaft. The plural helical flutes are arranged to be meshable with the plural projections or lobes, in a circumferential direction of the first rotating shaft.

Abstract: An insulated glass secondary edge sealing device that dispenses sealant to insulated glass units including at least two panes of glass separated by a spacer, including a fixed sealant dispensing head, a table that supports the insulated glass units, a fence, a depth sensor, a linear motion encoder, a metering device. The sealant dispensing head has a dispensing nozzle and a corner dam. The dispensing nozzle includes a floating insulated glass unit contact surface and the corner dam is shiftable between a retracted position and an extended position. A control unit receives signals from the depth sensor and the linear motion encoder and controls the metering device to dispense a measured flow of sealant based on the depth of the inset of the spacer and the movement of the insulated glass unit parallel to the fence and relative to the encoder.

Abstract: In a single screw compressor, gates (51) of gate rotors (50) are to be engaged with spiral grooves (41) of a screw rotor (40). In each spiral groove (41) of the screw rotor (40), an area extending from a start point of the spiral groove (41) to a position in a compression stroke is a suction-side portion (45), and the remaining portion (portion up to a terminal point of the spiral groove (41)) is a discharge-side portion (46). In the discharge-side portion (46), a clearance between a wall surface (42, 43, 44) therein and the gate (51) is substantially “0 (zero).” A clearance between the wall surface (42, 43, 44) in the suction-side portion (45) and the gate (51) is wider than that between the wall surface (42, 43, 44) in the discharge-side portion (46) and the gate (51), and is gradually narrowed from the start point toward the terminal point in the spiral groove (41).

Abstract: In a screw rotor (40), a first suction-side area (45) is formed in a first side wall surface (42) of a spiral groove (41). In the first side wall surface (42), a portion extending from a start point to a point until immediately before a compression chamber (23) is in a completely-closed state defines the first suction-side area (45). The first suction-side area (45) is thinner than a portion of the first side wall surface (42) other than the first suction-side area (45), and does not contact a gate (51) of a gate rotor (50).

Abstract: A single screw compressor structure includes a screw rotor and a casing. The screw rotor has a plurality of helical grooves formed in an outer peripheral surface thereof. The casing houses the screw rotor. The screw rotor includes a main tapered portion having a tapered outer diameter that becomes larger from an intake side toward a discharge side of the screw rotor, and a reversely tapered portion that is located on a downstream side of a maximum outer diameter portion of the outer surface and on the discharge side of the main tapered portion. The reversely tapered portion has a reversely tapered outer diameter that becomes smaller as the reversely tapered portion extends away from the maximum outer diameter portion.

Abstract: An axial flow positive displacement gas turbine engine component such as a compressor or a turbine or an expander includes a rotor assembly extending from a fully axial flow inlet to a downstream axially spaced apart axial flow outlet. The rotor assembly includes a main rotor and one or more gate rotors rotatable about parallel main and gate axes of the main and gate rotors respectively. The main and gate rotors having intermeshed main and gate helical blades extending radially outwardly from annular main and gate hubs, circumscribed about, and wound about the main and gate axes respectively. Intersecting main and gate annular openings in the axial flow inlet extend radially between a casing surrounding the rotor assembly and the main and gate hubs. The main helical blades transition from 0 to a full radial height in a downstream direction in an inlet transition section.

Abstract: A screw pump includes a casing including a main accommodating bore and plural sub accommodating bores, a main rotor adapted to be rotatably accommodated in the main accommodating bore, and plural sub rotors adapted to be respectively rotatably accommodated in the sub accommodating bores. Each sub rotor is adapted to engage the main rotor. A cross sectional shape of a flank surface of the main rotor, which is taken in a direction perpendicular to an axial direction of the main rotor, is formed along an epitrochoid traced by an edge of the sub rotor not to include an undercut shape. Further, a cross sectional shape of a flank surface of each sub rotor, which is taken in a direction perpendicular to an axial direction of the sub rotor, is formed along an epitrochoid traced by an edge of the main rotor not to include an undercut shape.

Abstract: A helical gear pump includes a second helical gear provided coaxially with a drive helical gear, a third helical gear engaged with the second helical gear and provided on a third shaft different from a shaft of the drive helical gear and a shaft of a driven helical gear, and a bearing for supporting the third shaft and receiving a thrust force.

Abstract: A positive displacement capture apparatus contains a plurality of positive displacement capture devices which each contain a rotor portion positioned inside a casing portion to act as a least area rotor which captures a volume and moves the volume along the length of the separator. The rotor portion contains a plurality of lobes which interact with grooves in the casing portion, such that the interaction of the lobes and grooves create barriers which capture the volume. The creation of the volume creates a flow barrier between a downstream end of the separator and an upstream end of the separator. The flow separator is coupled to a combustion portion to provide a flow of material to the combustion portion. The plurality of positive displacement capture devices are positioned, oriented and rotational timed such that eccentric loads created by the rotation of the rotor portions cancel each other out during operation.

Abstract: A multi-rotor compressor and method of manufacturing is provided. The compressor includes a housing with a plurality of identical planet rotors. The planet rotors are equally spaced apart at a fixed distance from a centerline. A single sun rotor is provided that is disposed to cooperate with the plurality of identical planet rotors in the compression of gas. The number and radial spacing of the plurality of identical planet rotors about said single sun rotor may be arranged in different configurations to change an output capacity parameter for said compressor.

Abstract: An axial flow positive displacement gas turbine engine component such as a compressor or a turbine or an expander includes a rotor assembly extending from a fully axial flow inlet to a downstream axially spaced apart axial flow outlet. The rotor assembly includes a main rotor and one or more gate rotors rotatable about parallel main and gate axes of the main and gate rotors respectively. The main and gate rotors having intermeshed main and gate helical blades extending radially outwardly from annular main and gate hubs, circumscribed about, and wound about the main and gate axes respectively. Intersecting main and gate annular openings in the axial flow inlet extend radially between a casing surrounding the rotor assembly and the main and gate hubs. The main helical blades transition from 0 to a full radial height in a downstream direction in an inlet transition section.

Abstract: A three rotor screw compressor is provided with a bearing cover, and an integral discharge case having a divider wall formed integrally with the bearing cover. The bearing cover closes bearing chambers for each of three rotor shafts, and the divider wall divides a plenum into two distinct chambers. By providing the divider wall, noise and efficiency losses from intermixing of two discharge flows from two separate compression chambers is eliminated. By forming a divider wall integrally with the bearing cover, leakage which has existed in the prior art is eliminated.

Abstract: A method of designing rotors for a Roots blower comprising a housing having cylindrical chambers, the housing defining an outlet port (19). The blower includes meshed, lobed rotors (37,39) disposed in the chambers, each rotor including a plurality N of lobes (47,49), each lobe having first (47a,49a) and second (47b,49b) axially facing end surfaces. Each lobe has its axially facing surfaces defining a twist angle (TA), and each lobe defines a helix angle (HA). The method of designing the rotor comprises determining a maximum ideal twist angle (TAM) for the lobe as a function of the number N of lobes on the rotor, and then determining a helix angle (HA) for each lobe as a function of the maximum ideal twist angle (TAM) and an axial length (L) between the end surfaces of the lobe. A rotor designed in accordance with this method is also provided.

Abstract: A pump including at least three rotors each being provided with a generally helical screw thread, the rotors being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the rotors or where one of the rotors has a larger outer diameter than the other rotors the outer diameter of the larger diameter rotor.

Abstract: A compressor includes a housing and one or more working elements. A muffler is located downstream of the discharge plenum and a helmholtz resonator is located in the discharge plenum upstream of the muffler.

Abstract: A pump including a power rotor and an idler rotor, the rotors each being provided with a generally helical screw thread and being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, the power rotor being connected to a driving means operation of which causes rotation of the power rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the power rotor, the depth of the threads is less than or equal to 0.2 times the outer diameter of the power rotor, and the root diameter of the idler rotor is less than 0.31 times the outer diameter of the power rotor.

Abstract: A pump including at least three rotors each being provided with a generally helical screw thread, the rotors being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the rotors or where one of the rotors has a larger outer diameter than the other rotors the outer diameter of the larger diameter rotor.

Abstract: A compressor has at least three-rotors. A first compression path between first inlet and outlet ports is associated with interaction of the first and second rotors. A second compression path between second inlet and outlet ports is associated with interaction of the first and third rotors. At least partial independence of the ports permits the first and second inlet ports to be at a different pressure or the first and second outlet ports to be at a different pressure. Fully or partially separate circuits in a refrigeration or air conditioning system may be associated with the first and second compression paths.

Abstract: A compressor includes a housing and one or more working elements. A muffler is located downstream of the discharge plenum. A centerbody is located in the discharge plenum upstream of the muffler spanning a major portion of a length between a bearing case and the muffler.

Abstract: A screw compressor is provided with a discharge chamber that receives alternating flows of compressed fluid from two compression chambers located on opposed sides of the screw compressor. The discharge chamber is provided with a central baffle plate separating the two flows. The baffle plate changes the fluid frequency of the system, and ensures that the fluid system will not operate at a frequency that approaches the natural frequency of the overall compressor, thus reducing undesirable vibrations. The baffle plate also reduces the magnitude of the fluctuations and the resultant noise.

Abstract: A screw rotor device has a housing with an inlet port and an outlet port, a male rotor, and a female rotor. The male rotor has a pair of helical threads with a phase-offset aspect, and the female rotor has a corresponding pair of helical grooves. The female rotor counter-rotates with respect to the male rotor and each of the helical grooves respectively intermeshes in phase with each of the helical threads. The phase-offset aspect of the helical threads is formed by a pair of teeth bounding a toothless sector. The arc angle of the toothless sector is a least twice the arc angle that subtends either one of the teeth. The helical grooves have a radially narrowing axial width at the periphery of the female rotor. The male and female rotors may include a buttress thread profile and may be limited in length to a single pitch.

Abstract: A pump including at least three rotors each being provided with a generally helical screw thread, the rotors being mounted for rotation in a housing such that the screw threads of the rotors mesh and rotation of one rotor causes rotation of the other rotor, wherein the pitch of the threads is less than 1.6 times the outer diameter of the rotors or where one of the rotors has a larger outer diameter than the other rotors the outer diameter of the larger diameter rotor.

Abstract: A compressor has male and female rotors with enmeshed screw-type body portions. A housing cooperates with the rotors to define inlet and outlet chambers for pumping of fluid from/to when the male rotor in a first direction and the female rotor rotates in an opposite direction. The housing cooperates with the rotors to define inlet and outlet ports at the inlet and outlet chambers for each of a male and female compression pocket. The inlet ports and/or outlet ports of the respective male and female compression pockets are positioned to respectively close or open sequentially.

Abstract: A pump includes a power screw and at least one idler screw which meshes with the power screw, the power screw and idler screw being rotatable in a housing, the idler screw having at least one screw form including a generally helical groove and a generally helical land surface, the land surface having a first, and a second edge portion, each of which is adjacent to the or a groove, the distance between the land surface and a longitudinal axis of the idler screw varying between the first edge portion and the second edge portion, the distance between the first edge portion and the longitudinal axis of the idler screw being substantially constant over the length of the screw form and the distance between the second edge portion and the longitudinal axis of the idler screw being substantially constant over the length of the screw form.

Abstract: A compressor has a housing assembly and at least one rotor held by the housing assembly for rotation about a rotor axis. The rotor has a first face and a first housing element has a second face in facing spaced-apart relation to the first face of the rotor. The housing has a coating on the second face and a plurality of inserts protruding from the second face into the coating.

Abstract: A screw rotor device has a housing with an inlet port and an outlet port and at least one pair of rotors. The rotors each have an identical number of threads (N), a buttress thread profile with a diagonal line, and a length that is either approximately equal to or less than a single pitch of the threads. The threads of the rotors intermesh as the rotors counter-rotate with respect to each other. The rotors can be twins or each one of the rotors can have different profiles.

Abstract: A multi-rotor screw compressor includes a compressor housing defining at least three parallel rotor housing sections, each rotor housing section containing a rotor, and adjacent rotors defining at least two compressor pairs, the housing further including a suction port and a discharge port for each of the compressor pairs, and further including at least two additional ports selected from the group consisting of first closed lobe ports, last closed lobe ports, and economizer ports, wherein at least one of the additional ports is communicated with a first pair of the at least two pairs, and another of the additional ports is communicated with a second pair of the at least two pairs whereby interaction between the additional ports is reduced.

Abstract: A screw compressor includes a compressor housing defining parallel rotor housing sections, each rotor housing section containing a rotor, and adjacent rotors defining compressor pairs, the housing further including a suction port and a discharge port for each of the compressor pairs, and further including additional ports selected from first closed lobe ports, last closed lobe ports, and economizer ports, wherein at least one of the additional ports is communicated with a first pair of the at least two pairs, and another of the additional ports is communicated with a second pair of the at least two pairs whereby interaction between the additional ports is reduced. In accordance with a further aspect of the invention, configurations are provided so that the first discharge port has a lower volume index ratio (Vi) than the second discharge port.

Abstract: An improved method and apparatus for reducing pressure pulsation when pumping fluids having highly entrained gas therein. The pump has a drive screw and a pair of idler screws. The screws are placed in a screw channel between a suction end and a discharge end. At least one of the clearances between the surfaces of the drive screw, side screw and screw channel is larger in area, from the discharge end to the suction end, than the remaining clearances. The area of the clearance is configured so that sufficient slip flow occurs between the discharge and suction ends to compress the entrained gas in a uniform and controlled fashion so that linear compression occurs throughout the flow path in the pump. Preferably, the clearance is achieved by reducing the outer diameter of the drive screw.

Abstract: A screw rotor device has a housing with an inlet port and an outlet port, a male rotor, and a female rotor. The male rotor has a pair of helical threads with a phase-offset aspect, and the female rotor has a corresponding pair of helical grooves. The female rotor counter-rotates with respect to the male rotor and each of the helical grooves respectively intermeshes in phase with each of the helical threads. The phase-offset aspect of the helical threads is formed by a pair of teeth bounding a toothless sector. The arc angle of the toothless sector is a least twice the arc angle that subtends either one of the teeth. The helical grooves have a radially narrowing axial width at the periphery of the female rotor.

Abstract: A housing for a screw compressor, includes a single-piece casting defining a motor housing section and a rotor housing section and has an inlet for compressor medium, an outlet end and a bridge member disposed between the motor housing section and the rotor housing section and defining an inlet side bearing housing; a discharge housing mounted to the outlet end and defining an outlet and a discharge side bearing housing; and at least one rotor disposed in the rotor housing section and rotatably mounted between the inlet side bearing housing and the discharge side bearing housing.

Abstract: A housing for a screw compressor, includes a single-piece casting defining a motor housing section and a rotor housing section and has an inlet for compressor medium, an outlet end and a bridge member disposed between the motor housing section and the rotor housing section and defining an inlet side bearing housing; a discharge housing mounted to the outlet end and defining an outlet and a discharge side bearing housing; and at least one rotor disposed in the rotor housing section and rotatably mounted between the inlet side bearing housing and the discharge side bearing housing.

Abstract: Two slide valves are located in the discharge end bearing case of a multi-rotor screw machine and independently coact with the sun rotor of the multi-rotor screw machine for controlling capacity and Vi. Movement of the slide valves is in a plane perpendicular to the axis of the sun rotor.

Abstract: A compressor in accordance with the present invention includes a male rotor which is axially aligned with and in communication with two female rotors. The male rotor is driven by a motor, in other words the male rotor is the drive rotor. The male rotor has a plurality of lobes which intermesh with a plurality of flutes on each of the female rotors. The male rotor comprises an inner cylindrical metal shaft with an outer composite material ring mounted thereon. The ring includes the lobes of the male rotor integrally depending therefrom. The lobes of the male rotor being comprised of a composite material allows positioning of the female rotors at a small clearance from the male drive rotor. This clearance is small enough that the liquid refrigerant itself provides sufficient sealing, cooling and lubrication. The positioning of the female rotors on opposing sides of the male rotor balances the radial loading on the male rotor thereby minimizing radial bearing loads.

Abstract: A compressor in accordance with the present invention includes a male rotor which is axially aligned with and in communication with two female rotors. The compressor includes a housing and a thrust balance configuration. The thrust balance configuration includes a stepped up portion mounted at the suction end of the male rotor and is exposed to fluid from the compressor at high pressure. The outside diameter of the thrust balance configuration is generally less than the crest diameter of the male rotor and sized to provide sufficient area to react thrust loads produced by the first rotor. The thrust balance configuration serves to balance the thrust loads imparted on the male rotor and allows for full axial discharge porting.

Abstract: The screw pump (1) has a driving screw (6) and at least one side screw (7), which are placed in a screw channel (5) in the pump body (2), between a suction space (3) and a pressure space (4). At least one of the clearances between the surfaces of the driving screw, side screws and screw channel is larger in the areas close to the suction and pressure spaces than the corresponding clearance in the middle portion of the pump channel. The magnitude of the clearances is so fitted that the total leakage flow (V) between the suction and pressure spaces through the clearances is substantially the same for all angles of rotation of the screws (6,7). Preferably the clearance fit is achieved by reducing the diameter of the screw at its ends so that the change in the external diameter of the reduced portion has at least two different values.

Abstract: A compressor in accordance with the present invention includes a male rotor which is axially aligned with and in communication with two female rotors. The male rotor is driven by a motor, in other words the male rotor is the drive rotor. The male rotor has a plurality of lobes which intermesh with a plurality of flutes on each of the female rotors. The male rotor comprises an inner cylindrical metal shaft with an outer composite material ring mounted thereon. The ring includes the lobes of the male rotor integrally depending therefrom. The lobes of the male rotor being comprised of a composite material allows positioning of the female rotors at a small clearance from the male drive rotor. This clearance is small enough that the liquid refrigerant itself provides sufficient sealing, cooling and lubrication. The positioning of the female rotors on opposing sides of the male rotor balances the radial loading on the male rotor thereby minimizing radial bearing loads.

Abstract: A compressor in accordance with the present invention includes a male rotor which is axially aligned with and in communication with two female rotors. The male rotor is driven by a motor, in other words the male rotor is the drive rotor. The male rotor has a plurality of lobes which intermesh with a plurality of flutes on each of the female rotors. The male rotor comprises an inner cylindrical metal shaft with an outer composite material ring mounted thereon. The ring includes the lobes of the male rotor integrally depending therefrom. The lobes of the male rotor being comprised of a composite material allows positioning of the female rotors at a small clearance from the male drive rotor. This clearance is small enough that the liquid refrigerant itself provides sufficient sealing, cooling and lubrication. The positioning of the female rotors on opposing sides of the male rotor balances the radial loading on the male rotor thereby minimizing radial bearing loads.

Abstract: A positive displacement rotary axial screw pump which comprises a series of sealed closures formed by meshing of the rotors for building the internal pressure gradient of the pump from the pump inlet to its outlet. A programmable logic circuit is provided for signaling impending abnormal pressure conditions in the pump and, upon the onset of such conditions, modifying pump operation to compensate for the abnormal conditions. A pressure monitoring device detects selected disruption in the normal pressure gradient of the pump indicative of the impending abnormal conditions and signals the logic circuit of the impending conditions. The pressure monitoring device includes a pressure sensing device associated with at least one isolated volume for sensing internal pressure gradients of the pump.

Abstract: In a displacement pump having at least one screw spindle which is mounted in an opening in a housing surrounding same between a suction chamber and a pressure chamber, the profile termination of the spindle, at the pressure end, is turned off in a conical configuration at the outside diameter (d), and the angle of inclination (w) of the conical surface (43) is below 10.degree.. In addition the spindle is to be provided at its end on the suction side with a conical surface with an angle of inclination (w.sub.1) which is below 5.degree., preferably below 3.degree..