Liquid injection type screw compressor

Abstract

A liquid injection type screw compressor in which, in a compression stroke of an working space formed by male and female rotors, liquids such as oil or water is prevented from leaking from the high pressure working space to a gas inlet side, suction resistance of gas sucked from the gas inlet to a rotor casing is reduced to improve volumetric efficiency, and shape forming of the casing is simplified. The liquid injection screw compressor has the male and female rotor pair of screw rotors, the rotor casing ( 1 a , 1 b ) having a bore for receiving the rotors, a gas suction opening and a gas outlet that are provided in both end sections of the casing and communicate with the bore, and a lip section ( 4 ) projected from a bore surface ( 2 ) positioned more on the upstream side than a suction seal line ( 5 ) of the casing in order to prevent a back flow of the liquid from the bore surface toward the gas inlet side. The lip section ( 4 ) is positioned in a region surrounded by the suction seal line ( 5 ) and a line separated by a distance of one screw pitch of the rotors from the suction closure line ( 5 ) to the suction opening side.

1 . A liquid injection type screw compressor, comprising:
 a pair of male rotor and female rotor,   a rotor casing comprising a pair of bores that accommodate the pair of male rotor and female rotor,   a gas inlet and a gas outlet that are connected to the pair of the bores, the gas inlet being provided at a first end part of the rotor casing, while the gas outlet being provided at a second end part of the rotor casing, and   a lip part that is provided on a surface of the bores and protrude inside so as to prevent the liquid on the surfaces of bores from back-flowing toward the gas inlet, the lip part being located at a gas upstream side of a suction seal line of the rotor casing;   wherein the lip part is placed in a range between the suction seal line and a line that is apart from the suction seal line within one screw pitch distance of the screw rotors.   
   
   
       2 . The liquid injection type screw compressor according to  claim 1 , whereby surfaces of the bores comprise
 a main bore face that comes in contact with rotor tooth tips with a slight fit tolerance, and   an expanded bore face that faces rotor tooth tips with a clearance larger than the fit tolerance, during at least a gas suction process out of whole working processes;   wherein the suction seal line exists between the main bore face and the expanded bore face.   
   
   
       3 . The liquid injection type screw compressor according to  claim 1 , the compressor further comprising:
 a straight development-line portion of the suction seal line in a development view, lying at right angles to a bore intersection line that is defined as a common generating line of a male rotor bore and a female rotor bore,   a lip-entering-edge of the lip part that is placed apart from the suction seal line toward the gas inlet side in a rotor axis direction, whereby the lip-entering-edge in response to the above-mentioned straight-line portion is bent so as to protrudes toward the suction seal line, and   a lip ending (trailing) edge of the lip part whereby the lip ending edge in response to the straight-line portion is placed parallel thereto so as to form a straight line portion of the lip ending edge in a development view, and   a thickened (wide in the rotor axis direction) lip part in response to the straight-line portion.   
   
   
       4 . The liquid injection type screw compressor according to  claim 3 , wherein
 the straight line portion of the suction seal line in a development view lies at right angles to the bore intersection line, and starts from a cross-point of the bore intersection and the suction seal line on the male bore surface as far as a point on the suction seal line on the female bore surface,   the lip-entering-edge of the lip part is placed apart from the suction seal line toward the gas inlet side in the rotor axis direction, and the lip-entering-edge in response to the above-mentioned straight line portion is bent so as to protrudes toward the suction seal line; wherein, a part of the lip-entering-edge in response to the straight line portion starts from a cross-point of the bore intersection line and the lip-entering-edge on the male bore surface, as far as a point on the lip-entering-edge on the female bore surface,   the lip ending (trailing) edge of the lip part in response to the straight-line portion is placed parallel thereto so as to form the straight line portion of the lip ending edge in a development view; wherein a straight line portion of the ending edge starts from a cross-point of the bore intersection line and the lip-ending-edge on the male bore surface, as far as a point on the lip-ending-edge on the female bore surface, and   the thickened (wide in the rotor axis direction) lip part in response to the straight-line portion is provided.   
   
   
       5 . The liquid injection type screw compressor according to  claim 1 , wherein the rotor casing with the gas inlet casing is formed in one piece or a plurality of divided-pieces from the lip ending edge toward a gas downstream side. 
   
   
       6 . The liquid injection type screw compressor according to  claim 1 , wherein a labyrinth structure is embodied on the inner surface which faces rotor tooth tips in the lip part. 
   
   
       7 . The liquid injection type screw compressor according to  claim 1 , wherein different outer diameters are applied to a pair of the male rotor and the female rotor so that the outer diameter of the male rotor is greater than that of the female rotor, and the number of the male rotor teeth is fewer than that of the male rotor teeth in a case when the same outer diameter is applied to a pair of the male rotor and the female rotor. 
   
   
       8 . The liquid injection type screw compressor according to  claim 1 , wherein the lip part is provided at the lower side of the casing bore surfaces. 
   
   
       9 . The liquid injection type screw compressor according to  claim 1 , the compressor further comprising:
 a slide valve (capacity control valve), and an internal volume ratio (U i ) adjusting valve;   
     whereby, the slide valve has
 a cut-out part, at a discharge end thereof, which regulates a gas discharge throat between a discharge end part (of gas discharge side) of the slide valve and an end face (of gas discharge side) of the rotor casing, and 
 a valve driving rod (a pushrod) that is prolonged toward the gas inlet casing on a rotor end face so that the valve driving rod protrudes across the gas inlet casing, through a storage space of the internal volume ratio adjusting valve that is provided on a side of the gas inlet casing which comes in contact with the rotor end face, the valve driving rod being connected to a drive source in order that the slide valve can move forward and backward along an axis of the driving rod by means of the drive source and the driving rod, 
 whereas the internal volume ratio adjusting valve in the storage space is placed adjacent to a gas inlet side end face of the capacity control valve (a slide valve), with a positioning means that adjusts variably the position of the internal volume ratio adjusting valve, along a direction to/from a gas discharge side, 
 wherein an internal volume ratio is adjusted such that the positioning means shifts the internal volume ratio adjusting valve to a predetermined position, while an internal gas capacity is adjusted by by-passing an inhaled gas back to the gas inlet side through a gap between the internal volume ratio adjusting valve, and the capacity control valve (a slide valve) that slides to and fro along the driving rod direction by means of the drive source, through the driving rod. 
 
   
   
       10 . The liquid injection type screw compressor according to  claim 9 , wherein the positioning means comprises:
 a hollow shaft which is placed concentric to the driving rod, having a screw part on an outer surface of the hollow shaft so that the screw part is engaged into a corresponding screw part inside the internal volume ratio adjusting valve, and   a rotation rod that is placed so as to intersect with the hollow shaft in order that the rod can transmit a rotational driving movement of the rod to the hollow shaft, via a connection part; whereby, the rotational movement transmitted to the hollow shaft is transformed into a to-and-fro movement of the internal volume ratio adjusting valve, through the mentioned screw engagement, so that the internal volume ratio adjusting valve is positioned to a predetermined position.   
   
   
       11 . The liquid injection type screw compressor according to  claim 10 , whereby the connection part between the hollow shaft and the rotation rod is formed with a bevel gear pair or a crossed helical gear pair.