An assembly adapted to be anchored at a subsurface location within a tubular well conduit to function as a self-closing safety valve. The assembly includes a flapper valve closure element pivotably mounted in a tubular valve housing and controlled by a pressure sensitive control mechanism. An anchoring means having radially expansible anchoring and sealing members is employed to secure the valve in place and to form a seal which forces fluid in the conduit to flow through a flow passage in the valve housing. The expansible anchoring and sealing means may be retracted to permit retrieval of the entire assembly. The control mechanism includes a pressure charged bellows chamber which moves in response to a drop in the pressure within the well conduit to cause the flapper to close the flow passage. 
     An incompressible fluid contained within the bellows of the control mechanism cooperates with a double acting valve to prevent over extension or over compression of the bellows by extremes in pressure differential. The force of a compressed spring is suddenly released by movement of the bellows to produce a short, strong movement which is transmitted to the flapper closure element causing it to snap into closed position.

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to means for controlling fluid flow through a flow conduit. In a specific application, the present invention relates to self-closing safety valves employed in the production tubing of a completed well to prevent uncontrolled fluid flow through the tubing following failure of or damage to the restraining structure at the wellhead. 
     2. Description of the Prior Art 
     In many wells producing from a high pressure, subterranean petroleum bearing formation, a self-closing safety valve is positioned in the production string when the well is initially completed to prevent uncontrolled flow through the well in the event the confining or restraining structure at the wellhead should be destroyed or become inoperative. In some cases, however, wells were not equipped with subsurface safety valves when the production tubing was installed and regulatory agencies have required that production from some of these wells be terminated until safety valves are installed. 
     Where the need for a downhole safety valve is known in advance, a suitable nipple is usually included in the tubing string as the string is initially positioned in the well. Thereafter, a safety valve is lowered into the tubing string and special dogs or other means on the valve spring into receiving grooves or the like formed in the nipple to hold the valve in operative position. In some cases, the wells are initially equipped with non-retrievable, subsurface safety valves which form a part of the tubing string itself. In those systems where the valve is a part of the tubing string itself, inspection, repair or replacement of the valve may often require a complete shut down of production while the tubing string is removed from the well. 
     Where the tubing string lacks special landing nipples for receiving the required safety valve, it is often necessary to withdraw the tubing string from the well, insert the required nipple and then replace the string. This procedure is undesirable primarily in that it may involve a significant loss in production time. 
     Conventional safety valves often employ relatively narrow flow passage openings which form a restriction to the flow of fluids through the well conduit. Restricted flow passages are normally undesirable, particularly where the formation pressure is relatively low, since the restriction limits production below that which would otherwise be possible. Small valve openings are also undesirable in that it is difficult or impossible for equipment to be lowered through the valve opening so that testing or other procedures may be conducted below the valve. Another shortcoming associated with restricted valve openings is the tendency of such valves to be cut away by abrasive materials carried in the petroleum fluids flowing through the valve. This is particularly evident where the valve closure surfaces are directly exposed to the fluid flow. 
     Conventionally, the sensing elements employed to close safety valves have included either flow sensitive or pressure sensitive devices. In these devices, an increase in flow rate or a decrease in pressure respectively indicate uncontrolled well flow which automatically triggers closing of the safety valve. Flow sensing elements are undesirable to the extent that the required flow monitoring element may restrict flow. In marginal wells having a relatively low bottomhole pressure, any restriction to flow can limit production below that which would otherwise be obtainable. 
     The prior art is replete with bellows driven pressure sensitive controls employed in conjunction with self-operating valving mechanism. In such prior art controls, bellows damage is often encountered because of extreme pressure differentials imposed across the bellow walls causing the bellows to be distorted beyond design limits. Another problem associated with conventional bellows operated controls stems from the fact that relatively slow, low force closing movements obtainable with the bellows may cause partial or improper seating of the valve. 
     SUMMARY OF THE INVENTION 
     The self-contained retrievable valving assembly of the present invention includes a retrievable packer, a valving mechanism and a control mechanism. The packer includes radially expansible anchoring means to secure the assembly internally of the well conduit at a subsurface location and expansible packing or sealing means to provide a pressure-proof seal about the packer body. The packer permits the valving assembly to be retrievably positioned within existing production tubing without the need for special landing nipples or other receiving means being inserted into the string before it is run into position. The packer may include either conventional friction slips, or where latching within a collar recess is desired, may include expansible dogs designed to move into and engage with the recess formed between two adjoining tubing lengths. 
     The assembly is retrievable to permit inspection, replacement, repair or adjustment of both the control mechanism and the valve mechanism without having to remove the tubing string from the well. 
     The valve mechanism of the assembly is equipped with a relatively large flow passage opening which reduces flow restriction and permits equipment to be moved through the valve. Abrasion and cutting of the valve structure is also reduced because of the relatively large flow passage opening. The valve mechanism is equipped with a low cost, dependable flapper type closure element which pivots out of the flow passage during normal operation to reduce wear on the seating surfaces of the element. 
     The control mechanism is self-contained and in its preferred form is sensitive to a drop in tubing pressure to automatically close the flapper valve element in the valve mechanism. The control mechanism may be easily removed and replaced and is not an integral portion of the valve mechanism itself. Because it is pressure sensitive, the control mechanism eliminates the need for a flow restrictive monitoring element such as is required in flow sensitive controls. Reopening of the valve is effected by simply pressuring up from the wellhead. 
     In the preferred form of the invention, the bellows sections in the control mechanism are filled with an incompressible fluid to protect the bellows from distortion caused by high pressure differentials. The fluid acts in conjunction with a double acting valving system so that the bellows sections are protected from damage caused by high pressure exerted either on the inside or the outside of the bellows wall. 
     The control means also includes a snap action which ensures complete closure of the valve element. Limited travel of the bellows releases the force of compressed spring means to exert a relatively fast, high force movement which is transmitted to the pivoted valve closure member to provide a snap action closure. 
     The foregoing and other features and advantages of the present invention will be more fully understood from the following specification, claims and the related drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial, vertical elevation, partially in section illustrating the self-contained retrievable valving assembly of the present invention in position within a production tubing string; 
     FIG. 2 is an enlarged scale, vertical elevation, partially in section illustrating the preferred form of the valve and control mechanisms in open position; 
     FIG. 3 is a partial, vertical elevation, partially in section illustrating the valve of FIG. 2 in closed position; 
     FIG. 4 is an enlarged scale, vertical elevation in quarter-section illustrating details in the construction of the preferred form of the control mechanism; 
     FIG. 5 is a vertical elevation, partially in section, illustrating a device for holding the closure element of the valve mechanism open; 
     FIGS. 6A and 6B are the upper and lower portions respectively of a modified form of the assembly of the present invention illustrated in vertical section; 
     FIG. 7 is a horizontal cross-sectional view taken along the line 7--7 of FIG. 2; 
     FIG. 8 is a horizontal cross-sectional view taken along the line 8--8 of FIG. 2; and 
     FIG. 9 is a detailed view of a flexible linking mechanism employed to transmit linear motion in the control mechanism to pivotal motion in the valve closure element. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the assembly of the present invention is indicated generally at 10 in position within a production tubing string T. The assembly 10 includes a packer P having a sealing means S and anchoring means A. A valve mechanism 11 operated by a control mechanism 12 is secured to the packer P by a connecting sleeve 14. 
     In the illustration of FIG. 1, the packer anchoring means A are illustrated as expansible dogs which have been radially expanded into the annular collar recess formed between upper and lower tubing sections T-1 and T-2, respectively which are joined together by a conventional collar C. An elastomeric material is employed for the sealing means S so that upon expansion of the sealing means, a pressure seal is formed between the body of the packer P and the surrounding conduit T. 
     The packer P is of the type which may be set within a tubing string and subsequently retrieved in conventional manner. The packer preferably includes a large central opening to permit relatively unimpeded flow of fluids through the tubing. Where collar recesses are not available, or where otherwise desired, the anchoring dogs A may be replaced by conventional slips having teeth formed along their external surfaces and adapted to be moved radially outwardly into friction locking engagement with the internal walls of the tubing string. The packer P may be similar to the packer described in U.S. patent application Ser. No. 857,047 filed Sept. 11, 1969 entitled ANCHOR ASSEMBLY FOR WELL TOOLS SUCH AS PACKERS AND THE LIKE, or U.S. patent application Ser. No. 272 filed Jan. 2, 1970 entitled TOOL STRING ASSEMBLY FOR USE IN WELLS. 
     As may best be seen by reference to FIG. 2, the valve mechanism 11 includes a tubular housing section 11a which surrounds flapper type valve closure member 11b adapted to be pivoted about a mounting pin 11c. When in closed position, as illustrated in FIG. 3, the valve closure member 11b engages and seals with an annular seat 11d formed about a flow passage 11e which extends through the valve housing 11a. When the assembly 10 is anchored in position within a well bore with the seal S expanded to provide the desired pressure seal, well effluents are forced to flow through the flow passage 11e and up through the central opening in the packer P. 
     Referring jointly to FIGS. 2 and 8, it may be seen that the control mechanism 12 is received in a semicircular recess 11f formed in the external body of the valve housing 11a. As illustrated in FIGS. 7 and 8, the composite cross-sectional area of the assembly is substantially circular in shape. The control mechanism 12 is threadably secured to the valve housing 11a as illustrated at 11g in FIG. 2 and is supported in the recess 11f by support bolts R illustrated in FIG. 8. Proper spacing of the control 12 with respect to the flapper valve member 11b  is effected by changing the threaded engagement 11g between the control and the housing 11a. Once properly adjusted, the control is held in position by the bolts R. Linear movement exerted by components contained within the control mechanism 12 is conveyed to the flapper closure element 11b through a shaft extending from a connecting linkage 12a which projects from the control mechanism into the valve mechanism. The linkage 12a includes a flexible shaft portion at its upper end and an enlarged tubular body section at its lower end. FIG. 7 of the drawings illustrates the separable connection formed between the upper end of the linkage 12a and the closure element 11b which permits separation of the two structures when the control mechanism 12 is removed from the valve mechanism 11. The upper tip of the linkage 12a is bent at a right angle to the main shaft and is loosely received in a lateral bore formed in the flapper element 11b. As the valve element rotates about the mounting pin 11c, the receiving bore moves in an arc and rotates about the tip of the linkage 12a. It will be appreciated that movement of the linkage 12a toward the pin 11c pivots the valve element 11b toward its closed position while movement away from the pin pivots the element to its open position. As best illustrated in FIG. 3, the pivotal movement of the flapper closure element 11b is accommodated in the linearly moving linkage 12a by flexing of the linkage's main shaft portion. 
     Details in the preferred form of the control mechanism 12 may best be described with reference to FIG. 4 where it is seen that a plural part, tubular housing 12b encases the components of the control 12. Internal components of the control include upper and lower bellows sections 12c and 12d, respectively. The bellows sections are of a conventional type adapted to axially elongate or contract in response to pressure differentials existing across the bellows wall. The upper bellows section is secured to the housing at 12e and the lower bellows section is secured to the housing at 12f. The free end of the bellows section 12c is connected to a central driving rod 12g while the free end of bellows section 12d is connected to a cap 12h equipped with a removable plug 12i. 
     The lower end of housing 12b is equipped with a removable cap 12j which is threadedly engaged to the control housing. Annular O-ring seals 12k are positioned between the cap 12j and housing 12b to provide a pressure tight seal. A conventional valve 12j' is positioned internally of the housing to provide a means for inserting gas into a pressure tight dome or chamber 12m formed between the bellows section 12d and the internal walls of the control housing 12b. 
     An internal shoulder provided by a component part 12b' of the control housing 12b supports the lower end of a coil spring 12n. A portion of the spring 12n extends upwardly within a depending sleeve carried by an axially movable valving component 12p and the uppermost end of the spring engages and bears against the body of the valving component 12p to bias the component upwardly. An annular, resilient sealing member 12p' is carried on the valving component 12p. In the lowermost axial position of component 12p illustrated in FIG. 4, the seal 12p' engages and seals with an internal seating surface 12b" to isolate an enclosed area 12d' below the seal from an enclosed area 12c' above the seal. The upper end of valving component 12p includes a sleeve which extends over the lower end of driving rod 12g. Upward movement of component 12p is transmitted to the drive rod 12g by engagement of shoulders formed on each of the two components. The component 12p engages the drive rod 12g in a free sliding fit whereby the valving component 12p and rod 12g may move in opposite directions under certain circumstances to be hereafter described. 
     Drive rod 12g is a plural part component which includes a shoulder section 12g' projecting radially away from the main body of the drive rod. A coil spring 12q is confined between the shoulder section 12g' and an internal shoulder formed within the housing 12b. A second coil spring 12r is confined between the shoulder section 12g' and a shoulder 12a' formed on the movable linkage 12a. A second shoulder 12a" formed on the linkage 12a supports the base of a coil spring 12s and the upper end of spring 12s engages an annular, radially extending shoulder 12g". A triggering member 12t having an annular recess 12t' formed about its central portion is supported on top of the drive rod 12g. Between the upper end of member 12t and the linkage 12a is confined a power spring 12u. A plurality of small metal balls 12v are carried in radial bores 12w extending through the tubular body section of linkage 12a. As will be seen, the balls 12v are retained in a radially extended position when illustrated trigger component 12t is in the position illustrared in FIG. 4. When in a radially extended position, the balls 12v engage upper and lower shoulders formed in the internal surfaces of the housing 12b as illustrated in FIG. 4 to prevent axial movement of the linkage 12a. When the triggering component 12t moves axially upwardly so that the recess 12t' is coincident with the balls 12v, the balls are permitted to retract radially inwardly and axial movement of the linkage 12a is then permitted. 
     In employing the self-contained, retrievable valving assembly of the present invention, the assembly is initially lowered into the well conduit T by means of a suitable wireline string or other apparatus until the desired subsurface location is reached. The slips or anchoring means A and the seal S are thereafter set and the positioning means is removed from the tubing string. Prior to positioning the assembly within the string T, the chamber 12m is filled with a compressible gas at a desired pressure. The gas pressure in the chamber is determined by the well conditions which are to be encountered by the assembly. 
     During the lowering procedure, the valve closure member 11b is retained in an open position by a hold open mechanism indicated generally at 13 in FIG. 5. The mechanism 13 includes a central bore 13a extending axially through the mechanism to permit flow through the assembly as the assembly is being lowered into a fluid containing tubing string. During the downward movement of the member 13 through the tubing string, the dogs 13b are depressed radially inwardly and spring out when they are coincident with the recess 14a. The lower movement of member 13 is limited by its engagement with a shoulder 14b formed internally of the sleeve 14. The lower end of member 13 includes a downwardly extending projection 13c which prevents the flapper valve 11b from moving into closed position. Once the assembly has been properly positioned within the tubing string T, the member 13 may be removed by a suitable retrieving means of conventional construction. Removal of the member 13 is effected with back pressure existing at the well head so that the flapper valve 11b remains in its open position even with the member 13 removed. The mechanism 13 may also be employed to remove the self-contained assembly 10 from the tubing string T. 
     When the assembly 10 is in position within the tubing string T, well pressures above a predetermined minimum valve act against the external surface of bellows section 12c tending to compress or axially foreshorten the bellows which in turn retains the drive rod 12g in its lowermost axial position. In the event unusually high pressures in the tubing string T are encountered, damage to bellows sections 12c and 12d is prevented by action of the sealing component 12b' which prevents the pressure acting against the bellows 12c from being communicated to the internal bellows area 12d'. Since the internal bellows area 12c' and 12d' and the area confined between the two sections are completely filled with an incompressible fluid, foreshortening of the bellows section 12c is limited to prevent the bellows from collapsing. In the reverse situation where an unusually low pressure acts against the external surface of bellows 12c, the pressure charge in the gas chamber 12m tends to compress and axially foreshorten the bellows 12d which in turn causes the valving component 12 p to move to its axially upper position where the sealing means 12p' is engaged with the seat 12b'". The fluid confined internally of the bellows chamber area 12d' prevents the bellows from collapsing and the valving action of component 12p prevents the pressure in chamber 12d' from being communicated to the bellows chamber 12c' so that the bellows section 12c is not distorted in an outward direction. 
     FIG. 4 illustrates the control mechanism as it appears under normal operating conditions with the valve open. When the pressure of the tubing string drops below a predetermined minimum value, the gas charge in chamber 12m exerts a compressing force on the fluid contained in chamber 12d' which is transmitted to the fluid in chamber 12c'. The bellows section 12d thus compresses and bellows section 12c expands. During this process, the seal 12p is moved upwardly and when it moves sufficiently upwardly, it engages and seals against the internal seating surface 12b'", to provide bellows protection. The spring 12n forces the valving component 12p to follow the upward movement of drive rod 12g. Because of the slip joint connection between the drive rod 12g and component 12p, the biasing force of spring 12n is required to cause the element 12p to follow the movement of rod 12g. The slip joint connection between rod 12g and element 12p is required because the fluid contained within the chamber sections is not absolutely incompressible and high pressure acting externally of the bellows 12c may tend to push the drive rod 12g slightly upwardly while the valving component 12p is held tightly in sealing position against seat 12b'". The slip joint permits this small relative movement to take place. 
     During the upward movement of the drive rod 12g, the springs 12r and 12u are being compressed. When the recess 12t' on member 12t moves up to the balls 12v, the balls can back into the recess and the linking assembly 12a is freed from locking engagement with the housing 12b. The compressed force of spring 12r is then suddenly released to push the linkage 12a quickly upwardly causing the flapper valve 11b to snap shut. The spring 12u also reacts against the top of the element 12t to assist in the snapping action.. During closure of the valve and movement of the linkage 12a upwardly, the spring 12s is compressed by the movement of the linkage shoulder 12a" toward rod shoulder 12g". Spring 12s stays highly compressed as long as the valve is closed. When pressure across the closed valve is equalized by pressuring up at the surface, the resilient force of spring 12s tends to drive the linking assembly 12a back downwardly and the rod 12g upwardly. This pulls the linking assembly 12a downwardly through the housing 12b and the spring 12u acts downwardly on the member 12t so that the balls 12v are pushed out of the recess 12t'  and into the bore 12w with the member 12t then moving further downwardly under the influence of spring 12u until the valve is again in the position illustrated in FIG. 4. 
     A modified control mechanism indicated generally at 112 is illustrated in FIGS. 6A and 6B. The modified control mechanism 112 includes a spring mounted, flexible linkage 112a carried within a spring mount 112a'. The spring mount 112a' is carried in a recess formed at the upper end of a drive rod 112g. The lower end of the drive rod is telescoped over a valving component 112p equipped with an annular resilient sealing means 112p'. The sealing element 112p' is designed to move between lower and upper sealing surfaces 112p" and 112p"', respectively formed within the internal walls of a tubular control housing 112b. A coil spring 112n extends between the lower end of the valving component 112p and an internal shoulder formed within the control housing 112b to cause the component 112p to follow upward movement of the rod 112g. 
     The lower end of the control 112, as illustrated in FIG. 6B, includes a removable cap 112j, an annular sealing O-ring 112k and a conventional gas valve 112j'. With the cap 112j removed, gas is vented through the valve 112j' into a pressure dome 112m contained within the tubular control housing 112b. The bellows portion of the control mechanism 112 includes a single bellows section 112c having its lower end 112e secured to the control housing 112b and its upper end 112e' secured to the drive rod 112g. 
     A piston /12h equipped with an annular O-ring seal 112d is adapted to move axially through a receiving piston bore in the housing 112b to provide substantially the same function as the bellows 12d employed in the preferred form of the control shown in FIG. 4. The enclosed areas 112d' and 112c' are filled with a non-compressible fluid to provide protection for the bellows 112c in a manner similar to that already described with reference to FIG. 4. 
     The linking means 112a is designed to transmit the linear motion induced by expansion and contraction of the bellows 112c and travel of the piston 112h to a flapper valve element 111b. The resilient mounting of the linkage 112a in the spring 112a' permits the linkage to flex and bend at its upper end to follow the pivotal movement of the flapper valve 111b during its opening and closing motion. 
     The foregoing disclosure and description of the invention is 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 within the scope of the appended claims without departing from the spirit of the invention.