Abstract:
A shaft seal assembly for maintaining a seal during shaft misalignment comprising a first sealing means adjacent said shaft with a defined clearance between said shaft and said sealing means, said shaft moveable axially in relation to said first sealing means; a second sealing means, said first sealing means partially encompassed within second sealing means and in cooperative communication with said second sealing means; a third sealing means, said second sealing means partially encompassed within third sealing means and in cooperative communication with said third sealing means, said third sealing means attached to said housing or vessel and allowing said first sealing means and second sealing means to cooperatively respond to said forces produced by angular misalignment of said shaft during rotation of said shaft while maintaining defined clearance between said shaft and said sealing means.

Description:
Applicant states that this utility patent application claims priority from U.S. patent application Ser. No. 11/405,207 filed on Apr. 17, 2006 and is a continuation of said utility patent application which claimed priority from both non-provisional patent application Ser. No. 10/177,067 filed on Jun. 21, 2002 and the provisional patent application filed on Jul. 9, 2005 and given Ser. No. 60/697,434 by the United States Patent and Trademark Office, all of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a shaft seal assembly with multiple embodiments. A labyrinth seal for retaining lubrication solution within the bearing cavity of a hub assembly, such as a bearing housing, for application to a rotatable shaft to keep contaminants out of the bearing cavity is disclosed and claimed. In another embodiment, the shaft seal assembly may be used as a product seal between a product vessel and a shaft therein. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     No federal funds were used to create or develop the invention herein. 
     REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
     (Not Applicable) 
     BACKGROUND OF THE INVENTION 
     For years there have been a multitude of attempts and ideas for providing a satisfactory seal when a rotatable shaft is angularly misaligned resulting in run out of the shaft. Typically the solutions presented have failed to provide an adequate seal while allowing for an acceptable amount of shaft misalignment during operation. The problem is especially acute in product seals where the potential for shaft to bore misalignment may be maximized. A typical solution in the prior art is to increase the operating clearance between the rotating shaft and sealing members to create a “loose” clearance or operating condition. “Loose” running for adjustment or response to operational conditions, especially misalignment of the shaft with respect to the stator or stationary member, however, typically reduces or lowers the efficiency and efficacy of sealing members. 
     Labyrinth seals, for example, have been in common use for many years for application to sealing rotatable shafts. A few of the advantages of labyrinth seals over contact seals are increased wear resistance, extended operating life and reduced power consumption during use. Labyrinth seals, however, also depend on a close and defined clearance with the rotatable shaft for proper function. Shaft misalignment is also a problem with “contact” seals because the contact between the seal and misaligned shaft typically results in greater wear. Abrasiveness of the product also affects the wear pattern and the useful life of the contact seals. 
     Prior attempts to use fluid pressure (either vapor or liquid) to seal both liquid and solid materials in combination with sealing members such as labyrinth seals or contact seals have not been entirely satisfactory because of the “tight” or low clearance necessary to create the required pressure differential between the seal and the product on the other side of the seal (i.e., the tighter the seal, the lower the volume of fluid required to maintain the seal against the external pressure of material.) Another weakness in the prior art is that many product seals expose the movable intermeshed sealing faces or surfaces of the product seal to the product resulting in aggressive wear and poor reliability. Furthermore, for certain applications, the product seal may need to be removed entirely from the shaft seal assembly for cleaning, because of product exposure to the sealing faces or surfaces. 
     The prior art then has failed to provide a solution that allows both a “tight” running clearance between the seal members and the stationary member for efficacious sealing and a “loose” running clearance for adjustment or response to operational conditions especially misalignment of the rotatable shaft with respect to the stator or stationary member. 
     SUMMARY OF THE INVENTION 
     The present art offers improved shaft sealing and product seal performance over the prior art. The shaft seal assembly solution disclosed and claimed herein allows both tight or low running clearance between seal members and the stationary member and a loose running clearance for adjustment or response to operational conditions especially misalignment of a rotatable shaft with respect to the stator or stationary member. 
     As disclosed herein, the present art describes and provides for improved function by allowing a labyrinth seal to adjust to radial, axial and angular movements of the shaft while maintaining a desired shaft-to-labyrinth clearance. The present art also permits equalization of pressure across the labyrinth pattern by permitting venting and thus improved function over currently available designs. Additionally, sealing fluid (air, steam, gas or liquid) pressure may be applied through the vent or port locations to establish an internal seal pressure greater than inboard or outboard pressure (over-pressurization). This enables the labyrinth to seal pressure differentials that may exist between the inboard and outboard sides of the seal. Pressurization of the internal portion of the shaft seal assembly effectively isolates the moving or engaging faces of the shaft seal assembly from contact with product by design and in combination with a pressurized fluid barrier. 
     It is therefore an object of the present invention to provide a shaft seal assembly for engagement with a housing which maintains its sealing integrity with a shaft upon application of axial, angular or radial force upon said shaft. 
     It is another object of the present invention to provide a shaft seal assembly, which may be mounted to a vessel wall for engagement with a shaft which maintains its sealing integrity with a shaft during or in response to axial, angular or radial force movement of said shaft. 
     Other objects and features of the invention will become apparent from the following detailed description when read with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective exterior view of the shaft seal assembly. 
         FIG. 2  is an exterior end view of the shaft seal assembly with the shaft element aligned. 
         FIG. 3  is a sectional view of a first embodiment of the shaft seal assembly, as shown in  FIG. 2  and mounted to a housing. 
         FIG. 3A  illustrates the first surface seal-shaft integrity during angular and radial shaft alignment. 
         FIG. 3B  illustrates second surface seal-shaft integrity during angular and radial shaft alignment. 
         FIG. 4  is an exterior end view with the shaft misaligned. 
         FIG. 5  is a sectional view of the first embodiment as shown in  FIG. 3  with both angular and radial misalignment of the shaft applied. 
         FIG. 5A  illustrates first seal-shaft integrity allowed by articulation during angular and radial shaft misalignment. 
         FIG. 5B  illustrates second seal-shaft integrity allowed by articulation during angular and radial shaft misalignment. 
         FIG. 6  is a sectional view of a second embodiment of the shaft seal assembly as shown in  FIG. 2 . 
         FIG. 7  is a sectional view of a third embodiment as shown in  FIG. 2 . 
         FIG. 8  is a perspective view of a fourth embodiment as mounted to a vessel wall. 
     
    
    
     DETAILED DESCRIPTION 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 ELEMENT LISTING 
               
             
          
           
               
                 Description 
                 Element No. 
               
               
                   
               
               
                 Shaft 
                  1 
               
               
                 Fixed stator 
                  2 
               
               
                 Fixed stator (part-line) 
                  2a 
               
               
                 Labyrinth seal 
                  3 
               
               
                 Radiused face 
                  3a 
               
               
                 Floating stator 
                  4 
               
               
                 Fluid return pathway 
                  5 
               
               
                 Shaft seal clearance 
                  6 
               
               
                 First o-ring 
                  7 
               
               
                 Anti-rotation pin 
                  8 
               
               
                 Vent 
                  9 
               
               
                 Anti-rotation groove (floating stator) 
                 10 
               
               
                 Spherical interface 
                 11 
               
               
                 Anti-rotation pin 
                 12 
               
               
                 Second o-ring 
                 13 
               
               
                 Labyrinth seal pattern grooves 
                 14 
               
               
                 First o-ring channel 
                 15 
               
               
                 Cavity for anti-rotation device (fixed stator) 
                 16 
               
               
                 Axial face of labyrinth seal 
                 17 
               
               
                 Axial face of floating stator 
                 18 
               
               
                 Second o-ring channel 
                 19 
               
               
                 First clearance between floating stator/fixed stator 
                 20 
               
               
                 Second clearance between floating stator/fixed stator 
                 21 
               
               
                 Throttle groove 
                 22 
               
               
                 Labyrinth pattern annular groove 
                 23 
               
               
                 Sleeve 
                 24 
               
               
                 Shaft seal assembly 
                 25 
               
               
                 Throttle (alignment skate) 
                 26 
               
               
                 Floating stator annular groove 
                 27 
               
               
                 Labyrinth seal passage 
                 28 
               
               
                 Floating stator passage 
                 29 
               
               
                 Housing 
                 30 
               
               
                 Angle of misalignment 
                 31 
               
               
                 Bearings and bearing cavity 
                 32 
               
               
                 Mounting bolts 
                 33 
               
               
                 Vessel wall 
                 34 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
       FIGS. 1-5  provide a view of a first embodiment of the shaft seal assembly  25  that allows for sealing various lubricating solutions within bearing housing  30 .  FIGS. 6 and 7  provide alternative embodiments of the shaft seal assembly  25  wherein sealing fluids are used. Applicant herein defines sealing fluids to include both liquids and vapors. Applicant considers air, nitrogen, water and steam as well as any other fluid which may work with the proposed shaft seal assembly to provide a pressurized fluid barrier for any and all embodiments disclosed herein to be within the purview of the present disclosure. The gas or fluid chosen is based on process suitability with the product to be sealed. 
       FIG. 1  is a perspective exterior view of the shaft seal assembly  25  arranged and engaged with a shaft  1  inserted through the fixed stator  2  of shaft seal assembly  25 .  FIG. 2  is an exterior end view of the shaft seal assembly with shaft  1  aligned within the shaft seal assembly  25 . 
       FIG. 3  is a sectional view of a first embodiment of the shaft seal assembly  25  shown in  FIG. 2  illustrating the shaft seal assembly  25  as a labyrinth seal for retaining lubrication solution within the bearing cavity  32  of housing  30 . The shaft  1  shown in  FIG. 3  is the type which may experience radial, angular or axial movement relative to the fixed stator element or portion of the fixed stator  2  during rotation. The fixed stator portion of the shaft seal assembly  25  may be flange-mounted or press-fit or attached by other means to a housing  30 . The invention will also function with a rotating housing and stationary shaft. (Not shown) As required by the particular application, the shaft  1  is allowed to move freely in the axial direction in relation to the shaft seal assembly  25 . 
     A labyrinth seal  3  having an interior surface is engaged with shaft  1 . A defined clearance  6  exists between the interior surface of said labyrinth seal  3  and the shaft  1 . Opposite the interior surface of said labyrinth seal  3  is the radiused surface  3   a  of said labyrinth seal  3 . The radiused surface  3   a  of the labyrinth seal  3  and the interior of the floating stator  4  forms a spherical interface  11 . O-ring channels  15  and o-rings  7  are disposed to cooperate with said radiused surface  3   a  of said labyrinth seal  3  to seal (or trap) fluid migration through, between and along engaged labyrinth seal  3  and floating stator  4  while maintaining spherical interface  11  which allows limited relative rotational movement (articulation) between labyrinth seal  3  and floating stator  4 . O-ring channels  15 , as shown, are machined into the floating stator  4  and positioned at the spherical interface  11  with labyrinth seal  3 . O-ring channels  15  are annular and continuous in relation to labyrinth seal  3 . The o-ring channel  15  and o-ring  7  may also be placed in the labyrinth seal  3  adjacent the spherical interface  11 . O-rings  7  should be made of materials that are compatible with both the product to be sealed and the preferred sealing fluid chosen. O-ring channels  15  and o-rings  7  are one possible combination of sealing means that may be used within the shaft seal assembly  25  as recited in the claims. Strategically placed anti-rotation pin(s)  12  inserted into anti-rotation grooves  10  limit relative rotational movement between labyrinth seal  3  and floating stator  4 . A plurality of anti-rotation grooves  10  and pins  12  may be placed around the radius of the shaft  1 . If the shaft seal assembly  25  is used in combination with a sealing fluid, strategic anti-rotation pins  12  may be removed allowing corresponding anti-rotation grooves  10  to serve as a fluid passage through vent  9  and lubricant return  5 . (See  FIG. 7 ) Additionally, the relationship of the diameters of anti-rotation pins  12  and anti-rotation grooves  10  may be selected to allow more or less angular misalignment of the shaft  1 . A small diameter anti-rotation pin  12  used with a large diameter anti-rotation groove  10  would allow for greater relative movement of the labyrinth seal  3  in relation to the floating stator  4  in response to angular misalignment of shaft  1 . Labyrinth seal  3  is one possible embodiment of a sealing means that may be used adjacent to the shaft  1  within the shaft seal assembly  25  as recited in the claims. 
     A continuous annular channel is formed within fixed stator  2  and defined by clearance  20  and  21  as allowed between the exterior of said floating stator  4  and said interior of said fixed stator  2  of shaft seal assembly  25 . The annular channel of fixed stator  2  is highlighted as A-A′ in  FIG. 2 . The annular channel of the fixed stator has interior surfaces which are substantially perpendicular to said shaft  1 . The exterior surfaces of the floating stator  4 , which is substantially encompassed within the annular channel of the fixed stator  2 , cooperatively engage with the first and second interior perpendicular faces of the fixed stator  2 . An inner annular interface is formed by the first (shaft seal assembly inboard side) perpendicular annular channel surface of the fixed stator  2  engaging with the first (inboard side) perpendicular face of the floating stator  4 . An outer annular interface is formed by the second (shaft seal assembly outboard side) perpendicular annular interior channel surface of the fixed stator  2  engaging with the second (outboard side) perpendicular face of the floating stator  4 . O-ring channels  19  and o-rings  13  disposed therein cooperate with the surfaces of floating stator  4  which are in perpendicular to relation to shaft  1  to seal (or trap) fluid migration between and along engaged floating stator  4  while allowing limited relative rotational movement between floating stator  4  and fixed stator  2 . Floating stator  4  and fixed stator  2  are one possible embodiment of cooperatively engaged sealing means that may be used in combination with labyrinth seal  3  within the shaft seal assembly  25  as recited in the claims. 
     O-ring channels  19  are annular and continuous in relation to shaft  1 . The o-ring channels  19  and o-rings  13  may be placed in the body of the floating stator  4  instead of the fixed stator  2  (not shown) but must be placed in similar proximal relation. O-rings  13  should be made of materials that are compatible with both the product to be sealed and the preferred sealing fluid chosen. O-ring channels  19  and o-rings  13  are one possible combination of sealing means that may be used within the shaft seal assembly  25  as recited in the claims. 
     Strategically placed anti-rotation pin(s)  8  inserted into anti-rotation groove(s)  16  limit both relative radial and rotational movement between floating stator  4  and interior side of fixed stator  2 . A plurality of anti-rotation grooves  16  and pins  8  may be placed around the radius of the shaft  1 . The relationship of the diameters of anti-rotation pins  8  and anti-rotation grooves  16  may also be selected to allow more or less angular misalignment of the shaft. A small diameter anti-rotation pin  8  and large diameter fixed stator anti-rotation groove allow for greater relative movement of the labyrinth seal  3  in response to angular misalignment of shaft  1 . 
     The labyrinth pattern seal grooves  14  may be pressure equalized by venting through one or more vents  9 . If so desired, the vents may be supplied with a pressurized sealing fluid to over-pressurize the labyrinth area  14  and shaft seal clearance  6  to increase the efficacy of shaft seal assembly  25 . A spherical interface  11  between the labyrinth seal  3  and the floating stator  4  allow for angular misalignment between the shaft  1  and fixed stator  2 . O-ring channels  19  are annular with the shaft  1  and, as shown, are machined into the fixed stator  2  and positioned at the interface between the fixed stator  2  and floating stator  4 . O-ring channel  19  may also be placed in the floating stator  4  for sealing contact with the fixed stator  2 . 
       FIG. 3A  illustrates seal-shaft integrity during angular and radial shaft alignment. This view highlights the alignment of the axial face  17  of the labyrinth seal  3  and the axial face  18  of the floating stator  4 . Particular focus is drawn to the alignment of the axial faces  17  and  18  at the spherical interface  11  between the floating stator  4  and labyrinth  3 .  FIG. 3B  illustrates the shaft-seal integrity during angular and radial shaft alignment at the surface opposite that shown in  FIG. 3A . This view highlights the alignment of the axial faces  17  and  18  of labyrinth seal  3  and floating stator  4 , respectively, for the opposite portion of the shaft seal assembly  25  as shown in  FIG. 3A . Those practiced in the arts will appreciate that because the shaft  1  and shaft seal assembly  25  are of a circular shape and nature, the surfaces are shown 360 degrees around shaft  1 . Again, particular focus is drawn to the alignment of the axial faces  17  and  18  at the spherical interface  11  between the labyrinth seal  3  and floating stator  4 .  FIGS. 3A and 3B  also illustrate the first defined clearance  20  between the floating stator  4  and the fixed stator  2  and the second defined clearance  21  between the floating stator  4  and fixed stator  2  and opposite the first defined clearance  20 . 
     In  FIGS. 2 ,  3 ,  3 A and  3 B, the shaft  1  is not experiencing radial, angular or axial movement and the width of the defined clearances  20  and  21 , which are substantially equal, indicate little movement or misalignment upon the floating stator  4 . 
       FIG. 4  is an exterior end view of the shaft seal assembly  25  with the rotatable shaft  1  misaligned therein.  FIG. 5  is a sectional view of the first embodiment of the shaft seal assembly  25  as shown in  FIG. 3  with both angular and radial misalignment of the shaft  1  applied. The shaft  1  as shown in  FIG. 5  is also of the type which may experience radial, angular or axial movement relative to the fixed stator  2  portion of the shaft seal assembly  25 . 
     As shown at  FIG. 5 , the defined radial clearance  6  of labyrinth seal  3  with shaft  1  has been maintained even though the angle of shaft misalignment  31  has changed. The shaft  1  is still allowed to move freely in the axial direction even though the angle of shaft misalignment  31  has changed. The arrangement of the shaft seal assembly  25  allows the labyrinth seal  3  to move with the floating stator  4  upon introduction of radial movement of said shaft  1 . The labyrinth seal  3  and floating stator  4  are secured together by one or more compressed o-rings  7 . Rotation of the labyrinth seal  3  within the floating stator  4  is prevented by anti-rotation means which may include a screws, pins or similar devices  12  to inhibit rotation. Rotation of the labyrinth seal  3  and floating stator  4  assembly within the fixed stator  2  is prevented by anti-rotation pins  8 . The pins as shown in  FIGS. 3 ,  3 A,  3 B,  5 ,  6  and  7  are one means of preventing rotation of the labyrinth seal  3  and floating stator  4 , as recited in the claims. Lubricant or other media to be sealed by the labyrinth seal  3  may be collected and drained through a series of one or more optional drains or lubricant return pathways  5 . The labyrinth seal  3  may be pressure equalized by venting through one or more vents  9 . If so desired, the vents  9  may be supplied with pressurized air or other gas or fluid media to over-pressurize the labyrinth seal  3  to increase seal efficacy. The combination of close tolerances between the cooperatively engaged mechanical portions of the shaft seal assembly  25  and pressurized sealing fluid inhibit product and contaminate contact with the internals of the shaft seal assembly  25 . The spherical interface  11  between the labyrinth seal  3  and the floating stator  4  allow for angular misalignment between the shaft  1  and fixed stator  2 . O-ring channel  19  and o-ring  13  disposed therein cooperate with the opposing faces of the floating stator  4 , which are substantially in perpendicular relation to shaft  1 , to seal (or trap) fluid migration between and along engaged floating stator  4  while allowing limited relative radial (vertical) movement between stator  4  and fixed stator  2 . 
       FIG. 5A  illustrates seal-shaft integrity allowed by the shaft seal assembly  25  during angular and radial shaft misalignment. This view highlights the offset or articulation of the axial faces  17  of the labyrinth seal in relation the axial faces  18  of the floating stator  4  for a first portion of the shaft seal assembly  25 . Particular focus is drawn to the offset of the axial faces  17  and  18  at the spherical interface  11  between labyrinth seal  3  and floating stator  4 . 
       FIG. 5B  illustrates seal-shaft integrity for a second surface, opposite the first surface shown in  FIG. 5A , during angular and radial shaft misalignment. This view highlights that during misalignment of shaft  1 , axial faces  17  and  18 , of the labyrinth seal  3  and floating stator  4 , respectively, are not aligned but instead move (articulate) in relation to each other. The shaft to seal clearance  6  is maintained in response to the shaft misalignment and the overall seal integrity is not compromised because the seal integrity of the floating stator  4  to fixed stator  2  and the floating stator  4  to labyrinth seal  3  are maintained during shaft misalignment. Those practiced in the arts will appreciate that because the shaft  1  and shaft seal assembly  25  are of a circular shape and nature, the surfaces are shown 360 degrees around shaft  1 . 
       FIGS. 5A and 5B  also illustrate the first clearance or gap  20  between the floating stator  4  and the fixed stator  2  and the second clearance or gap  21  between the floating stator  4  and fixed stator  2  and opposite the first clearance or gap  20 . 
     In  FIGS. 4 ,  5 ,  5 A and  5 B, the shaft  1  is experiencing radial, angular or axial movement during rotation of the shaft  1  and the width of the gaps or clearances  20  and  21 , have changed in response to said radial, angular or axial movement. (Compare to  FIGS. 3 ,  3 A and  3 B.) The change in width of clearance  20  and  21  indicate the floating stator  4  has moved in response to the movement or angular misalignment of shaft  1 . The shaft seal assembly  25  allows articulation between axial faces  17  and  18 , maintenance of spherical interface  11  and radial movement at first and second clearance,  20  and  21 , respectively, while maintaining shaft seal clearance  6 . 
       FIG. 6  is a sectional view of a second embodiment of the shaft seal assembly  25  as shown in  FIG. 2  for over-pressurization with alternative labyrinth seal pattern grooves  14 . In this figure the labyrinth seal pattern grooves  14  are composed of a friction reducing substance such as polytetrafluoroethylene (PTFE) that forms a close clearance to the shaft  1 . PTFE is also sometimes referred to as Teflon® which is manufactured and marketed by Dupont. PTFE is a plastic with high chemical resistance, low and high temperature capability, resistance to weathering, low friction, electrical and thermal insulation, and “slipperiness.” The “slipperiness” of the material may also be defined as lubricous or adding a lubricous type quality to the material. Carbon or other materials may be substituted for PTFE to provide the necessary sealing qualities and lubricous qualities for labyrinth seal pattern grooves  14 . 
     Pressurized sealing fluids are supplied to over-pressurize the lubricious labyrinth pattern  26  as shown in  FIG. 6 . The pressurized sealing fluids make their way into the annular groove  23  of the throttle  26  through one or more inlets. Throttle  26  is also referred to as “an alignment skate” by those practiced in the arts. Throttle  26  allows the labyrinth seal  3  to respond to movement of the shaft caused by the misalignment of the shaft  1 . The pressurized sealing fluid escapes past the close clearance formed between the shaft  1  and labyrinth seal  3  having throttle  26 . The close proximity of the throttle  26  to the shaft  1  also creates resistance to the sealing fluid flow over the shaft  1  and causes pressure to build-up inside the annular groove  23 . Floating annular groove  27  in cooperation and connection with annular groove  23  also provides an outlet for excess sealing fluid to be “bled” out of shaft seal assembly  25  for pressure equalization or to maintain a continuous fluid purge on the shaft sealing assembly  25  during operation. An advantage afforded by this aspect of the shaft sealing assembly  25  is its application wherein “clean-in place” product seal decontamination procedures are preferred or required. Examples would include food grade applications. 
       FIG. 7  illustrates shaft seal assembly  25  with the anti-rotation pin  12  removed to improve visualization of the inlets. These would typically exist, but are not limited to, a series of ports, inlets or passages about the circumference of the shaft seal assembly  25 .  FIG. 7  also shows the shape and pattern of the labyrinth seal  3  may be varied. The shape of throttles  26  may also be varied as shown by the square profile shown at throttle groove  22  in addition to the circular-type  26 . Also note that where direct contact with the shaft  1  is not desired, the shaft seal assembly  25  be used in combination with a separate sleeve  24  that would be attached by varied means to the shaft  1 . 
       FIG. 8  shows that another embodiment of the present disclosure wherein the shaft seal assembly  25  has been affixed to a vessel wall  34 . The shaft seal assembly  25  may be affixed to vessel wall  34  through securement means such as mounting bolts  33  to ensure improved sealing wherein shaft  1  is subjected to angular misalignment. The mounting bolts  33  and slots (not numbered) through the shaft seal assembly  25  exterior are one means of mounting the shaft seal assembly  25 , as recited in the claims. 
     Having described the preferred embodiment, other features of the present invention will undoubtedly occur to those versed in the art, as will numerous modifications and alterations in the embodiments of the invention illustrated, all of which may be achieved without departing from the spirit and scope of the invention.