Abstract:
A piston plug includes a cylindrical body having a longitudinal axis and an outer cylindrical surface. The outer cylindrical surface extends longitudinally between a first surface and a second surface opposite the first surface. The outer cylindrical surface defines a hole extending radially inward. The hole has a central axis perpendicular to the longitudinal axis of the cylindrical body. A first channel and a second channel are defined by cylindrical body. The first channel is in fluidic communication with the first surface and the hole. The second channel is in fluidic communication with the second surface and the hole. The first channel, the second channel, and at least a portion of the hole form a non-collinear flowpath. The piston plug is disposed in a plug hole in a piston and is retained in the plug hole via an interference fit between the piston plug and the plug hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent application having Ser. No. 61/780,544, which was filed Mar. 13, 2013. This priority application is hereby incorporated by reference in its entirety into the present application to the extent consistent with the present application. 
     
    
     BACKGROUND 
       [0002]    A reciprocating compressor (for example, a high speed reciprocating compressor) is an example of a positive-displacement compressor that uses one or more pistons driven by a crankshaft to deliver working fluids (for example, gases) at high pressure. Generally, the pistons are hollow and have a cavity therein. The reciprocating compressors typically operate to deliver compressed gases having a pressure from about 50 psi to about 2000 psi. Due to this high-pressure operation, gas may enter the cavity of the piston, and the pressure of the gas in the cavity may build over time. 
         [0003]    Generally, as per the safety standards set forth by the American Petroleum Institute (API), any chamber or cavity must be vented (for example, to equalize the pressure in the cavity with the outside pressure). In addition, to prevent excessive wear of parts any debris, such as casting sand, grit, debris due to machining, etc., within a chamber or cavity be contained therein and should not exit the cavity. In order to satisfy these requirements, piston valves or plugs are typically installed on an outer surface of the piston to vent the piston cavity by providing a flowpath for the gas in the piston cavity to exit the piston cavity. 
         [0004]      FIG. 1A  illustrates a cross-sectional view of a conventional piston plug  100 .  FIG. 1B  illustrates a cross-sectional view of a piston  110  in which the piston plug  100  has been installed in a plug hole  128  defined by an outer surface  124  of the piston  110 . Referring to  FIGS. 1A and 1B , the piston plug  100  has a ball  102  and a spring  104  axially disposed in a through hole  108  axially defined by the piston plug  100 . The ball  102  and the spring  104  are secured in the through hole  108  via a fastener  106 . The piston  110  is disposed to reciprocate axially in a bore  114  in a cylinder  112 . A fluid chamber  116  is formed by the piston  110  and the bore  114 . An inner surface  126  of the piston  110  is exposed to the fluid chamber  116 . The gas in the fluid chamber  116  may enter the piston cavity  111  from the fluid chamber  116 . When installed, a bottom surface  122  of the piston plug  100  is exposed to the piston cavity  111  and a top surface  120  of the piston plug  100  may be flush with the outer surface  124  of the piston  110 . When the pressure of the gas in the piston cavity  111  reaches or exceeds a predetermined value, the ball  102  is dislodged from its seat (for example, formed via the shoulder in the through hole  108 ) and the gas in the piston cavity  111  escapes via the piston plug  100 . The through hole  108  provides a straight (collinear) flowpath for the gas in the piston cavity  111  to escape. 
         [0005]    Because the through hole  108  of the piston plug  100  forms a flowpath  118  that is straight (collinear), debris inside the piston cavity  111  exits along with the gas in the piston cavity  111 . Also, the high-speed, high-pressure operation of the reciprocating compressor may cause frequent breaking of the spring  104 . Since the flowpath  118  through the piston plug  100  is collinear and extends along the direction of motion of the piston  110  in the cylinder  112 , spring fragments may also exit the piston plug  100  via the through hole  108 . 
         [0006]    Accordingly, there is a need for a piston plug that vents the piston cavity and also prevents debris from exiting the piston. 
       SUMMARY 
       [0007]    Embodiments of the disclosure may provide a piston plug. The piston plug may have a cylindrical body having a longitudinal axis and an outer cylindrical surface extending longitudinally between a first surface and a second surface. The second surface may be opposite the first surface. The outer cylindrical surface may define a hole extending radially inward. The hole may have a central axis perpendicular to the longitudinal axis of the cylindrical body. The piston plug may further include a first channel and a second channel, both defined by the cylindrical body. The first channel may be in fluidic communication with the first surface and the hole. The second channel may be in fluidic communication with the second surface and the hole. The first channel, the second channel, and at least a portion of the hole may form a non-collinear flowpath. 
         [0008]    Embodiments of the disclosure may provide a valve for regulating flow of fluid. The valve may define an inlet channel configured to accept the fluid. The inlet channel may terminate in a hole defined in the valve and extending radially inward from an outer surface of the valve. The hole may have a central axis perpendicular to a longitudinal axis of the valve. The valve may also define an outlet channel configured to eject the fluid. The outlet channel may also terminate in the hole. The inlet channel, the hole, and the outlet channel may form a non-collinear flowpath. 
         [0009]    Embodiments of the disclosure may provide a reciprocating compressor. The reciprocating compressor may include a housing having a bore, a piston slidably disposed in the bore, and a piston plug disposed in the piston. The piston and the bore may define a chamber therebetween. The piston may have an inner surface in fluidic communication with the chamber and an outer surface opposite the inner surface. The piston plug may be disposed in a plug hole defined on the outer surface of the piston. The piston plug may be retained in the plug hole via an interference fit between the piston plug and the plug hole. Further, the piston plug may define a non-collinear flowpath configured to restrict non-fluidic material from passing therethrough. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
           [0011]      FIG. 1A  illustrates a cross-sectional view of a conventional piston plug. 
           [0012]      FIG. 1B  illustrates a cross-sectional view of a piston having the conventional piston plug of  FIG. 1A  installed therein. 
           [0013]      FIG. 2A  illustrates a top view of a piston plug, according to example embodiments disclosed. 
           [0014]      FIG. 2B  illustrates a cross-sectional view of the piston plug of  FIG. 2A , according to example embodiments disclosed. 
           [0015]      FIG. 2C  illustrates the piston plug of  FIGS. 2A and 2B  with the ball, spring and fastener removed, according to example embodiments disclosed. 
           [0016]      FIG. 3A  illustrates the piston plug of  FIGS. 2A-2C  having a straight thread, according to example embodiments disclosed. 
           [0017]      FIG. 3B  illustrates the piston plug of  FIGS. 2A-2C  having a tapered thread, according to example embodiments disclosed. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
         [0019]    Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein. 
         [0020]      FIG. 2A  illustrates a top view of a piston valve or plug  200 , according to example embodiments disclosed. The piston plug  200  may have a generally cylindrical body defining a longitudinal axis  202  ( FIG. 2C ) and having a top surface  204 , a bottom surface  206  ( FIGS. 2B and 2C ), and an outer cylindrical surface  208 . Also illustrated in phantom, are the ball  102  and the spring  104  secured in the piston plug  200  via the fastener  106 . The fastener  106  may be any conventional fastener such as a screw, nut, plug, or the like that may secure the ball  102  and the spring  104  in a partially drilled hole  210  of the piston plug  200  (see below). 
         [0021]      FIG. 2B  illustrates a sectional view of the piston plug  200  taken along the line  2 B- 2 B in  FIG. 2A , according to example embodiments disclosed. The piston plug  200  may define a blind hole or a partially drilled hole  210  having a central axis  212  perpendicular to the longitudinal axis  202  ( FIG. 2C ) of the piston plug  200 . A blind hole or a partially drilled hole may refer to a hole that is reamed, drilled, or milled to a specified depth, thus without breaking through to the other side of a workpiece, herein, the piston plug  200 . The partially drilled hole  210  may be at least partially defined by the outer cylindrical surface  208  of the piston plug  200 . As illustrated, a first channel  214  may be formed in the piston plug  200 . The first channel  214  may be in fluidic communication with the partially drilled hole  210  and the top surface  204  of the piston plug  200 . Returning briefly to  FIG. 2A ,  FIG. 2A  illustrates the opening of the first channel  214  on the top surface  204  of the piston plug  200 . Referring to  FIG. 2B , a second channel  216  may be formed in the piston plug  200 . As illustrated, the second channel  216  may be an L-shaped channel in fluidic communication with a bottom  218  of the partially drilled hole  210  and the bottom surface  206  of the piston plug  200 . 
         [0022]    As illustrated in  FIG. 2B  and more clearly in  FIG. 2C , the bottom  218  of the partially drilled hole  210  may define an angle α with the inner sidewall  228  ( FIG. 2C ) of the partially drilled hole  210 , thereby providing a seat for the ball  102 . In an exemplary embodiment, the angle α is of about 118°; however, embodiments in which angle α is greater or lesser than 118° are contemplated herein. Accordingly, in an embodiment, angle α may range from about 114° to about 120°.  FIG. 2C  illustrates the piston plug  200  of  FIG. 2B  with the ball  102 , spring  104 , and the fastener  106  removed.  FIG. 2C  illustrates a flowpath  220  formed by the first channel  214 , the second channel  216 , and at least a portion of the partially drilled hole  210 . 
         [0023]    As seen in  FIGS. 2B and 2C , the flowpath  220  in the piston plug  200  is not straight or collinear (for example, includes bends or turns). In contrast, the flowpath  118  in the conventional piston plug  100  is a straight path (collinear) through the piston plug  100 . This flowpath  220 , also referred to as a labyrinth type flowpath, may prevent debris and other non-fluidic material (for example, material other than gas or liquid) from exiting the piston  110 . Further, the orientation (perpendicular to the motion of the piston  110  and the longitudinal axis  202 ) of the ball  102  and the spring  104  in the partially drilled hole  210  may reduce an inertial force acting on the ball  102  and the spring  104 , thereby reducing the failure rate of the spring  104 . 
         [0024]    As seen in  FIGS. 2A-2C , the top surface  204  of the piston plug  200  may have a notch  222  designed to facilitate screwing of the piston plug  200  into the piston  110 . It should be noted that, when installed in the piston  110 , the piston plug  200  may be orientated in the same way as the piston plug  100  in the piston  110 , and the top surface  204  of the piston plug  200  may be flush with the outer surface  124  of the piston  110 . 
         [0025]      FIG. 3A  illustrates the piston plug  200  having a straight thread  224  on the outer cylindrical surface  208 , according to example embodiments disclosed. The straight thread  224  may be a nonstandard straight thread. As is know, thread profiles, for example, the major diameter, the pitch diameter, and the like, are calculated as per standards set forth by an international standard-setting body, for example, the International Organization for Standardization (ISO). A straight thread having profiles based on these standards may be referred to as a standard straight thread. In the instant case, the straight thread  224  is a nonstandard straight thread, since the profiles of the straight thread  224  may not adhere to the defined standards. For example, the straight thread  224  may have a pitch diameter greater than a pitch diameter calculated as per the standard. In another example embodiment, the major diameter or any other thread profile may be varied from the defined standard to create a nonstandard straight thread. 
         [0026]    However, the threads in the plug hole  128  of the piston  110  may be standard straight threads (for example, class  3  threads). As a result, when the piston plug  200  is screwed in piston  110 , interaction between the standard threads of the plug hole  128  and the nonstandard threads of the piston plug  200  may provide an interference fit therebetween. As a result of the interference fit, the piston plug  200  may be secured in the piston  110  without requiring any additional mechanical and/or chemical methods. In contrast, since the conventional piston plug  100  has a standard thread, additional mechanical and/or chemical methods are required to secure the conventional piston plug  100  in the piston  110 . For example, an additional mechanical method may include peening the piston plug  100  to secure the piston plug  100  in the piston  110 . Since no additional mechanical and/or chemical methods are required to secure the piston plug  200 , manufacturing time may be reduced. 
         [0027]      FIG. 3B  illustrates the piston plug  200  having a tapered thread  226  as defined by the National Pipe Thread Taper (NPT) standard, according to example embodiments disclosed. When a piston plug having tapered thread is used, the threads in the plug hole may also be correspondingly tapered to accept the piston plug. In contrast to standard straight threads, a tapered thread  226  will pull tight when screwed and therefore make a fluid-tight seal. Regardless of the type of thread on the piston plug  200 , it should be noted that, when installed, the top surface  204  of the piston plug  200  is flush with the outer surface  124  of the piston  110 . 
         [0028]    The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.