Abstract: A device suitable for use in a body lumen and comprises an elongated control member having a distal and a proximal end, and a radially expansible member disposed at or near the distal end and adapted for collection and/or shearing of matter (i.e. thrombus) from a wall of the body lumen (i.e. a vein or an artery). The radially expansible member has a proximal end and a distal end and is adjustable between a contracted orientation and an expanded orientation. The elongated control member comprising a proximal arm connected at or adjacent to the proximal end of the radially expansible member and a distal arm connected at or adjacent to the distal end of the radially expansible member such that movement of one arm relative to the other arm effects adjustment of the diameter or radial strength of the radially expansible member. The device comprises a control mechanism operatively connected to both arms and adapted to provide resistance to the movement of one arm relative to the other.

Abstract: The disclosure includes a vein ablation system, comprising a catheter having an elongated body. In some embodiments, the vein ablation system comprises an ablation device at a distal portion of the elongated body. According to some embodiments, the vein ablation system comprises a control device at a proximal portion of the elongated body. The control device may comprise an input mechanism configured to simultaneously control at least two of a longitudinal translation of the ablation device through a target vessel, a rotation of the ablation device about a central longitudinal axis, and an infusion of a chemical agent into the target vessel.

Abstract: Apparatus and methods are described including a catheter, and first and second impellers configured to be inserted into a subject's body via the catheter, the first and second impellers being disposed in series with each other. A motor is configured to generate rotational motion. A rotation shaft extends from the motor to the first impeller and imparts the rotational motion from the motor to the first impeller. A gear mechanism disposed between the first and second impeller is configured to effect a change in rotational motion that is imparted from the first impeller to the second impeller, such that the second impeller rotates in a different manner from the first impeller. Other applications are also described.

Abstract: A yokeless stator for an axial flux machine, comprising a housing, the housing comprising a circumferential portion and a plurality of elongated portions extending radially inwards therefrom, and a plurality of discrete stator teeth arranged within the circumferential portion, each discrete stator tooth comprising a ferromagnetic material and an electrical winding; the housing further comprising an electrically isolating filling material filling empty space inside the housing. The circumferential portion of the housing is made of a first non-ferromagnetic material and the elongated portions are made of a second non-ferromagnetic material. The housing comprises a laminated structure, which comprises at least part of the plurality of inwardly directed elongated portions.

Abstract: A rotary screw compressor includes a compressor assembly and a drive motor assembly. The compressor assembly includes a compressor housing, a first screw rotor and a second screw rotor installed in the compressor housing and engaged with each other. An end of the first screw rotor is an engaging end. The drive motor assembly includes a motor housing, a motor rotor, a motor stator and a centering bushing installed in the motor housing, and the motor stator installed on an outer side of the motor rotor and capable of driving the motor rotor to rotate, and the centering bushing is passed and connected to the inner circumference of the motor rotor and has an end sheathed on the engaging end, so that the motor rotor can drive the first screw rotor to rotate through the centering bushing and the engaging end.

Abstract: A pneumatically driven apparatus, including a hand guided and/or hand held pneumatic power tool, includes a pneumatic rotary vane (PRV) motor, a working element and a gear arrangement for transmitting a rotational movement and torque. The PRV motor includes a housing defining a cylindrical chamber extending along a cylinder axis, and a cylindrical rotor located in the chamber and extending along and rotatable about an axis running to the cylinder axis. The rotor includes radially movable vanes forced radially outwards during rotation of the rotor. The gear arrangement is a magnetic gear arrangement, and that the rotor of the motor includes permanent magnets attached thereto between the vanes, so that the rotor of the PRV motor forms one of the rotating components of the magnetic gear arrangement.

Abstract: A pump unit provides a hydraulic pressure for actuating an actuator in the drive train of a motor vehicle, in particular a clutch actuator or gearbox actuator. The pump unit includes a pump, a storage container for hydraulic fluid, and at least one solenoid valve. The solenoid valve is arranged within the storage container such that it is surrounded by hydraulic fluid.

Abstract: A fluid-driven actuator system includes a fluid-driven actuator and at least one proportional control valve and at least one pump connected to the fluid-driven actuator to provide fluid to operate the fluid-driven actuator. The at least one pump includes at least one fluid driver having a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from the pump inlet to the pump outlet. The fluid-driven actuator system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover to adjust at least one of a flow in the fluid-driven system to a flow set point and a pressure in the fluid-driven actuator system to a pressure set point and concurrently establishes an opening of the at least one proportional control valve to adjust at least one of the flow to the flow set point and the pressure to the pressure set point.

Abstract: In a hydraulic control device, when it is detected that a pressure of first oil (output pressure) detected by an output pressure sensor pulsates, a transmission control unit as a TCU stops driving of a second pump or decreases a rotation number of the second pump as a first operation. Alternatively, when it is detected that the output pressure pulsates, the TCU increases the rotation number of the second pump to a rotation number (for example, maximum rotation number) that is higher than a target rotation number as a second operation.

Abstract: Size reduction of a compressor and cooling of an electric motor are effectively achieved. An oilless compressor, having: a compressor main body that has a rotor for compressing air, a rotor shaft for supporting the rotor, and a bearing for rotatably supporting the rotor shaft; an electric motor for producing drive force for driving the compressor main body; at least one gear for transmitting drive force to the rotor shaft; a lubricating oil pipe for conveying lubricating oil to the bearing and/or the gear; and an oil pump for pressure-feeding the lubricating oil; wherein the electric motor has, in the external peripheral direction of an armature, a cooling jacket for channeling the lubricating oil to an internal flow channel to cool the armature of the electric motor, and the lubricating oil circulates through the cooling jacket and the lubricating oil pipe.

Abstract: The present invention relates to a fuel pump for vehicle supplying power to a commutator and an armature through a brush to prevent the brush from shake, which comprises the brush, a spring mounted on a top of the brush, the commutator contacted to a bottom of the brush, a brush holder surrounding the brush and the spring, and a first hole formed for fuel flow at a front side of the brush holder in a rotational direction of the commutator based on the brush.

Abstract: A urea solution pump unit includes a bracket mounted to a lower side of a urea solution tank. A pump unit is horizontally disposed at a center of an upper part of the bracket and includes a pump suctioning a urea solution to one direction and a motor pumping the urea solution to another direction through a gap between a rotor and a stator of the motor inside the pump and discharging the urea solution to a lower side of the bracket. A pair of thawing units are fixedly disposed at both sides of the pump unit on the bracket. The thawing units transfer heat to the urea solution and prevent the urea solution from being frozen. A sensor unit is disposed at one side of one of the thawing units and detects a level, a temperature, and a pressure of the urea solution.

Abstract: A fuel pump includes an inner rotor, an outer rotor, a casing, and a housing. The inner rotor includes outward teeth. The outer rotor includes inward teeth geared with the outward teeth. The casing houses the inner rotor and the outer rotor, and forms a variable capacity pump chamber between the inward teeth and the outward teeth. The housing is formed in a cylindrical shape and includes a cylindrical inner portion, the casing being press fit into the cylindrical inner portion. A recessed portion is formed at a predetermined position in a circumferential direction of an outer circumferential surface of the casing, the recessed portion being recessed toward a radial direction center of the outer circumferential surface.

Abstract: An electric drivetrain of a device, such as a gas compression device, includes an electric machine and a system for supplying power to the electric machine, the electric machine including a rotor and a stator. The electric machine is an asynchronous electric machine, and the power supply system is suitable for supplying voltage to the stator of the electric machine, the power supply system making up a source of voltage.

Abstract: A hydraulic system for a hybrid module which is located between an engine and a transmission includes a parallel arrangement of a mechanical pump and an electric pump. Each pump is constructed and arranged to deliver oil to other portions of the hydraulic system depending on the operational mode. Three operational modes are described including an electric mode, a transition mode, and a cruise mode. Various monitoring and control features are incorporated into the hydraulic system.

Abstract: A variable output pump includes a fluid input, a control stage pump having an input portion and an output portion, a main stage pump having an input portion and an output portion, and a differential linkage in mechanical communication with the control stage pump and the main stage pump. The input portion of the control stage pump is in fluid communication with the fluid input and the input portion of the main stage pump is in fluid communication with the fluid input and the output portion of the control stage pump.

Abstract: A screw compressor includes a casing and a compression mechanism accommodated in the casing. The compression mechanism has a screw rotor, a gate rotor and a communication mechanism. The gate rotor has a flat plate shape. A rotational axis of gate rotor is orthogonal to a rotational axis of the screw rotor. The communication mechanism is arranged to communicate a high pressure space and a low pressure space in the casing.

Abstract: This invention relates to a gear pump (1) for delivering a fluid, comprising an externally toothed gearwheel (3) rotatably mounted on a journal (4), and an internally toothed annular gear (2), the gearwheel and gear meshing so as to produce a delivery action, and arranged together with an electrically commutatable stator (7) inside a housing (5). The stator (7) extends concentrically around the annular gear (2) and cooperates with a magnetic ring (6) in order to generate an electromotive force and the magnetic ring (6) together with the annular gear (2) rotate in order to produce the delivery action. The annular gear (2) is mounted by means of a sliding bearing (25).

Abstract: A fuel pump assembly may include a housing and a fuel pump within a fuel pump cavity. The fuel pump may include a motor, a pumping element driven for rotation by the motor, a pump body that maintains the position of the pumping element relative to the motor and the housing, and a flexible seal. The seal may be disposed between the pump body and the housing to provide a fluid tight seal between them. A portion of the seal may be disposed radially outwardly of a distal end of the pump body to radially position the pump body within the fuel pump cavity and a portion of the seal may be disposed axially outwardly of the distal end of the pump body to axially position the pump body within the fuel pump cavity.

Abstract: A positive displacement pump is provided. The pump includes a housing, and first and second meshed rotors rotatably disposed in the housing and arranged to transform relatively low-pressure inlet port air into relatively high-pressure outlet port air. The pump additionally includes first and second meshed timing gears fixed relative to the first and second rotors, respectively, for preventing contact between the first and second rotors, and sufficiently enclosed to generate a flow of lubricating fluid. Furthermore, the blower includes an input drive adapted to be rotatably driven at speeds proportional to speeds of an internal combustion engine and arranged to drive the first and second timing gears.

Abstract: A rotor mechanism for use in moving fluid. The rotor mechanism has six rotor units spherically arranged, with at least one rotor unit including a port through it's body. Each rotor has the form of a truncated cone with two symmetric spiral recesses provided on the lateral surface of the rotor which acts to cooperate with the adjacent rotors. Rotation of at least one rotor unit causes rotation of adjacent rotor units which thereby moves fluid without compression between the outside of the mechanism and the port via a central substantially spherical free space cavity formed by the cooperation of inner surfaces of the rotor units. The rotor mechanism is fully submersible.

Abstract: A compressor including a compression mechanism configured and positioned to receive vapor from an intake passage and provide compressed vapor to a discharge passage. An opening is positioned in the compression mechanism in fluid communication with the discharge passage. A valve has an aperture formed therein, the aperture configured and positioned in fluid communication with a passageway to provide a path for a pressurized vapor flow to a first chamber and a first piston without mixing with vapor in the discharge passage. A second chamber is in fluid communication with a second piston and the discharge passage, the first piston and the second piston of the valve configured to move together. First piston and second piston movement are controllable in response to predetermined conditions to maintain the magnitude of pressure of the compression mechanism immediately upstream of the opening at substantially the same pressure magnitude at the discharge passage.

Abstract: An oil-flooded screw compressor drives a pair of rotors at a rotational speed which is low enough not to increase torque for a short amount of time after start-up and accelerates the pair of rotors up to a normal-operation rotational speed after oil discharge. Alternatively, the oil-flooded screw compressor rotates the pair of rotors for a short amount of time after the remaining compressed gas is discharged after a halt, thereby allowing the oil accumulated inside the working chambers to be discharged and ensuring smooth start-up after the halt.

Abstract: An exemplary pump-head includes a pump housing having first and second housing portions forming a pump-cavity and a magnet-cavity. The pump-cavity contains a movable pumping element, and the magnet-cavity contains a driven magnet coupled to the movable pumping element. The magnet is driven by a moving external magnetic field, which correspondingly moves the pumping element in the pump-cavity in a pumping manner. The second housing portion has inlet and outlet ports and defines at least respective portions of the magnet-cavity and pump-cavity. The first housing portion is detachable from the second housing portion to allow the pumping element to be accessed and carried away with the first housing portion, without disturbing the second housing portion.

Abstract: A liquid pump (10) comprises a pump assembly (14) attached to a motor (12). The pump assembly (14) comprises an inlet chamber (50) and pump chamber (28). The pump chamber (28) accommodates a drive gear (22) driven by an output shaft (16) of the motor (12) and driven gear (26) meshed with the drive gear (22). An inner cover (68) is disposed within the pump chamber (28). An outer cover (20) overlies the inner cover (68) with an elastic member (70) disposed there between. The outer cover (20) exerts a force to the inner cover (68) through the elastic member (70) and holds the inner cover 968) in sliding contact with an axial end of the drive and driven gears (22, 26). An outlet chamber (72) formed between the inner cover (68) and the outer cover (20) is in fluid communication with and the pump chamber (28).

Abstract: An oil pump apparatus in which an electrical pump can be easily disposed is provided. A mechanical pump including: an inner gear which is configured to be driven by an engine; and an outer gear which is configured to mesh with the inner gear, and an electrical pump including: an outer gear which is configured to be driven by a motor section; and an inner gear which is configured to mesh with the outer gear are installed adjacent to each other in the axial direction in a pump installation space of a pump housing having suction ports and ejection ports. A blocking plate which is configured to block communications between the suction ports and the ejection ports is disposed between the mechanical pump and the electrical pump.

Abstract: An electric oil pump is coupled to a pump receptacle including an oil inflow passage and an oil outflow passage. The electric oil pump includes a motor, a pump rotor, a housing, and a check valve. The housing accommodates the motor and the pump rotor. The housing closes an opening of the pump receptacle and includes at least a fitted portion fitted into the pump receptacle. An oil compartment is formed between the pump receptacle and the housing. Oil flows into the oil compartment from the oil inflow passage when the pump rotor is rotated. The fitted portion is partially immersed in the oil collected in the oil compartment. The housing includes a suction port and a discharge port. A check valve, located in the housing, limits reversed flow of the oil from the oil compartment to the oil inflow passage.

Abstract: A variable oil pump capable of rapidly ejecting a required amount of working fluid using an oil pressure of the working fluid generated according to an engine RPM, and improving a lubrication effect to improve engine efficiency. Also described is a variable oil pump, in which a gap is provided between a plunger and a cylinder to easily operate the plunger using an oil pressure output from an oil pump, enabling more rapid supply of a required amount of oil using an oil pressure varied according to variation in an engine RPM. A variable oil pump is described in which the plunger is perpendicularly operated with respect to a flow direction of the working fluid, such that the plunger can be operated in a direction in which a pressure of the working fluid is applied to operate the oil pump.

Abstract: An air compression device is applied in an air compressor. A rotatable pressure regulating disk and a valve are disposed in a rotor set. When external air enters an air chamber in the rotor set, the air is exhausted after being compressed through rotation of a first rotor and a second rotor. When the two rotors compress the air, a user may control the pressure regulating disk to rotate to advance or postpone exhaust of the air from the valve, so as to change an exhaust pressure in the air chamber to adjust an exhaust volume output by the rotor set. An adjustable air intake disk may further be added, so that timing adjustment can be performed during both air intake and exhaust.

Abstract: A twin screw compressor has a working chamber bypass that is used at start-up of the compressor. This system provides pressure relief by allowing oil or other fluid to pass through it. The bypass includes a fluid passage that extends from the working chamber to the discharge port with a one way valve disposed inside the passage.

Abstract: A gear pump has a pair of meshed gears for rotating within a gear pump chamber, and a motor driving at least one of the gears. A discharge line passes fluid downstream from the gear pump chamber, and a suction line delivers fluid into the gear pump chamber. A bypass valve communicates with the discharge line. A shutoff valve communicates with the discharge line. The bypass valve opens at a lower pressure than the shutoff valve. A bypass line communicating the discharge line to the suction line when the bypass valve is open. The gear pump is configured to compress air. In addition, a gear pump arrangement that can be mounted in either of two attitudes is described, as is a method of operating a gear pump.

Abstract: A rotary piston engine comprises at least two rotors, a power component and a blocking component, which interact and have spur gearings, the number of teeth of which differs by one, the rotors and an engine housing accommodating the rotors delimiting working compartments. The rotors are twisted at a defined angle to each other. The power component is driven by and rotationally connected to an electric motor arranged on the same axis. The motor has an internal stator and an external rotor, the engine housing being directly connected to the motor. The engine housing has a supporting tube section projecting into and supporting the internal stator. The external rotor has a bell which encloses the internal stator and has a center drive shaft extending through the supporting tube section and rotationally connected to the power component, the drive shaft being mounted towards the inner wall of the supporting tube section.

Abstract: An electric pump includes a housing and a motor unit having a stator disposed in the housing. A rotor is rotatably disposed on the stator and a rotating shaft is inserted in and passing through the rotor. A pump comprises an inner rotor coupled to one end of the rotating shaft and an outer rotor, and the pump has an inserting recess for receiving the pump.

Abstract: Power unit (101) comprising: a tank (104) for hydraulic oil; an electric motor (105); a power pack body (102) inside of which a hydraulic circuit extends; a hydraulic pump (103) integrated in a cavity (102a) of the power pack body (102).

Abstract: A gear pump includes a pump body 22 which defines a cavity hole 72 which holds a separate cavity body. The cavity body defines channels and a pump cavity holding a pair of gears. An inlet and outlet are connected to the channels. The separate cavity body may be manufactured separately and only this component needs to be manufactured to very accurate tolerances.

Abstract: An immersion pump is provided, the pump having an integral housing with an inlet opening on an intake side, an outlet opening on a delivery side, a passage for electrical lines, an electronic unit for processing power and optionally information signals, an electric motor, a pressure chamber and a pump unit. The electronic unit, the electric motor, the pressure chamber and the pump unit may be pre-assembled to an insert, with the pre-assembled insert being supported on one end of the housing. An axial clamping and/or fastening system, in particular a tapered locking arrangement, is provided on the opposite end of the housing.

Abstract: A method of running a down hole rotary pump using a top drive, sucker rod or any drive shaft from surface. A first step involves providing a gear box having an input end and an output end. The gear box is being capable of receiving an input of a first speed at the input end and producing an output of a second speed which is one of either faster or slower than of the first speed at the output end. A second step involves positioning the gear box down hole with the input end coupled to a remote lower end of a sucker rod and the output end coupled to a rotary activated pump. A third step involves applying a driving force to the sucker rod to rotate the sucker rod at the first speed, with the rotational force being transmitted to the rotary activated pump through the gear box which rotates the rotary activated pump at the second speed.

Abstract: A submersible electric pump includes a housing adapted to be submerged within a fluid to be pumped having apertures extending therethrough. An electric motor stator is positioned within the housing in communication with the apertures and is adapted to be in contact with the fluid. Inner and outer pump rotors are positioned within the housing in meshed engagement with one another to pump fluid when rotated. A plurality of permanent magnets are fixed for rotation with the outer rotor.

Abstract: A nonmetallic pump with a gear pump assembly having an adapter spool mounted to an electric motor. The pump assembly is designed to reduce manufacturing costs and to provide access for many service and maintenance tasks to be performed without breaking any of the pipe connections. The pump assembly also includes a splined shaft system and a lubricating fluid circulation system with spiral grooves located inside a pair of bearings disposed on opposite sides of the gear flights. The assembly also includes a replaceable precision liner that surrounds the gear flights to maintain a tight tolerance for optimal performance of the pump. Also, an O-ring disposed inside the front cover of the assembly provides for operation of the pump over a wide temperature variation with relatively loose manufacturing tolerances.

Abstract: An object of the invention is to provide a structure for coupling two rotary shafts, which can be made smaller in size. A driving shaft for pumps is rotatably supported by a first bearing and a second bearing, while a rotary shaft of an electric motor is rotatably supported by the second bearing and a third bearing. Each one end of the driving shaft and the rotary shaft is inserted into the common second bearing, so that rotation of the rotary shaft is transmitted to the driving shaft.

Abstract: A pump comprising a housing having a first cavity and a second cavity, where the first cavity has a first motor and a pump element located therein. The first cavity is also connected to an external gear connected to the outside of the housing for receiving rotation power from a vehicle engine. The second cavity has a second motor that selectively connects to the pump element in the first cavity to provide toque.

Abstract: A compressor is provided that includes a hermetically sealed container; a stator fixedly installed within the hermetically sealed container; a first rotary member that rotates, within the stator, around a first rotary shaft that extends concentrically with a center of the stator by a rotating electromagnetic field of the stator, and including first and second covers fixed to upper and lower parts thereof, respectively; a second rotary member that compresses a refrigerant in a compression space formed between the first and second rotary members while rotating, within the first rotary member, around a second rotary shaft; a vane that transmits the rotational force to the second rotary member from the first rotary member, and partitions the compression space into suction and compression regions; and first and second bearings fixed inside of the hermetically sealed container that rotatably support the first and second rotary members in an axial direction.

Abstract: A submersible electric pump includes a housing adapted to be submerged within a fluid to be pumped having apertures extending therethrough. An electric motor stator is positioned within the housing in communication with the apertures and is adapted to be in contact with the fluid. Inner and outer pump rotors are positioned within the housing in meshed engagement with one another to pump fluid when rotated. A plurality of permanent magnets are fixed for rotation with the outer rotor.

Abstract: The multistage dry vacuum pump is disclosed, in which it is possible to prevent a pump from being adhesively stuck, which problem occurs due to a difference in thermal expansions between a cylinder body and a rotor, by making thermal expansion conditions between a cylinder body and a rotor of a pump similar by concurrently cooling the cylinder body and the rotor of the pump. The gas passage for transferring gas compressed by each cylinder is provided at each cylinder body in a shape of surrounding an outer side of each cylinder, and a cooling water jacket for circulating cooling water is provided close to an outer side of the gas passage, and a communication passage is formed at a gas passage contacting with the cooling water jacket and is connected with an exhaust space of the cylinder.

Abstract: An internal gear fluidic machine, in particular a pump for the lubrication circuit of a motor vehicle engine, comprises an operating part including an external gear (2) and an internal gear (4), which is housed within an axial cavity (25) of the external gear (2) and meshes with the latter. The external gear (2) is associated with a translating mechanism (8, 22), arranged to cause an axial sliding thereof relative to the internal gear (4) in order to vary the capacity and the fluid flow rate of the machine. The translating mechanism (8, 22) defines a first capacity, adjustment space (24) in communication with a high pressure chamber (48) of the machine, and a second capacity adjustment space (15) where pressure conditions exist that are dependent on the operating conditions of an element, different from the high pressure chamber (48), of a fluidic circuit in which the machine (1) is connected.

Abstract: A stator is fixedly fastened at its outer periphery by a cylindrical and thin metal collar. One end of the collar is engaged with a pump housing. Multiple metal nuts are embedded in insulators fitted to stator cores through insert molding. The stator of a brushless motor is fixed by screwing bolts passed through the pump housing from a pump plate, to nuts embedded in the insulators.

Abstract: A method of controlling a gear pump comprising two meshing gear wheels (11, 12), wherein the two gear wheels (11, 12) are driven via respective shafts (2, 3) each by a drive unit (7, 8). A current position of the one gear wheel (11, 12) is determined with respect to the current position of the other gear wheel (12, 11), and the current position of the one gear wheel (11, 12) is continuously adjusted with respect to the current position of the other gear wheel (12, 11) according to specified predefined operating conditions.

Abstract: Disclosed is a hydraulic power steering pump including a wet type motor with an open type magnet, the hydraulic power steering pump including: a housing; a gear pump module supported at one side of the housing and pressurizing a fluid; and a motor module supported at the other side of the housing and providing driving force to the gear pump module, the motor module including a stator that is supported by the housing and receives electric current based on supplied power, and a rotor that includes a motor rotation shaft rotated by the stator and a permanent magnet generating magnetic force, and an outer side of the permanent magnet being supported by the motor rotation shaft to have an exposed portion exposed toward the stator.

Abstract: A gear pump includes a driven gear and an idler gear each mounted for rotation in a housing. The driven gear and the idler gear include respective gear teeth in a meshing relationship and forming an inlet space and an outlet space in the housing and adjacent to the meshing gear teeth. The inlet space is in fluid communication with the inlet port and the outlet space is in fluid communication with the outlet port. A flow indicating element is located in the housing and is mounted for rotation independent of the driven gear and the idler gear. The flow indicating element is configured to be rotated by the viscous fluid to indicate when the fluid is moving from the inlet port and inlet space to the outlet space and outlet port.

Abstract: An oil-flooded screw compressor drives a pair of rotors at a rotational speed which is low enough not to increase torque for a short amount of time after start-up and accelerates the pair of rotors up to a normal-operation rotational speed after oil discharge. Alternatively, the oil-flooded screw compressor rotates the pair of rotors for a short amount of time after the remaining compressed gas is discharged after a halt, thereby allowing the oil accumulated inside the working chambers to be discharged and ensuring smooth start-up after the halt.