Abstract:
The pressure biased shuttle valve assembly in the pressure biased shuttle valve operates in conjunction with a remote operated vehicle (ROV) to actuate blow-out preventers and thus shut in the well during emergency situations. The pressure biased shuttle valve assembly opens in response to fluid pressure from the ROV. It requires little or no flow to open. These pressure biased shuttle valves are typically located subsea on a lower marine riser platform (LMRP). These platforms are sometimes brought to the surface for a periodic testing and maintenance. The pressure biased shuttle valve assembly is also used as a repair kit which facilitates easy maintenance and repair when the LMRP is brought to the surface. In one embodiment, the shuttle is rigidly connected to a piston rod. In another embodiment, there is a flexible connection between the piston rod and shuttle. The purpose of the flexible connection is to encourage a better seal in smaller size valves.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/452,594, for a Low Interflow Hydraulic Shuttle Valve, filed on Dec. 1, 1999, which is assigned to Gilmore Valve Company. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     This invention relates to valves, and more particularly to shuttle valves. The invention is an improvement upon shuttle valves of the type made and sold by applicant&#39;s assignee, Gilmore Valve Company, which is the owner of the other U.S. patents for improved shuttle valves including U.S. Pat. Nos. 3,533,431 and 4,253,481. 
     B. Description of the Prior Art 
     Shuttle valves have been used for many years to control the flow of gases as in U.S. Pat. Nos. 1,529,384 and 2,408,799. Other shuttle valves have been used to control the flow of liquids as in U.S. Pat. Nos. 1,686,310 and 1,795,386. 
     Shuttle valves used to control hydraulic fluid, particularly those used in underwater oil field equipment, must be designed taking into consideration working pressures, up to several thousand psi and flow rates of up to several hundred gpm. It is especially important that underwater shuttle valves used in connection with operation of subsea blowout preventers (BOPs) have a long trouble-free life because of their inaccessibility. The differential pressure on the shuttle often results in high momentum as it moves from one valve seat to another. When a shuttle contacts a valve seat, the repeated impact can break or crack the cage or cause it to be warped, and can otherwise disrupt proper valve operation. 
     One way to address the problem of shuttle impact is to lighten the shuttle and provide rubber cushions in the form of thick sealing elements as shown in U.S. Pat. No. 3,038,487. Yet another way of addressing shuttle impact is a hydraulic cushion as shown in U.S. Pat. No. 4,253,481 owned by applicant&#39;s assignee. The hydraulic cushion discussed above is similar to the action of a hydraulic cushioned slush pump valve as shown in U.S. Pat. Nos. 2,197,455 and 2,605,080. U.S. Pat. No. 2,654,564 discloses a metal to metal seat to take the axial load imposed on the shuttle and thereby to limit the pressure on the rubber seal ring so that the rubber is prevented from being overloaded, cut or extruded by the action of high pressure fluid. 
     The shuttle valve disclosed in U.S. Pat. No. 4,253,481 was sold for many years by Gilmore Valve Company for use with underwater oil field equipment. This prior art valve shuttle valve was limited to two inputs and was relatively expensive to manufacture. To overcome some of these limitations, Gilmore introduced the Mark I shuttle valve in 1997 as shown in FIG. 1 of the drawings. The Mark I relied upon two elastomeric o-rings mounted around the central flange of the shuttle to achieve a seal. The end portions of the shuttle were relatively thin and were prone to cracking because of shuttle impact. In addition, the o-rings were sometimes cut or blown off due to operational pressures and flow rates. 
     In order to overcome some of the limitations of the Mark I, Gilmore developed a retrofit design known as the Mark II which was introduced in 1998 as shown in FIG. 2 of the drawings. The Mark II design included an increased thickness of the end portions or cage, a decrease in hole size, larger o-rings which were stretched around the shuttle and a pair of plastic teflon bearings to center the shuttle and reduce vibration as it traveled back and forth. The Mark II eliminated many of the problems of the Mark I; however, at the highest operational flow rates, o-rings were still lost. The present invention is designed for operation at 5,000 psi; the ½ inch model is designed for an 80 gpm flow rate, the 1 inch model is designed for a 250 gpm flow rate and the 1½ inch model, is designed for a 350 gpm flow rate. 
     In an effort to overcome the limitations of the Mark I and Mark II, applicant has developed an improved design which is the subject of the present invention. In order to overcome some of the problems associated with elastomeric seals, the present invention has eliminated such seals and now relies upon a metal to metal seal. The metal to metal seal of the present invention is progressively coined because of repeated contact between opposing tapered sealing surfaces surrounding a central flange on the shuttle and opposing metal valve seats. 
     The present invention includes alternative embodiments having a modular design that allows the components to be stacked one upon the other to receive more than two inputs. Another stackable, multi-input valve is disclosed in U.S. Pat. No. 4,467,825. This design uses a plurality of spool valve members to direct a superior fluid input signal to the outlet. 
     The present invention is less expensive to manufacture than prior shuttle valves sold by Gilmore Valve Company as disclosed in U.S. Pat. No. 4,253,481. Alternative embodiments of the present invention allow the shuttle valve to receive 3 or more inputs which was not possible with the shuttle valve disclosed in U.S. Pat. No. 4,253,481. In addition, the present invention overcomes the limitations of the Mark I and Mark II discussed above. 
     In emergency situations or during testing, it may be necessary to close the subsea BOPs using a remote operated vehicle (ROV). The ROV is an unmanned submarine with an on-board television camera so the ROV can be maneuvered by topside personnel on board a ship. The ROV is equipped with a plug that stabs into a receptacle on the ROV docking station on the lower marine riser platform (LMRP). The LMRP sets on top of the BOPs. A hose runs from the receptacle on the ROV docketing station to a biased shuttle valve. 
     In an emergency or during testing, the ROV is maneuvered to stab into the receptacle on the ROV docking station. The ROV injects hydraulic fluid at relatively high pressures (greater than 1,000 psi) and relatively low flow rates into the hose to the biased shuttle valve to close the BOPs. Gilmore Valve Company has sold a flow biased shuttle valve to work with the ROV, but it has operational limitations. This prior art flow biased shuttle valve was flow activated and it needed the following minimum flow rates to activate: one-half inch model, 5 GPM; 1-inch model 20 GPM and one and one-half inch model 50 GPM. Some ROVs on the market may not be able to produce sufficient flow rates in the larger sizes to activate the prior art Gilmore flow biased shuttle valve. 
     In order to address this need, a pressure biased shuttle valve was developed that operates on pressure, not flow. The pressure biased shuttle valve of the present invention needs a minimum operating pressure of 1000 psi and little or no flow. Most, if not all ROVs currently on the market, can produce operational pressures well in excess of 1,000 psi, and thus can operate the pressure biased shuttle valve of the present invention. The pressure biased shuttle valve uses the coining technique to achieve a metal to metal seal. 
     Some prior art shuttle valves had problems with switchback. This phenomena occurs only on return flow and is the result of fluid momentum shifting the shuttle after closing pressure is relieved and prior to opening pressure being applied. This results in an indefinite flow path for return flow. Most return flow paths in the closing circuit exhaust to the ocean, so usually this does not create an operating problem. The exception to this is when one of the possible return paths is an ROV port. Such ports are commonly plugged to prevent saltwater ingress into the system. If the return flow becomes inadvertently switched to a plugged ROV port, it will substantially increase the opening time of the BOP. The present invention was developed to reduce switchback. The present invention employs a spring which biases the return flow to the non-biased port. The biased port is energized by pressure, permitting operation with low volume pumps employed on ROV&#39;s. In addition, the spring is preloaded so that saltwater may exceed the ambient hydraulic system pressure by up to 100 psi without leakage of salt water into the hydraulic system. 
     SUMMARY OF THE INVENTION 
     The preferred embodiment of the present invention includes two coaxial inlets or supply ports and a single transverse outlet or function port. A metal valve seat surrounds each of the coaxial opposing supply ports. An elongate shuttle is coaxial with the metal valve seats and the supply ports. The shuttle valve moves from one valve seat to the other in response to differential fluid pressure. The shuttle includes a central circumferential flange with opposing tapered sealing surfaces that alternatively engage the metal valve seats around the supply ports. Each metal valve seat has a chamfer which forms an obtuse metal point. As the shuttle moves back and forth into alternative engagement with the metal valve seats, the opposing tapered sealing surfaces strike the obtuse points and displaces a portion of the metal into each respective chamfer. This displacement occurs repeatedly as the shuttle strikes the obtuse points. This displacement of metal from the obtuse point into the chamfer insures a good metal to metal seal between the valve seats and the tapered sealing surfaces on the flange of the shuttle. This phenomena is also known as “progressive coining.” 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above-identified features, advantages, and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiment thereof which is illustrated in the appended drawings. 
     It is noted, however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Reference the appending drawings, wherein: 
     FIG. 1 is a section view of the Mark I shuttle valve, a prior art design, sold by Gilmore Valve Company. 
     FIG. 2 is a section view of the Mark II shuttle valve, a prior art design, sold by Gilmore Valve Company. 
     FIG. 3 is a perspective view of the low interflow hydraulic shuttle valve of the present invention with two supply ports. 
     FIG. 4 is a top view of the shuttle valve shown in FIG.  3 . 
     FIG. 5 is an end view of the shuttle valve of FIG. 3 along the line  5 — 5 . 
     FIG. 6 is a section view of the shuttle valve of FIG. 3 with the shuttle in engagement with the valve seat of the second supply port allowing fluid flow from the first supply port to the function port. 
     FIG. 7 is a section view of the shuttle valve of FIG. 6, except the shuttle has moved to the mid-point of travel, which is a low or no flow position. 
     FIG. 8 is a section view of the shuttle valve of FIG. 6, except the shuttle has moved into engagement with the valve seat of the first supply port allowing fluid flow from the second supply port to the function port. 
     FIG. 9 is an enlarged view of a portion of the metal valve seat and a portion of the shuttle before any coining has occurred. 
     FIG. 10 is an enlarged view of a portion of the metal valve seat and a portion of the shuttle after coining has occurred and sealing engagement has been established. 
     FIG. 11 is a section view of an alternative embodiment of the present invention with three supply ports. 
     FIG. 12 is an alternative embodiment of the present invention with four supply ports. 
     FIG. 13 is a section view of a prior art flow biased shuttle valve sold by Gilmore Valve Company. 
     FIG. 14 is a section view of the pressure biased shuttle valve of the present invention in the closed position. 
     FIG. 15 is a section view of the pressure biased shuttle valve of FIG. 14 in an intermediate position. 
     FIG. 16 is a section view of the pressure biased shuttle valve in the open position. 
     FIG. 17 is an enlarged section view of the piston rod head and piston before any coining has occurred. 
     FIG. 18 is an enlarged section view of the piston rod head and piston after coining has occurred and sealing engagement has been established. 
     FIG. 19 is a section view of the pressure biased shuttle valve installed in a valve with seven supply ports. 
     FIG. 20 is a section view of the pressure biased shuttle assembly which is sold as a repair kit for the pressure biased shuttle valve shown in FIGS. 14-19. 
     FIG. 21 is a section view of an alternative embodiment of the pressure biased shuttle assembly. It can be sold as an alternative to the repair kit of FIG.  20 . It can likewise be used in the pressure biased shuttle valve of FIGS. 14-19. 
     FIG. 22 is an enlarged section view showing a portion of the alternative embodiment of FIG.  21 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Subsea wellheads are often relied upon during deep water exploration for oil and natural gas. The subsea wellheads includes a stack of BOPs. Annular BOPs are actuated on a routine basis to snub or otherwise control pressure during normal drilling operations. Other blow-out preventers, such as blind rams, pipe rams, kelly rams and shear rams will also be included in the stack on the subsea wellhead. When these types of rams are actuated, operations in the well cease in order to control pressure or some other anomaly. Blind rams, pipe rams, kelly rams and shear rams are periodically tested to make sure that they are operational. 
     The control pod is a capsule attached to the LMRP which extends from the subsea wellhead. The accumulators (tanks with air space in the tops) are mounted on the LMRP. At least one shuttle valve of the present invention may be attached to each BOP on the subsea wellhead. Fluid flows from the accumulators through valves on the control pod through the shuttle valve of the present invention, to activate the BOPs. 
     FIG. 1 is a section view of the Mark I shuttle valve, a prior art design sold by Gilmore Valve Company. The shuttle valve  10 , has a first inlet or supply port  12 , a coaxial second inlet or supply port  14  and a transverse outlet or function port  16 . The supply ports  12  and  14  are in fluid communication with the accumulators and the function port  16  is in fluid communication with the BOP on the subsea wellhead. The shuttle valve  10  mounts via a bracket  18  to a BOP. The shuttle  20  includes a central circumferential flange  22  which is located between a first o-ring groove  24  and a second o-ring groove  26 . A first o-ring  28  is positioned in the first o-ring groove  24 . A second o-ring  30  is positioned in the second o-ring groove  26 . 
     The shuttle  20  has elongate end portions or cages  32  and  34 . The first end portion  32  includes a central bore  36  which is perforated by apertures  38 ,  40 ,  42  and fourth aperture not shown in the drawing. These apertures allow fluid to flow from the first supply port  12  through the bore  36 , through the apertures  38 ,  40  and  42  through a passageway  43  in the body  54  and out through the function port  16 . The other end portion or cage  34  has a bore  44  and apertures  46 ,  48 ,  50  and a fourth aperture not shown. 
     The first supply port  12  is formed by an adapter  52  which threadably engages the body  54 . The second supply port  14  is formed by an adapter  56  which also threadably engages the body  54 . The first supply port  12  and the second supply port  14  are located on opposite sides of the body  54  and are coaxial. The adapter  52  further defines a tubular valve seat  58  which engages and seals with the o-ring  28  on the shuttle  20 . The other adapter  56  likewise defines a tubular valve seat  60  which engages and seals with the o-ring  30  as shown in this figure. During operation of this prior art shuttle valve, o-rings were sometimes cut or lost and the end portions, or cages were cracked due to shuttle impact. 
     FIG. 2 is a section view of the Mark II shuttle valve, a prior art design sold by Gilmore Valve Company. The Mark II was developed as a retrofit design to overcome some of the limitations in the Mark I. In this embodiment, the shuttle  20  was redesigned with deeper o-ring grooves  27  and  31  and larger o-rings  63  and  65 . In addition, the diameter of the bores  36  and  44  was diminished, thereby thickening the wall of the end portions or cages  32  and  34 . The diameter of the holes was decreased thus necessitating more holes to accommodate the same volume of fluid flow. End portion  32  was redesigned with six holes  66 ,  68 ,  70 ,  72  and two other holes not shown in the drawing. Likewise, end portion or cage  34  was redesigned with six holes  74 ,  76 ,  78 ,  80  and two other holes not shown. (The Mark I only had four holes.) In order to reduce valve impact and vibration, a circumferential channel  82  was formed in end portion  32  to receive a plastic teflon bearing  84 . Likewise, a circumferential channel  86  was formed around end portion  34  to receive another plastic teflon bearing  88 . These improvements in the design overcame many of the limitations of the prior art shown in FIG. 1; however, at the highest flow rates, o-rings were still being lost. Further improvements were needed. 
     FIG. 3 is a perspective view of the present invention, which is a low interflow hydraulic shuttle valve, generally identified by the numeral  100 . The shuttle valve  100  includes a body  102  which is supported by a bracket  104 . The valve  100  includes a first adapter  106  and a second adapter  108  coaxially aligned on opposite sides of the body  102 . The first adapter  106  forms an inlet or supply port  110  and the second adapter  108  forms a second inlet or supply port  112 . Each supply port  110  and  112  is connected to a separate hose or piping, not shown in the drawings. The body  102  forms a transverse outlet or function port  114 . The function port  114  is connected to a hose or piping, not shown, in the drawing. Fluid enters the valve  100  either through the first supply port  110  or the second supply port  112  and exits the valve  100  through the function port  114 . 
     FIG. 4 is a top view of the valve  100  of FIG.  3 . The bracket  104  includes a first aperture  116  and a second aperture  118  for mounting purposes. Looking down into the function port  114 , the shuttle  120  is shown in a right-hand position shutting off any fluid flow from the second function port  112 . 
     FIG. 5 is an in view of the valve  100  and the bracket  104  along the line  5 — 5  of FIG.  3 . The second supply port  112  is formed by the second adapter  108 . 
     FIG. 6 is a section view of the present invention with the shuttle  120  in the right hand position sealing off fluid flow from the second supply port  112 . In this view, fluid can flow from the first supply port  110  through a passageway  111  in the body  102  and out the function port  114  as shown by the flow arrows in the drawing. The first adapter  106  threadably engages an aperture  122  in the body  102 . An o-ring  124  seals the adapter  106  to the body  102 . The second adapter  108  includes a recess  126  to engage the bracket  104 . The second adapter  108  threadably engages an aperture  128  in the body  102 . An o-ring  130  seals the adapter  108  to the body  102 . The adapter  106  includes a metal valve seat  132  and the second adapter  108  includes an opposing coaxial metal valve seat  134 . The shuttle  120  includes a centrally located circumferential flange  136  which has opposing tapered sealing surfaces  138  and  140 . As shown in this drawing, sealing surface  140  is in sealing engagement with the metal valve seat  134  blocking any fluid flow from the second supply port  112 . 
     The shuttle  120  may be produced from a variety of materials as a matter of manufacturing choice including, but not limited to, Nitronic 60 (ASTMA-276 TP S21800) or 17-4PH Stainless Steel. The material should have good wear characteristics. In the case of the aforementioned stainless steel, the shuttle  120  may be nitrided by Houston Unlimited, Inc. of Houston, Tex. Other hardening processes, such as conventional heat treating may also be suitable depending on the application. Nitriding, like heat treating, is widely available from other vendors on a national basis. It is not necessary to nitride a shuttle  120  produced from Nitronic 60. 
     FIGS. 6,  7  and  8  show a section view of the preferred embodiment of the present invention with the shuttle  120  in three different operational positions. In FIG. 6, the shuttle  120  is shown in the right hand position in sealing engagement with the metal valve seat  134  of second supply port  112 . This allows fluid to flow from the first supply port  110  through the bore  146  and apertures  148 ,  150 ,  152  and  156  through the passageway  111  of valve  100  to the function port  114 . In FIG. 7 the shuttle  120  has disengaged with the valve seat  134  of the second supply port  112  and is shown at the mid point of its travel where there is little or no interflow from the first supply port  110  or the second supply port  112  into the passageway  111  or the function port  114 . In FIG. 8 the shuttle  120  has moved into the left hand position in sealing engagement with the valve seat  132  of the first supply port  110 . As shown by the flow arrows in FIG. 8, fluid can now pass through the second supply port  112  through the passageway  111  of valve  100  and out the function port  114  as indicated by the flow arrows in the drawing. 
     FIG. 7 is a section view of the shuttle valve  100  with the shuttle  120  at its mid point of travel between valve seat  134  and valve seat  132 . The shuttle  120  has a first end portion or cage  142  that includes a central bore  146  and a total of six apertures  148 ,  150 ,  152 ,  156  and two others not shown. The other end portion or cage  158  includes a bore  160  that is coaxial with the bore  146  and a total of six apertures  162 ,  164 ,  166 ,  168  and two others not shown. 
     FIG. 8 is a section view of the shuttle valve  100  with the shuttle  120  in sealing engagement with the metal seat  132  so that fluid can not flow from the first supply port  110  to the function port  114 . In FIG. 8, fluid flows from the second supply port  112  through the central bore  160  of the end portion or cage  158  through the apertures  162 ,  164 ,  166  and  168  into a central passageway  111  in the body  102  and out the shuffle valve  100  through the function port  114  as shown by the flow arrows in the drawing. 
     Due to differential pressure, the shuttle  120  will travel from the right hand position as shown in FIG. 6 to the mid-point position shown in FIG. 7 to the left hand position shown in FIG.  8 . This movement of the shuttle  120  from right hand position to the left hand position, occurs quickly and creates impact forces on the shuttle  120  and the valve seats  132  and  134 . Cracking of the end portions or cages was one of the problems in the prior art design shown in FIG.  1 . The cracking problem has been overcome through the use of holes with a smaller diameter thus allowing more structural metal in the cage between the holes and a smaller diameter bore  146  and  160  thus allowing a thicker cage wall  172  and  174  when contrasted with the prior art design of FIG.  1 . These dimensions vary with each size valve. Applicant has found that a six hole design with. holes having a diameter of 0.328 inches and a cage wall thickness of 0.113 inches works well for a 1 inch valve. However, a shuttle with a different number or size of holes and a different cage wall thickness is within the scope of this invention provided that it does not result in cracks due to valve impact or otherwise damage the valve  100 . 
     FIG. 9 is an enlarged section view of a portion of the shuttle  120  and a portion of the adapter  108 . FIG. 9 shows the sealing surfaces after the valve  100  has been manufactured but before any coining has occurred. FIG. 10 shows the sealing surfaces after coining has occurred. In FIG. 9 the shuttle  120  includes a circumferential external flange  136  with opposing outwardly tapered metal sealing surfaces  138  and  140 . Applicant believes that a taper of approximately 8 degrees is optimum for this application. However, other tapers are within the scope of this invention so long as they will create a coining effect on the metal valve seats  132  and  134  of the adapters  106  and  108 . Other tapers may be suitable for other applications possibly in the range of 5 to 15 degrees. The only requirement for the angle of taper is to achieve coining and therefore sealing with the metal valve seats  132  and  134 . 
     The adapter  108  includes a chamfer  176  recessed behind the metal valve seat  134  to thereby create an obtuse metal point  180  that will contact the tapered metal sealing surface  140  on the flange  136  of the shuttle  120 . FIG. 9 shows the metal valve seat  134  and the metal sealing surface  140  on the shuttle  120  before any coining has occurred. Applicant uses a chamfer with a 15 degree angle and a 0.015″ radius. However, the exact size and depth of the chamfer are not particularly critical because this is merely a recess or space into which displaced metal will move due to progressive coining. A stepped back shoulder or other recess would be sufficient to achieve the goals of this invention, provided that there is room to receive the displaced metal from the point  180  such that it does not interfere with movement of the shuttle  120 . When adapter  106  is first manufactured it likewise has a chamfer  177  recessed behind the metal valve seat  132  to thereby create an obtuse metal point  181  that will contact the tapered metal sealing surface  138  on the flange  136  of the shuttle  120 . The point  181  is progressively coined in the same fashion as the point  180  by the impact of the shuttle  120 . 
     FIG. 10 is an enlarged section view of a portion of the shuttle  120  and a portion of the second adapter  108  after coining has occurred. As the tapered metal sealing surface  140  of the shuttle  120  impacts the point  180  of the metal valve seat  134 , a portion of the metal in the point  180  is displaced into the chamfer  176 . This displaced metal is identified by the numeral  182 . A metal to metal seal is therefore achieved between the metal valve seat  134  and the outwardly tapered metal sealing surface  140  of the flange  136  on the shuttle  120 . 
     Likewise, the outwardly tapered metal sealing surface  138  will impact point  181  on the metal valve seat  132  and will displace a portion of the metal into the chamfer, thus creating a metal to metal seal between the metal valve seat  132  and the outwardly tapered sealing surface  138  on the flange  136  of shuttle  120 . 
     FIG. 11 is a section view of an alternative embodiment of a low interflow hydraulic shuttle valve with three supply ports. (The embodiment in FIG. 3 has two supply ports.) The shuttle valve  200  includes a first body portion  202  and a second body portion  204  that are held together by a plurality of bolts  206  and  208  and a plurality of nuts  210 ,  212 ,  214  and  216  that mechanically grip the two body sections  202  and  204  thus joining them together into an integral assembly. An alignment pin  220  fits into a bore  222  of the body  202  and a coaxial bore  224  of the body  204 . A zig-zagged interconnecting passageway  226  is formed in the body  202  and is in fluid communication with a second zig-zag passageway  227  in the body  204 . A connector  228  is positioned in a bore  230  of the body  202  and another coaxial bore  232  in the body  226 . The connector  228  has a first seal  234  and a second seal  236  to prevent fluid from leaking from the zig-zagged passageways  226  and  227 . The connector  228  also helps align the body portions  202  and  204 . 
     A first supply port  236  is formed in the body  202  and is in fluid communication with the passageway  226 . A second supply port  238  is formed in a first adapter  240 . The adapter  240  threadably engages the body  202 . The adapter  240  is sealed against the body  202  by an o-ring  242 . A metal valve seat  244  is formed on one end of the adapter  240 . A second metal valve seat  246  is formed in the body  202  and is coaxial with valve seat  244 . A shuttle  250  moves from sealing engagement with the metal valve seat  244  of the adapter  240  to alternative sealing engagement with the valve seat  246  of the body  202 . 
     A third supply port  250  is formed in another adapter  252 . The adapter  252  threadably engages the body  204  and is sealed by an o-ring  254 . A mounting bracket  105  is positioned between the body  204  and the adapter  252 . The adapter  252  includes a metal valve seat  256 . An opposing metal valve seat  258  is formed in the body  204  and is coaxial with valve seat  244 . A shuttle  260  travels back and forth into alternative sealing engagement with the metal valve seat  256  and the metal valve seat  258  depending on differential fluid pressure in the third supply port  250  and the passageway  227 . A function port  260  is formed in the body  204  and connects to the BOP, not shown. 
     A first supply line, not shown in the drawing, connects to the first supply port  236 , a second supply line, not shown in the drawing, connects to the second supply port  238  and a third supply line, not shown in the drawing, connects to the third supply port  250 . If the pressure into the first supply port  236  is greater than the fluid pressure in the second supply port  238  or the third supply port  250 , the shuttle  248  and the shuttle  260  will be urged into sealing engagement with the metal valve seats  244  and  256  as shown in FIG.  11 . This allows fluid to flow from the first supply port  236  through the zig-zagged passageways  226  and  227  and out the function port  260  to the BOP, not shown. 
     If fluid pressure in the second supply port  238  is greater than fluid pressure in the first supply port or the third supply port, the shuttle  248  will unseat and move into sealing engagement with the metal valve seat  246  of the body  202 . This will allow fluid to flow from the second supply port  238  through the zig-zagged passageways  226  and  227  and out the function port  260  to the BOP, not shown. If, in the alternative, fluid pressure in the third supply port  250  is greater than fluid pressure in the first supply port  236  or the second supply port  238 , then the shuttle  260  will disengage from the metal valve seat  256  and engage the metal valve seat  258  of the body  204 . This allows fluid to flow from the third supply port directly to the function port  260  and the BOP. The shuttle  248  progressively coins the metal valve seats  244  and  246  in similar fashion as the shuttle  120  described in FIGS. 3-10. Likewise, the shuttle  260  progressively coins the metal valve seats  256  and  258 . 
     FIG. 12 is an alternative embodiment with a four supply design for a low interflow hydraulic shuttle valve  300 . The design in FIG. 12 is identical to the three supply valve  200  shown in FIG. 11 except another supply port and another body section have been added. The four supply valve  300  includes a first body section  202 , a second body section  204  and a third body section  302 . The body sections are aligned and connected by the first alignment pin  220  and a second alignment pin  304 . Zig-zagged passageways  226 ,  227  and  229  are formed in the respective bodies  202 ,  204  and  302  and are interconnected and sealed against the bodies via a first connector  228  and a second connector  306 . The second connector  306  is identical to the connector  228  shown and described in FIG. 11 except connector  228  joins body sections  202  and  204  and connector  306  joins body sections  204  and  302 . The respective body sections  202 ,  204  and  302  are connected by a plurality of nuts  210 ,  212 ,  214  and  216  and bolts  206  and  208 . The valve  300  is mounted via brackets  310  and  312  to a BOP, not shown. Brackets  310  and  312  are used to mount the valve  300 . 
     The body section  202  includes a first supply port  236  and a second supply port  238  formed in the adapter  240 . The adapter defines a first metal valve seat  244  and the body  202  defines a coaxial second metal valve seat  246 . The shuttle  248  moves from alternative sealing engagement with the first metal valve seat  244  to the second metal valve seat  246  in response to differential fluid pressures in the first supply port  236  or the second supply port  238 . 
     The second adapter  252  defines another metal valve seat  256  and the body portion  204  defines an opposing coaxial metal valve seat  258 . The shuttle  260  moves back and forth into alternative sealing engagement with the metal valve seat  256  or the metal valve seat  258  depending on differential fluid pressures exerted upon the shuttle  260 . A third adapter  314  defines a fourth supply port  316  and another metal valve seat  318 . An opposing coaxial metal valve seat  320  is formed in the body section  302 . A third shuttle  322  moves into alternative sealing engagement with the metal valve seat  318  of the adapter  314  or the metal valve seat  320  of the body  302  depending on differential fluid pressures. 
     FIG. 12 shows the valve  300  with the highest pressure in the first supply port  236  which a) urges the shuttle  246  into sealing engagement with the metal valve seat  244  of the second supply port  238 , b) urges the shuttle  260  into sealing engagement with the metal valve seat  256  of the third supply port  250 , and c) urges the shuttle  322  into sealing engagement with the metal valve seat  318  of the fourth-supply port  316 . This allows hydraulic fluid to pass from the first supply port  236  through the zig-zagged passageways  226 ,  227  and  229  of the body portions  202 ,  204  and  302  into the function port  322  and thereafter to the BOP, not shown. 
     In the alternative, a higher differential pressure in the second supply port  238  will cause the shuttle  248  to move into sealing engagement with the metal valve seat  246  thereby allowing fluid to pass from the second supply port  238  through the zig-zagged passageways  226 ,  227  and  229  to the function port  322  and into the BOP, not shown. Higher differential pressures in the third supply port  250  will likewise cause the shuttle  260  to move and engage the metal valve seat  258  and allow fluid to pass from the third supply port  250  through the passageways  226 ,  227  and  229  into the function port  322  and out to the BOP, not shown. If the highest fluid pressure occurs in the four supply port  312 , the shuttle  322  will move into sealing engagement with the metal valve seat  320 , thus allowing fluid to flow from the fourth supply port  316  into the function port  322  and thereafter to the BOP, not shown. 
     Using the modular body approach, as shown in FIGS. 11 and 12, it is possible to create low interflow hydraulic shuttle valves with as many supply ports as needed depending on the specific application. 
     FIG. 13 is a section view of a prior art flow biased shuttle valve sold by Gilmore Valve Company, generally identified by the numeral  399 . The shuttle  121  is in the right-hand position sealing off fluid flow from the remote operated vehicle (ROV) supply port  113 . The ROV supply port  113  is connected by a hose (not shown) to an ROV docking station. In emergencies or during testing, an ROV may be maneuvered by topside personnel to engage the ROV docking station. Fluid is then injected by the ROV through the fluid line into the ROV supply port  113 . When this occurs, the shuttle  121  moves into the left-hand position, not shown in the drawing, thus allowing the hydraulic fluid to pass from the ROV through valve  399  to the BOPs. 
     The shuttle valve  399  includes a body  102  which is supported by a bracket, not shown. The valve  399  includes a first adapter  106  and a second adapter, sometimes referred to as the ROV adapter,  402 . The first adapter  106  and the ROV adapter  402  are coaxially aligned on opposite sides of the body  102 . The first adapter  106  forms an inlet or supply port  110  and the ROV adapter  402  forms a second inlet or supply port sometimes referred to as the ROV supply port,  113 . The supply port  110  is connected to a hose or piping, not shown in the drawings, which connects to a pressurized fluid source. The ROV supply port  113  connects via a hose or piping, not shown in the drawings, to an ROV docking station, not shown in the drawings. 
     The body  102  forms a transverse outlet or function port  114 . The function port  114  is connected to a hose or piping, not shown in the drawings. Fluid enters the valve  399  either through the first supply port  110  or the ROV supply port  113  and exits the valve  399  through the function port  114 . When fluid leaves the function port  114  it goes to the BOPs. 
     In FIG. 13, fluid can flow from the first supply port  110  through a passageway  111  in the body  102  and out the function port  114 . The first adapter  106  threadibly engages an aperture  122  in the body  102 . An o-ring  124  seals the adapter  106  to the body  102 . The ROV adapter  402  threadibly engages an aperture  128  in the body  102 . An o-ring  130  seals the ROV adapter  402  to the body  102 . 
     The adapter  106  has a metal valve seat  132  and the ROV adapter  402  has an opposing coaxially metal valve seat  129 . The shuttle  121  includes a centrally located circumferential flange  136  which has opposing sealing services  139  and  141 . As shown in FIG. 13, sealing surface  141  is in sealing engagement with the metal valve seat  129  on the ROV adapter  402 , blocking any fluid flow from the ROV supply port  113 . 
     The flow biased shuttle assembly generally identified by the numeral  400  in this prior art device, has a number of components including the elongate tubular ROV adapter  402 , piston rod  404  with a head  406  on one end and a threaded point  408  on the other end which threadibly engage an aperture  409  in the shuttle  121  and a spring  410 . A central bore  401  in the ROV adapter  402  allows fluid to move from the ROV supply port  113 , through the central bore  401  and into the passageway  111  of the valve  399  when the shuttle  121  disengages from the valve seat  129  on the ROV adapter  402 . When the piston rod  402  moves axially, the shuttle,  121  likewise moves axially. A spring  410  surrounds the piston rod  404  and is captured between the head  406  and the end  407  of the shuttle  121 . 
     When fluid is injected by the ROV into the ROV supply port  113 , the shuttle  121  moves from the position shown in the drawing to engagement with the valve seat  132 . This causes compression of the spring  410 . When the fluid flow subsides, the compressed spring  410  exerts forces on the head  406  which is translated through the piston rod  404  to the shuttle  121  causing it to move from engagement with the valve seat  132  back to engagement with the valve seat  129 , as shown in FIG.  13 . 
     The shuttle  121  has a first end portion or cage  142  that includes a central bore  46  with a total of six apertures,  148 ,  150 ,  152 ,  156  and two others not shown. The other end portion or cage  158  includes a bore  160  that is coaxially with the bore  146  and a total of six apertures,  162 ,  164 ,  166 ,  168  and two others not shown. When fluid flows from the inlet port  110 , it moves through the bore  146  and the apertures  148 ,  150 ,  152 ,  156  and then into the passageway  111 . From the passageway  111 , it exits the function port  114 . When the shuttle moves into the opposite position, fluid flows from the ROV support port  113  through the central bore  401 , through the bore  160  and out the apertures  162 ,  164 ,  166 ,  168  and two others not shown. The fluid then flows into the passageway  111  and out the function port  114 . This prior art device  399  had certain limitations because it was actuated by flow only. If an ROV did not generate sufficient flow rates, the apparatus would not always function properly. In order to make sure that the biased shuttle valve would function with all different types of ROVs, the design was changed so that it would function based on pressure and not flow. 
     FIG. 14 is a section view of the pressure biased shuttle valve generally identified by the numeral  499 . In this view, the shuttle is in the right-hand position allowing fluid to flow as indicated by the flow arrows. The pressure biased shuttle assembly is generally identified by the numeral  500 . 
     The pressure biased shuttle valve  499  includes a body  102  which is supported by a bracket  104 . The valve  499  includes a first adapter  106  and a second ROV adapter  501 , coaxially aligned on opposite sides of the body  102 . The first adapter  106  forms an inlet or supply port  110  and the second adapter, generally referred to as the ROV adapter  501 , forms an inlet or supply port  113 , also referred to as the ROV supply port. Each supply port  110  and  113  is connected to a separate hose or piping, not shown in the drawings. The ROV supply port  113  is connected to an ROV docking station and receives hydraulic fluid from the ROV, as previously discussed. The inlet port  110  is connected to a different pressurized fluid source, not shown. The body  102  forms a transverse outlet or function port  114 . The function port  114  is connected to a hose or piping, not shown in the drawings. The function port  114  connects to the BOPs. Fluid enters the valve  499  either through the first supply port  110  or the ROV supply port  113  and exits the valve  499  through the function port  114 . 
     The first adapter  106  threadibly engages an aperture  122  in the body  102 . An o-ring  124  seals the adapter  106  to the body  102 . The ROV adapter  501  threadibly engages an aperture  128  in the body  102 . An o-ring  130  seals the adapter  501  to the body  102 . The adapter  106  includes a metal valve seat  132  and the ROV adapter  501  includes an opposing coaxially metal valve seat  133 . The shuttle  119  includes a centrally located circumferential flange  136  which has opposing tapered sealing services  138  and  140 . As shown in this drawing, the sealing surface  140  is in sealing engagement with the metal valve seat  133  blocking any fluid flow from the ROV supply port  113 . 
     The shuttle  119  has a first end portion or cage  142  that includes a central bore  146  and a total of six apertures  148 ,  150 ,  152 ,  156  and two others not shown. The other end portion or cage  158  includes a bore  160  that is coaxially with the bore  146  and a total of six apertures  162 ,  164 ,  166 ,  168  and two others not shown. In FIG. 14, the shuttle  119  is in the right-hand position in sealing engagement with the metal valve seat  133  of the ROV adapter  501 . This allows fluid to flow from the first supply port  110  through the bore  146  and the apertures  148 ,  150 ,  152  and  156  through the passageway  111  of the valve  100  to the function port  114 , as shown by the flow arrows in the drawing. 
     The pressure biased shuttle assembly is generally identified by the numeral  500 . It includes an ROV supply port  113  on one end and a metal valve seat  133  on the other end. A central bore  503  is formed on the longitudinal axis of the ROV adapter  501  and allows fluid communication from the ROV supply port  113  past the metal valve seat  133 . 
     A piston rod  502  is formed with a head,  506  on one end and a threaded point  508  on the other end. The threaded point  508  threadibly engages a similarly threaded receptacle  507  formed in the shuttle  199 . Adjacent to the threaded end  508  of the piston rod  502  is a radial flange  509 . The radial flange abuts a shoulder  511  formed in the shuttle  119 . A spring  510  surrounds the piston rod  502 . A piston  512  is positioned inside the central bore  502  of the ROV adapter  501 . An o-ring channel  513  is formed in the outer circumference of the piston  502  and receives an o-ring  514 . The o-ring  514  provides a seal between the piston  510  and the inside diameter of the bore  503 . The spring  510  is captured between the back side of the piston  512  and a shoulder  515  formed in the ROV adapter  501 . In order to function in response to pressure rather than in response to fluid flow, the outside diameter of the piston  512  must be larger than the outside diameter of the shuttle  119  as measured between the points A and B on the circumferential flange  136 . For example, in the present invention for a one-inch valve, the outside diameter of the shuttle  119  as measured between the points A and B on the circumferential flange  136  is nominally 1⅜ inches and the outside diameter of the piston  512  is nominally 1½ inches. This larger diameter on the piston  512  insures that pressure from the ROV supply port  113  exerted upon the piston  512  will cause the shuttle to open against the spring force of spring  510 . 
     Applicants have determined that a spring  510  with a spring rate of 85 lb./inch is suitable for a ½ in size pressure biased shuttle valve and a spring  510  with a spring rate of 175 lb./inch is suitable for a 1 inch size pressure biased shuttle valve. Springs with different spring rates may also be suitable depending on the size and configuration of a particular valve. 
     A frustro-conical valve surface  507  is formed on the backside of the head  506  of the piston rod  502 . A valve seat  513  is formed in a depression in the piston  512 . A metal-to-metal seal is achieved between the valve  507  and the seat  513 , as better shown in FIGS. 17 and 18. The piston  512  has a central aperture  522  through which fluid flows when the valve  507  is disengaged from the seat  513 , as better seen in FIG.  16 . In FIG. 14, the valve  502  and the seat  513  are engaged and there is no flow from the ROV supply port  113  to the function port  114 . 
     FIG. 15 is a section view of the pressure biased shuttle valve  499  like FIG. 14, except the ROV has injected fluid into the ROV port  113  causing the shuttle  119  to move from the right-hand position to the left-hand position into sealing engagement with the metal valve seat  132  on the adapter  106 . This pressurized fluid exerts a force across the entire diameter of the piston  512  and the head  506  of the piston rod  502 . As shown in FIG. 15, the valve  507  is in sealing engagement with the seat  513  so that no fluid can pass through the aperture  522 . The force being exerted upon the piston  512  and the head  506  is transferred through the piston rod  502  to the shuttle  119  causing it to move from the right-hand position of FIG. 14 into the left-hand position shown in FIG.  15 . There is no flow through the function port  114  when the valve is in the position shown in FIG.  15 . 
     FIG. 16 is a section view of the pressure biased shuttle valve  499  of FIG. 14, except the valve has now opened and fluid can flow from the ROV supply port  113  around the head  506  through the annular passageway  522 , through the bore  503 , through the bore  160  and through the apertures  162 ,  164 ,  166 ,  168  and two others not shown, into the passageway  111  and out the function port  114 , as shown by the flow arrows in the drawings. 
     In FIG. 16, the valve  507  has disengaged from the seat  513  and the tapered sealing service  140  has disengaged from the metal valve seat  133 , again allowing fluid to flow as indicated by the flow arrows from the ROV supply port  113  through the pressure biased shuffle assembly  500  through the valve  499  and out the function port  114 . This fluid flow only occurs during emergencies to shut down the well or during tests of such emergency equipment. 
     FIG. 17 is an enlarged section view of a portion of the pressure biased shuttle assembly  500  showing the piston rod head  506  before any coining has occurred between the valve  507  and the seat  513 . The angle of the frustro-conical valve  507  is mismatched when compared with the angle of the seat  513 . The seat  513  forms a point  515  which contacts the frustro-conical valve  507 . FIG. 17 is a drawing of a portion of the pressure biased shuttle valve  499  after manufacture, but before any testing or operation of the valve. After the pressure biased shuttle valve  499  has been tested and/or actuated, coining or displacement of metal at the point  515  occurs, as shown in the next figure. 
     FIG. 18 is an enlarged section view of a portion of the pressure biased shuttle valve assembly  500 , after coining has occurred and sealing engagement has been established between the frustro-conical valve  507  and the seat  513 . After the head  506  has been stroked axially several times, the metal in the point  515  is progressively coined and/or displaced at  520 . This displacement of the metal on the seat  513  creates a metal-to-metal seal between the seat  513  and the frustro-conical valve  507 . As the shuttle  119  moves axially, the piston rod  502  likewise moves axially, causing the head  506  to contact the piston  512 . This causes the frustro-conical valve  507  to contact the seat  513  at the point  515  to continually refresh the metal-to-metal seal between the head  506  and the piston  512 . A seal is likewise established between the o-ring  514  and the inside diameter of the passageway  503  of the ROV adapter  501 . 
     FIG. 19 is a section view of an alternative embodiment of the pressure biased shuttle valve  600  with seven supply ports. (The embodiment shown in FIGS. 14-18 has two supply ports.) 
     The pressure biased shuttle valve  600  includes a first body portion  610 , a second body portion  612 , a third body portion  614 , a fourth body portion  616 , a fifth body portion  618  and a sixth body portion  620 . The body portions  610 ,  612 ,  614 ,  616 ,  618  and  620  are held together by a plurality of bolts  622  and  624  and a plurality of nuts  626  and  628 , that mechanically grip the six body sections, thus joining them together into an integral assembly. 
     An alignment pin  630  fits into a bore  632  of the body  610  and a coaxial bore  634  of the body  612 . A zig-zag interconnecting passageway  636  is formed in the body  610  and is in fluent communication with a second zig-zag passageway  638  in the body  612 . A connector  640  is positioned in a bore  642  of the body  610  and another coaxial bore  646  in the body  612 . The connector  640  has a first seal  644  and a second seal  650  to prevent fluid from leaking from the zig-zag passageways  636  and  638 . The connector  640  also helps align the body portions  610  and  612 . 
     An alignment pin  652  fits into a bore  654  of the body  612  and a coaxial bore  656  of the body  614 . A zig-zag interconnecting passageway  658  is formed in the body  614  and is in fluid communication with the zig-zag passageways  636  and  638 . A connector  660  is positioned in a bore  662  of the body  612  and another coaxial bore  664  in the body  614 . The connector  660  has a first seal  668  and a second seal  670  to prevent fluid from leaking from the zig-zag passageways  638  and  658 . The connector  660  also helps align the body portions  612  and  614 . 
     An alignment pin  672  fits in a bore  674  of the body  614  and a coaxial bore  676  of the body  616 . A zig-zag interconnecting passageway  678  is formed in the body  616  and is in fluid communication with the other zig-zag passageways,  658 ,  638  and  636 . A connector  680  is positioned in a bore  682  of the body  614  and another coaxial bore  684  of the body  616 . The connector  680  has a first seal  686  and a second seal  688  to prevent fluid from leaking from the zig-zag passageways  678  and  658 . The connector  680  also helps align the body portions of  614  and  616 . 
     An alignment pin  690  fits into a bore  692  of the body  616  and a coaxial bore  694  of the body  618 . A zig-zag interconnecting passageway  696  is formed in the body  618  and is in fluid communication with the other zig-zag passageways  678 ,  658 ,  638  and  636 . 
     A connector  698  is positioned in a bore  700  of the body  616  and another coaxial bore  702  in the body  618 . The connector  698  has a first seal  704  and a second seal  706  to prevent fluid from leaking from the zig-zag passageways  698  and  678 . The connector  698  also helps align the body portions  618  and  616 . 
     An alignment pin  708  fits into a bore  710  of the body  618  and a coaxial bore  712  of the body  620 . A zig-zag interconnecting passageway  724  is formed in the body  620  and is in fluid communication with the other zig-zag passageways  696 ,  678 ,  658 ,  638  and  636 . A connector  714  is positioned in a bore  716  of the body  620  and another coaxial bore of  718  in the body  620 . The connector  714  has a first seal  720  and a second seal  722  to prevent fluid from leaking from the zig-zag passageways  724  and  696 . The connector  714  also helps align the body portions  620  and  618 . 
     A connector  728  is positioned in a bore  730  of the body  620  and another coaxial bore  732  in the whatchamacallit  726 . The connector  728  has a first seal  734  and a second seal  736  to prevent fluid from leaking from the passageways  738  and  724 . The connector  728  also helps align the body portion  620  and the whatchamacallit  726  (Harold help me). The pressure biased shuttle assembly  500  is the same shuttle assembly shown in FIGS. 14-18. 
     A first supply port  740  is formed in the body  610  and is fluid communication with the passageway  636 . A second supply port  742  is formed in a first adapter  744 . The adapter  744  threadibly engages the body  610 . The adapter  744  is sealed against the body  610  by an o-ring  746 . The metal valve seat  748  is formed on one end of the adapter  744 . A second metal valve seat  750  is formed in the body  610  and is coaxially with the valve seat  748 . A shuttle  752  moves from sealing engagement with the metal valve seat  748  of the adapter  744 , as shown in the drawing, to alternative sealing engagement with the valve seat  740  of the body  610 . A third supply port  754  is formed in a third adapter  756 . The adapter  756  threadibly engages the body  612 . The adapter  756  is sealed against the body  612  by an o-ring  758 . A metal valve seat  760  is formed on one end of the adapter  756 . An opposing metal valve seat  762  is formed in the body  612  and is coaxial with the valve seat  760 . A shuttle  764  moves from sealing engagement with the valve seat  760  of the adapter  756 , as shown in the drawing, to alternative sealing engagement with the valve seat  762  of the body  612 . 
     A third supply port  766  is formed in a third adapter  768 . The adapter  768  threadibly engages the body  614 . The adapter  768  is sealed against the body  614  by an o-ring  770 . A metal valve seat  772  is formed on one end of the adapter  768 . A second metal valve seat  774  is formed in the body  612  and is coaxial with the valve seat  772 . A shuttle  776  moves from sealing engagement with the metal valve seat  772  of the adapter  768 , as shown in the drawing, to alternative sealing engagement with the valve seat  774  of the body  614 . 
     A fourth supply port  780  is formed in a fourth adapter  784 . The adapter  784  threadibly engages the body  616 . The adapter  784  is sealed against the body  616  by an o-ring  782 . A metal valve seat  786  is formed on one end of the adapter  784 . A second metal valve seat  788  is formed in the body  616  and is coaxial with the valve seat  786 . A shuttle  789  moves from sealing engagement with the metal valve seat  786  of the adapter  784 , as shown in the drawing, to alternative sealing engagement with the metal valve seat  788  of the body  616 . 
     A sixth supply port  790  is formed in the adapter  792 . The adapter  792  threadibly engages the body  618 . The adapter  792  is sealed against the body  618  by an o-ring  794 . A metal valve seat  796  is formed on one end of the adapter  792 . A second metal valve seat  798  is formed in the body  618  and is coaxial with the valve seat  796 . A shuttle  799  moves from sealing engagement with the metal valve seat  796  of the adapter  792 , as shown in the drawing, to alternative sealing engagement with the valve seat  798  of the body  618 . 
     The ROV supply port  113  is formed in the ROV adapter  501 . The ROV adapter  501  threadibly engages the body  620 . The ROV adapter  501  is sealed against the body  620  by an o-ring  800 . A metal valve seat  133  is formed on one end of the ROV adapter  501 . A second metal valve seat  802  is formed in the body  620  and is coaxial with the valve seat  133 . A shuttle  119  moves from sealing engagement with the metal valve seat  133  of the ROV adapter  501 , as shown in the drawing, to alternative sealing engagement with the metal valve seat  802  of the body  620 . 
     A first supply line, not shown in the drawing, connects to the first supply port  740 , the second supply line, not shown in the drawing, connects to the second supply port  754 , a third supply line, not shown in the drawing, connects to a third supply port  766 , a fourth supply line, not shown in the drawing, connects to a fourth supply port  780 , a fifth supply line, not shown in the drawing, connects to a fifth supply port  790 , and a seventh supply line, not shown in the drawing, connects to an ROV docking terminal and the ROV supply port  113 . If pressure in the first supply port  740  is greater than the fluid pressure in the second supply port  742 , the third supply port  754 , the fourth supply port  766 , the fifth supply port  780 , the sixth supply port  790 , and the ROV supply port  113 , the shuttles  752 ,  764 ,  776 ,  789 ,  799  and  119  will be urged into sealing engagement with the respective valve seats  748 ,  764 ,  772 ,  786 ,  796  and  133 , as shown in FIG.  19 . This allows fluid to flow from the first supply port  740  through the zig-zag passageways  636 ,  638 ,  658 ,  618 ,  696 ,  742  and  738  and out the function port  804 , to the VOP, not shown. 
     If fluid in the second supply port  742  is greater than fluid pressure in the first supply port  740 , the second supply port  754 , the third supply port  766 , the fourth supply port  780 , the fifth supply port  790 , or the ROV supply port  113 , then the shuttle  752  will unseat and move into sealing engagement with the metal valve seat  750  of the body  610 . This will allow fluid to flow from the second supply port  742  through the zig-zag passageways  638 ,  658 ,  618 ,  696 ,  724  and  738  and out the function port  804  to the BOP, not shown. The other supply ports work in similar function. The supply port with the highest fluid pressure will open and the others will remain closed, allowing fluid from the highest supply port to move to the function port  804 . 
     The shuttles  752 ,  764 ,  776 ,  789 , and  799  progressively coin the respective opposing metal valve seats in similar fashion as the shuttle  120  described in FIGS. 3-10. Likewise, the shuttle  119  progressively coins the valve seats  133  and  124  to achieve a metal to metal seal. 
     FIG. 20 is a section view of the pressure biased shuttle assembly  500 , which is sold as a repair kit for the pressure biased shuttle valve shown in FIGS. 14-19. The pressure biased shuttle valve assembly includes all of the components shown, including the elongate tubular ROV adapter  501 , the piston rod  502 , the piston  512 , the shuttle  119  and the spring  510 . From time to time, it is necessary to service the pressure biased shuttle valve which is normally located subsea. In order to service the valve, it and accompanying apparatus is brought to the surface. Time is therefore of the essence and anything that can be done to speed repair and replacement of the valves is desirable. The pressure biased shuttle valve assembly repair kit  500  can therefore be sold as a separate component and used on board during repair and maintenance. 
     FIG. 21 is a section view of an alternative embodiment of the pressure biased shuttle assembly and is generally identified by the numeral  850 . The elongate tubular ROV adapter  501  includes an ROV supply port  113  on one end and a metal valve seat  133  on the other end. A central bore  503  is formed along the longitudinal axis of the ROV adapter  501 .  133 . 
     A piston rod  502  is formed with a head or valve,  506  on one end and an abutment  852  on the other end. The shuttle  121  has a first end portion or cage  142  that includes a central bore  146  and a total of 6 apertures,  148 ,  150 ,  152 ,  156  and two others not shown. The other end portion or cage  159  includes a bore  161  that is coaxial with the bore  146 . The cage  159  has 6 apertures, not shown in the drawing, similar to the apertures in the opposing cage  146 . In FIG. 21, the shuttle  121  is in the right-hand position and sealing engagement is achieved between the metal valve seat  133  of the ROV adapter  501  and the sealing surface  140 . When the shuttle  121  disengages from the valve seat  133  fluid can flow from the ROV supply port  113  through the central bore  503  and past the metal valve seat  133 . 
     FIG. 22 is an enlarged section view of the shuttle  121  and a portion of the ROV adapter  501 . An abutment  852  is formed on one end of the piston rod  502  opposite the valve  506 . A transverse hole  855  is formed in the abutment  852 . The tip  854  of the abutment  852  is rounded. However, other surfaces are within the scope of this invention such as a point or a frustro-conical projection. 
     A hole  861  and an opposing coaxial hole  863  are formed in the cage  159 . The holes  861  and  863  are sized and arranged to receive the crosspin  862 , which is pressed to fit into the holes  861  and  863 . The outside diameter of the crosspin  862  is primarily a matter of manufacturing convenience. However there should be a gap  870  between the outside diameter of the crosspin  862  and the inside diameter of the hole  855  allowing some slop so that the shuttle  121  has some freedom of movement relative to the piston rod  502 . In other words, there is a flexible connection between the shuttle  121  and the piston rod  502 . This allows the sealing surfaces  138  and  140  on the circumferential flange  136  of the shuttle  121  to make a better seal with the metal valve seats  132  and  133 . 
     In other words, the shuttle  121  has the ability to slightly pivot about the tip  854  of the piston rod  502  because of the slop  870  between the crosspin  862  and the hole  855 . This flexible connection allows the shuttle  121  to find and make a better seal, especially in smaller size valves.