Screw compressor pulsation damper

Abstract

A screw compressor ( 10 ) comprises a housing ( 12, 14, 16 ), a slide valve assembly ( 23 ) and a pulsation damper. The housing ( 12, 14, 16 ) receives a supply of working matter from a pair of intermeshing screw rotors ( 18, 20 ), and comprises a slide recess ( 51 ), a pressure pocket ( 32 ), and a piston cylinder ( 54 ). The slide valve assembly ( 23 ) regulates the capacity of the screw compressor ( 10 ), and comprises a slide valve ( 36 ) axially movable within the slide recess ( 51 ) and the pressure pocket ( 32 ), a piston head ( 40 ) axially movable within the piston cylinder ( 54 ), and a piston shaft ( 38 ) connecting the slide valve ( 36 ) with the piston head ( 40 ). The pulsation damper comprises a flange ( 58 ) for separating the pressure pocket ( 32 ) from the piston cylinder ( 54 ), a bore ( 60 ) for receiving the piston rod ( 38 ), and a damping channel ( 46 A) extending through the flange ( 58 ).

1 . An outlet case for a screw compressor comprising:
 a main body portion having:
 a first end configured for receiving discharged working matter from screw rotors in the compressor; 
 a second end configured for receiving a piston cylinder of a slide valve assembly; and 
 a rod flange dividing the first end from the second end; and 
   a pulsation damper carried by the main body to dampen pressure pulsations in the discharged working matter entering the piston cylinder.   
     
     
         2 . The outlet case for a screw compressor of  claim 1  wherein:
 the first end is configured as a discharge pocket for receiving a slide valve of the slide valve assembly;   the rod flange includes an opening for receiving a piston rod of the slide valve assembly; and   the pulsation damper comprises a channel extending through the rod flange.   
     
     
         3 . The outlet case of  claim 2  wherein the second end of the main body portion is connected to a slide case having a piston cylinder for receiving a piston head of the slide valve assembly, the piston cylinder axially aligning with the rod flange and the discharge pocket. 
     
     
         4 . The outlet case of  claim 2  wherein the channel extends between the piston cylinder and the discharge pocket. 
     
     
         5 . The outlet case of  claim 4  wherein the channel permits working matter discharged from the screw rotors to pressurize the piston cylinder. 
     
     
         6 . The outlet case of  claim 5  wherein the pressurized working matter within the piston cylinder compresses to extract energy from working matter attempting to enter the piston cylinder. 
     
     
         7 . The outlet case of  claim 2  wherein the channel reduces an amplitude of a sound wave in the working matter as the working matter passes through the damping bore. 
     
     
         8 . The outlet case of  claim 1  wherein the pulsation damper comprises a plurality of channels extending into the internal cavity. 
     
     
         9 . The outlet case of  claim 8  wherein the plurality of channels have different geometries. 
     
     
         10 . The outlet case of  claim 9  and further comprising a plurality of tubes inserted into the plurality of damping bores. 
     
     
         11 . A screw compressor comprising:
 a housing for receiving a supply of working matter, the housing comprising:
 a rotor case having a suction pocket and a slide recess; 
 an discharge case having a discharge pocket axially aligned with the slide recess; and 
 a slide case having a piston cylinder axially aligned with the discharge pocket; 
   a pair of intermeshing screw rotors disposed within the rotor case between the suction pocket and the slide recess for compressing the working matter and discharging the working matter into the discharge pocket;   a slide valve assembly disposed adjacent the pair of intermeshing screw rotors and axially_movable within the slide recess, discharge pocket and piston cylinder to regulate the capacity of the screw compressor; and   a pulsation damper carried by the discharge case to dampen pressure pulsations of working matter discharged from the screw rotors to the discharge pocket and passing into the piston cylinder.   
     
     
         12 . The screw compressor of  claim 11  wherein:
 the slide valve assembly comprises:
 a slide valve axially movable within the slide recess and the discharge pocket; 
 a piston head axially movable within the piston cylinder; and 
 a piston shaft connecting the slide valve with the piston head; and 
   the pulsation damper comprises:
 a flange for separating the discharge pocket from the piston cylinder; 
 a bore for receiving the piston rod; and 
 a damping channel extending through the flange. 
   
     
     
         13 . The screw compressor of  claim 12  wherein the damping channel dampens vibration generated by the working matter. 
     
     
         14 . The screw compressor of  claim 12  wherein the pulsation damper comprises:
 a resonance chamber enclosed within the piston cylinder between the piston head and the flange such that working matter pressurizes the resonance chamber.   
     
     
         15 . The screw compressor of  claim 14  wherein the damping channel reduces an amplitude of the working matter as the working matter enters the resonance chamber. 
     
     
         16 . The screw compressor of  claim 14  wherein the pulsation damper comprises a plurality of damping channels. 
     
     
         17 . The screw compressor of  claim 16  wherein the lengths and diameters of the damping tubes are selected to produce a Helmholtz resonator having a natural frequency matching a frequency of the discharged working matter. 
     
     
         18 . The screw compressor of  claim 16  and further comprising a plurality of damping tubes inserted through the plurality of damping channels. 
     
     
         19 . The screw compressor of  claim 11  wherein the pulsation damper further comprises a seal positioned between the bore and the flange. 
     
     
         20 . A screw compressor comprising:
 a housing for receiving a supply of working matter;   a pair of intermeshing screw rotors disposed within the housing for compressing and discharging the working matter in a series of discharge pulses;   a slide valve assembly movable within the housing to regulate the capacity of the screw compressor, the slide valve assembly comprising:
 a slide valve axially movable between the pair of intermeshing screw rotors; and 
 a piston axially connected to the slide valve for actuating the position of the slide valve; and 
   a Helmholtz resonator axially positioned between the slide valve and the piston, and configured to extract energy from the discharged pulses of the working matter.   
     
     
         21 . A method for reducing discharge pulsations in a screw compressor, the method comprising the steps of:
 passing a working matter from a suction port of the screw compressor, through a set of screw rotors, and to a discharge port in the screw compressor to reduce a volume of the working matter;   positioning a slide valve along the screw rotors such that the slide valve extends into the discharge port;   connecting a piston assembly to the slide valve such that a piston rod extends from the discharge port, through a rod flange, and into a piston cylinder; and   positioning an inlet of a fluid compressing pulsation damper on the rod flange such that working matter entering the discharge port passes by the pulsation damper inlet to attenuate pulsations within the working matter as the working matter exits the set of screw rotors.   
     
     
         22 . The method for reducing discharge pulsations of  claim 21  and further comprising passing at least a portion of the working matter discharged from the set of screw rotors through the damping openings and into a resonance chamber positioned within the piston cylinder. 
     
     
         23 . The method for reducing discharge pulsations of  claim 21  and further comprising matching a natural frequency of the damping openings to a discharge frequency of the working matter from the set of screw rotors. 
     
     
         24 . The screw compressor of  claim 20  and further comprising:
 a piston cylinder connected to the housing through a rod flange; and   a piston rod extending through the rod flange to connect the slide valve to the piston;   wherein the Helmholtz resonator is defined by the rod flange, the piston cylinder and the piston.