Pressure balanced spring loaded overtravel sealing apparatus

An apparatus includes a cage and a main plug disposed in the cage. The main plug is movable between a main plug closed position and a main plug open position. A seal assembly disposed on the main plug, the seal assembly having a seal that is configured to contact the cage when the main plug is in the main plug closed position, and configured to reduce contact with the cage when a pressure differential across the seal is reduced. The apparatus includes a pressure balancing assembly movable between a closed position, an overtravel position and an open position. The pressure balancing assembly is configured to balance the pressure differential across the seal when in the overtravel and open position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention is related to U.S. patent application Ser. No. 13/681,795 of Thomas Henry Cunningham, titled APPARATUS AND METHOD FOR REDUCING ACTUATOR THRUST REQUIREMENTS IN A CONTROL VALVE filed concurrently herewith, assigned to the same assignee as the present invention.

TECHNICAL FIELD

The subject matter disclosed herein generally relates to pressure balanced control valves and, more particularly, to pressure balanced control valves with enhanced sealing qualities for use at high temperatures.

BACKGROUND

Control valves are used to control the flow of fluids in systems used in the oil and gas processing, power generation, refining, petrochemical, and water control industries. Conventional control valves typically include a valve body with an inlet and an outlet. A cage and a seat ring are disposed between the inlet and outlet. The cage has at least one port allowing fluid communication between inlet and outlet of the control valve. The term “fluid communication” means allowing fluid to pass between or through, as in fluid passing from one volume to another volume through a conduit. A plug is concentrically disposed in the cage and allowed to axially translate exposing the cage port(s) and modulating the fluid flow. The plug is connected to an actuator by means of a stem. The actuator is a device that supplies force and motion to open or close a valve, and may be powered by mechanical, pneumatic, hydraulic or electrical means.

Some control valves are designed to balance the pressure across the valve plug to reduce the amount of force necessary to open and close the valve with the actuators. Balanced control valves typically include a cage, a plug, a stem, a seat ring, and a balance seal. The plug has at least one conduit or orifice allowing fluid communication between the top and bottom which will balance the pressure across it. A seal ring may be provided between the plug and the cage to minimize fluid leakage. Balanced control valves, typically will have two main possible fluid leakage paths when closed. The first leakage path is between the plug and seat ring, where sufficient actuator force will provide hard metal-to-metal contact to impede flow. This leakage may occur even when the plug is in contact with the valve seat. A second possible leakage path is the seal ring disposed between the plug and cage.

The American National Standards Institute (“ANSI”) has established leakage classifications (ANSI/FCI 70-2) for control valves. The standard categorizes seat leakage into six classes (Class I to Class VI). The leakage criteria become more stringent as the class number increases. Class V represents what is commonly referred to as an “effectively zero-leakage” control valve. The standard for Class V valves requires that the maximum leakage allowed through a valve is 0.0005 ml of water per minute, per inch of port diameter, per PSI differential pressure as measured from an inlet port of the valve to an outlet port of the valve.

Balanced valves may be used with a number of different seals disposed between the plug and the cage, such as for example a piston ring seal. Piston ring seals may be manufactured from a variety of materials—such as Teflon, metal, and graphite—depending on the valve application (i.e., type of fluid, temperature, pressure). Teflon piston ring seals, for instance, may allow for a reasonably tight shutoff but be limited in usage by fluid temperature. Graphite and metal piston ring seals may allow for the valve to be used in higher temperature applications, but such materials may not allow for tight shut-off.

A typical piston ring seal may generate considerable friction while in contact with its sealing surface. This friction may be acceptable for applications that allow for leakage higher than the leakage requirements of FCI 70-2 Class V. For example, Class II, Class III or even Class IV, require less contact pressure to meet their respective leakage requirements, but Class V is several orders of magnitude tighter in comparison. To achieve Class V shutoff with a piston ring type sealing member at temperatures above the usable range of elastomers or thermoplastics will typically result in high friction resulting in a high actuation requirement (i.e. a high force is required to open and close the valve) making it difficult to operate the valve.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention can reduce the friction of the seal at high temperatures thereby reducing the amount of actuation thrust required to throttle the valve.

In one exemplary non-limiting embodiment, an apparatus includes a cage and a main plug disposed in the cage. The main plug is movable between a main plug closed position and a main plug open position. The apparatus includes a seal assembly disposed on the main plug, the seal assembly having a seal that is configured to contact the cage when the main plug is in the main plug closed position, and configured to reduce or eliminate contact with the cage when a pressure differential across the seal is reduced. The apparatus also includes a pressure balancing assembly movable between a closed position, and overtravel position and an open position. The pressure balancing assembly is configured to reduce the friction between the seal and the cage when the pressure balancing assembly is in the overtravel position.

In another embodiment, a method for controlling fluid flow through a valve trim includes sealing an outlet conduit with a main plug disposed in a cage. The main plug is seated against a seat ring coupled with the cage. The method includes applying a force against a seal to close off a space between the main plug and the cage, and to maintain a sealing pressure in the space when the main plug is seated against the seat ring. The method includes balancing the differential pressure across the seal, and unseating the main plug from the seat ring.

In another embodiment, a system for controlling fluid flow through a valve trim includes a cage, a main plug disposed in the cage, and a seat ring configured to engage the main plug. A subsystem is provided to apply a force against a seal to close off a space between the main plug and the cage and maintain a pressure differential across the seal when the main plug is seated against the seat ring. A subsystem that balances the pressure differential across the seal before any movement of the main plug is also provided. The system also includes a subsystem that unseats the main plug from the seat ring.

DETAILED DESCRIPTION OF THE INVENTION

The valve trim according to this disclosure includes a cage, a plug, a seat ring, and a pressure balancing assembly. The valve trim also includes a seal assembly including a seal configured to contact the cage when the main plug is in the closed position. The seal is also configured to reduce or eliminate contact with the cage when the pressure differential across the seal is essentially balanced. The seal is provided with a predetermined resiliency or stiffness associated with the strain energy so that the seal will tend to move away from the cage as the pressure differential acting to force it against the cage decreases. The pressure balancing assembly in combination with the seal assembly provides the required tight shutoff of the seal while the main plug is in the closed position, while reducing or eliminating contact and undesirable friction during main plug throttling (movement of the main plug between a closed and open position) when the tight shutoff is no longer required. The pressure balancing assembly provides relief of the high pressure differential seen when the valve is closed before any relative motion between the cage and the main plug. The main plug and seal assembly provide a radial seal (without steps or reduced diameter surfaces of the plug or cage) and allow for easy field replacement and the possibility of trim upgrades. The valve trim according to this disclosure allows for use of a high temperature metallic material as a radial cylinder seal for tight shutoff while removing undesirable frictional characteristics during throttling and eliminating excessive actuator thrust requirements.

FIG. 1is a partial cut away view of a trim assembly11according to one embodiment. The trim assembly11includes a cage13having a cage port14. A main plug15is disposed inside the cage13. A seat ring21is disposed below the cage13. The upper portion17of the main plug15includes a cavity24. The main plug15may also be provided with one or more balancing conduit(s)25fluidly coupled to a pilot chamber27, and a longitudinal conduit26. A pilot plug33is disposed inside the cavity24and is connected to a pilot stem35and an actuator36and is provided with a pilot flange39. The pilot sealing surface37is adapted to engage a pilot seat40on the main plug15. The pilot flange39may be provided with one or more axial conduits41that are in fluid communication with cavity24. A retaining ring43is coupled to the upper portion17of the main plug15and is adapted to engage the pilot flange39when the pilot plug33is raised. Disposed adjacent to the upper portion17of the main plug15is seal assembly46that includes a pressure energized seal (seal47), a load transfer assembly49and resilient member50. One or more low friction flow restrictor51is disposed between the main plug15and the cage13. The interior surface of the cage13, the exterior surface of the main plug15, the seal47and the low friction flow restrictor51define a seal balancing volume52. Seal balancing volume52is in fluid communication with balancing conduit25and the pilot chamber27. The components and their operation are described in more detail below with reference toFIGS. 2-6which are schematic renderings of the components and operation of another embodiment and their operation.

FIG. 2illustrates a perspective exterior view of a trim assembly11according to one embodiment of the present invention. The trim assembly11includes a cage13having one or more cage port(s)14.

FIG. 3is a cross section view taken along the line inFIG. 2that is labeled A-A and illustrates the trim assembly11that may be integrated into a control valve (not shown). Note that dimensions and relationships are shown merely schematically and not to scale, and the relative dimensions of the components are exaggerated for clarity of illustration. Typically, there is a tight fit and relative close tolerance between components. The trim assembly11includes a cage13having a cage port14through which fluid may flow when the trim assembly11is in an open position. The cage13may be in the shape of a hollow cylinder and the cage port14may be one of a variety of distinct aperture shapes through the cage13to allow fluid flow to the exterior of the cage13. Disposed inside the cage13is a main plug15which may be a single component having a lower portion16, an upper portion17and a main seating surface18. Also disposed beneath the cage13is a seat ring21. Seat ring21may be a ring shaped component and may be provided with a beveled internal surface that engages the main seating surface18of the main plug15. Seat ring21and main seating surface18of the main plug15create a tight seal when trim assembly11is in the closed position.

FIG. 4illustrates the trim assembly11ofFIG. 3illustrating the different volumes and cavities of the trim assembly11. The relative spacing between components is exaggerated in comparison toFIG. 4, to illustrate the different volumes, chambers and cavities described. An upstream volume22(corresponding to the dashed line22inFIG. 4) is sealed from a downstream volume23(corresponding to the dashed line23inFIG. 4) by the tight seal created by the main plug15and the seat ring21. The terms “downstream” and “upstream” are relative terms and the relative meaning may depend on whether the valve is a “flow to open” or a “flow to close” valve. As used herein the term “upstream” refers to the higher pressure region of the system.

In one embodiment the upper portion17of the main plug15includes a cavity24(corresponding to the dashed line24inFIG. 4). The cavity24may be considered part of the upstream volume22. The main plug15may also be provided with one or more balancing conduit(s)25fluidly coupled to a pilot chamber27(corresponding to the dashed line27inFIG. 4). The main plug15is also provided with a longitudinal conduit26that provides fluid communication between the upstream volume22and the cavity24.

The trim assembly11is provided with a pressure balancing assembly31. In one embodiment, the pressure balancing assembly31includes a pilot plug33disposed inside the cavity24. The pilot plug33may be one of a variety of shapes, including a bulbous shape as illustrated inFIG. 3, a cylinder with a beveled end surface or a conical shape, among others. The pressure balancing assembly31includes a pilot stem35connected to an actuator36, a pilot sealing surface37and a pilot flange39. The pilot sealing surface37is adapted to engage a pilot seat40on the main plug15. The pilot flange39may be provided with one or more axial conduits41that are in fluid communication with cavity24. A retaining ring43is coupled to the upper portion17of the main plug15and is adapted to engage the pilot flange39when the pilot plug33is raised.

Disposed adjacent to the upper portion17of the main plug15is seal assembly46. Seal assembly46includes seal47that engages a first sealing surface48formed on the main plug15. The sealing effectiveness of seal47increases as the pressure differential acting on the seal47(seal pressure) increases. Seal assembly46includes a load transfer assembly49and resilient member50, such as a spring, that applies a force on the seal47to maintain the seal47in high friction contact with the cage13when the main plug15is in the closed position. The load transfer assembly49may be attached to the pilot stem35and is adapted to be displaced with the displacement of the pilot stem35. The resilient member50may be a Belleville style washer.

One or more low friction flow restrictor51is disposed between the main plug15and the cage13. The low friction flow restrictor51may be of a type selected from pressure energized polymeric rings, metal rings, a combination of TFE and resilient materials and a combination of metal and graphite, among others. The low friction flow restrictor51provide a relatively low friction seal and facilitate the pressurization of the pilot chamber27and seal balancing volume52in a regulated metered manner (i.e. controls the flow and prevents leakage).

The interior surface of the cage13, the exterior surface of the main plug15, the seal47and the low friction flow restrictor51define a seal balancing volume52(corresponding to the dashed lines52inFIG. 4). Seal balancing volume52is in fluid communication with balancing conduit25and the pilot chamber27.

The various components of the trim assembly11may be manufactured using a variety of materials. The specific materials depend upon operating parameters such as fluid pressure and operating temperature, chemical characteristics of the fluid, cost, and piping system considerations. For example, corrosive fluid applications may require one or more of the cage13, main plug15, pilot plug33, seat ring21, and pilot stem35to be made from stainless steel or any other appropriate material (e.g., titanium, duplex stainless steels, or Nickel alloys).

Turning to the operation of the components of the trim assembly11,FIG. 3illustrates the trim assembly11in the closed position. The pressure balancing assembly31and the pilot plug33are also in the closed position. The main plug15seals the cage port14and the downstream volume23from the upstream volume22. The upstream volume22is at an upstream pressure (P1) and the downstream volume23is at a downstream pressure (P2). The upstream pressure (P1) is higher than the downstream pressure (P2). The pilot plug33seals the pilot chamber27from the cavity24. Seal47seals the seal balancing volume52from the cavity24. When the main plug15is in the closed position the pressure in the cavity24will be maintained at the upstream pressure (P1) by means of longitudinal conduit26that fluidly couples the cavity24with upstream volume22. The pressure in the seal balancing volume52is maintained at the downstream pressure (P2) because of the connection of the seal balancing volume52with the downstream volume23. The low friction flow restrictor51allows sufficient flow so that the pressure in the seal balancing volume52is equalized with the pressure in the downstream volume23after sufficient time has passed. Seal47is maintained in contact with the cage by load transfer assembly49. Seal47is forced against the cage13by the combination of the load from the load transfer assembly49and the pressure differential (the difference between the upstream pressure (P1) and the downstream pressure (P2)) acting on the seal47, The pressure differential acting on the seal47increases the effectiveness of the seal. The seal assembly46provides a high friction seal when the main plug15is in the closed position.

FIG. 5illustrates the trim assembly11ofFIG. 3with the pressure balancing assembly31in the pressure balanced position. The pilot plug33is displaced upwardly and is unseated from the pilot seat40(open pilot plug position) thereby exposing the pilot chamber27to fluid at the upstream pressure (P1). The low friction flow restrictor51restricts the fluid flow from the seal balancing volume52to the downstream volume23to a rate sufficiently lower than the rate at which fluid flows from the upstream volume22through balancing conduit25thereby pressurizing the seal balancing volume52. The pressure in pilot chamber27and seal balancing volume52is consequently balanced with the pressure at the upstream volume22(P1). At this point, trim assembly11and the pilot plug33are in an overtravel position. An overtravel is any travel position of the actuator36and pilot stem35that does not move the main plug15. As the pressure in the pilot chamber27is increased to the upstream pressure (P1) the pressure differential acting on seal47is reduced. Additionally, load transfer assembly49is displaced so that the load exerted on the seal47by load transfer assembly49is reduced or eliminated. The removal of the load and the balancing of the pressure reduce or eliminate the friction and contact of the seal47with the cage13before the main plug15is displaced thereby reducing the thrust requirements of the actuator36. All other reference numbers inFIG. 5have previously been described with reference toFIG. 3.

Although in this embodiment the main plug15travels upwardly when opened, other embodiments may be configured in a manner that the main plug15travels downwardly when opened. Additionally, the terms “upwardly” and “downwardly” are used with reference to the orientation of the Figures, and are not intended to be limiting in any way. As used in this disclosure “balanced” means that the pressure in the seal balancing volume52is increased so as to reduce the difference between the pressure of the fluid in cavity24and the pressure of the fluid in the seal balancing volume52.

FIG. 6illustrates the trim assembly11ofFIG. 3with the pressure balancing assembly31in the open position. In the open position, the pilot plug33is in a fully open position and the pilot flange39engages the retaining ring43. The displacement of the pilot plug33will cause the main plug15to be displaced into the open position. Because the contact between seal47and cage13has been reduced or eliminated, the friction created by the displacement of the main plug15is significantly reduced. All other reference numbers inFIG. 5have previously been described with reference toFIG. 3.

FIGS. 7 and 8illustrate further embodiments of the seal47. In the embodiment ofFIG. 7the seal47may be a pressure energized twist seal that twists upon the application of a load or a pressure differential. The seal47may have the shape of a conical frustum of varying cross sectional thickness along the slant height. The seal47may be provided with a thicker midsection to minimize the body stresses to a desired level. The seal47is seated on the first sealing surface48on the main plug15. The configuration of the first sealing surface48may vary, for example it may be straight, slanted or concave. The seal47may be made of metal having a high strength to elastic modulus ratio such as austenitic nickel-chromium-based superalloys that exhibit superior high temperature properties and creep life. The seal47is provided with sufficient resiliency, or stiffness, to relieve sealing contact with the cage13when the fluid pressure or load from the load transfer assembly49is reduced. The seal47may be provided with a bottom contour or gland55shaped to engage a detent surface57on the first sealing surface48. The gland55and the detent surface57facilitate the sliding between seal47and the main plug15such that seal47can extend radially outward to close the predetermined clearance with the cage13under a smaller axial thrust from the actuator36. For example, in the embodiment illustrated inFIG. 7, the detent surface57is wedge shaped and adapted to engage a gland55that is convex in shape. In the embodiment illustrated inFIG. 8a detent surface57that is concave in shape is adapted to engage the gland55that is convex in shape to provide an adequate seal.

The bottom portion of the seal47also ensures that the contact pressure generated at the contact between seal47and plug remains at an optimum level so as to block any secondary leakage pathways and at the same time minimize any excessive plastic deformation of the seal47.

Illustrated inFIG. 9is a second embodiment of a trim assembly11. The trim assembly11includes a cage13having a cage port14, and a main plug15disposed within the cage13. The main plug15may be shaped like an annular tube and is configured to slide within the cage13.

The main plug15is provided with a main seating surface18that engages a seat ring21disposed below the cage13. The main plug15includes a balancing conduit75having an opening76. The main plug15may also be provided with a plug platform98at the bottom of the main plug15.

The trim assembly11is provided with a seal47—a high friction twist seal—disposed on a first sealing surface48formed in the main plug15. Seal47is forced against the cage13by two mechanisms, the load transfer assembly91and the pressure differential acting on the seal47. One or more passages92may be formed in the load transfer assembly91. As increasing pressure is applied to the seal47, it deforms and continues to seal against the seal surfaces with higher internal stress and contact pressure. The trim assembly11is also provided with a low friction flow restrictor51. The interior of the cage13, the exterior of the main plug15together with the seal47and the low friction flow restrictor51define a seal balancing volume99(corresponding to dashed line99inFIG. 9). The balancing conduit75is fluidly coupled to the seal balancing volume99. Disposed below the main plug15is an upstream volume22(corresponding to dashed line22inFIG. 9) at an upstream pressure (P1), and disposed above the main plug15is a pressurizing volume100(corresponding to a dashed line100inFIG. 9). The pressurizing volume100is also maintained at the upstream pressure (P1) by means of longitudinal conduit101coupling the pressurizing volume100with upstream volume22. The upstream volume22and the pressurizing volume100may be considered a single volume at upstream pressure (P1). The terms “above” and “below” are used to refer to relative locations of identified elements with reference to the drawings and are not intended to denote the orientation of the components of the trim assembly11in actual use.

The trim assembly11also includes a stem assembly79having a stem81in the shape of an elongated rod. The trim assembly11also includes a nut85having a diameter larger than the diameter of the stem81, and a pressure balancing assembly96including a sealing flange97also having a diameter larger than the diameter of the stem81. The pressure balancing assembly96is movable between a closed position, an overtravel position and an open position. The stem assembly79may be biased with a resilient member50that engages the sealing flange97. The stem assembly79may be coupled to an actuator36that drives the stem assembly79and causes the stem assembly79to slide within the cage13. The load transfer assembly91may be biased with resilient member102such as for example a Belleville washer.

FIG. 9shows an embodiment of the trim assembly11with the pressure balancing assembly96and the main plug15in the closed position. The load transfer assembly91is in contact with the seal47, forcing the seal47into contact with the cage13. In the closed position, upstream volume22is maintained at the upstream pressure (P1), and the cage port14is maintained at a downstream pressure (P2). The main seating surface18of the main plug15is seated against the seat ring21forming a tight seal. The main plug15is forced against the seat ring21by the actuator36. The sealing flange97seals the balancing conduit75. The seal47and the low friction flow restrictor51seal off the seal balancing volume99that is maintained at the downstream pressure (P2). The low friction flow restrictor51permits a limited flow of fluid so that the pressure of the seal balancing volume99is substantially the same as the downstream pressure (P2) of the fluid at the cage port14. Pressurizing volume100is in fluid communication with the upstream volume22through longitudinal conduit101, thereby maintaining the pressure in the pressurizing volume100at the upstream pressure (P1). When the main plug15is in the closed position, the sealing flange97covers the opening76and the pressure differential between the pressure in the seal balancing volume99(P2) and the pressure in pressurizing volume100(P1) keeps the seal47fully pressurized and in a tight sealing relationship with the cage13. The pressurizing volume100, the seal balancing volume99, the balancing conduit75and the sealing flange97perform as a pressure balancing assembly when the stem81is displaced.

FIG. 10shows the trim assembly11ofFIG. 9with the pressure balancing assembly96in an overtravel position and the main plug15in a pressure balancing position. In this position, the stem assembly79has been displaced a sufficient distance for the sealing flange97to be displaced, thereby uncovering the balancing conduit75. The seal balancing volume99is then fluidly coupled with the pressurizing volume100that is at upstream pressure P1. Leakage of the fluid through low friction flow restrictor51is less than the inflow to the seal balancing volume99so that, after an interval of time, the pressure in the seal balancing volume99is increased to the upstream pressure thereby reducing or eliminating the pressure differential acting on the seal47. The result is that the pressure exerted against the cage13by the seal47is significantly reduced or the contact between the seal47and the cage13is eliminated before any movement of the main plug15. All other reference numbers inFIG. 10have previously been described with reference toFIG. 9.

FIG. 11shows the trim assembly11ofFIG. 9with the pressure balancing assembly96in an open position and the main plug15in an open throttling position. The stem assembly79is displaced upwardly and the nut85engages the bottom of the main plug15. The pressure acting on the seal47has been balanced thereby reducing or eliminating the contact of the seal47with the cage13. The friction between the seal47and the cage13is consequently reduced. The reduction in friction reduces the thrust required by the actuator36to displace the main plug15. All other reference numbers inFIG. 11have previously been described with reference toFIG. 9.

Although only two examples of assemblies for balancing the pressure across the seal47have been described (pressure balancing assembly31inFIG. 2-4and the stem assembly79inFIGS. 9-11) it would be apparent to one of ordinary skill in the art to provide equivalent mechanisms for balancing the load without departing from the spirit of the invention. Similarly other arrangements that reduce the force on the seal47when the pressure on the seal47is balanced are contemplated, as may be apparent to one having ordinary skill in the art.

FIG. 12illustrates a method105, implemented by embodiments of the trim assembly11, for controlling fluid flow through the operation of a trim assembly11.

Referring toFIGS. 2,4,5,8,9,10, and11, as indicated by box107the trim assembly11seals an upstream volume22with a main plug15disposed in a cage13, the main plug15being seated against a seat ring21.

As indicated by box109axial overtravel occurs and the trim assembly11applies a force against a seal47to close off the seal balancing volume52between the main plug15and the cage13and provide for a tight seal between the upstream pressure P1and the downstream pressure (P2), when the main plug15is seated against the seat ring21. In this step, the force may be applied by a load transfer assembly49.

As indicated by box111the trim assembly11maintains an upper portion of the main plug15at a sealing pressure P1. This may be accomplished by the pressure balancing assembly31illustrated inFIG. 2, when the pilot sealing surface37is seated on the pilot seat40thereby generating a differential pressure across the seal47. Alternately this may be accomplished by the sealing flange97inFIG. 9covering the opening76.

As indicated by box113the trim assembly11balances the pressure across the seal47. This is accomplished by displacement of the pressure balancing assembly31illustrated inFIG. 2or displacement of the sealing flange97inFIG. 8.

As indicated by box115the trim assembly11reduces the force against the seal47. This may be accomplished through an actuator36that engages a load transfer assembly49.

As indicated by box117the pressure balancing assembly31engages the main plug15.

As indicated by box119the trim assembly11unseats the main plug15from the seat ring21.

Although method steps may be described in a sequential order, such methods may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described in this patent application does not, in and of itself, indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order practical. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, does not imply that the illustrated process or any of its steps are necessary to the invention, and does not imply that the illustrated process is preferred.

Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided herein, unless specifically indicated. The singular forms “a,” “an,”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that, although the terms first, second, etc. may be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. The term “and/or” includes any, and all, combinations of one or more of the associated listed items.