US2653008A - Well jar - Google Patents

Description

Sept. 22, 1953 WELL JAR 4 Sheets-Sheet l Filed D90. 29. 1949 f. L PO f6 INVENTOR.

ATTORNEY E. L. POTTS Sept. 22, 1953 Filed Deo. 29, 1949 R. W mf/ wwwwf W Ma wm A E inf/vv/IIZ/' `A mw m m r\..\\\\\ \\\\\\\\\|& L.,

sept. 22, 1953 Filed Dec. 29, 1949 E. L. POTTS WELL JAR 4 Sheets-Sheet 3 E, L Po zs INVENTOR.

ATTORNEY sept. 22, 1953 E. L. POTTS A2,653,008

WELL. JAR

Filed Deo. 29, 1949 4 Sheets-Sheet 4 E. L P0 1s INVENTOR.

Patented Sept. 22, 1953 WELL JAR Ernest L. Potts, Houston, Tex., assigner, by mesne assignments, to Cicero C. Brown, Houston, Tex.

Application December 29, 1949, Serial N o. 135,567

(Cl. Z55- 27) Claims.

This invention relates to jars employed in the Well drilling industry and particularly to improvements in the tripping or release means employed with such jars.

Jars are employed in the well drilling industry for applying sharp impacts or blows to Various tools or objects which have become lodged in a well bore, in order to eliect the release of such tools or objects so that they may be withdrawn from the well bore.

Essentially, all jars comprise a pair of telescoping members, one of which is adapted to be iixedly connected to the tool or object to be released and the other to an operatingT string, such as a pipe string, by which relative longitudinal movement between the jar members is effected to produce the jarring force. The tele scoping members are ordinarily provided with axially spaced striking abutments which, when brought into mpactive engagement by relative movement of the telescoping members, produce the desired jarring blow. Due to the inertia in the ordinarily long operating strings, it is normally necessary to provide some form of trip or release mechanism between the jar members by which substantial energy may iirst be stored in the operating string and then suddenly released in order to produce the high-energy impacts which are desired.

Numerous types of such release or tripping mechanisms have heretofore been devised and used with varying degrees of success. One known form of such tripping mechanisms, which has been constructed in numerous modiications, employs a cooperating lug-an-:l-shoulder arrangement, the design of which is such as to first eliect temporary locking engagement between the lug and the shoulder when the jar members are moved in the direction in which the blow is vapplied and while the jarring abutments remain spaced apart, and then to cause release between the jar and shoulder when the forces, including the coeilicient of friction, which resist release between the engaged lug and shoulder, are exceeded by axially directed force which may be exerted either in tension or compression through the operating string in the direction of the desired impact. Energy will be stored in the operating string in developing the force necessary to overcome the resistance to release of the lug and shoulder, and upon release, this energy will be suddenly imparted to the movable jar member to produce high-energy impacts between the jarring abutments.

Among the principal problems encountered in the construction and operation of existing types of jars is in providing simple and eiective means for regulating and controlling the magnitude of the mpactive force, so that blows of greater or lesser force may be selectively struck in accord- 2 ance with various conditions which may be encountered in operation and in the various types of tools with which the jars are employed.

The present invention has for its principal objects the provision of an improved type of jar which overcomes the disadvantages of existing jar constructions; which provides a jar of relatively simple mechanical construction; and which includes simple but highly ecient control means for the tripping mechanism by which maximum flexibility is provided in regulating the magnitude of the jarring force which may be applied; and by which the magnitude of the jarring blows may be selectively controlled.

Generally stated and in accordance with this invention, the jar structure comprises a pair of telescopically connected generally tubular jar members having suitable jarring abutments arranged thereon for impact upon relative axial movement between the members. A tripping or release means of the l-ug-and-shoulder type as generally described above is arranged between the jar members for effecting delayed release of the members. Torque-producing control means are disposed in the jar structure and constructed and arranged to exert a holding force on the tripping mechanism. The torque-producing means may be actuated by spring pressure or by hydraulic pressure, whereby the torque pressure may be varied to correspondingly vary the force necessary to trip the jar.

More specifically and in accordance with one illustrative embodiment of this invention, the telescopically arranged jar members are provided with lug-and-shoulder release elements which are inter-engageable by relative rotational and longitudinal movement, and which are provided with engaging surfaces shaped to permit these elements to slip past one another upon the application to the engaged members of opposing generally axially directed forces which exceed the forces tending to hold the release elements in engagement. The torque-producing means comprises a pair of axially engageable clutch elements having engaging surfaces shaped to constitute helical cams, one of which is iixedly mounted on one of the jar members and the other of which is mounted on a piston which is non-rotatively mounted in the other jar member but is slidable therein for axial engagement with the rst mentioned clutch element. When the clutch elements are forced into engagement, as in response to hydraulic pressure axially applied thereto, relative rotation is effected between the jar members in a direction tending to increase the normal forces holding the lugs and shoulders in engagement. The magnitude of the increased holding force so produced will be determined by the hydraulic pressure exerted on the piston-type control element, thereby determining and regulating the 3 tripping force necessary to overcome the holding pressure, and ultimately thereby selectively determining and controlling the magnitude of the jarring blows in accordance with the hydraulic pressure exerted on the piston element.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate embodiments in accordance with this invention.

In the drawings:

Fig. l is a view illustrating the device disposed in a well and attached to an object to be released, the parts being shown in the positions occupied immediately preceding initiation of the jarring impact;

Fig. 2 is a view similar to Fig. l showing the parts of the jar in the positions occupied at completion of the jarring impact;

Figs. 3 and 4l, taken together, comprising a longitudinal sectional view of the structure with the parts in the positions occupied immediately preceding tripping;

Figs. 5 and 6, taken together, comprise a view similar to Figs. 3 and 4 with the parts in the position occupied at or immediately after the completion of the jarring impact;

Fig. 7 is a perspective view showing one modication of a tripping lug and shoulder arrangement for the structure illustrated particularly in Figs. l to 6, inclusive;

Fig. 8 is a cross-sectional view taken along line 8 8 of Fig. 3;

Fig. 9 is a longitudinal view partly in section of another jar embodiment in accordance with this invention;

Fig. 10 is an elevational View of tripping elements of the embodiment illustrated in Fig. 9;

Fig. ll is a cross-sectional view along line of Fig. 9;

Fig. l2 is a cross-sectional view along line |2-I2 of Fig. 9; and

Fig. 13 is a fragmentary view in longitudinal section illustrating another embodiment in accordance with this invention.

Referring to the drawings, the jar structure is composed of tubular outer and inner jar members I5 and I5, respectively, connected for telescopic movement. The upper end of outer member I5 is provided with the usual internally threaded tool joint box or socket I'I for connecting the outer or sleeve member I5 to operating pipe string i8 in which may be interposed one or more conventional drill collars |9 which are adapted to provide concentration of weight in the operating string immediately adjacent the jar structure. The lower end of inner or stem member I5 is provided with an externally threaded tool joint pin which is adapted to connect the stem member to any of the various conventional grappling or shing tools such, for eX- ample, as a conventional spear 2| (Fig. 1) which is adapted to be inserted in, and to rigidly grasp, a hollow object, such as a pipe 22, which has fallen into or become lodged in the bore of a well 23 and is sought to be removed therefrom.

The major portion of stem member I6 is reduced in external diameter for insertion into the bore of sleeve member I5 thereby providing an annular shoulder 24 adjacent its lower end to limit the extent of inward relative longitudinal movement between the jar members. A cylindrical jarring head 25 is mounted on the inner end of stem I6 and is of somewhat larger 4 diameter than the stem to provide an annular downwardly facing jarring abutment 26 in the annular space between the stem and the inner wall of the outer sleeve member I5. A sealing ring 21, such as a conventional O-ring, is arranged between the outer surface of jarring head 25 and the adjacent wall of sleeve I5. A plurality of clutch teeth 28, generally formed integrally with jarring head 25, project upwardly in va generally circular arrangement from the upper end thereof. Each of the teeth 28 has one of its faces 29 sloping or curved downwardly in a generally clockwise direction, the opposite faces 3l) of the teeth being generally vertical. rI'he sloping faces 29 form cams for purposes to be described more fully hereinafter.

A tubular jarring head 3| is screwed into the lower end of sleeve I5, and slidably surrounds stem I6. The inserted inner end of jarring head 3| forms an annular upwardly facing jarring abutment 32 which is thus mounted in sleeve I5 and extends into the annular space between stem I5 and sleeve I5 and is adapted to strike jarring abutment 2S carried by stem I6 when the jar members are moved toward each other. A plurality of relief ports 33 are provided in the wall of sleeve I5 just above abutment 32. The lower end of sleeve i5 has connected thereto a metal facing ring 34 which is adapted to lodge on shoulder 24 when the jar members are in the collapsed or inoperative position (Figs. l and 4).

The wall of jarring head 3l is provided on diametrically opposite sides with a. pair of generally vertical slots 35 which extend upwardly from ring 34 to an intermediate point below abutment 32. The upper ends of slots 35 terminate in lateral recesses 36 which extend in the genera-l anti-clockwise direction from the slots and terminate in inner end walls 31. Lower walls 38 of the recesses are shaped to slope or taper generally downwardly and rearwardly from end walls 36 into the upper ends of the respective slots 35. (See particularly Fig. 7.) Stem I6 carries a pair of oppositely extending lugs 39 which project into slots 35 and are dimensioned to be slidable longitudinally thereof and to enter recesses 3G upon relative rotation between the sleeve and stem to lock the jar members together in the non-jarring position. The lower faces 40 of lugs 39 are sloped or tapered at an angle generally complementary to that of lower walls 38 of recesses 3E, which thus form lug-receiving shoulders in sleeve I5. Generally speaking, the surfaces of faces 40 and shoulders 38 are shaped to form slidably engageable cam-type surfaces which, when subjected to axial forces oppositely directed to eiect engagement of the surfaces, will remain thus engaged until these opposing forces exceed those forces, including the frictional coefficients, which tend to hold these surfaces in engagement, whereupon a rotational component will be developed in the engaged cam surfaces to produce a degree of relative rotation between the engaged surfaces suiiicient to allow one of these surfaces to slip past the other and trip the locking connection between the jar members. Inner walls 3l form stops to limit the extent of rotational movement of lugs 39 into recesses 36.

A cylindrical piston 4I is mounted for sliding longitudinal movement in the bore of sleeve I5 between the lower end of box II and the upper end of stem I6. Longitudinal splines 42 project radially inwardly from the wall of sleeve I5 and project into cooperating grooves 43 cut longitudinally in the outer surface of piston 4| (see particularly Fig 8) to thereby permit 1ongitudinal movement of piston 4| relative to sleeve |5 while preventing relative rotational movement between these parts. A seal ring 44, such as a conventional O-ring, is circumferentially disposed between the exterior of piston 4| adjacent its upper end and the adjacent wall of sleeve l5 to form a fluid-tight sliding seal therebetween. The lower end of piston 4| is provided with integral downwardly projecting clutch teeth 45 having surface shapes generally complementary to those of teeth 28, that is, curved or cam faces 46 matching faces '29, and vertical fa-ces 4`| matching vertical faces 3U. In assembling the structure, teeth 45 will be angularly oriented or olf-set with respect to teeth 28 so that, upon engagement of the teeth in response to relative axial movement between the jar sleeve and stem, the lower ends of sloping faces 46 will first engage the outer ends of sloping faces 29 and as the teeth continue to move toward each other, a degree of relative rotation will be developed between the teeth-carrying members. Theteeth may perhaps be best described as helical cams which, upon axial engagement produce relative rotational movement between the teeth-carrying members. An axial passageway 48 extends through piston 4| and is provided at its upper end with a flow constrictingv member, such as a choke bushing 48. Fluid conducting passages 50 and 5| are provided in sleeve member l5 and stem I6, respectively, in order to conduct operating fluid through the tool from the operating pipe string.

The above-described device operates in the following manner: The jar structure will be inserted in the usual string of operating pipe with the outer jar member connected to the `operating pipe, and the inner jar member connected to the shing tool. The string will be run into the well and the fishing tool hooked on to the lost object in any manner which is conventionally employed to grasp the object. At this stage of operation it is generally immaterial whether or not lugs 39 are engaged in recesses 36, as the jar members may be either in the collapsed or extended positions. `Once the fishing tool has firmly grasped the object to be removed, the operating string is lowered to place the jar'members in the collapsed positions, as illustrated particularly in Figs. 1, 3 'and 4, wherein `lugs 3'9 will be opposite or actually engaged in recesses 36. Until fluid under pump pressure from the surface-has been started through the string, piston`4| will be in a more or less floating position inside sleeve member I5 although its teeth may be partly engaged with the teeth on stem |6 by virtue of the weight of the piston. Pumping of fluid through the string will be begun and as it passes through the interior of the jar structure it will be -constrained by reason of seals 44 to now through passage 48 and the flow restriction provided by choke bushing 49. Due to this flow restriction, fluid pressure will be'exerted on the upper end of piston 4|, driving it downwardly and forcing teeth 45 into sliding engagement with teeth 28. Because of the angularly off-set arrangement of the teeth, as described above, and of the direction of their slope or curvature,` a torsional or. rotational component will develop between the teeth tending to rotate one of the jar members with respect to Ythe other. As the stem is xed against rotationloy its attachment to thesh, this 6. rotational component will be imparted to piston 4| and, through its splined connection to sleeve member I5, will produce rotation of the latter with respect to stem I6. The direction of slope of the engaged teeth will have been designed to rotate the sleeve member about the stem in a direction to cause recesses 36 to move toward lugs 39 whereby the latter will enter recesses 36 and come up against inner walls 31 thus stopping the relative rotation, although torque pressure exerted through the engagement of the clutch teeth will continue to be forcibly applied between lugs and engaging surfaces in recesses 36. Contemporanecusly with or immediately following the engagement of lugs 39 in the recesses, upward pull will be applied to the operating string at the surface. The upward pull will be resisted in part by the frictional coeicients between the engaging surfaces of shoulders 38 and surfaces 40 of the lugs, and to a greater extent by the fluid pressure exerted through piston 4| on these engaged surfaces. Due to the 4rearward slope of these surfaces, when the force of the upward pull applied to the operating string exceeds the total .force tending to hold the surfaces in engagement, a resultant force in the form of a reverse rotational component will develop suiiicient to overcome the opposing torque pressure applied through the clutch elements causing retraction of piston 4| and permitting sleeve member I5 to rotate in the anti-clockwise direction, that is opposite to the engaging direction, until recess shoulders 36 clear lugs 39 whereupon the latter will enter longitudinal slots 35 thereby tripping the connection between the jar members. Immediately upon such release, sleeve member l5 will move upwardly relative to stem i5 at a high rate of speed and with the energy stored in the operating string in developing the releasing force. As a result, jarring abutment 32 will be caused toV strike an upwardly directed jarring blow against jarring abutment 26 which is carried by the stem (Fig. `6) and the forcev of this upward blow will be transmitted through the stem to the fish in order to jar it loose from its lodgement inthe well bore, `Re

peated jarring blows may be struck, if necessary, by repeating the described operations.

, By` means of the described arrangement, the holding force resisting release of the jar members will be largely dependent on the angle of slope of shoulders 38, the area of piston 4|, and the fluid pressure applied thereto. Since the slope of shoulders 38 and the area of piston 4| are ixed, the magnitude` of the jarring blow will be more or less directly proportional to the fluid pressure, and may, therefore, be eectively regulated and controlled simply by appropriate regulation of the pump pressure at the surface. By way of example, in a jar structure in accordance with the illustrative embodiment, wherein the angle of shoulders 38 is 15 and the diameter of piston 4| is 2% inches, a jarring impact of as much as 100,000 pounds may be struck at pump pressure of about 1000 pounds per square inch. In a larger size having a piston 41/2 inches in diameter, a jarring impact of up to 400,000 pounds may be obtained with the same pump pressure. At lower or higher pump pressures the magnitude of the forceY of the jarring impacts will be proportionally lower or higher. It will be understood that the distribution in the holding force between torque pressure and fricl tional `coemcients may be varied by varying the angle of shoulder 38. The more acute this angle the greater will be the frictional components and the lower the torque pressure component. Generally, it will be preferable to make the shoulder angle as small as possible to thereby provide maximum frictional coeillcient and correspondingly reduced torque pressure which will, in turn, provide a maximum degree of control of the jarring force by means of the pump pressure.

Figs. 9 to l2, inclusive, illustrate another embodiment in accordance with this invention, which is adapted to strike either upwardly or downwardly directed jarring blows as may be desired. In this embodiment there is provided an outer sleeve member 55 which is adapted to be connected at its upper end to the operating string, and an inner stem member 56 arranged for telescopic movement in the sleeve member, and adapted to be connected at its lower end to the shing tool or grapple. The tripping element carried by the outer member comprises a pair oi diametrically spaced longitudinal slots 51 cut in the wall of the sleeve member and closed at their opposite ends by upper and lower end walls 58 and 59, respectively, which also serve as upper and lower jarring abutments on the sleeve. Intermediate the ends of slots l a series of longitudinally spaced recesses are cut laterally .in one wall thereof. The uppermost and lowermost of these recesses are designated by the numerals 60 land 6l, respectively, and intermediate ones by the numeral 62. Each of the recesses has its upper wall sloping upwardly and inwardly and its lower wall -sloping downwardly toward slots 5l, these walls forming upward and lower lug-receiving shoulders 63 and 6&5, respectively. Stem member 5G carries a corresponding plurality of longitudinally spaced lugs projecting radially into slots 51 and slidable longitudinally therein and movable into .and out of the corresponding recesses in response to relative rotation between the inner and outer jar members. The uppermost and lowermost of these lugs are numbered 'G5 and 55, respectively, and the intermediate lugs are numbered 61. Lugs 65 and 66 also function as upper and lower jarring abutments carried by the inner jar member 56 and are adapted to jarringly impact end walls 58 and 59, respectively, depending upon the direction of the jarring blow. With respect to their jar-tripping function it will be evident that the several lugs in this embodiment cooperate with their respective recesses in substantially the same manner as 'in the previously described embodiment. Thus, with member 56 Iixedly attached to the fish and the lugs engaged in the recesses, an upward pull on outer member 55 sufficient to overcome the frictional engagement between 'the lower edges of the lugs `and the lower shoulders '64 of the recesses, will cause the shoulders to slip past the lugs bringing lower walls 59 of slots 5l sharply upwardly against the lower 'edge of the lowermost lug B6 to produce ajarring impact on the fish in the upward direction. If the blow is to be struck in the opposite or downward direction, the weight of the operating string will be imposed downwardly to engage upper shoulders 63 with the upper edges of the lugs, and sumcient downwardly applied weight will be imposed to overcome the frictional engagement of these surfaces, whereupon upper shoulders 63 will slip downwardly past the lugs and cause upper wall 58 to strike a sharp downward blow on uppermost lug V65 thereby imparting a downward jar to the iishf The mechanism for increasing and controlling the magnitude of the jarring blows by means of fluid pressure applied at the surface by means of a pump will now be described.

Inner member 56 has an axial fluid passage 68 which is constricted at its lower end by means of a. choke bushing 69. A wash pipe 'I0 is connected into the upper end of passage 58 and extends upwardly therefrom for a short distance. A tubular piston 'H surrounds the upper end of inner member 56 and is sldable in the annular space between the inner member and outer member 55. The upper end of piston 1l is provided with an annular packing head 12 which forms a fluid tight sliding seal between the exterior of the wash pipe and the inner wall of outer member 55. The upper end of wash pipe 'l0 is open to the bore of outer member 55 above head 12. Piston Il carries a plurality of angularly spaced inwardly projecting splines 'I3 which are engaged in longitudinal grooves 'M cut in the outer wall of inner member 56 adjacent its upper end, thus locking the piston against rotative movement relative to inner member 56 while permitting relative longitudinal movement between these members. The lower edge of piston Il carries a plurality of circularly arranged downwardly projecting clutch teeth 'l5 of substantially the same shape as teeth 45 in the previously described embodiment. A set oi matching clutch teeth 'I6 are flxedly mounted on the interior wall of outer member 55 and project upwardly for engagement with teeth 15. It will be understood that the respective sets of teeth will be slightly oriented angularly with respect to each other when the structure is assembled, so that when the teeth are moved axially toward each other, they will produce relative rotation between their connected elements, just as in the previously described embodiment.

In operation this embodiment functions in very much the same manner as the previously described embodiment. When nuid pressure is applied to the upper end of piston 1l, teeth 'I5 will be forced in sliding engagement with teeth 'I6 producing relative rotation between the outer and inner members 55 and 56, respectively, to produce torque pressure applied to a direction tending to hold the .lugs in engagement in their respective recesses and resisting separation between these tripping elements under axially opposed forces. In order to trip the jar members to produce an upwardly directed blow, suiiicient upward pull will be applied to outer member 55 to overcome the holding forces, whereby tripping will occur and outer member -55 will move upwardly, thereby bringing lower abutment '59 sharply iup against lower lug 66 and imparting the desired upward blow through inner member 56 to .the fish connected thereto. 'To strike a downwardly directed blow, a portion of the weight of ,the operating string sufficient to overcome 'the holding .forces is applied downwardly to the engaged tripping elements, whereupon the tripping will occur in the downward direction to bring upper abutment 5 8 downwardly against upper rlug 65, and thereby transmitting a downward Ajarring blow through inner member 56 to the attached fish The embodiment of Fig. 1,3 vis, 4substantially identical in construction with the .embodiment illustrated vin Figs. l to .8, inclusive, except that a coil spring is inserted in compression between the upper end of piston -4I and the shoulder formed by the inner end of box l1. Spring 80 will at all times resiliently urge piston 4| down-A wardly in jar member I5 to force teeth 45 into engagement with teeth 28 whereby to produce torque pressure on the tripping elements which will correspond to the force exerted by the spring. Primarily the torque pressure thus exerted will be -determined by the strength of the spring which is selected, and will, therefore, be a constant pressure, if so desired. However, the torque pressure may be varied by applying hydraulic pressure to the piston in the manner previously described. The hydraulic pressure will supplement that of the spring and may be employed as in the previously described embodiment, to selectively Vary the torque pressure in order to vary the force of the jarring impacts. In still another example, the torque pressure may be varied by applying to the operating pipe to which jar member I5 is connected a suitable degree of twist in a direction tending to intensify the force of engagement of lugs 39 in recesses 36. The twisting force thus applied will supplement the torque pressure applied through the pressure of spring 80 and will be selectively variable in accordance with the amount of twist applied to the pipe. Hydraulic pressure may also be applied to further controllably vary the total torque pressure and thereby the jarring force.

From the foregoing it will be evident this invention provides a jar structure employing a lug and shoulder tripping mechanism and having torque applying means controllable to selectively determine the force of the jarring impacts.

It will be understood that numerous alterations and changes may be made in the details of the illustrative embodiment Within the spirit of this invention and without departing from the scope of the appended claims.

What I claim and desire to secure by Letters Patent is:

l. A well jar, comprising, a pair of telescopically connected tubular jar members having axially spaced jarring abutments engageable by relative axial movement of said members, said members being adapted to be connected between sections of an operating pipe string for applying relative axial and rotational forces to said members, tripping elements mounted on the respective jar members having cooperating inclined surfaces engageable by limited relative rotation in one direction between said jar members to normally hold said members in longitudinally spaced non-jarring relation and releasable by relative rotation in the opposite direction resultant from the application to said jar members of opposed axially directed forces in said pipe string exceeding the rotational engaging force in said one direction to thereby release said jar member for forcible jarring engagement, and control means separate from said tripping elements for controlling the magnitude of the jarring force, said means comprising, separable cam elements non-rotatably mounted in the respective jar members, one of said cam elementsbeing axially movable by fluid pressure in said pipe string into engagement with the other of said cam elements independently of the relative axial movement of said jar members, said cam elements having cooperating engaging surfaces relatively shaped to exert rotational torque pressure between said jar members in said one direction to an extent determined by the fluid pressure applied to said one cam element.

2. A well jar according to claim l, wherein said control means comprises, a first cam means xedly secured to one of said jar members, a second cam means non-rotatably mounted in the other jar member and axially slidable therein, means connected to said second means and actuatable by fluid pressure in the pipe string to move said second cam means into engagement with said first cam means, the engaging faces of said cam means being relatively shaped to exert rotational torque pressure between the jar members in said one direction to an extent determined by said fluid pressure.

3. A well jar according to claim l, wherein said control means comprises, a rst cam means xedly secured to one of said jar members, a second cam means non-rotatably mounted in the other jar member, and axially slidable therein, said second cam means including a piston member rigidly secured thereto and actuatable by fluid pressure in the pipe string to move said second cam means into engagement with said rst cam means, the engaging faces of said cam means being relatively shaped to exert rotational torque pressure between the jar members in said one direction to an extent determined by said fluid pressure.

4. A well jar according to claim 1, wherein said control means comprises, a first cam means fixedly secured to one of said jar members, a second cam means non-rotatably mounted in the other jar member and axially slidable therein, said second cam means including a piston member rigidly secured thereto, circumferential sealing elements about said piston member engaging the wall of said other jar member to form a fluidtight seal therewith, a restricted uid ow passage through said piston member communicating with the bore of said pipe string, said piston member being actuatable by fluid pressure in said pipe string to move said second cam means into engagement with said rst cam means, the engaging faces of said cam means being relatively shaped to exert rotational torque pressure between the jar members in said one direction to an extent determined by said fluid pressure.

5. A well jar according to claim 1, wherein said control means comprises, a flrst cam means fixedly secured to one of said jar members, a second cam means non-rotatably mounted in the other jar member and axially slidable therein, said second cam means including a piston member rigidly secured thereto and actuatable by fluid pressure in the pipe string to move said second cam means into engagement with said rst cam means, a spring member mounted in compression between said piston and the adjacent end of said other jar member, the engaging faces of said cam means being relatively shaped to exert rotational torque pressure between the jar members in said one direction to an extent determined by said fluid pressure and the pressure of said spring member.

ERNEST L. POTTS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,029,579 McCullough Feb. 4, 1936 2,101,968 Wickersham Dec. 14, 1937 2,153,882 Erwin Apr. 11, 1939 2,550,142 Dumble Apr. 24, 1951

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