Abstract:
A two-position, three-way subsea non-interflow valve design comprises a plug assembly. An elongated member is positioned within the valve for relative movement with respect to the plug assembly. A first seal on the plug assembly remains closed until a second seal with the elongated member circumscribes the function port. Further movement of the elongated member opens the first seal to allow flow from the supply to the function port. Two seals are presented in the flow path of the supply port to eliminate interflow to any other valve opening.

Description:
FIELD OF THE INVENTION 
     The field of the invention relates to subsea pilot operated valves. 
     BACKGROUND OF THE INVENTION 
     Offshore production control systems typically involve a floating production control facility. Generally speaking, a hydraulic power source is mounted on the production facility. Coupled to the hydraulic power source is a master control manifold. Multiline hoses extend from the control manifold to a control pod mounted subsea adjacent the wellhead. The control pod is used to direct movement of valves mounted adjacent the wellhead. Each wellhead valve has an actuator mounted on it. Pilot valves are frequently used between the hydraulic power supply and the actuators of wellhead valves to initiate movement of wellhead valve actuators. Commonly used in subsea hydraulic control systems are pilot valves that are three-way two-position valves. 
     Prior designs such as the type 80 SPM valve manufactured by Koomey, Inc. have had problems with interflow. Interflow is a leakage flow from the supply port of the pilot valve through the internals of the valve and out through the vent port. This usually occurs during shifting. The type 80 valve contained a unitary sliding cage which could selectively block off the supply port while opening the vent port of the function port. Movement of a slide off of the main seal isolating the supply port from the function port simultaneously obstructed the supply and vent ports by virtue of the sliding metal to metal fit between the cage and said supply and vent ports. Further movement of the cage resulted in a blockage of the vent port and the alignment of the supply port with the function port. This design and others similar to it were prone to some interflow especially when the cage moved slightly off the main seal between the function port and the supply port. After such initial movement, there remained only the metal to metal fit between the cage and the supply port to prevent hydraulic fluid from passing through the supply port and into the vent port. 
     The apparatus of the present invention presents a design to eliminate interflow by virtue of two seals isolating the supply port from the vent port. Additionally, one seal on the supply port is biased in a closed position until such time as another or shear seal can be placed in position circumscribing the function port and thus isolating the vent port from the supply port. 
     SUMMARY OF THE INVENTION 
     A two-position, three-way subsea non-interflow valve design comprises a plug assembly. An elongated member is positioned within the valve for relative movement with respect to the plug assembly. A first seal on the plug assembly remains closed until second seal with the elongated member circumscribes the function port. Further movement of the elongated member opens the first seal to allow flow from the supply to the function port. Two seals are presented in the flow path of the supply port to eliminate interflow to any other valve opening. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 contains a schematic of a typical subsea control circuit. 
     FIG. 2 illustrates a pilot valve of the present invention in the closed position. 
     FIG. 3 illustrates the valve of the present invention in the open position. 
     FIG. 4 is a section through lines 4--4 on FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a typical subsea control system is illustrated. A wellhead valve, not shown, typically has a valve actuator 10 mounted thereon. A pair of two position three-way valves 12 and 14 operate in tandem to move the piston 16 of valve actuator 10. Valves 12 and 14 can be placed in one of three positions: closed 18, noninterflow 20, and open 22. 
     As can be seen from FIG. 1, when valve 12 is in the open position 22, valve 14 is in the closed position 18 and vice versa. The noninterflow position is a transient position for both valves. Both valves 12 and 14 are pilot operated. Two pilot lines 24 and 26 extend from the surface to valves 12 and 14. A surface pilot control valve 28 selectively directs pilot pressure into line 24 or line 26 from a supply 30. Accordingly, valve 28 has three positions. The three positions are: straight through 32, closed 34, and crisscross 36. In position 32, pilot supply pressure is directed into line 24 and line 26 is vented. As a result valve 12 is placed in the open position with valve 14 in the closed position. Line 38 is therefore directed into a vent line 40 with the net result being movement of actuator 16 in the direction of arrow 48. Placement of valve 28 in the crisscross position aligns supply 30 with line 26 thereby placing valve 14 in the open position 22 while simultaneously putting valve 12 in the vent position 18. As a result, valve 12 aligns line 44 with vent line 46 and allows movement of piston 16 in the direction of arrow 42. As shown in FIG. 1, both valves 12 and 14 have a spring 50 acting to place both valves 12 and 14 in the closed position in the event of a failure in the supply 30. The main source of hydraulic supply for physically moving piston 16 is provided from hydraulic supply 52 which is connected to valves 12 and 14 by lines 54 and 56, respectively. 
     Referring now to FIG. 2 which is a sectional view of the valves 12 or 14 illustrated in FIG. 1, the valve V includes a body B with an elongated cavity C extending longitudinally therethrough. Disposed within body B are supply sealing means S and function sealing means F. Supply sealing means S is disposed adjacent supply port 58 in body B. As shown, supply port 58 is radially oriented but can extend from the bottom 60 of body B without departing from the spirit of the invention. Supply sealing means S comprises a plug assembly 62 which further comprises: plug 64 and tubular segment 66. Plug 64 has preferably a tapered seating surface 68 which mates with surface 70 on seat 72. Seat 72 is an annular element which circumscribes the cavity and is in contact with internal wall 74 of cavity C. Valve body B has a removable bottom section 76 held to body B by bolts 78. Seal 80 prevents leakage between bottom section 76 and body B. Bottom section 76 has an annular extension segment 82 which has an upper end 84 in contact with seat 72. Accordingly, when bolts 78 secure bottom section 76 to body B, annular extension segment 82 secures seat 72 firmly in position against surface 86 in cavity C. 
     Bottom section 76 includes an internal depression formed by surfaces 90, 92 and 94. Biasing means in the form of a spring 96 is provided to maintain seating surface 68 in contact with seating surface 70. It is understood that alternative methods of biasing surfaces 68 and 70 together can be employed without departing from the spirit of the invention. A peripheral seal 98 is disposed between seat 72 and internal wall 74 of cavity C. A backup resilient seal 100 can be placed in seating surface 70 for contact with seating surface 68 as a secondary or backup seal to the metal-to-metal contact between surfaces 68 and 70. With surfaces 68 and 70 in firm contact as a result of the action of spring 96, flow through supply port 58 and into cavity C within body B is prevented. 
     Plug assembly 62 also contains tubular segment 66. Tubular segment 66 effectively extends from seating surface 68 and has an annular shape including an outer surface 102 and an inner surface 104. In the preferred embodiment tubular segment 66 is cylindrically shaped. Cavity C has a mating cylindrically-shaped wall 106 disposed adjacent to outer surface 102. Seals 108 and 110 are disposed between wall 106 and outer surface 102 for sealng therebetween. 
     Tubular segment 66 contains a plurality of ports 1112 to allow fluid communication from supply port 58 into a space defined by inner surface 104 and adjacent annular surface 114 as well as inclined surface 116. For the purpose of reference, such space will be referred to by number 118. 
     Function sealing means F includes an elongated member 120 having an upper section 122, a middle section 124 and a lower section 126. Lower section 126 is preferably cylindrically shaped having an inner surface 128 and an outer surface 130. Outer surface 130 is disposed to be in slidable, sealable contact with inner surface 104 of tubular segment 66. The sealing between surfaces 130 and 104 is accomplished by seals 132 and 134. Middle section 124 has a bottom surface 136 which engages a step 138 on tubular segment 66 upon selective movement of function sealing means F. Accordingly, relative movement is possible between lower segment 126 and tubular segment 66 until bottom surface 136 engages step 138. Thereafter further movement of function sealing means F results in displacement of plug assembly 62 by overcoming the spring force of spring 96 and separating surface 68 from surface 70. Once separation between surfaces 68 and 70 has occurred, fluid communication is established from supply port 58 through bores 112, into chamber 118, and into a chamber defined within cylindrical surface 128 hereafter referred to by 140. As seen in FIG. 2, lower segment 126 is open at its bottom thereby allowing flow communication between chamber 118 and 140. 
     Middle section 124 has a lower end 142 which has a preferably square cross-section, see FIG. 4. As shown in FIG. 4, lower end 142 comprises opposed parallel flat surfaces 144 and 146 and a second pair of parallel opposed surfaces 148 and 150. 
     Within the range of movement of lower end 142, cavity C has a pair of opposed flat surfaces 152 and 154. Thus, flat surface 144 is parallel and faces surface 152 while flat surface 146 is parallel to and faces surface 154. Lower end 142 preferably has a bore 156 extending therethrough from surface 144 to surface 146. As shown in FIG. 4, bore 156 is enlarged adjacent surfaces 144 and 146. Insert seals 158 and 160 are disposed in contact with cylindrical surfaces 162 and 164, respectively, (see FIG. 4). Seals 166 and 168 prevent fluid passage between insert seals 158 and 160 and their respective housing surfaces 162 and 164. Spring washers 170 and 172 bias insert seals 158 and 160, respectively into contact with surfaces 152 and 154, respectively. Thus, contact is made between sealing surface 174 on insert seal 158 and flat surface 152. Similarly, running contact is maintained between sealing surface 176 and flat surface 154. It should be noted that insert seal 160 and bore 164 are provided for the purpose of pressure balance on middle section 124 in a manner that is readily appreciated by those skilled in the art. 
     As seen in FIG. 2, when insert seal 158 is out of alignment with function port 178, flow communication betwen chamber 140 and function port 178 is interrupted as a result of the sealing contact between paired surfaces 174 and 152 as well as surfaces 176 and 154. 
     With elongated member 120 positioned as shown in FIG. 2, an axial flow path 180 is maintained between function port 178 and vent port 182 (see also FIG. 4). 
     Referring to FIG. 3, it can be seen that bore 184 in insert seal 158 has a larger diameter than function port 178. Thus, as elongated member 120 moves with respect to plug assembly 62, bore 184 comes into alignment with function port 178 as bottom surface 136 engages step 138. In this position, the volume of chamber 118 has been effectively reduced and chamber 140 is in flow communication with function port 178. At this point, there is still a sealing engagement between seating surface 68 and surface 70. However, axial flow path 180 is effectively cut off from function port 178 by virtue of sealing surface 174 circumscribing function port 178. It is only upon further movement of elongated member 120 that seating surface 68 is separated from surface 70 thereby aligning supply port 58 to function port 178. Flow can occur through supply port 58 between surfaces 68 and 70, through bores 112, through cavities 118 and 140 and into function port 178 through bore 184. It should be noted that interflow from supply port 58 to vent port 182 is eliminated by virtue of the positioning of two seals within the flow path prior to the actual initiation of flow into supply port 58. Thus, the one seal isolates the supply pressure and is disposed between surfaces 68 and 70. Another seal occurs by virtue of contact between sealing surface 174 and flat surface 152 when sealing surface 174 circumscribes function port 178. Even with the valve in the position shown in FIG. 2, there is still a seal between surfaces 68 and 70 as well as seals 108 and 110. Chamber 140 is isolated from function port 178 and vent port 182 by seals 158 and 160. 
     It should be noted that surfaces 152 and 154 can be removably mounted within body B as shown in FIGS. 2 and 3. Renewal of surfaces 152 and 154 may become necessary due to prolonged use. 
     Volume compensation is provided in chamber 140 by virtue of compensating piston 186 which is biased by spring 188. Seals 190 and 192 prevent fluid flow between piston 186 inner surface 128. As seen in comparison between FIGS. 2 and 3, movement of elongated member 120 results in compression of spring 188 coupled with displacement of compensating piston 186. Displacement of piston 186 effectively enlarges the volume of cavity 140. Fluid is displaced from above piston 186 through bores 194 and eventually out through vent port 182. It should be noted that the upper or vent segment of middle section 124 which houses piston 186 has a cylindrical outer surface 196 which is of equal or comparable diameter to outer surface 130 on lower section 126. Thus, with cylindrical surfaces 130 and 196, having a smaller diameter than the wall of the surrounding cavity C, axial flow path 180, traversing square section 142, is thereby defined. 
     Finally, middle section 124 includes an inclined sealing surface 198 which is positioned to selectively come in contact with inclined seat 200 effectively blocking off vent port 182 from function port 178. It should be noted that as bottom surface 136 contacts step 138, inclined sealing surface 198 is still not in contact with seat 200. However, at that time, sealing surface 174 circumscribes function port 178 and by virtue of contact with surface 152, further movement of elongated member 120 results in the position illustrated in FIG. 3 with seating surface 68 displaced from seat 70 and with inclined sealing surface 198 in contact with seat 200. This arrangement further insures against leakage into vent port 182. 
     Actuation of elongated member 120 is accomplished in a conventional manner. Upper section 122 of elongated member 120 is disposed in pilot subchamber 202. Seals 204 and 206 isolate pilot subchamber 202 from the remainder of cavity C by virtue of their contact with upper segment 122. A piston 208 is connected to upper section 122. Spring 210 biases piston 208 so as to maintain surfaces 68 and 70 in firm contact in the event of total hydraulic failure. Normally, hydraulic pressure is selectively applied to either ports 212 or 214 to actuate piston 208 thereby positioning elongated member 120 as necessary. 
     As can readily be seen, the valve of the present invention offers the advantage of having a poppet type seal between surfaces 68 and 70 as well as a shear type seal between surface 174 and 152 in the flow path between supply port 58 and function port 178. Furthermore, when surface 68 is separated from surface 70 thereby allowing supply flow into port 58, additional isolation of vent port 182 is accomplished by the contact between inclined sealing surface 198 and seal 200. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.