WO2014164637A1

WO2014164637A1 - Self-venting piston plugs

Info

Publication number: WO2014164637A1
Application number: PCT/US2014/023067
Authority: WO
Inventors: Bryan DUKE; Malcolm CLIFF; Chris GOWDY; Robert HOSTOTTLE; Bryce SHEFFLER
Original assignee: Dresser Rand Co
Current assignee: Dresser Rand Co
Priority date: 2013-03-13
Filing date: 2014-03-11
Publication date: 2014-10-09
Anticipated expiration: 2015-09-13
Also published as: GB2525814B; CN105378257B; GB2525814A; CN105378257A; GB201515830D0; US20170009757A1; US10480498B2

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

SELF-VENTING PISTON PLUGS

Cross -Reference to Related Applications

[0001]This application claims priority to U .S. Utility Patent Application having Serial No. 1 4/202,001 , which was filed March 10, 201 4 and U.S. Provisional Patent Application having Serial No. 61 /780,544, which was filed March 1 3, 201 3. These priority applications are hereby incorporated by reference in their 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, efc, 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] Figure 1 A illustrates a cross-sectional view of a conventional piston plug 100. Figure 1 B illustrates a cross-sectional view of a piston 1 10 in which the piston plug 100 has been installed in a plug hole 1 28 defined by an outer surface 1 24 of the piston 1 10. Referring to Figures 1 A and 1 B, the piston plug 1 00 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 1 08 via a fastener 106. The piston 1 1 0 is disposed to reciprocate axially in a bore 1 14 in a cylinder 1 12. A fluid chamber 1 1 6 is formed by the piston 1 1 0 and the bore 1 14. An inner surface 126 of the piston 1 10 is exposed to the fluid chamber 1 1 6. The gas in the fluid chamber 1 1 6 may enter the piston cavity 1 1 1 from the fluid chamber 1 16. When installed, a bottom surface 122 of the piston plug 1 00 is exposed to the piston cavity 1 1 1 and a top surface 120 of the piston plug 100 may be flush with the outer surface 1 24 of the piston 1 1 0. When the pressure of the gas in the piston cavity 1 1 1 reaches or exceeds a predetermined value, the ball 1 02 is dislodged from its seat (for example, formed via the shoulder in the through hole 1 08) and the gas in the piston cavity 1 1 1 escapes via the piston plug 100. The through hole 108 provides a straight (collinear) flowpath for the gas in the piston cavity 1 1 1 to escape.

[0005] Because the through hole 108 of the piston plug 100 forms a flowpath 1 1 8 that is straight (collinear), debris inside the piston cavity 1 1 1 exits along with the gas in the piston cavity 1 1 1 . Also, the high-speed, high-pressure operation of the reciprocating compressor may cause frequent breaking of the spring 104. Since the flowpath 1 18 through the piston plug 100 is collinear and extends along the direction of motion of the piston 1 10 in the cylinder 1 12, spring fragments may also exit the piston plug 1 00 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] Figure 1 A illustrates a cross-sectional view of a conventional piston plug.

[0012] Figure 1 B illustrates a cross-sectional view of a piston having the conventional piston plug of Figure 1 A installed therein.

[0013] Figure 2A illustrates a top view of a piston plug, according to example embodiments disclosed.

[0014] Figure 2B illustrates a cross-sectional view of the piston plug of Figure 2A, according to example embodiments disclosed. [0015] Figure 2C illustrates the piston plug of Figures 2A and 2B with the ball, spring and fastener removed, according to example embodiments disclosed.

[0016] Figure 3A illustrates the piston plug of Figures 2A-2C having a straight thread, according to example embodiments disclosed.

[0017] Figure 3B illustrates the piston plug of Figures 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] Figure 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 (Figure 2C) and having a top surface 204, a bottom surface 206 (Figures 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 1 06. 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] Figure 2B illustrates a sectional view of the piston plug 200 taken along the line 2B-2B in Figure 2A, according to example embodiments disclosed. The piston plug 200 may define a blind hole or a partially drilled hole 21 0 having a central axis 212 perpendicular to the longitudinal axis 202 (Figure 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 21 4 may be in fluidic communication with the partially drilled hole 210 and the top surface 204 of the piston plug 200. Returning briefly to Figure 2A, Figure 2A illustrates the opening of the first channel 21 4 on the top surface 204 of the piston plug 200. Referring to Figure 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 Figure 2B and more clearly in Figure 2C, the bottom 218 of the partially drilled hole 210 may define an angle a with the inner sidewall 228 (Figure 2C) of the partially drilled hole 210, thereby providing a seat for the ball 102. In an exemplary embodiment, the angle a is of about 1 18°; however, embodiments in which angle a is greater or lesser than 1 18° are contemplated herein. Accordingly, in an embodiment, angle a may range from about 1 14° to about 120°. Figure 2C illustrates the piston plug 200 of Figure 2B with the ball 1 02, spring 104, and the fastener 106 removed. Figure 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 Figures 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 1 1 8 in the conventional piston plug 1 00 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 1 10. Further, the orientation (perpendicular to the motion of the piston 1 10 and the longitudinal axis 202) of the ball 102 and the spring 1 04 in the partially drilled hole 210 may reduce an inertial force acting on the ball 1 02 and the spring 104, thereby reducing the failure rate of the spring 104.

[0024] As seen in Figures 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 1 1 0. It should be noted that, when installed in the piston 1 10, the piston plug 200 may be orientated in the same way as the piston plug 100 in the piston 1 10, and the top surface 204 of the piston plug 200 may be flush with the outer surface 124 of the piston 1 10.

[0025] Figure 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 1 10 may be standard straight threads (for example, class 3 threads). As a result, when the piston plug 200 is screwed in piston 1 10, 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 1 10 without requiring any additional mechanical and/or chemical methods. In contrast, since the conventional piston plug 1 00 has a standard thread, additional mechanical and/or chemical methods are required to secure the conventional piston plug 1 00 in the piston 1 10. For example, an additional mechanical method may include peening the piston plug 100 to secure the piston plug 100 in the piston 1 10. Since no additional mechanical and/or chemical methods are required to secure the piston plug 200, manufacturing time may be reduced.

[0027] Figure 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 1 10.

[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.

Claims

Claims We claim:

1 . A piston plug, comprising:

a cylindrical body having a longitudinal axis and an outer cylindrical surface extending longitudinally between a first surface and a second surface opposite the first surface, the outer cylindrical surface defining a hole extending radially inward, such that the hole has a central axis perpendicular to the longitudinal axis of the cylindrical body; a first channel in fluidic communication with the first surface and the hole; and a second channel in fluidic communication with the second surface and the hole, the first channel, the second channel, and at least a portion of the hole forming a non-collinear flowpath.

2. The piston plug of claim 1 , wherein the flowpath is configured to restrict flow of non- fluidic material.

3. The piston plug of claim 1 , wherein a notch is defined on at least one of the first surface and the second surface.

4. The piston plug of claim 1 , wherein a straight thread is defined on the outer cylindrical surface.

5. The piston plug of claim 4, wherein the straight thread is a nonstandard straight thread configured to provide an interference fit.

6. The piston plug of claim 1 , wherein a tapered thread is defined on the outer cylindrical surface.

7. The piston plug of claim 1 , further comprising:

a ball and a spring disposed in the hole; and a fastener disposed in the hole and configured to retain the ball and the spring in the hole.

8. The piston plug of claim 1 , wherein the hole is a partially drilled hole and a bottom of the partially drilled hole forms an angle of about 1 1 8° with an inner sidewall of the partially drilled hole.

9. The piston plug of claim 8, wherein the first channel is in fluidic communication with the inner sidewall of the partially drilled hole and the second channel is in fluidic communication with the bottom of the partially drilled hole.

1 0. A valve for regulating a flow of fluid, comprising:

an inlet channel configured to accept the fluid, the inlet channel terminating in a hole extending radially inward from an outer surface of the valve, the hole having a central axis perpendicular to a longitudinal axis of the valve; and

an outlet channel configured to eject the fluid, the outlet channel terminating in the hole, such that the inlet channel, the hole, and the outlet channel form a non-collinear flowpath.

1 1 . The valve of claim 10, wherein a straight thread is defined on the outer surface of the valve.

1 2. The valve of claim 1 1 , wherein the straight thread is a nonstandard straight thread configured to provide an interference fit.

1 3. The valve of claim 1 0, wherein a tapered thread is defined on the outer surface of the valve.

1 4. The valve of claim 10, wherein the valve has a cylindrical body having the outer surface extending longitudinally between two opposite circular surfaces, one of the two circular surfaces defining a notch.

1 5. The valve of claim 10, wherein the flowpath is configured to restrict a flow of non- fluidic material.

1 6. A reciprocating compressor, comprising:

a housing having a bore;

a piston slidably disposed in the bore, the piston and the bore defining a chamber therebetween, the piston having an inner surface in fluidic communication with the chamber and an outer surface opposite the inner surface; and

a piston plug disposed in a plug hole defined on the outer surface, the piston plug being retained in the plug hole via an interference fit between the piston plug and the plug hole, and the piston plug defining a non-collinear flowpath configured to restrict non-fluidic material from passing therethrough.

1 7. The reciprocating compressor of claim 1 6, wherein the piston plug comprises: a cylindrical body having a longitudinal axis and defining:

a partially drilled hole extending radially inward from an outer cylindrical surface of the cylindrical body, the partially drilled hole having a central axis perpendicular to the longitudinal axis;

a first channel in fluidic communication with a first circular surface of the cylindrical body and the partially drilled hole, the first circular surface being flush with the outer surface of the piston; and

a second channel in fluidic communication with a second circular surface of the cylindrical body and the partially drilled hole, the second circular surface being opposite the first circular surface,

wherein at least a portion of the partially drilled hole, the first channel, and the second channel form the non-collinear flowpath.

1 8. The reciprocating compressor of claim 17, wherein a bottom of the partially drilled hole forms an angle of about 1 18° with an inner sidewall of the partially drilled hole, and wherein the first channel is in fluidic communication with the inner sidewall of the partially drilled hole and the second channel is in fluidic communication with the bottom of the partially drilled hole.

1 9. The reciprocating compressor of claim 1 7, wherein the piston plug defines a nonstandard straight thread on the outer cylindrical surface, the nonstandard straight thread configured to provide the interference fit between the piston plug and the plug hole.

20. The reciprocating compressor of claim 17, wherein the piston plug defines a tapered thread on the outer cylindrical surface.