Motor driven drill assembly for oil wells and the like

May 3, 1966 κ. d. brown 3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962 7 Sheets-Sheet 1

<img file="US3249162A_D0001.tif" />

Kenard D. Brown

DV

<img file="US3249162A_D0002.tif" />

ATTORNEYS

May 3, 1966 κ. d. brown 3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962 7 Sheets-Sheet 2

<img file="US3249162A_D0003.tif" />

ATTORNEYS

May 3, 1966

K. D. BROWN

3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962

Sheets-Sheet 3

<img file="US3249162A_D0004.tif" />

<img file="US3249162A_D0005.tif" />

ATTORNEYS

May 3, 1966 κ. d. brown 3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962 7 Sheets-Sheot. λ

<img file="US3249162A_D0006.tif" />

<img file="US3249162A_D0007.tif" />

ATTORNEYS

May 3, 1966

K. D. BROWN

3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962

Sheets-Sheet 5

<img file="US3249162A_D0008.tif" />

<img file="US3249162A_D0009.tif" />

INVENTOR.

Kenard D. Brown

<img file="US3249162A_D0010.tif" />

ATTORNEYS

May 3, 1966 _K. d. brown 3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962 7 Sheets-Sheet 6

<img file="US3249162A_D0011.tif" />

INVENTOR.

Kenard D. Brown

<img file="US3249162A_D0012.tif" />

ATTORNEYS

May 3, 1966 κ. _{D BROWN} 3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Filed Nov. 23, 1962

<img file="US3249162A_D0013.tif" />

130 l itj. /4

INVENTOR.

Kenord D. Brown

<img file="US3249162A_D0014.tif" />

attorneys

3,249,162

Patented May 3, 1966

United States Patent Office

3,249,162

MOTOR DRIVEN DRILL ASSEMBLY FOR OIL WELLS AND THE LIKE

Kenard D. Brown, Wheatridge, Colo. (1227 S. Willow St., Casper, Wyo.)

Filed Nov. 23,1962, Ser. No. 239,563

Claims. (CI. 175—96)

This invention relates to drilling apparatus for oil wells and the like and particularly to an improved fluid motor driven drill assembly and control therefor which is effective for deep well drilling.

Drill bits of the grinding type which are employed for drilling deep wells are provided with very hard grinding materials such as carborundum and diamonds. The diamond bits commonly comprise small industrial diamonds of about the size of a grain of wheat embedded in a suitable matrix such as brass. These grinding bits operate very successfully provided their speed and loading are within optimum ranges. When operating a grinding bit on a conventional drill string of joined pipe the great weight of the string makes it extremely difficult to control the loading of the bit to assure efficient operation and minimum damage to the bit. Damage and breaking of the bits may result from bumping or dropping due to erratic control of the feed of the very heavy string during the drilling operation. Accordingly it is one object to this invention to provide an improved driving assembly for grinding bits used in deep well drilling which secures efficient operation of the grinding bit over extended periods of time.

It is another object of this invention to provide an improved driving and control assembly for grinding bits for drilling deep wells which may be operated efficiently with minimum likelihood of damage to the bit.

It is another object of this invention to provide an improved deep well drilling unit employing a grinding bit and which affords operation at high drilling rates.

It is another object of this invention to provide an improved fluid motor driving arrangement for deep well drilling and the like.

Much time is consumed in installing and removing the conventional drill strings, and in addition to this, it happens at times that the walls of the well may collapse or fill in above the drill and render removal even more difficult or even impossible. For example, the swelling of a bentonitic clay formation may close the well bore. In other cases the string may cut a slot or keyseat at a corner or turn in the well bore and render it very difficult to pull the drill assembly from the well. Accordingly it is a further object of this invention to provide an improved motor driven grinding drill assembly which may be reeled in and out of the well bore on a continuous supply tubing and may easily be retrieved regardless of closures or keyseat in the bore above the assembly.

It is another object of this invention to provide an improved control for fluid motor driven grinding bit assemblies.

Briefly, in carrying out the objects of this invention in one embodiment thereof, a drill assembly having a long cylindrical or tubular housing is provided with a rotatable fixture at its bottom end on which is mounted a grinding drill. The drill is driven by a rotary fluid motor arranged in the housing above the rotatable fixture. The motor is of a rotary blade impulse type and drives the rotatable fixture and drill through a pinion and a ring gear. A second fluid motor is mounted near the upper end of the housing and is connected to drive a grinding bit of upwardly pointing cone shaped configuration. A valve control is provided to direct the driving fluid alternatively to the upper or lower motors. The valve control is ar2 ranged to direct the fluid into the upper motor when the lower bit is raised, and overspeed or runaway of the drill caused by underloading is thus prevented. The driving of the upper drill makes it possible to retract the drill as5 sembly through restrictions occurring above the assembly.

The entire assembly is lowered into the well and retracted on a continuous flexible tubing, and a second or return tubing may also be employed to provide an escape path for discharged fluid in the event of plugging of the 10 well bore above the drill assembly.

The driving fluid is the drilling mud conventionally employed in oil well drilling, the material removed by the drill being returned to the surface with the mud. During the drilling operations the housing is prevented from ro15 tating by mechanism engaging the bore wall and which is retracted upon release of the drilling mud pressure.

_ The features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. The 20 invention itself, however, both as to its organization and manner of operation together with further objects and advantages thereof will be better understood upon reference to the following description taken in connection with the accompanying drawing in which:

²⁵ FIG. 1 is a diagrammatic view illustrating a section of an oil well and reservoir formation with an apparatus embodying the invention installed in position for operation;

FIG. 2 is an enlarged elevation view of the drilling unit ³⁰ of the apparatus of FIG. 1;

FIG. 3 is an enlarged elevation view partly in section of the lower end of the drilling unit of FIG. 1;

FIG. 4 is a side elevation view partly in section of a portion of the unit shown in FIG. 3 turned at ninety de³ gree thereto and with the drill broken away;

FIG. 5 is a sectional view taken along the line 5—5 of FIG. 3;

FIG. 6 is a sectional view of a portion of the unit ₄θ taken along the line 6—6 of FIG. 3;

FIG. 7 is an elevation view partly in section of the upper portion of the drill unit of FIG. 1;

FIG. 8 is a sectional elevation view similar to FIG. 7 illustrating the upper portion of the unit in position for _4g driving the upper drill;

⁰ FIG. 9 is a sectional plan view taken along the line 9—9 of FIG. 8;

FIG. 10 is an elevation view partly in section and partly broken away of the main body portion of the drill as₅₀ sembly;

FIG. 11 to a top plan view of the unit of FIG. 10;

FIG. 12 is a sectional elevation view of one of the ro- tation preventing elements of FIG. 10;

FIG. 13 is an enlarged view of one of the rotation pre₅₅ venting elements shown in FIG. 10;

FIG. 14 is an elevation view partly in section illustrating another embodiment of the invention; and

FIG. 15 is a fragmentary sectional view taken along . the line 15—15 of FIG. 14.,

Referring now to the drawings, FIG. 1 illustrates a drilling rig 10 directly over a well bore 11 within which a drilling unit or assembly 12 is suspended on a reinforced tubing 13 which extends upwardly through the well and over a pulley or wheel 14 and thence to a drum or bull ₆₅ wheel 15 driven by a motor 16. The drilling unit 12 has been illustrated as at the bottom of the well in a geologic section 17 and has a grinding bit 18 shown resting at the bottom of the well. The assembly 12 also includes an upper drilling bit 20 which is also of the grinding type.

₇₀ Both the bits 18 and 20 are driven by fluid motors mounted to be described below, the driving fluid being supplied through the tubing 13 by operation of a conventional mud

3,249,162 pump 21 which is connected to deliver drilling fluid or mud through a conduit 22 to a hollow shaft 23 of the drum 15 which shaft is connected to the tubing 22 in a manner well kno wn in the art. The fluid delivered through the conduit 22 passes first through a pressure regulator or pop-off control 24 and then through a flowmeter 25 before reaching the hollow shaft 23. Drilling fluid is supplied to the pump 21 through an inlet conduit 26 from a sump or reservoir 27.

The drilling fluid supplied through the tubing 13 is employed for drilling in a conventional manner. However, before it reaches the drill it passes through a fluid motor arranged within a lower portion 28 of the unit and drives the drill 18. In the normal course of drilling the exhausted drilling fluid flows upwardly through the well bore 11 and is returned to the sump 27. However, should an obstruction occur in the bore above the drilling assembly 12, such as that indicated generally at 30, the drilling fluid may be removed from the bore through a second tubing 31 secured to the top of the drill assembly at 32 and which passes over a wheel or pulley 33 and therice to a drum 34 driven by a motor 35. The drilling fluid flows into the tubing 31 at its end adjacent the drill 20 and flows from the tubing 31 into a hollow shaft of the drum 34 indicated generally at 36 and thence through a conduit 37 to the sump 27.

When it is desired to remove the drill assembly from the well the obstruction 30 may be removed by operation of the upper drill 20 which is driven by a fluid turbine or motor mounted within the upper portion of the unit as indicated at 38, the motors within the portions 28 and 38 being operated alternatively so that the driving fluid is supplied either to one or to the other depending upon the condition of operation of the drill assembly. When the drill assembly is moved upwardly against the obstruction 30 the drill 20 removes the obstruction and allows the drill assembly to be removed from the bore.

During the operation of either of the motors for driving the bits 18 and 20 rotation of the assembly is prevented by a plurality of upper and lower stop elements 40 and 41 which are forced into engagement with the walls of the well during the operation of either of the motors.

The outside appearance of the general features of construction of the. drilling unit are more clearly shown in FIG. 2. In this figure a set of jars 42 has been shown secured between the reinforced flexible hose 31 and the connector 32 so that the reinforced hose 31 may be employed to actuate the set of jars and facilitate releasing of the unit should it become stuck or wedged in position in the well bore.

The external surfaces of the tubings 13 and 31 are constructed of smooth tough plastic such as nylon which provides minimum friction with the material with which it may come in contact. For example, when the well is restricted as indicated at 30, the tubing may readily be moved up and down through the restriction because of its low friction. By employing the continuous reinforced tubing capable of carrying the load of the drill assembly, the time necessary to lower the drill assembly into position and to withdraw it from position is greatly reduced over that necessary when employing the conventional drill pipe which is handled in sections added as the pipe is being inserted in the well and withdrawn section by section as it is removed from the well.

Bits of the grinding type as illustrated in the drawing are very effective and operate efficiently provided they are not overloaded or underloaded. In order to avoid overloading of the bit 18 the motors 16 and 35 are provided with torque controls to compensate for the varying weights of the tubing as it is introduced into the well and withdrawn from the well. With this control the weight of the drill assembly is the effective maximum weight on the drill 18 regardless of the depth of the well. The control arrangement of the driving fluid supplied to the motor for the drill 18 is such that, in the event of underloading by virtue of a lifting force, for example, on the drill assembly, the fluid is diverted from the motor driving the drill 18 and operation of the drill at underloaded condition is prevented. Furthermore, this control also prevents over5 speed or runaway conditions of the drill 18 when underloaded or free in the well. The cuttings produced by the grinding type bit are small and readily carried away with the drilling fluid or mud by which they are carried to the surface.

The relatively light weight of the reinforced hose or tubing and its control by the torque control motors eliminates the difficult control present when a heavy string of conventional tubing is employed; the great weight of the conventional tubing makes it virtually impossible to control 15 the loading of the bit 18 and the hazard and possible breaking of the bit depends upon the skill of the operator, and the tremendous mass or weight of the drill string makes it virtually impossible to avoid occasional breaking and disintegration of the bits of the grinding type due to 20 the momentary drops or bumping of the drill string.

The construction of the motor within the casing 28 and its drive connection to the drill 18 are clearly shown in FIGS. 3, 4, 5 and 6. As shown in these figures the casing 28 is secured to the lower end of the barrel or 25 collar ,12 by a threaded fitting 45 and the drill 18 is threaded into a fitting 46 which is threaded onto a rotary collar 47 mounted for rotation in an annular space between the casing 28 and a sleeve or housing 48 threaded on the upper end of the casing as indicated at 50. Bear30 ing and sealing assemblies are provided between, the rotatable sleeve 47 and the· casing 28 and sleeve 48 as indicated at 51 and 52, respectively. The bearings in the assemblies 51 and 52 and indicated at 53 and 54, respectively, are of the radial ball bearing type. The bear35 ings 53 and 54 are mounted between packing assemblies 55 and 56, respectively, threaded onto the lower ends of the casings 28 and 48, respectively, and which are provided with Ο-ring seals as indicated at 57 and 58.

The upper end of the rotatable sleeve 47 is provided 40 with a ring gear 60 which is rotated by operation of an impulse-type rotor 61 mounted on a shaft 62 extending diametrically of the casing 28 and having a driving pinion 63 at its left end and an idler pinion 64 at its right end. In addition to the pinions 63 and 64, four other pinions at equally spaced intervals and indicated as 65, 66, 67 and 68 in FIG. 5 are employed to distribute the load evenly about the ring gear 60. The upward thrust from the drill 18 to the assembly is carried by these pinions and it is for this reason that the simple radial bearings 53 and 54 are employed. The shaft 62 is mounted in bearings 70 and 71 and is sealed by ring seals 72 and 73 mounted between the bearings and the interior passage of the casing 28.

The motor 61 comprises a rotor having buckets 76, _5g shown by way of example as four in number, each of which is shaped in the form of an elongated cup, as clearly shown in FIG. 3, so that the outer peripheries of the buckets 76 fit the wall of the interior bore or passage of the casing 28 and are spaced slightly there_6Q from to afford free movement. The mud or drilling fluid ^υ is directed against the blades by a nozzle or passage formed by a baffle 77 which is rigidly secured to the fitting 45 and extends downwardly and is provided with an opening 78 shown in FIG. 6 and positioned immediately _6g above the rotor 61. The nozzle opening 78 directs the fluid in a stream against the lefthand blade as indicated in FIG. 4 and leaves the blades to the right of this blade free to move in the fluid about the rotor.

The baffle 77 is formed to provide an upper sloping 70 portion 80 of generally semi-circular cross section and which is secured in the fitting 45, and with a lower cylindrical portion 80α fitting within the casing 28 and formed to provide the nozzle 78. Thus the liquid is directed into a conveying path and then at high velocity through 75 the nozzle opening and against the buckets 76.

3,249,162

The drilling fluid discharged from the motor 61 flows out through the fitting 46 and the hollow passage at the center of the drill 18 and thence about the drill through grooves 81 and thus enters the well bore, through which it is returned to the surface. The motor 61 thus operates to drive the ring gear 60 through the pinion 63.

The construction of the upper drill assembly and motor and the fluid flow control are shown in FIGS, 7, 8 and 9. As shown in these figures, the grinding drill bit 20, which is of generally conical configuration, is mounted for rotation about an upwardly extending sleeve or boss 82 which is an integral part of the housing 38. The bit 20 is carried on a motor assembly or cylinder 83 to which it is threadedly connected. The motor cylinder is mounted on a pair of lower ring type ball bearing assemblies 84 and an upper assembly 85, these assemblies carrying the thrust when the drill is moving up and down, respectively.

The drill 20 is provided with a multiplicity of holes 86 extending therethrough to afford escape of the driving liquid when it is discharged from the motor 83. The driving liquid is supplied to the motor 83 through six radial ports 87 formed in the lower end of the section 82 of the housing 38. These ports direct the liquid against a multiplicity of blades 88 and drive the rotor by the. reaction forces. The driving liquid, which is the drilling fluid, is supplied to the motor 83 from the tubing 13 under control of a valve assembly 90 when the valve is in the position illustrated in FIG. 8, wherein its four radial ports indicated at 91 are in communication with the radial ports 87 in the extension 82. The ports 91 and a second set of four radial ports 92 are formed in the lower end of.a tubular fixture 93 which is secured to the flexible tubing 13 by a detachable coupling 94.

The lower end of the tubular member 93 is closed as indicated at 95 and the portion of the tube in which the ports 91 and 92 are formed is of enlarged cross section so that a shoulder 96 is provided at the upper end which engages the bottom end of the interior wall of the extension 82 providing a shoulder indicated at 97. This pair of shoulders provides the lifting arrangement for the pump assembly since, when the reinforced tubing is lifted to raise the pump assembly, the tubular section 93 moves upwardly so that the shoulders 96 and 97 are in engagement. The enlarged lower end of the tubular portion 93 is provided with a ring seal indicated at 100 and the lower end of the passage in the extension 82 . is provided with a similar ring seal 98 which engages the tubular portion. These two seals prevent leakage around the tube between the two ends thereof.

When the tube 93 is in its position shown in FIG. 7, which is its lower position, the drilling fluid is directed into the lower portion and flows through passages 101 formed in a fitting 102 secured to the lower end of the casing 38. The fitting 102 is formed to provide a cylindrical lower portion or chamber 103 and a partition wall 104 through which a rod 105 extends from the tubular section 93 into the chamber 103. A compression spring is arranged within the chamber as indicated at 106 and engages the partition wall 104 and a disk 107 secured to the lower end of the rod 105 by a nut 108 locked to the rod. The tube 93 is thus biased toward its lower position, which is that of FIG. 7. When the reinforced tubing 13 is lifted to raise the drill assembly the spring 106 is compressed and the shoulders 96 and 97 of the tube 93 are engaged so that the tube 93 will lift the entire assembly. In this position the upper radial passages 91 are in communication with the motor passages 87 and the fluid is directed into the motor 83.

It will thus be apparent that, when the drill assembly is being employed for drilling, the valve assembly is in its lower position as indicated in FIG. 7 and the liquid is directed downwardly into the main housing 12 and thence to the lower motor 61. When the flexible tubing is raised to lift the drill assembly, the valve moves to its position as shown in FIG. 8 and the upper motor is actuated by the registry of the ports 91 with the motor ports 87. Thus as the drill assembly is moved upwardly, 5 should it strike an obstruction such as that indicated at 30 in FIG. 1, the drill 20 will remove the obstruction and afford ready passage of the drill assembly back up through the well bore 11. It will be understood that the fitting 102 is threaded into the top of the main body portion 12 10 of the drill assembly, suitable threads 110 being provided at the lower end of the fitting 102 for this purpose.

In the event the drill assembly is caught in the bore and does not become dislodged when the motor 16 is operated to raise the flexible tubing 13, the set of jars 42 15 may be brought into operation to facilitate the loosening of the drill assembly. The jars 42 are connected to the drill assembly through a link 111 engaging a perforated lug 112 which is attached to a collar 113 on the upper end of the extension 82. Thus the jars are operated to pro20 duce a hammering effect upwardly against the rigid body walls of the drill assembly.

During the operation of the drill assembly it is of course essential that the housing or main body portion be maintained stationary with respect to the wall of the well bore. 25 In order to lock the casing against the well bore an arrangement is provided which is actuated by the admission of drilling fluid under pressure to the main housing for driving the motor 61. This arrangement includes the radially movable elements 40 and 41 indicated in FIGS. 30 1 and 2 and more clearly illustrated in FIGS. 10 through 13. The elements 40 and 41 are of identical construction and this construction and the manner in which the elements operate will be understood from the following description of the elements 40.

Each of these elements, as clearly indicated in FIGS. 12 and 13, comprises a sharp edged wheel 113 mounted on a forked plunger or shaft 114 which passes through a retaining disk 115 held rigidly in position against the bottom of a bore 116 within the wall of the housing 12 ⁴⁰ by a threaded bushing 117 which has a passage of sufficient diameter to accommodate the wheel 113. Wheel 113 is normally urged into its retracted position within the recess in the bushing 117 by a compression spring 118 which is arranged between the plate 115 and a disk 120 45 at the end of the plunger 114. The disk 120 acts as a piston in a cylinder 121 comprising an extension of the bore 116 and which has a port 122 providing communication with the interior of the housing 12. It will now be apparent that, when the liquid under pressure is supplied 50 to the interior of the housing, the piston 120 will be moved outwardly and will force the wheel 113 out of its position in the bushing 117 and against the well bore as indicated in FIG. 2.

The wheel 113 is made in the form of a cutting wheel 55 so that when it engages the wall it readily cuts a groove which prevents radial movement of the drill assembly in the bore while affording movement along the bore. The plurality of these rotation preventing elements 40 and 41 is sufficient to assure nonrotation of the drill body dur60 ing the motor driven operation of either of the top or bottom drills.

As clearly shown in FIGS. 10 and 11, the main body portion 12 of the drill assembly is of heavy cylindrical construction with a bore 123 extending entirely- there65 through. The upper end of the housing 12 is provided with internal threads 124 for engagement with the lower end of the fitting 102 and the lower end of the housing is provided with external threads 125 formed on a reduced portion of the housing and which are provided to 70 engage the upper internal threads of the fitting 45 of the lower motor assembly.

It will now be apparent that the construction of the main body portion 12 is such that it may be made of any desired length, and, furthermore, one or more lengths 75 of the housing or drill collar may be employed depending

3,249,162 • 7 upon the weight of drill assembly desired for operation of the lower drill 18.

The drilling assembly described above may be designed so that at the rate of speed of the drills and the desired rate of supply of the drilling mud the drill may be turned and supplied with mud within an optimum operating range so that the most effective use of the grinding type drill is realized. The arrangement of the control valve assembly 90 minimizes the possibility of either overloading or overspeeding the drill during operation. Furthermore, the control is such that not only is the drilling fluid diverted from the lower drill motor when the assembly is raised, but in addition the upper motor is actuated and driven so that, should there be an obstruction in the well bore above the drill assembly, the upper drill will cut through the obstruction and facilitate removal of the equipment from the well.

The use of the smooth walled reinforced tubing for raising and lowering the drill assembly makes it possible to control the effective weight of the drill through torque controlled motors and lessens the time required for running the drill assembly into and out of the well.

Another embodiment of the invention is illustrated in FIGS. 14 and 15 wherein a drill assembly 127 is provided which includes a housing 128 having a collar 129 provided with threads 130 for attaching a conventional drill collar and drill bit in the usual manner. The assembly 127 is mounted for operation on a drill stem or tube 132 which has a section 133 of reduced cross section fitted within the cylindrical passage in the housing 128. The section 133 terminates in a stop member 134 and has a solid extension 135 of square cross section which fits in a square guideway 136 in the fitting 129. The guideway 136 is formed in a cylindrical body 137 secured on upper and lower spider arms 138 and 139 which afford free passage of the drilling fluid or mud through the fitting 129.

Mud for the drilling operation is supplied from the tube 132 through the hollow extension 133 and thence through ports 141 to passages 142 when the parts of the assembly are in the position illustrated, which is the position during lifting of the assembly. When the drill and assembly are resting on the bottom of the well, the extension 133 and member 135 move downwardly until the stop 134 engages a lower seat 143 in which position the ports 141 are in communication with passages 144 extending downwardly through the fitting 128 in communication with the interior of the fitting 129 so that the drilling mud is supplied to the drill collar and bit (not shown) attached to the lower end of the. assembly.

During normal operation of the drill assembly as illustrated in FIG. 14, the drill is actuated by rotation of the tubing 132 while drilling fluid is supplied under pressure through the ports 141 and downwardly through the assembly to the drill. When the assembly 127 is raised on the tubing 132, the ports 141 are placed in communication with the passages 142 as illustrated in the drawing and the drilling fluid then moved upwardly and out through a multiplicity of openings 146 in an upper coneshaped drill 147 which is threadedly secured to the fitting 128 and extends upwardly and inwardly about the tube 132. Should the drill assembly meet an obstruction in the well bore above the assembly, the rotation of the tubing 132 would effectively drill away the obstruction by operation of the drill 147, thus operating in a manner similar to the other embodiments described above.

The embodiment of FIGS. 14 and 15 thus provides an arangement for supplying drilling fluid selectively to a lower drill or to an upper drill in a manner similar to that of the other embodiments and thereby facilitates normal drilling operation as well as assuring ready removal of the drill assembly from the well bore regardless of obstructions which may have formed in the bore above the assembly.

•8

While this invention has been illustrated and described in connection with a specific structural arrangement, various modifications and other applications will occur to those skilled in the art. Therefore, it is not desired that the invention be limited to the details of construction illustrated and it is intended by the appended claims to cover all modifications which fall within the spirit and scope of the invention.