Abstract: This invention relates to a device for controlling the internal compression in a screw compressor and to a screw compressor equipped with a device for internal compression control. In the compressor housing (10) an axially movable sliding vlave (17) for controlling the internal compression is located in paralllel with the rotors on the discharge side thereof. In the position yielding the highest internal compression, the sliding valve extends over the major part of the length of the rotors and outwardly over the inlet end plane (18) of the compressor.

Abstract: The invention relates to a device for controlling a screw compressor, in which a rotor housing (10) includes a compression space (15) with two intermeshing rotors. In parallel with the rotors, at their discharge side two axially movable sliding valves (20, 21) are located, viz. one inner (20) and one outer sliding valve (21). The inner sliding valve (20) is movable in the outer sliding valve (21). One of the sliding valves is arranged for controlling the internal compression in the compression space (15), while the second sliding valve is arranged for controlling the capacity of the compressor.

Abstract: The invention relates to a valve arrangement for capacity control of an oil-injected screw compressor. One or more piston valves are arranged one after the other in the axial direction of the rotors at the portion of the rotor barrels where the internal compression phase occurs. The compressor control valves are actuated by the discharge pressure, which in their turn open or close the piston valves. When the piston valves are open, a portion of the gas in the compression space is discharged to a bleed off passageway and it flows back to the inlet port of the compressor so that substantially no compression work is spent on this portion of the gas.

Abstract: This invention relates to a method at oil-injected screw-compressors for balancing axial forces at at least one of the rotors of the compressor, for sealing the gaps between rotor housing and rotor shafts and for cooling and lubricating the bearings of the rotor shafts. At the high-pressure end of the compressor oil under pressure of such magnitude is supplied to the bearing spaces (28a,28b) at the ends of both rotors that an oil flow inward to the compression space along the gaps (32a, 32b) between the rotor shafts and the rotor housing is obtained for sealing against leakage from the compression space. Oil at this pressure further is supplied via a connection (42) from the bearing space (28b) of the female rotor to a pressure space (38) at the low-pressure end of the female rotor for balancing the axial force arising on the shaft end (31) of the female rotor on the high-pressure side due to the oil supplied to the bearing space (28b) of the female rotor.

Abstract: The invention relates to the design of the profiles of two meshing rotors, which are provided with helical lands and intervening grooves and adapted for rotation around parallel axes in a working space in a rotary screw machine, where one groove in one rotor (female rotor 1) co-operates with a corresponding land on a second rotor (male rotor 2), so that a chevron shaped chamber is formed by the flanks of the groove and the land, with the open legs of the chamber ending at the high-pressure end of the machine. The flank profiles according to the invention are designed so that the torque acting on the female rotor by the gas forces in the machine is 17-19.5%, preferably about 18.5%, of the corresponding torque on the male rotor, and that the blow hole area formed hereby at the high-pressure side of the rotor mesh does not exceed a value corresponding to 25 mm.sup.

Abstract: The invention relates to a valve system for capacity control of an oil-injected screw compressor. One or more valves (17-20), preferably at least two valves, are located in the wall of the rotor barrel (12, 13). The pressure in the compressed-air tank of the compressor actuates control valves, which in their turn open or close the valves (17-20). When the valves are opened, a direct connection between two consecutive thread volumes of at least one of the rotors (14, 15) is established, whereby the closed space capable to be used for the internal compression, is reduced.

Abstract: The invention relates to an arrangement at oil-injected screw compressors for high pressures. The arrangement is characterized in that the length/diameter ratio of the rotors is lower than 1,3:1, that taper roller bearings in pairs (19-21) are used at both shaft ends (15-18) of the rotors, that the bearings (19,21) at the high-pressure end (13) of the rotors are arranged so that the wider edges of the inner rings of the bearings are facing toward each other and are capable to take up both radial and axial forces, that the bearings (20,22) at the low-pressure end (14) of the rotors are arranged so that the narrower edges of the inner rings of the bearings are facing toward each other and are capable to take up only radial forces, and that oil-pressure actuated balancing pistons (23,24) are provided at the shaft ends (16,18) on the low-pressure end of the rotors to take up the major part of the axial forces initiated by the compressor.

Abstract: This invention relates to a method at oil-injected screw-compressors for balancing axial forces at at least one of the rotors of the compressor, for sealing the gaps between rotor housing and rotor shafts and for cooling and lubricating the bearings of the rotor shafts. At the high-pressure end of the compressor oil under pressure of such magnitude is supplied to the bearing spaces (28a,28b) at the ends of both rotors that an oil flow inward to the compression space along the gaps (32a,32b) between the rotor shafts and the rotor housing is obtained for sealing against leakage from the compression space. Oil at this pressure further is supplied via a connection (42) from the bearing space (28b) of the female rotor to a pressure space (38) at the low-pressure end of the female rotor for balancing the axial force arising on the shaft end (31) of the female rotor on the high-pressure side due to the oil supplied to the bearing space (28b) of the female rotor.