Patent Publication Number: US-2023151809-A1

Title: Reciprocating compressor with a jacket around the piston rod

Description:
TECHNICAL FIELD 
     The subject-matter disclosed herein relates to a reciprocating compressor. 
     BACKGROUND ART 
     Conventional reciprocating compressors have a piston housed inside a cylinder and a rod mechanically connected to the piston in order to drive it. The cylinder has an opening wherein the rod can slide in order to allow reciprocating motion of the rod. This opening needs to be sealed around the piston rod in order to reduce gas leakage from the cylinder. 
     According to known solutions, sealing of the opening of the cylinder around the piston rod is accomplished by a packing arrangement comprising a series of rings made of semi-crystalline thermoplastic, such as polyether ether ketone commonly known as “PEEK”, arranged around the piston rod and housed in so-called “cups”. The PEEK rings are basically split in design and are embraced by spring elements which compress the split rings circumferentially so that they protrude against the piston rod, positively sealing the clearance between the rings and the piston rod. 
     Disadvantageously, the PEEK rings pressed against the piston rod do not provide a perfect sealing and, some gas may escape from the cylinder through the cups during the reciprocating motion of the piston rod. Also, the PEEK rings pressed against the piston rod determine friction during the reciprocating motion of the piston which leads to energy consumption and to wear of the piston rod. 
     SUMMARY 
     A reciprocating compressors with a cylinder having an improved sealing of the gap around the piston rod would be desirable. 
     According to a first aspect, the subject-matter disclosed herein relates to a reciprocating compressor; the reciprocating compressor includes a cylinder and a piston sliding inside the compression chamber of the cylinder; a piston rod is mechanically connected to said piston and passes through a hole of the cylinder so that there is an annular gap between the piston rod and the hole; in order to avoid (or at least limit) leakage of gas from the gap, a jacket is arranged around the piston rod; the jacket is attached to the piston on one side and to the cylinder of the other side. 
     According to a second aspect, the subject-matter disclosed herein relates to a method of avoiding or limiting leakage from a compression chamber of a reciprocating compressor; in particular, leakage occurs through a gap around a rod of a piston of the reciprocating compressor; leakage is avoided (or at least limited) by isolating the piston rod from the gas in the compression chamber; advantageously, isolation is accomplished by arranging a jacket around the piston rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosed embodiments and of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG.  1    shows a schematic cross-section of an embodiment of a reciprocating compressor in a first position during operation, namely when the piston is in its head-side position; 
         FIG.  2    shows a schematic cross-section of the embodiment of  FIG.  1    in a second position during operation, namely when the piston is in its crank-side position; and 
         FIG.  3    shows an enlarged view of the cross-section of  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In prior-art reciprocating compressor, i.e. compressors in which a piston moves back and forth inside a compression chamber, gas may exit the compression chamber from a gap between a rod of the piston and a hole in a wall of the compression chamber while the piston rod moves back and forth through the hole. In order to avoid the exit of the gas, in the inventive reciprocating compressors, the piston rod has a sealing jacket so that gas surrounding the piston rod cannot get in contact with the piston rod and flow through the gap around the piston rod. 
     Reference now will be made in detail to embodiments of the disclosure, an example of which is illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. 
       FIGS.  1 ,  2  and  3    show a reciprocating compressor  100 . These figures, in particular  FIG.  1    and  FIG.  2   , show one cylinder  110  and one piston  130  of reciprocating compressor  100 . However, alternative reciprocating compressors according to the subject-matter disclosed herein may have any number of cylinders and pistons; in particular, according to some embodiments, one piston may be mechanically connected to two piston rods on opposite sides the piston. 
     A piston rod  134  is mechanically connected to piston  130  and protrudes from a first side of piston  130 . Piston rod  134  may be integral with piston  130  or rigidly connected to it. 
     Cylinder  110  has a compression chamber  111 ; in  FIG.  1   , reference number  111  is placed both above and below piston rod  134  to make it clear that the compression chamber surrounds laterally the piston rod and may be cylinder-shaped. Alternative reciprocating compressors according to the subject-matter disclosed herein may have another compression chamber on the opposite side of the piston which side is not shown in  FIG.  1   . 
     Piston  130  is slidably arranged in compression chamber  111  in order to be movable in a reciprocating translational motion along an axis of translation “T” to compress the gas inside compression chamber  111 ; piston rod  134  has a corresponding reciprocating translational motion. In particular, piston  130  is movable between a head-side position, corresponding to the position of the piston in  FIG.  1   , and a crank-side position, corresponding to the position of the piston in  FIG.  2   ; in the head-side position a big portion of piston rod  134  is located inside compression chamber  111  while in the crank-side position a small portion of piston rod  134  is located inside compression chamber  111 . 
     According to the embodiment of the figures, cylinder  110  comprises a lateral wall  112 , a crank-side wall  115  and a head-side wall, not shown in the annexed figures; the lateral wall may be cylindrical; the crank-side wall and head-side wall may be circular. Lateral cylindrical wall  112  has one or more flow passages  113  fluidly coupled to valves (not shown in the annexed figures) which control the inlet gas flow and outlet gas flow to and from compression chamber  111 . The head-side wall and the crank-side wall are arranged perpendicularly to the axis of translation “T”. Crank side wall  115  has an opening  116  for piston rod  134 , in particular located at the axis of translation “T”, an internal surface  117  facing compression chamber  111  and an external surface  118  opposite to internal surface  117 . Piston rod  134  is arranged to pass through opening  116 . 
     According to alternative embodiments, both the crank-side wall and the head-side wall may have an opening, in particular both located around the axis of translation “T”, for two piston rods; in this case, the reciprocating compressor has two compression chambers. 
     According to the embodiment of the figures, a so-called “packing body”  119  is sealingly connected to crank-side wall  115  at opening  116 . Packing body  119  has a hole  120  for piston rod  134 , preferably located along the axis of translation “T”. Piston rod  134  is slidably inserted through hole  120 , and has a head-side end mechanically connected to piston  130  and is located inside compression chamber  111  at any operating time of the alternating compressor, and a crank-side end mechanically connected to a crank mechanism (not shown in the annexed figures) and is located outside of compression chamber  111  at any operating time of the alternating compressor. The crank mechanism is arranged to drive piston  130  in its reciprocating motion. Packing body  119  may be arranged to provide a degree of sealing to hole  120  when piston rod  134  moves inside it with reciprocating motion. 
     Advantageously, packing body  119  is or includes a flanged bushing  121  defining hole  120  and having a flange  122  arranged to be fastened to crank-side wall  115 , as it is shown in  FIG.  3   . 
     In particular, flange  122  of bushing  121  has an annular surface  123  arranged to be pressed against crank-side wall  115 . Preferably, a sealing element is interposed between annular surface  123  of the packing body  119  and crank-side wall  115 . Tie rods  126  may be used to press packing body  119  against crank-side wall  115  in order to sealingly couple them. In the configuration shown in the figures (see in particular  FIG.  3   ), packing body  119  may be installed on and removed from crank-side wall  115  from the outside of compression chamber  111 . 
     Bushing  121  is completely inserted into opening  116  when packing body  119  is mounted to crank-side wall  115 ; alternatively, the bushing is inserted only partially into the opening. Advantageously, bushing  121  has another annular surface  124  arranged to face compression chamber  111  when packing body  119  is mounted to crank-side wall  115 , that may be used for attaching a jacket of the piston rod that will be described in the following; in particular, the radial position of annular surface  124  is inner with respect to the radial position of annular surface  123 . 
     Advantageously, cylinder  110 , in particular crank-side wall  115 . has a recess  127  for housing at least partially a jacket that will be described in the following. In the embodiment of the figures (see in particular  FIG.  3   ), recess  127  is part of opening  116  and partially defined by annular surface  124  of the packing body  119  internal surface  117  of the crank-side wall  115  (see dashed line in  FIG.  3   ). 
     Reciprocating compressor  100  further includes a jacket  150  arranged around piston rod  134 , and located inside compression chamber  111 , in order to seal compression chamber  111  with respect to hole  120 . Jacket  150  extends from a piston-side end  152  to a cylinder-side end  154 . Thanks to the sealing effect provided by the jacket, the packing body may be designed so to provide no sealing or only limited sealing to the hole where the piston is inserted. 
     The piston-side end  152  of the jacket  150  is sealingly attached to piston  130 , in particular to a piston flange  136  fixed to piston  130  in order to sealingly couple piston-side end  152  to piston  130 . Preferably, jacket  150  and the piston flange  136  are bounded through pressing process and/or by using a bonding agent. Advantageously, piston flange  136  is arranged around piston rod  134  and has an inner e.g. cylindrical surface  137  which faces piston rod  134  and match with the shape of an outer surface e.g. cylindrical of piston rod  134 . 
     Cylinder-side end  154  of jacket  150  is sealingly attached to cylinder  110 , in particular to the packing body  119  that is fixed to crank-side wall  115  of cylinder  110 . Advantageously, cylinder  110  comprises a cylinder flange  128  fastened to inner annular surface  124  of packing body  119 , in order to sealingly connect cylinder-side end  154  of jacket  150  to packing body  119 . Preferably, jacket  150  and cylinder flange  128  are bounded through pressing process and/or by using a bonding agent. Advantageously, cylinder flange  128  is arranged around piston rod  134  and has an inner e.g. cylindrical surface  129  which faces piston rod  134  and match with the shape of an outer surface e.g. cylindrical of piston rod  134 . 
     Jacket  150  is arranged to adapt to different positions of piston  130  between the head-side position (see  FIG.  1   ) and the crank-side position (see  FIG.  2   ). In particular, jacket  150  is extendable along the axis of translation “T”; in the head-side position of piston  130  corresponding to the maximum distance of piston  130  from packing body  119 , jacket  150  is in its extended configuration or maximum extension; in the crank-side position of piston  130  corresponding to the minimum distance of piston  130  from packing body  119 , jacket  150  is in its retracted configuration or minimum extension. It is to be noted that, according to the embodiment of the figures, jacket  150  is always partially housed in recess  127 ; however, in the retracted configuration a bigger part of the jacket is housed in the recess up to the whole jacket. 
       FIG.  2    differs from  FIG.  1    in that piston  130  is closer to crank-side wall  115  of cylinder  110  and packing body  119 ; consequently, piston flange  136  is closer to cylinder flange  128 ; jacket  150  is retracted; the volume of compression chamber  111  is smaller. 
     Preferably, jacket  150  is made of a gas-poof, flexible and durable material such as a synthetic rubber material or a flexible composite material. 
     According to the embodiment of the figures, jacket  150  is bellow-shaped and foldable in order to adapt to the different positions of piston  130  between the head-side position and the crank-side position. Advantageously, jacket  150  may be not only bellow-shaped but also elastically extendable. 
     According to other embodiments not illustrated in the annexed figures, the piston may have a recess located around the piston rod in order to house at least partially the jacket especially when the jacket is in its retracted configuration and the piston is in its crank-side position. 
     According to still other embodiments not illustrated in the annexed figures, both the cylinder and the piston may have recesses in order to house at least partially the jacket especially when the jacket is in its retracted configuration and the piston is in its crank-side position. 
     According to another aspect, the subject matter described herein related to a method of avoiding (or at least limiting) leakage from a compression chamber of a reciprocating compressor through a gap around a rod of a piston sliding inside a cylinder of the reciprocating compressor. The method is implemented for example by the embodiment of reciprocating compressor described above and shown in the annexed figures; the following description of the method will make reference to this embodiment without any limiting intention. 
     The method comprises a step of sealingly isolating the piston rod from the gas in the compression chamber. For example, according to the above mentioned embodiment, piston rod  134  is isolated from the gas in the compression chamber  111  at any operating time of the alternating compressor. 
     Advantageously, for example in the embodiment of the annexed figures, the step of isolating comprises arranging a jacket, labeled  150  in the annexed figures, around the piston rod, labeled  134  in the annexed figures. 
     In order to achieve sealing, a piston-side end  152  of the jacket  150  may be sealingly attached to the piston  130  and/or cylinder-side end  152  of the jacket  150  may be sealingly attached to the cylinder  110 , in particular to a so-called “packing body”  119  of the cylinder as previously described.