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CROSS REFERENCE 
     This is a Continuation-in-Part of application Ser. No. 10/017,097 filed Dec. 14, 2001, now U.S. Pat. No. 6,702,024, and entitled Dual Energized Hydroseal. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present seal assembly will function when pressured acts on it from two different directions. It is therefore sometimes referred to as a bi-directional seal or a dual energized hydroseal. The present invention can be used in a variety of different types of valves where a dual energized seal assembly is needed, as well as in cases where single-direction control is necessary. 
     2. Background of the Invention 
     The dual energized hydroseal includes a seal spool, two O-rings and two opposing seal cups. This bi-directional seal assembly can be used in a dirty fluid valve and a variety of other applications where a bi-directional seal assembly is needed, as well as in cases where a single direction seal assembly is necessary. For purposes of example, the dual energized hydroseal will be described in a dirty fluid valve, which is a type of cartridge valve frequently used in downhole tools. A plurality of dirty fluid valves are positioned in a downhole tool that is used for sampling wellbore fluids. A plurality of empty sample collection bottles are located in the downhole tool. When the tool is inserted in the wellbore, all of the dirty fluid valves are in the closed position as shown in  FIG. 1 . When the downhole tool reaches a depth that needs to be sampled, a pilot valve is pulsed, causing the seal carrier to slide the dual energized hydroseal assembly along opposing seal plates and open the supply port, as shown in  FIG. 2 . This allows wellbore fluids to enter the supply port of the dirty fluid valve and move through the longitudinal passageway of the valve and out the function port to a sample collection bottle. A plurality of sample collection bottles are often included in a single tool so that the wellbore may be sampled at different depths. 
     External pressures in a wellbore often exceed 20,000 psi absolute. After a sample has been collected, a pilot valve is pulsed, causing the seal carrier to move back to the close position as shown in  FIG. 1 . The pressure inside the sample collection bottle is the same as the pressure in the wellbore at the collection depth. As the downhole tool is brought back to the surface, external pressure drops to standard atmospheric pressure, but the pressure inside the sample collection bottle remains at wellbore pressure, which may be in excess of 20,000 psi absolute. 
     The present seal assembly will function when pressure acts on it from two different directions. The present invention can be used in a variety of different types of valves. When the seal assembly of the present invention is constructed, the O-rings are squeezed into position and/or compressed approximately 40%. The squeeze of the O-rings causes them to act as springs urging the seal cups into contact with the opposing seal plates. By contrast, O-ring manufacturers such as Parker generally recommend that O-rings be squeezed axially approximately 20%–30% for static seal designs. The present invention is a static seal design. Other O-ring manufacturers, such as Apple, recommend that O-rings be squeezed axially for static seal in the range of approximately 25%–38%. Squeezing the O-rings more than recommended by most manufacturers improves the function in the present invention. The O-rings in the present invention perform a dual function as both the spring and the seal. They act as a spring to force the seal cups into contact with the opposing seal plates, at lower pressures and they act as a seal at higher pressures. 
     The present invention is rated to operate up to 30,000 psi and 350° F. Gilmore Valve Co., the assignee of the present invention, has previously produced a dirty fluid valve with a bi-directional seal that was rated to operate up to 20,000 psi absolute and 250° F. (see Gilmore Valve Co. drawing No. 25082, a copy of which is enclosed in the Informational Disclosure Statement which is filed concurrently herewith). The present invention uses two compressed O-rings to energize the bi-directional seal. The prior art dirty fluid valve from Gilmore Valve Co. used only one O-ring to energize a bi-directional seal. The prior art O-ring used by Gilmore Valve Co. in the dirty fluid valve shown in drawing No. 25082 was produced by Greene Tweed of Houston, Tex. from Viton® 90 durometer anti-explosive decompressive material. The present invention uses two O-rings produced from Buna-N 90 durometer material. Applicants have determined that a Parker No. 2-004 O-ring is suitable for use in the present invention. The Viton of the prior art is relatively stiff and the Buna-N of the present invention is more resilient. Buna-N has more of a memory and therefore works better than the Viton as a spring. The prior art Gilmore Valve Co. seal, described in drawing No. 25082, although it was bi-directional, loses sealing integrity at operational pressures in excess of 25,000 psi. The present invention is rated to operate up to 30,000 psi. The present invention functions at higher operational pressures because there are two O-rings instead of one, the O-ring material is different than the prior art, the mechanical and hydraulic sealing forces are improved, and the present seal design is less complicated. 
     U.S. Pat. No. 5,662,166 to Shammai, discloses an apparatus for maintaining at least downhole pressure of a fluid sample of upon retrieval from an earthbore. The Shammai device has a much more complex series of seal than the present invention. Further, the Shammi device does not have a dual-energized seal like the present invention. 
     U.S. Pat. No. 5,337,822 issued to Massie et al, discloses a wellfluid sampling tool. The Massie device maintains samples at the pressure at which they are obtained until they can be analyzed. The device does not, however, maintain this pressure by means of a dual-energized hydroseal. Rather, the device of Massey uses a hydraulically driven floating piston, powered by high-pressured gas such as nitrogen acting on another floating piston, to maintain sample pressure. 
     SUMMARY OF THE INVENTION 
     The seal assembly of the present invention uses two O-rings that are squeezed more than 38.5% causing them to act as springs urging the seal cups into sealing engagement at very low pressures with the seal plates and as seals at higher pressures. At higher pressure a seal is achieved because pressure on the rear of the seal cups forces them into sealing engagement with the opposing seal plates. The pressure forces act on the seal cups to achieve a tight metal to metal seal. The bi-directional seal assembly of the present invention is shown in a dirty fluid valve which is positioned in a downhole tool for sampling wellbore fluids. The seal assembly of the present invention can be used in a variety of other types of valves that require bi-directional seal assemblies and in other types of valves that only require a uni-directional seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a valve with the dual energized hydroseal. The valve is in the closed position in an unpressurized state. 
         FIG. 2  is a section view of the valve of  FIG. 1  except the valve is in the open position and Fluid is shown flowing through the valve by the flow arrows. 
         FIG. 3  is a perspective view of the seal spool. 
         FIG. 4  is an enlarged section view of the seal spool and O-rings in a relaxed position. 
         FIG. 5  is a perspective view of one seal cup. 
         FIG. 6  is an enlarged cross sectional view of one seal cup. 
         FIG. 7  is an enlarged cross sectional view of the dual energized hydroseal exposed to supply pressure. 
         FIG. 8  is an enlarged cross sectional view of the dual energized hydroseal exposed to function pressure. 
         FIG. 9  is a sectional view of a valve with an alternative embodiment of the dual energized hydroseal. The valve is in the closed position in an unpressurized state. 
         FIG. 10  is an enlarged sectional view of a valve with an alternate embodiment of the dual energized hydroseal showing details of an alternate O-ring seal arrangement. 
         FIG. 11  is an enlarged sectional view of a portion of the valve showing the dual energized hydroseal exposed to supply pressure with the valve in a closed position. 
         FIG. 12  is an enlarged sectional view of the dual energized hydroseal showing the O-ring seals in an outward position as seen in  FIG. 11  with the fluid pressure being applied on their inner perimeter. 
         FIG. 13  is an enlarged sectional view of a valve showing the O-ring seals compressed to an inner position with the fluid pressure being applied to the O-rings on their outer perimeter. 
         FIG. 14  is an enlarged perspective view of an outer seal back-up ring. 
         FIG. 15  is an enlarged perspective view of an inner seal back-up ring. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , the dirty fluid valve is generally identified by the numeral  10 . The valve  10  is a normally closed, two position, two-way valve. The valve  10  is sometimes referred to as a “cartridge” type valve, because it is often manufactured in the configuration of  FIG. 1  and it is slipped into a valve chamber in the body of a downhole tool. The downhole tool typically have—or more dirty fluid valves, to test wellbore fluids at different well depths. Each valve  10  is in fluid communication with the wellbore and a sample collection bottle to hold wellbore fluids. The valve  10  is typically rated for operational pressures of up to 30,000 psi and temperatures of up to 350° F. 
     The valve  10  has a generally cylindrical body  12  which defines a longitudinal bore  14  which is sized and arranged to receive a seal carrier  16 . The seal carrier moves from a normally closed position shown in  FIG. 1  to an open position shown in  FIG. 2 . 
     The body  12  has threads  18  formed on one end to threadably engage the cap  20 . A cylinder cover  22  surrounds a portion of the body  12 . The cylinder cover  22  is rotationally held in place on the body by a set screw  24  and longitudinally in place by cap  20 . 
     The body  12  defines an open pilot port  26  which is in fluid communication with an open chamber  28 . The body  12  and the cylinder cover  22  define a close pilot port  30  which is in fluid communication with the close chamber  32  which is defined by the longitudinal bore  14  in body  12 , the cap  20  and the seal carries  16 . The open pilot port  26  is in fluid communication with a pilot open valve, not shown. The close pilot port  30  is in fluid communication with a pilot close valve, not shown. Both pilot valves are connected to a source of pressurized pilot fluid, not shown. 
     The seal carrier  16  has a transverse bore  34  sized and arrange to receive a bi-directional seal assembly generally identified by the numeral  36 . A transverse flow passageway  38  is also formed in the seal carrier  16  to facilitate fluid flow through the valve when it is in the open position. 
     A bore  40  is formed in the body  12  and is sized and arranged to receive the first seal plate  42 . A through bore  44  is formed in the seal plate  42  and is in fluid communication with a supply port  46  formed in the cylinder cover  22 . 
     A bore  48  is formed in the body  12  and is sized and arranged to receive the second seal plate  50 . A through bore  52  is formed in the seal plate  50  and is fluid communication with a supply port  54  formed in the cylinder cover  22 . For purposes of claim interpretation, the body  12  and the cylinder cover  22  may collectively be referred to as the body, although for manufacturing convenience, they are produced as two separate parts. 
     When the downhole tool is placed in the wellbore, pressures may reach 30,000 psi, depending on the depth of the well. Wellbore fluids exert this “supply pressure” as indicated by the arrow in  FIG. 1 . 
     To shift the valve  10  from the closed position of  FIG. 1  to the open position of  FIG. 2 , the pilot open valve is actuated allowing pilot pressure to enter the open port  26  and the open chamber  28 . The force of the pressurized pilot fluid acting on the seal carrier  16  shifts it to the open position of  FIG. 2 . 
     Referring to  FIG. 2 , the valve  10  is shown in the open position. Wellbore fluids indicated by the flow arrows, pass through the open ports  46  and  54  of the cylinder cover  22  and the through bore  44  and  52  of seal plates  42  and  50 . The wellbore fluids then pass through the flow passageway  38  in the seal carrier  16 , the longitudinal bore  14  and out the function ports  56  and  58 , as indicated by the flow arrows, to the sample collection bottle, not shown. After the sample has been taken, the pilot close valve is actuated and pressurized pilot fluid enters the close port  30  and the close chamber  32 . The pilot fluid is typically pressurized in the range of 1,500 to 10,000 psi. The force of this pilot fluid on the seal carrier causes it to shift from the open position of  FIG. 2  to the closed position of  FIG. 1 . A spring  102  is positioned in the close chamber  32 . A typical spring rate for the valve  10  is 261 lb./in. The spring  102  urges the seal carrier  16  into the normally closed position of  FIG. 1 . 
     An O-ring groove  104  is formed in the cap  20  and is sized and arranged to receive O-ring  106  which seals the cap  20  against the valve chamber in the downhole tool. A groove  108  is formed in the cylinder cover  22  and is sized and arranged to receive T-seal  110  which seals the cylinder cover  22  against the valve chamber in the downhole tool. 
     A groove  112  is formed in the body  12  and is sized and arranged to receive T-seal  114 . A groove  116  is formed in the body  12  and is sized and arranged to receive T-seal  118 . A groove  120  is formed in the body  12  and is sized and arranged to receive T-seal  122 . T-seals  114  and  118  seal and isolate the function port  56  against the valve chamber in the downhole tool, not shown. T-seals  118  and  122  seal and isolate the pilot open port against the valve chamber in the downhole tool, not shown. 
     A groove  124  is formed in the seal carrier  16  and is sized and received to receive an O-ring  126  and a lock-up ring  128 . The O-ring  126  and backup ring  128  seal and isolate the open chamber  28  from the other flow passageways in the valve  10 . 
     A groove  130  is found in the other end of the seal carrier  16  and is sized and arranged to receive an O-ring  132  and backup ring  134 . The O-ring  132  and backup ring  134  seal and isolate the close chamber  32  from the other flow passageways in the valve  10 . 
     The bi-directional seal assembly generally identified by the numeral  36  is positioned in the transverse bore  36  of seal carrier  16 . The seal assembly functions when supply pressure (pressure from wellbore fluids) enters the through bore  44  of first seal plate  42  and the through bore  52  of seal plate  50  and is applied to the seal assembly  36 . The seal assembly also functions when function pressure (from the sample collection bottle) enters the longitudinal bore  14 , and the transverse bore  34  in the seal carrier  16  and is applied to the seal assembly  36 . The seal assembly  36  is therefore referred to as “bi-directional” because it functions when exposed to both supply pressure (pressure from wellbore fluids in the well) and function pressure (pressure from the stored wellbore fluids in the sample collection bottle). 
     The seal assembly  36  includes a first seal cup  160 , a second seal cup  162 , a seal spool  164 , a first O-ring  166  and a second O-ring  168 . 
     Referring to  FIG. 3 , the seal spool  164  is shown in perspective view. The seal spool  164  has a central axle  200  bisected by a circular collar  202 . The axle  200  has a first end  204  and a second opposing end  206 . 
     Referring to  FIG. 4 , the seal spool  164  is shown in section view with two O-rings  166  and  168 . The O-ring  166  fits on the first end  204  of axle  200  and the second O-ring  168  fits on the second end  206  of the axle  200 . The circular collar  202  is formed on an angle of approximately 10°. However, a 90° angle between the collar  202  and the axle  200  also functions satisfactorily. 
     O-rings are used in two basic applications generally referred to as “static” and “dynamic” by those skilled in the art. The O-rings  166  and  168  in the bi-directional seal assembly  36  are considered as static. In a static seal, the mating gland parts are not subject to relative movement. In the present invention, the transverse bore  34 , the seal spool  164 , and the seal cups  160  and  162  are nonmoving. 
     O-ring manufacturers, for example Parker Seals of Parker Hannifin Corp. of Lexington, Ky., generally recommend that some squeeze be applied to O-rings for maximum sealing effectiveness. Squeeze can be either axial or radial. The O-rings  166  and  168  shown in  FIG. 4  are in a relaxed state. However, when placed in the seal assembly  36  in the transverse bore  34 , the O-rings are typically squeezed axially more than the amount typically recommended by O-ring manufacturers. 
     In the present invention, a Parker No. 2-004 O-ring is suitable for use as O-rings  166  and  168 . These O-rings are formed from Buna-N 90 durometer material and the maximum operational temperature suggested by Parker is 350° F. Applicants recommend an axial squeeze of 40% or more. The July 1999 Parker O-ring Handbook Design Chart 4-2, a copy of which is included in the Information Disclosure Statement, filed concurrently herewith recommends an axial squeeze for No. 2-004 through 050 of 19 to 32 percent. Design chart 4-2 is for static O-ring sealing. Other O-ring manufacturers, for example, Apple Rubber Products of Lancaster, N.Y., recommends an axial squeeze for an O-ring with a 0.070 cross-section of between 25.5 and 38.5 percent for a static seal. (See page 17 of the Apple Rubber Products Seal Design Catalog, portions of which are included in the Information Disclosure Statement filed concurrently herewith). 
     Referring to  FIG. 5  and  FIG. 6 , the first seal cup  160  is shown. The first seal cup  160  has a through bore  220  a portion  222  of which is sized and arranged to receive the first end  204  of the axle  200  of seal spool  164 . The seal cup  160  has a flat sealing surface  224  that seals against flat sealing surface  226  of first seal plate  42 . 
     Referring to  FIG. 7 , an enlarged section view of the seal assembly  36  is shown. O-rings  166  and  168  are squeezed axially about 40% or more against the collar  202  by the seal cups  160  and  162 . The second seal cup  162  has a flat sealing surface  228  formed thereon to seal against an opposing flat sealing surface  230  of seal plate  50 . Seal cup  162  has a through bore  232 , a portion  234  of which is sized and arranged to receive the second end  200  of the axle. 
     In  FIG. 7 , the arrows indicate supply pressure (from wellbore fluids) that passes through bore  44  in the seal plate  42  and bore  220  in first seal cup  160  urging O-ring  166  away from first axle portion  204  and against the transverse bore  34 . Likewise supply pressure (from wellbore fluids) passes through bore  52  in seal plate  50  and bore  232  in second seal cup  162 , urging O-ring  168  away from second axle portion  206  and against the transverse bore  34 . As O-rings  166  and  168  deform against the id of the transverse bore, the supply pressure exerts force against the rear surface  240  of first seal cup  160  and the rear surface  242  of second seal cup  162 . This supply pressure exerted on rear surfaces  240  and  242  creates a metal to metal seal between the seal cup  160  and seal plate  42  and seal cup  162  and seal plate  50 . 
     After the valve  10  has been opened and wellbore fluids, sometimes at pressures as much as 20,000 psi are stored in the sample collection bottle, the downhole tool is removed from the hole. At the surface, pressure on the outside of the tool at seal level is one atmosphere, but the pressure in the sample collection bottle will still be at wellbore pressure, perhaps 20,000 psi. For this reason the seal assembly  36  must be bi-directional and be able to seal when function pressure from the sample collection bottle exceeds ambient pressures surrounding the downhole tool. 
     In  FIG. 8 , the arrows indicate function pressure (from the sample collection bottle) that passes through the longitudinal bore  14  and passes between the transverse bore  34  and first seal cup  160  and second seal cup  162 , urging O-rings  166  and  168  into contact with axle portions  204  and  206  and away from transverse bore  34 . As O-ring  166  and  168  deform against the id of the axle portions  204  and  206 , function pressure exerts force against the rear surface  240  of seal cup  160  and the rear surface  242  of seal cup  162 . The function pressure exerted on rear surfaces  240  and  242  creates a metal-to-metal seal between the seal cup  160  and seal plate  42  and seal cup  162  and seal plate  50 . 
     O-rings  166  and  168  are squeezed axially more than the amount recommended by the manufacturers because the O-rings  166  and  168  perform actual purpose. First, the O-rings  166  and  168  act as springs and second, they act as seals. At low pressures, it is important to ensure that first seal cup  160  engages first seal plate  42  at low pressures. Because O-ring  166  is squeezed axially, it exerts force against the seal cup  160  like a spring to ensure contact. However, sealing between seal cup  160  and seal plate  42 , at higher pressure, is due to forces exerted on the rear  240  of the seal cup  160  by either supply or function pressure. 
     Likewise it is important to ensure that second seal cup  162  engages second seal plate  50  at low pressures. Because O-ring  168  is squeezed axially, it exerts force against the seal cup  162  like a spring to ensure contact. However sealing between seal cup  162  and seal plate  50 , at higher pressures, is due to forces exerted on the rear  242  of the seal cup  162  by either supply or function pressure. 
     In  FIGS. 7 and 8 , seal cup  160  has a lip  250  that extends into the through bore  220 . Likewise seal cup  162  has a lip  252  that extends into through bore  254 . In an alternative embodiment, the lips  250  and  252  are eliminated. 
       FIG. 9  is a section view of an alternative embodiment  254  of the seal assembly. The seal assembly  254  is the same as seal assembly  36 , except first seal cup  256  and second seal cup  258  do not have lips  250  or  252 . In all other respects, the seal assembly  254  functions in the same fashion as seal assembly  36 . 
       FIGS. 10–15  show an additional embodiment of the present invention which is similar in construction and operation to the valve embodiments disclosed above. Like numbers throughout the various figures designate like or similar parts that are described above. Because these parts are described above, those parts need not be described again herein. The embodiment shown in  FIGS. 10–15  show back-up rings  301  and  302  to provide additional support for the O-rings  166  and  168  carried by the seal spool  164 . There are a pair of back-up rings  301  and  302  positioned at each end portion  204  and  206  of the axle  200 . The rings  301 ,  302  are preferably made of PEEK (poly-ether-ether-ketone). The use of the back-up rings  301 ,  302  permit the valve to be operated at higher pressures and temperatures than valves without the back-up rings. The collar  202  separates the two O-rings,  166  and  168 . The rings  301  are outer positioned rings and the rings  302  are inner positioned rings. The pair of rings  302  are each positioned adjacent a respective end portion  204 ,  206  of the spool  200 . These rings engage the outer perimeter or surface of axle  200  and have a first surface  310  for engagement with a respective surface  240  or  242  of the respective seal cup  160  or  162 . The rings  302  also have a surface  312  which is generally cylindrical and is in engagement with an exterior surface or outer perimeter of the axle  200 . A third surface  314  extends between ends of the surfaces  310  and  312  providing a surface for engagement with the respective O-ring  166 ,  168  at least when the O-rings are in the position shown in  FIG. 13  when the valve is open. The rings  302  prevent the O-rings  166 ,  168  from flowing or deforming (extruding) into the space between the seal cup  160 ,  162  and the respective end portions of the axle  200 . The rings  302  are positioned around and in contact with the first and second end portions  204 ,  206  of the axle  200 ,  204 ,  206  between the respective seal cup  160 ,  162  and the respective O-ring. 
     The back-up rings  301  are generally triangularly shaped, having surfaces  320  for engagement with the respective surface  240 ,  242  of the seal cups  160 ,  162 , respectively. Each of the rings  301  has a second surface  322  for engagement with the surface defining the bore  34 . The rings  302  thereby bridge the gap between the seal carrier  16  and the respective seal cups  160 ,  162 . When an O-ring  166 ,  168  is pressurized or its inner perimeter is moved to an outer or expanded condition as shown in  FIG. 11 . The use of the rings  301  prevent the O-ring from flowing or deforming (extruding) into the gap between the surface defining the bore  34  and the outer perimeter of the seal cups  160  and  162 . The rings  301  have a third surface  324  for engagement with the outer surface of the respective O-ring  166 ,  168 . 
     Each of the O-rings  166 ,  168  is compressed axially by its respective seal cup  160  and  162  and their respective pair of back-up rings  301 ,  302  against the collar  202 . The collar  202  has generally oppositely facing surfaces that engage the O-rings. The surfaces of the collar  202  engaging the O-rings may be generally normal (0°) to the longitudinal axis of the axle  200  or may be inclined toward the center of the collar  202  at an angle of up to 10°. When the O-rings are compressed between the respective seal cup and collar  202  and their respective back-up rings  301  and  302 , the O-rings act not only as seals but as springs urging the seal cups  160 ,  162  into contact with the opposing seal plates  42  and  52 . 
     The O-rings  166 ,  168  move radially inwardly and outwardly depending upon the source of pressure. When the source of pressure is in the direction of the arrows seen in  FIG. 11  the O-rings move to an outward or expanded position. When the pressure is applied in the direction of the arrows in  FIG. 13 , the O-rings  166 ,  168  move inwardly to engage the axle  200 . Preferably, there is some clearance provided so that the seal plates  42 ,  52  and seal cups  160 ,  162  can move inwardly. The seal plates  42  and  52  are provided with T-heads that engage a shoulder to prevent excessive inward movement and over-compression or pressurization of the O-rings  166  and  168 . 
     When the seal assembly is exposed to supply pressure, as discussed above, and as seen in  FIG. 11 , the seal cups  160 ,  162  energize the respective O-ring forcing it out of contact with the axle and into sealing contact with the surface defining the transverse bore  34  of the seal carrier so supply pressure can force both the seal cups into sealing engagement with the seal plates. When the seal assembly is exposed to function pressure as seen in  FIG. 13 , the function pressure enters the transverse bore  34  of the seal carrier energizing the O-rings, forcing them out of contact with the surface defining the transverse bore  43  and into sealing contact with the seal spool  164 , the axle  200 , the rings  302  and the seal cups  160 ,  162 , so the function pressure can force both seal cups into sealing contact with the seal plates, as disclosed above. To effect sealing, the O-rings are squeezed axially more than 38.5% between the collar and the seal cups. 
     Thus, the seal arrangement shown in the embodiment of  FIGS. 10–15 , and notably that shown specifically in  FIG. 10 , replaces the seal arrangement shown in  FIGS. 1–9 , and more specifically, for example, that shown in  FIG. 4 .

Summary:
A bi-directional seal assembly can be used in various types of cartridge valves including dirty fluid valves and a variety of other valves. The present seal assembly utilizes a seal spool, two O-rings and opposing seal cups. Back-up rings are provided to engage the O-rings to control deformation of the O-rings. The O-rings are compressed during manufacture of the seal assembly and the valve more than typically recommended by O-ring manufacturers. Because of this compression, the O-rings serve a dual function. At lower pressures, the O-rings act as a spring causing the seal cups to contact the opposing seal plates and at higher pressures they act as seals between the seal assembly and the valve.