Abstract:
A dynamic sealing arrangement for preventing leakage of a fluid along a shaft includes multiple seals and pressurized barrier sealant. According to one aspect, at least three seals are arranged along the shaft with pressurized barrier sealant between the first and second seals and a collection area is provided between the second and third seals to collect any leakage that might occur. Collected leakage, if any, is ported to an output port. According to another aspect, a unitary seal block member is provided that supports the dynamic sealing arrangement for the shaft and defines a piston chamber and a drilled passageway connecting the piston chamber and barrier sealant pressurization chamber between two seals. A substantial amount of plumbing is self contained in a single body minimizing the need for additional components or complexity.

Description:
FIELD OF THE INVENTION 
   This invention pertains to seal assemblies and more particularly to pressurized dynamic seal arrangements. 
   BACKGROUND OF THE INVENTION 
   The proposed use of a pressurized barrier sealant fluid between two seals for fluid control apparatus such as pumps, valves and the like is generally known. For example, pressurized dynamic shaft sealing arrangements are disclosed in U.S. Pat. No. 5,746,435 to Arbuckle, U.S. Pat. No. 6,161,835 to Arbuckle, U.S. Pat. No. 5,772,216 to Bredemeyer and U.S. Pat. No. 5,607,165 to Bredemeyer. Such pressurized dynamic sealing arrangements may be used in the process gas industry for valves and the like to better ensure that process gas (e.g. natural gas, gaseous fuel, etc.) does not leak or cause a hazardous external environment. 
   These patents disclose that use of pressurized barrier sealant provides opposing axial fluid forces on two spaced apart seals. In these arrangements, the barrier sealant fluid pressure is typically greater than the process gas pressure such that if leakage is to occur, most or all of the leakage would be the barrier sealant rather than process gas. Indicating mechanisms are disclosed in these patents that indicate whether sealant leakage is occurring. 
   The problem with the concepts disclosed in the foregoing patents is that the concepts appear to be complex and costly to implement. More specifically, these proposals have complex plumbing arrangements, are not practical to structurally implement, and/or require numerous complex components for establishing a preload barrier. Further, the indicating mechanism disclosed in at least some of these patents may have accuracy problems, may not readily indicate the exact source of the problem and/or may be difficult or impractical to implement in the field or across different applications. Finally as will be appreciated by the present invention, these prior art concepts are subject to potential premature failure or leakage. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, the invention provides a dynamic sealing arrangement for preventing leakage of a fluid along a shaft, comprising at least three seals arranged along the shaft with pressurized barrier sealant between the first and second seals and a collection area to collect any leaked gas or barrier sealant between the second and third seals. 
   An apparatus including this sealing arrangement includes a housing adapted to receive the fluid. A shaft extends through the housing and is movable relative thereto. A first seal is supported by the housing and sealingly engages the shaft. A second seal is also supported by the housing and sealingly engages the shaft in spaced axial relation to the first seal. Barrier sealant contained between the first and second seals is pressurized by a load member to provide opposing axial forces on the first and second seals. The invention further includes a third seal supported by the housing sealingly engaging the shaft in spaced relation to the second seal and collection area in the housing between the second and the third seals. A collection passageway in the housing connects the collection area to an output port which can be mounted to instrumentation and/or collection apparatus which can be used to determine how well the sealing arrangement is performing, or it can be plugged and sealed off or vented through a filter that prevents ingress of material. 
   One aspect of the preferred embodiment is that the third seal is arranged as an external seal proximate the external environment to prevent ingress of dust, grit and other contaminants, thereby ensuring that the seals which are subject to axial barrier sealant loads are free of contaminants from the external contaminant that could cause premature failure. 
   In accordance with another aspect of the present invention, a unitary seal block member is provided that supports the dynamic sealing arrangement for the shaft and defines a piston chamber and a drilled passageway connecting the piston chamber and barrier sealant pressurization chamber between two seals. Thus, a substantial amount of plumbing is self contained in a single body minimizing the need for additional components or complexity. 
   Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional schematic view (schematic in that the flow passages are all shown in a single figure to provide a better understanding of the present invention is a single figure of a seal mounting block for a movable shaft according to an embodiment of the present invention. 
       FIG. 2  is an enlarged view of a portion of  FIG. 1  to better illustrate the details about the sealing arrangement along the movable shaft. 
       FIG. 3  is a cross sectional view of a seal mounting block mounted between a spring housing and a valve body for sealing against a movable shaft according to an embodiment of the present invention. 
       FIG. 4  is a cross sectional view of the seal mounting block shown in  FIG. 3  along a section perpendicular to that taken in  FIG. 3  to illustrate the details to the loading piston and the collection passageway. 
       FIG. 5  is a view of a seal assembly similar to  FIG. 2  but with fewer components in accordance with another embodiment of the present application. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 3 , a preferred embodiment of the present invention has been illustrated as a seal assembly  10  for preventing leakage of process fluid and for preventing ingress of dirt, contaminants and other foreign material along a movable shaft  12 . The invention is preferably incorporated into a separate seal block member  14 , or other appropriate type of housing. In the preferred embodiment, the seal block member  14  is sandwiched between a spring housing  16  and a valve body  17 . The movable shaft  12  may be linearly and or rotatably translatable. As shown herein, the movable shaft  12  is integrally connected to a valve member  20  that slides linearly in the valve body  17  to regulate process fluid flow along a valve passageway  21 . 
   The novel sealing arrangement as shown herein may be employed in an electrically actuated well head valve as disclosed in Greeb et al., U.S. patent application Ser. No. 10/340,017, filed on Jan. 10, 2003, assigned to Woodward Governor Company, the entire disclosure of which is hereby incorporated by reference. However, it will be understood that certain claims appended hereto are written in a broad manner and are therefore intended to cover other applications where sealing occurs between a movable shaft and a housing. 
   Referring to the seal block member  14 , and according to one aspect of the invention, it is a single solitary solid steel member that has formed passageways, ports, bores, chambers and/or holes formed therein. A central stepped bore  22  is formed centrally through the seal block member  14  to slidably receive the shaft  12 . With the orientation shown in the figures, the stepped bore  22  includes a bottom retaining shoulder  24  and a pair of enlarged annuluses  26 ,  27  that may be used to help fluid communication into axially spaced chambers  28 ,  30  (collection chamber  30 , and barrier sealant chamber  28 ). 
   The seal assembly  10  is inserted into the bore  22  coaxial about the shaft  12 . As shown in  FIG. 2 , the seal assembly  10  includes three seals  32 ,  34 ,  36 , a pair of perforated spacer rings  38 ,  40 , a plurality of seal retainer rings  42   a–d , a cylindrical bearing retainer  42   e , a washer  44  and a snap ring  46 . The shoulder  24  axially supports and retains the seal assembly  10  at one end while the snap ring  46  that is removably mounted in an anchor or groove  48  at the other end of the bore  22  retains the seal assembly  10  in the bore  22 . The seal retainer rings  42   a–e  (and shoulder  24  at one end which serves as a retainer) are placed on opposing sides of each of the seals,  32 ,  34 ,  36 , and allow for some limited axial movement of the seals  32 ,  34 ,  36 . 
   The perforated spacer rings  38 ,  40  define throughports  50  so as to communicate fluid radially through the seal assembly  10 . The perforated spacer rings  38 ,  40  are arranged in respective annuluses  26 ,  27  and communicate fluid between the shaft surface and the respective annulus  26 ,  27  or inside surface of the bore. 
   In a preferred embodiment, the seals  32 ,  34 ,  36  are of identical construction and are all radial seals (also known as wiper seals), and may include a generally U-shaped elastomeric member  52  and a generally U-shaped metal spring member  54  that urges the legs of the elastomeric member  52  inward and outward. In this manner, each of the seals  32 ,  34 ,  36  sealingly engages radially inward against the shaft  22  and radially outward against the bore  22 . The seals  32 ,  34 ,  46  are arranged in spaced relation along the shaft being separated by appropriate spacer rings  38 ,  40  and/or retaining rings  42   a–e.    
   The first chamber  28  contains any appropriate barrier fluid such as grease, that is loaded to a pressure typically greater than the pressure in the valve passageway  21 . To accomplish loading, the seal mounting block member  14  defines a barrier fluid passageway  56  that connects the first annulus  26  and/or chamber  28  to a formed cylindrical piston chamber  58  which is also formed in the seal block member  14 . 
   A piston  60  (which may or may not be spring biased) is slidably mounted in the piston chamber  58  with an O-ring gasket  84  between the piston and seal block member. The piston  60  is enclosed in the piston chamber  58  by an end cap  62  that is fastened to the seal block member  14 . An level indicating rod  64  integrally connected to the piston projects axially through a formed bore in the end cap  62 . The level indicating rod  64  may be graduated (e.g. scale marked with spaced markings and/or numbers) to indicate how much barrier sealant fluid is contained in the system. A pair of O-ring seals  66 ,  68  seal between the end cap  62  and the seal block member  14  and the level indicating rod  64  and the end cap  62 . An inlet passage  70  defined in the seal block member  14  provides means to fill the piston chamber  58  with barrier sealant fluid. A grease inlet port fitting stub  72  is mounted into the entrance port of the inlet passage  70 . 
   One side of the piston  60  acts upon the barrier sealant fluid in the piston chamber  58  to pressurize the barrier sealant fluid. The other side of the piston  60  is exposed to the process fluid pressure contained in the valve passageway  21  via a drilled passage  74  extending through the seal block member  14 . In this manner, the pressure of the process fluid is used to pressurize the barrier sealant fluid which in turn is communicated to the chamber between the two internal seals  32 ,  34 . The piston  60  is selectively sized such that it may pressurize the barrier fluid to a pressure greater than the fluid pressure in valve passageway  21 . Specifically a larger face is exposed to the process fluid than the barrier fluid as a result of the indicating rod  64  which is exposed to the low pressure external environment (differential piston effect). As a result, the barrier fluid pressure is self regulating and automatically adjusts to changes in process fluid pressure, if any. If desired, other types of loading apparatus may be used, such as spring mechanisms, external pressures or loads, and the like that can also exert pressure on the barrier fluid. 
   If leakage were to occur, which could occur after an extended service interval, leakage would most likely be barrier sealant past either of the two internal seals  32 ,  34  rather than process fluid. This advantageously prevents leakage of process fluid and thereby lowers environmental emissions and/or reduces the potential for a hazardous condition. Further, because barrier sealant would ordinarily be the fluid leaked, the piston  60  would tend to move or push out barrier sealant past the seal meaning that the level indicating rod  64  which is recessed would become exposed and provide an indication that there might be a leakage problem. 
   In accordance with an aspect of the present invention, the barrier sealant system is substantially self contained in the single unitary mass of the seal block member  14 . The seal block member  14  may mount directly to a valve body  18  or other pressurized reservoir or body (e.g. a pump) with a single O-ring static seal element  76  arranged and compressed therebetween to prevent leakage. No external plumbing, hydraulic couplings, tubes, conduits are needed, which substantially reduces the complexity and provides for reduced potential for leakage or failure. In addition, the pressurizing piston  60  is offset from the shaft  12  which simplifies the construction of the seal assembly  10  and thereby is thought to increase reliability of the seal assembly  10 . 
   In accordance with one aspect of the present invention, both of the seals  32 ,  34  which are acted upon by pressurized barrier sealant are internal type seals and therefore not exposed to mud, dirt, contaminants or other foreign matter from the external environment. This is achieved by arranging the third seal  36  as the external seal to prevent the ingress of contaminants and preventing such contaminants from reaching seals  32 ,  34 . As a result, the seals  32 ,  34  (and particularly seal  34 ) that are subject to the largest stresses and pressures are both internal seals that are free of further stress or wear that would otherwise be induced by foreign material from the external environment. 
   Even further, there is a significant advantage in that the collection chamber  30  is formed between seals  34 ,  36 . A drilled collection passageway  78  connects an output port  80  on the outside of the seal block member  14  with the collection chamber  30 . This can be used for a number of purposes depending upon application, including for example instrumentation or a gas or barrier fluid sensor mechanism  82  as schematically shown. The sensor mechanism  82  is adapted to sense leakage of fluid and/or barrier sealant past the second seal. This provides an additional feature that can sense whether leakage is occurring even if not indicated by the level indicating rod for such reasons as if the piston were to be stuck, or the barrier sealant passageway plugged, or other possible reasons. If gas leakage is occurring rather than barrier sealant leakage, then the level indicating rod may not indicate a problem which the sensor mechanism  82  would. In addition, and depending upon application, mechanism  82  could alternatively be a plug plugging the output port  80 , a vent filter mounted to the output port preventing external contaminants from acting upon the intermediate seal  34 , and/or a pressure relief valve in fluid communication with the collection passageway arranged to allow one way flow from the collection area to the output port. Such a pressure relief valve may have a mechanism on it to show whether it has been opened also identifying whether a problem may exist. 
   Another embodiment of the invention with fewer components is shown in  FIG. 5 . In this embodiment, retainer components  42   a – 42   d  (see  FIG. 2 ) have been eliminated. The remaining components are the same and like reference characters are used. It will be appreciated that this embodiment functions in a similar manner to the first embodiment. 
   All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
   The use of the terms “first”, “second”, and “third” as it pertains to the seals or other structures are used for purposes of differentiation only and do not provide any numerical differentiation or relative position limitations for the seal or other recited structure. Other terms are used in the claims for such purposes. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
   Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.