US3460639A

US3460639A - Latch for drill bit control apparatus

Info

Publication number: US3460639A
Application number: US664878A
Authority: US
Inventors: William R Garrett
Original assignee: Smith International Inc
Current assignee: Smith International Inc; Smith Industries International Inc
Priority date: 1967-08-31
Filing date: 1967-08-31
Publication date: 1969-08-12
Anticipated expiration: 1986-08-12

Description

Aug. 12, 1969 W. R. GARRETT LATCH FOR DRILL BIT CONTROL APPARATUS Filed Aug. 3l, 1967 4 Sheets-She y /3 fl?? Aug. 1.2, 1969 W. R, GARRETT 3,460,639

LATCH FOR DRILL BIT CONTROL APPARATUS Filed Aug. 31, 1967 4 Sheets-$heet 2 W//a nr Ga fr e f! INVENTOR.

W. R. GARRETT LATCH FOR DRILL [31T CONTROL APPARATUS Aug. l2, 1969 4 Sheets-Sheet 5 Filed Aug. 31, 1967 W////am f?. Gar/'eff I NVENTQR.

Aug. l2, 1969 w. R. GARRETT 3,460,639

LATCH FOR DRILL BIT CONTROL APPARATUS Filed Aug. 51, 19e? 4 Sheets-Sheet 4 W//am R. G arr e INVISNTOR.

United States Patent O 3,460,639 LATCH FOR DRILL BIT CONTROL APPARATUS William R. Garrett, Midland, Tex., assignor to Smith Industries International, Inc., a corporation or California Filed Aug. 31, 1967, Ser. No. 664,878 Int. CI. E21b 17/10, 7/04; E21c 9/00 U.S. Cl. 175-230 10 Claims ABSTRACT F THE DISCLOSURE The hydraulic guide lbarrel for a drill bit mandrel is releasably latched to mandrel in lower position of barrel on Imandrel by a latch pin radially reciprocable in mandrel into and out of engagement with a slot in the barrel. The pin is positively driven lby a cam which reciprocates axially in barrel in response to predominating of Vtwo forces, namely, an upward -force provided by a helical compression spring and a downward force provided by iluid in the mandrel acting against piston connected to cam.

CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION Field of the invention This invention pertains to apparatus useful in boring holes in the earth, especially petroleum wells. The apparatus is luseful to guide the bit so that the hole will proceed in the desired direction.

Description of prior art According to the prior art, as exemplified by the aforementioned Garrett et al. patent, the guide barrel is latched to the lbit mandrel by a pin radially reciprocable in the mandrel into and out of engagement with a slot in the barrel, as `shown in FIGURE 9 of said patent. The latch is freely reciprocable in the mandrel and urged outwardly into engagement with the barrel slot by fluid pressure differential, e.g. when `the apparatus is in use with the slush pump in operation maintaining a higher fluid pressure inside the mandrel than in the well bore annulus outside the mandrel. However with the pump on, the rbarrels hydraulic shoes are propelled into engagement with the well wall to anchor the barrel in the hole, and upon downward motion of the mandrel in drilling the barrel pushes against the beveled side of the latch pin and forces it inwardly so that relative motion -of mandrel and barrel can proceed. When the downward travel of the mandrel relative to the barrel reaches its limit, the mandrel is elevated until the latch pin is in position to engage the slot in the barrel. Thereupon lluid pressure in the mandrel causes the latch to move out into engagement with the slot in the barrel. The pump is then turned oit and -the resiliently mounted wall engaging shoes of the barrel retract, thereby freeing the barrel. At the same time a lock member, axially reciprocable in the mandrel and normally held down by fliuid pressure but blased upwardly 'by a helical compressing spring, moves into position behind the latch pin to prevent its moving inwardly, The barrel can then be positively moved downward in the hole -by moving the mandrel down, the lock preventing the barrel from `overriding the latch pin. When the `barrel is lowered to the desired level, the pump is turned on again to activate the -barrel shoes into wall engagement. At lthe same time the fluid pressure in the mandrel acts against a piston carried by the lock to force the lock downwardly against the force of the compression spring, thereby unlocking the latch pin so that on downward movement of the mandrel the barrel can ride `over the latch pin.

In the foregoing construction, it: will `be observed that in order to effect positive latching of the mandrel to the barrel it is necessary rst to turn the pump on to move the latch pin into position and thereafter to turn the pump off to position the lock behind the pin. When the pump is turned yon again after repositioning of the Ibarrel has has been completed `and drilling is to proceed, the fluid pressure created lby the pump moves the barrel shoes out to anchor the barrel and moves the lock out from behind the latch pin, but the latch pin remains in engagement with the barrel slot. llt is necessary for the barrel to ride over the pin in order for driling to proceed.

The primary object of the present invention is to provide a latch actuating means that will positively retract the latch from barrel engagement whenever the fluid pressure differential is at the level corresponding to drilling operations, e.g. when the pump is on, and will positively extend the latch into barrel engagement whenever the fluid pressure differential falls below that level, e.g. when the pump is off. This simplified operation of the latch provides greater reliability, as is highly essential in apparatus of this kind.

SUMMARY OF THE INVENTION According to the invention a cam is axially reciprocably mounted in the mandrel. The cam is biased upwardly by a helical compression spring and is connected to a piston which moves it downwardly under ruid pressure differential. The cam engages a latch pin radially reciprocatable in the mandrel into and `out of engagement with the barrel slot. FIlhe cam and latch pin are positively engaged, the latch pin passing through a slot` in the cam.

The cam has a small slot through which the body connecting the follower portions of the latch pin may pass and also a larger slot through which the follower portions and tail ends of the latch pin can be passed. Therefore the latch pin can be made as an integral member.

rPhe latch pin extends clear across the mandrel bore so that both ends of the latch pin are supported in bores in the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 1 and 2 are axial sections through apparatus embodying the invention;

FIGURES 3 and 4 are elevations of the alignment spears of the apparatus shown in FIGURES 1 and 2;

FIGURE 5 is an elevation of the cam and guides of the apparatus shown in FIGURES 1 and 2;

FIGURES 6 and 7 are elevations of the latch pin of the apparatus shown in FIGURES 1 and 2;

FIGURE 8 is an elevation of a drill bit control apparatus in which the invention is incorporated; and

FIGURES 9 and l0 are sections taken at planes 9 9 and 10-10 of FIGURE 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURES 1 and 2 there is shown a tubular steel mandrel 10 and a tubular steel barrel therearound including a main body portion 11 and an alignment spear portion 12 screw connected to the main portion at the lower end thereof. Packing 13 lheld between the spear and body portions of lthe barrel forms a seal between the barrel and mandrel at the lower end of the pressurized annular chamber 14 therebetween. An internally iluted rubber sleeve bearing 15 secured inside the barrel supports the mandrel for relative rotation and reciprocation. Since the upper ends of the barrel and mandrel are the same as described in the aforementioned Garrett et al. patent, no further description thereof need be given, reference being made to said Garrett et al. patent for a further and fuller description thereof.

An alignment spear is screw connected to the mandrel. As shown in FIGURES 3 and 4, the

alignment spears

12 and 20 are simply steel tubes helically out off at angle to the axis forming

spear tips

21, 22. The helicoidal form of the spear surfaces is described in more detail in said Garrett at al. patent. The base of each spear is provided with a short slot as shown at 23, 24, the ends of the slots being rounded as shown at 25, 26. The barrel spear is further provided with a slot 27 at its side 180 degrees removed from tip 21. As best shown in FIG- URE 2 the ends of the slot 27 are beveled as shown at 28, 29, flaring inwardly toward the axis of the barrel and mandrel.

Referring now to FIGURE l the threaded pin 39 of a drill bit 40 is screwed into the lower end of the mandrel. A fluid ow responsive unit 41 comprising a check valve and a cam actuating means is disposed inside the mandrel between the upper end 42 of the rock bit pin and a downwardly facing beveled shoulder 43 in the mandrel. The cam actuating means includes a steel sleeve 44 having a beveled upper end 45 adapted to engage the shoulder 43. The lower end 46 of sleeve 44 is internally threaded to receive the threaded tupper end 47 of the steel body 48 of the check valve 49.

A pair of arms 50, only one of which appears in the drawing, extend downwardly from valve body 48 to base ring 51. A spacer ring 52 is screw connected to the base ring, the spacer ring resting against opper end 42 of drill 40.

The check valve 49 includes a valve seat 53 having an elastomeric seal ring 54 emplaced therein and protruding beyond the valve seat. A steel ring 55 is pressed inside the seal ring to hold it in place.

A valve closure 56 is pivotally connected to the valve body at 57, and is urged to closed .position by a torsion spring (not shown) coaxial with the pivot shaft.

The purpose of the cheek valve is to prevent upward flow of uid in the drill bit 40 and the bit control apparatus when the drill string is being lowered into the well bore through the drilling fluid, e.g. liquid or mud. Whenever there is no fluid pressure differential acting upwardly on the valve closure 56, the torsion spring holds it in closed position against the force of gravity. If there is down ow of liquid through the valve, the closure 56 opens and may vibrate slightly. There is an elastomer disc 58 bonded to the upper face of the closure to cushion the contact thereon of the tubular steel piston rod 59 when the latter is extended below valve seat 53. Without the rubber disc 58, the closure 56 may be destroyed by fretting in the course of a few hours.

The piston rod 59, forming part of the cam actuation means, extends coaxially inside sleeve 44. Near the upper end of the piston rod 59 there is a piston 60 comprising an annular external rib 65 against which is shouldered a steel ring 66 of T cross-section. A steel piston body 67 is secured to the rod 59 between T ring 66 and a steel split snap ring 67 received in groove 68 in the piston rod. An elastomer O-ring 69 in groove 70 in the piston body seals the body to the rod. The outer periphery of the body includes la hemi-toroidal portion 72. Around the outer periphery of the piston body, snapped over the hemitoroidal enlargement thereof, is an elastomeric seal ring 4 73 having double lip seals 74, 75, 76, 77 at each end thereof. The hemi-toroidal portion of the piston body provides a partial back up for the seal ring 73.

In FIGURE l, the piston comprising body 72, seal ring 73, T ring 65, snap ring 67', and O-ring 69, is shown at the upper limit of its travel, the snap ring 67 bearing against steel stop ring 80. Ring is held between shoulder 81 in the sleeve 44 and a steel snap ring 82. The stop ring includes a neck 83 which contacts the snap ring 67. The main body of the stop` ring is provided with a plurality of ports as shown at 88. The piston moves axially within enlarged bore 89 of the sleeve 44. The downward travel of the piston is limited 'by upwardly facing shoulder 90 which engages the lower surface 91 of the outer periphery of the T ring 65.

Tlhe tongue 95 of the T ring bears against the upper end of steel zhelical compression spring 96. The lower end of spring 96 bears against the top of flapper valve 49, there lbeing a spring seat 97 lfonmed at the bottom of the threaded neck 47. The spring is disposed coaxially around the piston rod 59 inside sleeve 44. The spring 96 urges the piston upwardly to the limit of its travel. The spring is preloaded so that it bears against the lpiston with considerable upward 'force even when the piston is at the upper limit of its travel.

A choke 100 made of tungsten carbide is secured in the lower end ofthe tubular piston rod between downwardly facing shoulder 101 and a steel snap ring 102 received in groove 103 in the piston rod. The pressure differential across choke 100, piston rod 59, and piston 60 existing when fluid -is being pumped through the man-drel is designed to be great enough to overcome the force of spring 96 and :move the piston downwardly to the lower limit of its tnavel.

It is to be observed that when fluid is flowing down the mandrel, the closure 56 of the check valve will be in open position and there is ample room for the piston rod 59 to move through the valve seat as the piston 60 moves to the lower limit of its travel.

The cam actuating means comprises sleeve 44, spring 96, spring seat 97, piston 60, piston rod 59, stop ring 80, and choke 100. The cam actuating [means actuates oam means which in turn actuates latch means for connecting the mandrel 10

tothe barrel

11, 12.

The cam means 110, shown in FIGURES 2 and 5 comprises a bar 111 having generally at parallel

vertical sides

112, 113. Near the ends of the bar the

sides

112, 113, are connected by cylindrically curved outer peripheral guide surfaces 114, 115, 116, 117 adapted to slide on the inner periphery 118 of mandrel 10 as the cam means reciprocates coaxially therein. The space between the Hat sides of the bar and the inner periphery 118 of the manidrel -provides space for uid low in the mandrel past the lbar.

The lower and |upper ends of the bar are cut back away from the inner periphery 118 of the mandrel to provide cylindrically

curved seats

119, 120, 121, 122 to receive cylindrically

curved tongues

123, 124, 125, 126 extending from the upper end of the tubular piston rod 59 and the lower end of tube 127 of an orienting instrument receiver. Seat 122 and tongue 126 are shorter than the other seats rand tongues to insure correct orientation of the receiver with respect to the bar during assembly. The tongues are fastened to the seats by roll pins 128 driven thnough holes in the tongues and through holes 129 the ends of the bar between the seats. The pins iit loosely in the tongues so that the cam means will not bind inside the mandrel due to misalignment.

The orienting instnument receiver 130 comprises a steel tube adapted to reciprocate axially within the mandrel, being provided with

guide iblocks

140, 141 Welded to its outer periphery to center the tube 127 within the mandrel. Within the tube 127 is an alignment key 142 formed integral with one of the guide blocks 140 yand extending through a slot in tube 127.

The upper ends ot the

guide portions

150, 151 of the bar 111 and of the upper end 152 of the bar are beveled as shown at 160, 161, 162, 163, 164, 165, 166, 167, 168 to streamline these portions of the bar relative to downward flow of drilling iluid such as air, gas, water, or mud, which may be used in the drilling process.

Between the

guide portions

150, 151 the bar 111 is cut at an angle to the cylinder axis of the lguide portions to form front and back cam surfaces 170, 171. The cam body 172 between

surfaces

170, 171 is provided with a slot 173 extending from near the yguide portion 150 at the lower end of the bar 111 upwardly toward the guide portion 151 near the upper end of the bar. The upper end of the slot merges with a larger slot 175 adjacent upper guide portion 151. The part 176 of bar 111 around slot 175 is of `greater thickness than that between at

surfaces

112, 113 defining the thickness of the remainder of the bar. The enlarged part 176 is beveled at 177, 178 to merge smoothly with the remainder of the bar. To facili- .tate assembly with the steel latch pin 180, the back side of the bar adjacent enlargement 17 6 is relieved belofw the plane dened by rear cam surface 171, as shown at 179.

Referring now to FIGURES 2, 6, and 7, the front end of the latch pin 180 is adapted to reciprocate in a bushed aperture in the mandrel provided by bushin-g 181 received in bore 182. The back end of the latch pin is slidab'ly supported 4in cylindrical socket 183 bored in the mandrel 10. The latch pin 180 is a bar having flat vertical

parallel sides

185, 186 and cylindrically curved upper and

lower surfaces

187, 188. The back end of the latch pin is bevefled as shown at 189, 190. The

curved surfaces

187, 188 slide on the inner surface of bushing 181 and inside socket 183 as the latch pin reciprocates forward and backward relative to barrel slot 27. The chisel point 192 formed by bevels y189, 190 cuts through any detritus accumulated in the socket and forces it out through the space between

ats

185, 186 and the interior of socket 183.

The thickness of the latch pin 180 between

sides

185, 186, is slightly less than the width of slot 175 in the cam bar 111 so that the latch pin can be passed through slot 175. A threaded hole 193 in the front end of the latch pin is adapted to receive a handling tool to facilitate insertion of the latch pin through mandrel bushing 181 and cam slot 175 into mandrel socket 183. This assembly is accomplished when the cam slot 175 is in alignment with the socket and bushing. To effect such assembly the barrel is moved along the mandrel to a position such that the barrel does not cover bushing 181 in the mandrel. The ow responsive unit comprising the `check valve actuating means can be lowered whenever the drill bit 40 is not connected to the mandrel, and by lowering the flow responsive unit the cam slot 175 can be brought into alignment with the mandrel bushing and socket.

Near the lmidportion of the latch pin, there is a thin section 200 connecting the `front and back ends ofthe latch pin. The thin portion has flat

parallel sides

201, 202.

Shoulders

203, 204, 205, 206 at the junctures o'f the fiat sides 185, 186 with at

sides

201, 202 provide the follower surfaces of lthe latch pin. These sides are inclined to the horizontal or cylinder axis of the latch pin at an angle x which is equal to the angle of inclination to the vertical of mandrel axis of

carn surfaces

170, 171. The perpendicular distance lbetween the `front follower surfaces 203, 204 and the back follower surfaces 205, 206 is slightly larger than the perpendicular ydistance between the front and back cam surfaces 170, 171, so as to make a loose sliding lit therewith.

During assembly, after the latch pin has been passed through bushing 182 and cam slot 175 into socket 191, the cam bar 111 is elevated. The thin connecting portion 200 of the latch pin enters the -thinner slot 173 in the cam bar 111, the cut away portion 179 on the back side ot the cam bar facilitating entry of cam surfaces 170, 171 between the lfollower surfaces olf the latc-h pin. Once the drill bit has been screwed into the mandrel, the cam bar can no longer be lowered suiciently to align slot with the latch pin, so that the latch pin is positively retained by the cam bar.

'Ilhe front end of the latch pin is of circular cross section, including a cylindrical guide portion 210 slidably mounted in the bushing 181. The bushing (see FIG. 2) has a flange 212 on its inner end supported by inwardly facing shoulder 213 between bore 182 and a counter bore 215 in the mandrel 10. The bushing is inserted through one end of the mandrel and pushed out against shoulder 213. An elastomer O-ring 216 (see FIG. 6) in annular groove 217 on the latch pin, seals the latch pin to the bushing.

The outer extremity or -tip 220 of the latch pin is coni cally tapered, flaring inwardly. This facilitates entry of the latch pin into slot 27. It also helps cam the latch pin inwardly should it not be Ifully retracted and the barrel need to ride over it.

The operation of the apparatus is simple. When drilling has proceeded to the limit of the downward travel of the mandrel 10 in the barrel, the mandrel is elevated to the upper limit of its travel. The pump is then shut off lowering the fluid pressure in the mandrel. This not only releases the hydraulic shoes of the anchor barrel from engagement with the wall of the well bore but allows spring 86 to `drive the cam bar 111 upwardly, forcing latch pin 1-80 into slot 27. The mandrel is then lowered, carrying the barrel down the well bore to a new |lower position. The pump is then turned on, causing iiuid pressure in the mandrel to` increase. This not only moves the hydraulic shoes of the anchor barrel to wall engaging position, but it drives the piston, piston rod, and choke downwardly. Downward movement of the piston rod moves the cam bar 111 downward, positively retracting Rlatch pin from slot 27. The motion of the latch pin is thus synchronized with that of the hydraulic shoes of the anchor barrel.

The overall operation of the invention with reference to the entire bit control 'apparatus may be more fully understood by reference to FIGURES 8, 9 and 10. As shown in FIGURE 8, the bit control apparatus includes mandrel 10 adapated to be screw connected to the lower end 249 (eg. a tool joint or sub) of a drill string by means of threaded pin 250. Axially and rotatably slidable on the mandrel is the barrel including spear portion 12, lower seal portion 251, lower bearing portion 252, anchor portion 253, middle bearing -portion 254, middle seal 255, upper bea-ring 256, and detritus seal 257. A port 258 in the mandrel opens into the pressurizable annular chamber or space 14 around the mandrel inside the barrel between the lower seal and middle seal. The

alignment spears

12, 20 rotate the barrel into predetermined azimuthal position relative to the mandrel whenever the spears are brought into engagement by elevating the mandrel relative to the barrel. Mandrel spear 20 and the sub 249 limit relative yaxial travel of the barrel and mandrel so that port 258 is always in communication with chamber 14.

Referring also to FIG. 9, there are a plurality of steel anchor shoes 260 radially reciprocatably mounted in the barrel. Elastomer seals 261 bonded to the shoes and to steel retaining rings 262 normally hold the shoes in retracted position, the rings having outwardly facing shoulders 263 bearing against inwardly facing shoulders 264 in the apertures 265 in the barrel. If desired, the bonded elastomer seals may be replaced bv sliding -seals so that the shoes are not biased toward retracted position but are merely movable to retracted position under external mechanized or huid pressure. Fluid pressure inside the mandrel exceeding that outside the barrel will extend the -anchor shoes into engagement with the wall 270 of the well bore. The shoes are asymmetrically disposed around the barrel to push the barrel and mandrel to one side of the hole as determined `by the azimuthal 7 positioning of the barrel. Upon drop in pressure the elast-omer seals retract the anchor shoes.

Referring also to FIGURE 10, latch pin 180 is seen to be extended into barrel slot 27. When uid pressure rises in the mandrel to extend the anchor shoes, the latch pin 180 will at the same time be retracted. When the mandrel pressure drops, retracting the anchor shoes, the latch pin will at the same time Ibe extended, provided the mandrel is positioned relative to the barrel to permit such extension. If not so positioned, the latch pin will remain retracted, acting backwards through the cam to prevent the spring 86 from moving cam bar 111 upwardly. Then as soon as the latch pin and slot come into register, the latch pin will be extended by the cam bar moving under the `force of the spring.

Whenever the latch pin 180 is in slot 27, not only can the barrel be moved up and down in the well bore with the mandrel to Ithe desired elevation but it can also be rotated to the desired azimuthal position; the alignment spears orienting the barrel relative to the mandrel and the mandrel orientation being known from a surveying instrument lowered through the drill string and oriented in receiver 127 by key 142.

While a preferred embodiment yof the invention has been described, many modifications thereof can be made by one skilled in the art without departing `from the spirit of the invention.

I claim:

1. Drill bit control apparatus including a tubular mandrel adapted to be connected in a drill string, a barrel disposed around the mandrel axially and rotatably slidable relative thereto, upper and lower seal means between the mandrel and barrel spaced apart axially defining the upper and lower ends of -a pressurizable annular chamber around the mandrel inside the barrel, means limiting the axial travel of the barrel relative to the mandrel, port means placing the interior of the mandrel in communication with the annular chamber in all positions of the barrel and mandrel within the limits of relative axial travel thereof, anchor shoe means radially reciprocably disposed in said barrel and extensible under pressure of uid transmitted to `said chamber from said mandrel, and latch means extendible from the mandrel into engagement with the barrel to prevent relative motion therebetween, said drill bit control apparatus being distinguished by the inclusion of means lfor retracting said latch means from engagement with the barrel in response to uid pressure in said mandrel in synchronism with the extension of said anchor shoe means thereby.

2. Subject matter of ella-im 1 further distinguished by said latch retraction means including cam means engaged with said latch means and fluid pressure responsive means for actuating said cam means.

3. Subject matter of claim 2 further distinguished by said latoh retraction means also serving as latch extension means. said cam means being movable between a position positively extending said latch means and a position positively retracting said latch means, said fluid pressure responsive means moving said cam means from one position to the `other according to the iluid pressure in said mandrel.

4. Subject matter of claim 3 further distinguished by said iluid pressure responsive means including piston means acting to move said cam means to latch retracting position and spring means acting to move said cam means to latch extending position.

5. Subject matter of claim 4 further distinguished by said cam means including a lbar axially reciprocable in said mandrel, said bar having guide surfaces correlative to and cooperable with the inner periphery of said mandrel and having parallel cam surfaces inclined at au acute angle to the axis of the mandrel, said latch means ihaving parallel follower surfaces cooperating with said cam surfaces and inclined at the same angle to the axis of said mandrel.

6. Subject matter of claim 5 further distinguished by said latch means having a thin connecting portion between said portions thereof lhaving said `follower surfaces, said cam bar having a slot therethrough dividing each of said cam surfaces into a pair of coplanar surfaces, said connecting portion of said latch means being slidably disposed in said slot.

7. Subject matter of claim 6 wherein said mandrel includes 1an aperture and said barrel includes a slot, said apparatus being further distinguished by said mandrel having a socket opposite said aperture, said latch means comprising a pin having a front end reciprocable in said aperture into and o'u't of said slot land having a back end reciprocable in said socket.

8. Subject matter of claim 7 further distinguished by said cam bar having a second slot therethrough connected to but larger than the first mentioned slot therethrough, said second slot being large enough to permit passage of said back end of the latch pin therethrough, said back end of the pin being too large to pass through the irst slot whereby to lock said pin in said cam bar when said pin is in said first slot.

9. Subject matter of claim 7 lfurther distinguished by said socket being cylindrical and said back end of the latch pin including cylin-drically curved surfaces cooperating with said socket, said pin having surfaces relieved below the cylindrical surfaces thereof to provide ilow passages between the socket and back end of the pin, the tip of the Iback end of the pin being beveled to a ohisel point.

10. Subject matter of claim 4 further distinguished by said iiuid pressure responsive means including `a tubular steel piston rod, said spring means being ooaxially disposed around said rod, said piston means being connected to the upper end of said rod, said piston rod having a choke disposed in its lower end, said spring means and piston rod land piston means being `disposed inside a sleeve ooaxially mounted in said mandrel and sealed thereto, said piston means being adapted to reciprocate within and seal with said sleeve, said apparatus including a check valve connected to the lower end of said sleeve, said check valve including a pivotally mounted closure, said closure having an elastomeric covering over its surface adjacent said sleeve to reduce fretting upon contact therewith of said piston rod when extended through said valve by fluid pressure in said mandrel.

References Cited UNITED STATES PATENTS 2,179,567 11/1939 Strength 175-73 2,316,409 4/ 1943 Downing 175-73 2,819,040 l/1958 James et al -76 3,042,125 7/1962 Duncan 175-73 3,105,561 10/1963 Kellner 175-230 3,326,305 6/1967 Garrett 175-230 X CHARLES E. OCONNELL, Primary Examiner RICHARD E. FAVREAU, Assistant Examiner U.S. Cl. X.R. 175-81