Two-stage screw compressor

Abstract

A two-stage screw compressor of the invention includes a low pressure stage casing provided with a low pressure stage compression mechanism, a discharge casing provided on a discharge side of the low pressure stage casing, a high pressure stage casing provided with a high pressure stage compression mechanism, and intermediate stage casings for connecting the discharge casing and the high pressure stage casing, and accommodating an electric motor. In such a two-stage screw compressor, a cavity is formed on a discharge casing side in the slide valve so as to enlarge the capacity of a discharge space formed in the discharge casing. Thereby, internal resonance occurring in the discharge casing is prevented.

1 . A two-stage screw compressor, comprising: 
 a low pressure stage casing for accommodating a low pressure stage compression mechanism and a bearing member, the low pressure stage casing being provided with a capacity control part which is constituted by a slide valve, a rod and a piston;    a discharge casing provided on a discharge side of said low pressure stage casing for accommodating a bearing member supporting the low pressure stage compression mechanism;    a high pressure stage casing for accommodating a high pressure stage compression mechanism and a bearing member; and    an intermediate stage casing for connecting said discharge casing and said high pressure stage casing, the intermediate stage casing accommodating an electric motor, wherein    a cavity is formed on a discharge casing side in the slide valve so as to enlarge the capacity of a discharge space formed in said discharge casing.    
   
   
       2 . The two-stage screw compressor according to  claim 1 , wherein the length in an axial direction of the cavity formed in the slide valve is half or more of the length in an axial direction of the slide valve.  
   
   
       3 . The two-stage screw compressor according to  claim 1 , wherein a porous material is provided in the cavity formed in the slide valve.  
   
   
       4 . The two-stage screw compressor according to  claim 3 , wherein said porous material is a demister constructed by arranging a plurality of metal wires in a net form.  
   
   
       5 . The two-stage screw compressor according to  claim 3 , wherein said porous material is glass wool.  
   
   
       6 . A two-stage screw compressor, comprising: 
 a low pressure stage casing for accommodating a low pressure stage compression mechanism and a bearing member, the low pressure stage casing being provided with a capacity control part which is constituted by a slide valve, a rod and a piston;    a discharge casing provided on a discharge side of said low pressure stage casing for accommodating a bearing member supporting the low pressure stage compression mechanism;    a high pressure stage casing for accommodating a high pressure stage compression mechanism and a bearing member; and    an intermediate stage casing for connecting said discharge casing and said high pressure stage casing, the intermediate stage casing accommodating an electric motor, wherein    the length in an axial direction of a discharge space formed in said discharge casing is enlarged by forming a cavity on a discharge casing side in the slide valve so as not to correspond to a wavelength of noise generated by the low pressure stage compression mechanism.    
   
   
       7 . The two-stage screw compressor according to  claim 6 , wherein the wavelength of the noise generated by the low pressure stage compression mechanism is based on a meshing frequency of rotors.  
   
   
       8 . The two-stage screw compressor according to  claim 7 , wherein said meshing frequency is a frequency including a fundamental frequency which is obtained by multiplying a number of teeth of a male rotor by a rotational frequency, and a higher harmonic component thereof.