Patent Application
20200088000
The present invention relates to a bypass valve for connection in series with a tubing string within a wellbore which opens to release pressure in the tubing string when the pressure exceeds a prescribed pressure limit.
In performing various wellbore operations, it is common to pump fluid through a tubing string within a wellbore. Occasionally, pressure surges in the fluid being pumped can result in damage to various equipment, requiring costly and time-consuming repair. To minimize damage, tubing drains are sometimes connected in series with a tubing string in which the tubing drain includes a drain port which is opened by shearing action to release pressure; however, the tubing string must be removed from the wellbore to replace the sheared components in this instance which is also costly and time-consuming.
According to one aspect of the invention there is provided a bypass valve for use with a tubing string within a wellbore, the bypass valve comprising:
a tubular housing having a longitudinal passage communicating therethrough between longitudinally opposing ends of the tubular housing and a bypass port communicating from the longitudinal passage to an exterior of the tubular housing, the ends of the tubular housing being adapted to be connected in series with the tubing string;
a sliding sleeve supported on the tubular housing so as to be longitudinally slidable along the tubular housing in a first direction from a closed position preventing escape of fluid through the bypass port from the longitudinal passage of the tubular housing to an exterior of the bypass valve and an open position in which the bypass port is in open communication between the longitudinal passage and the exterior of the bypass valve;
a spring operatively connected to the sliding sleeve so as to bias the sliding sleeve relative to the tubular housing in a second direction towards the closed position;
a first sealing interface at a location which is offset from the bypass port in the first direction and which is arranged to maintain a fluid seal between the sliding sleeve and the tubular housing throughout movement of the sliding sleeve between the open and closed positions thereof;
a second sealing interface at a location which is offset from the bypass port in the second direction and which is arranged to maintain a fluid seal between the sliding sleeve and the tubular housing only in the closed position of the sliding sleeve;
the spring being adapted to apply a prescribed closing force to the sliding sleeve such that the spring is adapted to (i) retain the sliding sleeve in the closed position when pressure within the tubular housing which acts on the sliding sleeve through the bypass port is below the prescribed closing force of the spring, (ii) allow the sliding sleeve to be displaced from the closed position towards the open position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port exceeds the prescribed closing force of the spring, and (iii) displace the sliding sleeve into the closed position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port falls below the prescribed closing force of the spring.
The bypass valve of the present invention allows pressure in a tubing string to release at a set amount of fluid pressure, which forces a spring housing to move down a mandrel, pushing a metal seat of a sealing interface of the valve downward to allow the excess fluid to escape down the annulus. Pressure against an O-ring pushes the spring housing towards an open configuration. A coil spring is compressed upon assembly and when the pressure surge has reduced, the coil spring pushes the spring housing back up the mandrel to reseal a metal on metal seat on the mandrel. The coil spring keeps the spring housing sealed when the oil well is pumping fluid through the tubing string to surface and into the facilities. An increase in pressure in the tubing string forces fluid through the bypass ports on the mandrel and creates a hydraulic force on the O ring in the spring housing to push the housing down, releasing the unwanted pressure surge in the tubing string. Lock screws hold the compressed ring in place which keeps the seats mated and holding tubing pressure. The bypass valve will be threaded into the tubing string at a predetermined place by the oil company. Typical tubing drains are used five joints above the bottom hole pump assembly, but once they shear, the producer has to pull all the tubing in the well and replace the tubing drain. Pressure surges have been responsible for many costly well service jobs in the past. The bypass valve will be set at a lower pressure to shift open than the bottom hole tubing drain. The bypass valve can open and close many times in a year and will be changed out each time the tubing string and the downhole pump assembly are removed and re-ran by the oil company.
Preferably the second sealing interface comprises sealing faces on the tubular housing and on the sliding sleeve which are oriented transversely to a longitudinal direction of tubular housing, for example at an end of the sliding sleeve in the longitudinal direction of the sliding sleeve. In this manner, the sealing faces of the second sealing interface become separated from one another immediately upon displacement of the sliding sleeve from the closed position. The second sealing interface may comprise metallic sealing faces on each of the tubular housing and the sliding sleeve.
When the bypass valve is used in combination with a tubing string within the wellbore having a tubing drain connected in series with the tubing string in which the tubing drain is adapted to open when pressure within the tubing string exceeds a prescribed upper limit, preferably the prescribed closing force of the spring is adapted to be overcome by a prescribed intermediate pressure limit which is less than the prescribed upper limit of the tubing drain. In some instances, the bypass valve may be connected in series with the tubing string in proximity to a top end of the tubing string.
The bypass valve may further include a gate member supported on the tubular housing so as to be longitudinally slidable along the tubular housing independently of the sliding sleeve between an open position in which the bypass port is unobstructed by the gate member and a closed position in which the bypass port is closed by the gate member. When the gate member is closed, the sliding sleeve of the bypass valve is isolated from the pressure within the tubing string. Closing the gate member thus allows the pressure within the tubing string to be increased above the set point of a tubing drain so that the tubing drain can be forced open with pressure to drain the tubing string if desired without the bypass valve releasing the pressure from the tubing string.
In some embodiments, the sliding sleeve may be supported externally of the tubular housing, and the gate member may be supported internally within the tubular housing.
When used with an insert pump having a working barrel defining an outer diameter, the gate member may comprise a tubular sleeve having a main portion with a first internal diameter and a seat portion with a second internal diameter which is reduced relative to the first internal diameter and which is arranged to receiving the outer diameter of the working barrel of the insert pump seated therein. In this instance, the second internal diameter of the seat portion of the gate member preferably frictionally receives the outer diameter of the working barrel of the insert pump by interference fit therein such that the gate member is movable between the open and closed positions thereof together with longitudinal displacement of the working barrel of the insert pump relative to the tubing string.
The tubular housing may further include a retainer recess formed in an inner wall of the tubular housing. In this instance, the gate member may include a locking portion which is biased from an unlocked position in which the locking portion does not interfere with displacement of the gate member between the open and closed positions, towards a locked position in which the locking portion protrudes from an outer diameter of the gate member so as to be received in the retainer recess in the open position of the gate member for retaining the gate member in the open position.
The retainer recess may comprise an annular groove in the inner wall of the tubular housing and the locking portion may comprise a plurality of fingers extending axially from one end of the tubular housing to respective free ends of the fingers supporting respective protrusions thereon which are received within the annular groove in the open position of the gate member.
According to a second aspect of the present invention there is provided a bypass valve for use with a tubing string within a wellbore having a tubing drain connected in series with the tubing string in which the tubing drain is adapted to open when pressure within the tubing string exceeds a prescribed upper limit, the bypass valve comprising:
a tubular housing having a longitudinal passage communicating therethrough between longitudinally opposing ends of the tubular housing and a bypass port communicating from the longitudinal passage to an exterior of the tubular housing, the ends of the tubular housing being adapted to be connected in series with the tubing string;
a sliding sleeve supported on the tubular housing so as to be longitudinally slidable along the tubular housing in a first direction from a closed position preventing escape of fluid through the bypass port from the longitudinal passage of the tubular housing to an exterior of the bypass valve and an open position in which the bypass port is in open communication between the longitudinal passage and the exterior of the bypass valve;
a spring operatively connected to the sliding sleeve so as to bias the sliding sleeve relative to the tubular housing in a second direction towards the closed position;
the spring being adapted to apply a prescribed closing force to the sliding sleeve such that the spring is adapted to (i) retain the sliding sleeve in the closed position when pressure within the tubular housing which acts on the sliding sleeve through the bypass port is below the prescribed closing force of the spring, (ii) allow the sliding sleeve to be displaced from the closed position towards the open position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port exceeds the prescribed closing force of the spring, and (iii) displace the sliding sleeve into the closed position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port falls below the prescribed closing force of the spring;
the prescribed closing force of the spring being adapted to be overcome by a prescribed intermediate pressure limit which is less than the prescribed upper limit of the tubing drain.
According to a further aspect of the present invention there is provided a bypass valve in combination with a tubing string within a wellbore, the bypass valve comprising:
a tubular housing having a longitudinal passage communicating therethrough between longitudinally opposing ends of the tubular housing and a bypass port communicating from the longitudinal passage to an exterior of the tubular housing, the ends of the tubular housing being connected in series with the tubing string;
a sliding sleeve supported on the tubular housing so as to be longitudinally slidable along the tubular housing in a first direction from a closed position preventing escape of fluid through the bypass port from the longitudinal passage of the tubular housing to an exterior of the bypass valve and an open position in which the bypass port is in open communication between the longitudinal passage and the exterior of the bypass valve;
a spring operatively connected to the sliding sleeve so as to bias the sliding sleeve relative to the tubular housing in a second direction towards the closed position;
the spring being adapted to apply a prescribed closing force to the sliding sleeve such that the spring is adapted to (i) retain the sliding sleeve in the closed position when pressure within the tubular housing which acts on the sliding sleeve through the bypass port is below the prescribed closing force of the spring, (ii) allow the sliding sleeve to be displaced from the closed position towards the open position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port exceeds the prescribed closing force of the spring, and (iii) displace the sliding sleeve into the closed position when the pressure within the tubular housing which acts on the sliding sleeve through the bypass port falls below the prescribed closing force of the spring;
the bypass valve being connected in series with the tubing string in proximity to a top end of the tubing string.
One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:
In the drawings like characters of reference indicate corresponding parts in the different figures.
Referring to the accompanying figures there is illustrated a tubing string bypass valve assembly generally indicated by reference numeral 10. The bypass valve assembly is particularly suited for use in a tubing string 12 which is positioned to extend longitudinally within a wellbore 14, for example for use in a variety of wellbore operations.
The wellbore 14 is formed in the ground and lined with a casing in the usual manner. The tubing string 12 extends longitudinally down into the wellbore from a wellhead 16 at surface so as to define a tubing passage 18 extending longitudinally through the tubing string and an annular passage 20 extending longitudinally within the wellbore in the annular space between the tubing string and the surrounding casing. The tubing string in the illustrated embodiment is formed of jointed sections of pipe 22 which are connected in series with one another using threaded connections.
According to a first embodiment of the present invention, a pump 24 is shown supported at the bottom end of the tubing string for pumping fluids upwardly through the tubing string under pressure. A tubing drain 26 is shown connected in series with the tubing string at a location in close proximity to the pump but spaced upwardly above the pump. The tubing drain is a conventional, commercially available tubing drain of the type including a sliding sleeve operable between a closed position and an open position relative to fluid ports in which shear pins are used to retain the sleeve in the closed position. When pressure from the tubing string exceeds an upper limit of the tubing drain, the pins will shear causing the sleeve to be irreversibly displaced towards the open position. Further pumping operations must cease until the tubing string is pulled up to surface for servicing the tubing drain to replace the shear pins so that pumping operations can resume.
The bypass valve assembly 10 according to the present invention is shown connected in series with the tubing string in proximity to the top end of the tubing string. The bypass valve assembly 10 has a pressure threshold associated therewith which is arranged to be less than the upper pressure limit associated with the tubing drain. In this manner, when pressure exceeds the pressure threshold of the bypass valve, the bypass valve assembly will open to release pressure and allow the pressure to fall before the tubing drain is sheared open. As soon as the pressure within the tubing string falls below the pressure threshold of the bypass valve assembly, a biasing mechanism of the bypass valve assembly automatically returns the valve assembly to the closed position so that pumping operations can continue without interruption.
The bypass valve assembly 10 includes a tubular housing 30 which is elongate a longitudinal direction of the tubing string. An external threaded connector 32 is formed at the first bottom end of the tubular housing for threaded connection with an adjacent section of pipe of the tubing string. A collar 34 is formed at the top end of the housing in which the collar defines an upper portion of the tubular housing which is enlarged in outer diameter relative to a remaining lower portion of the tubular housing therebelow such that the tubular housing is stepped in profile along the length thereof. A socket is formed within the collar at the top end of the housing which is internally threaded for forming a threaded connection with an adjacent section of pipe 22 of the tubing string thereabove. A longitudinal passage extends fully through the tubular housing between opposing top and bottom ends thereof for open communication with the longitudinal passage extending through the tubing string.
The stepped profile of the outer diameter of the tubular housing 30 results in an annular end face 36 at the inner or bottom end of the collar 34 of the tubular housing. The annular end face defines a first metal sealing face which forms a groove therein extending about the circumference of the tubular housing in which the groove has a V shaped profile in the radial direction.
The tubular housing also includes a plurality of bypass ports 38 formed therein to communicate radially from the longitudinal passage within the tubular housing to an exterior of the tubular housing at an intermediate location along the lower portion of the tubular housing spaced below the collar 34 at the top end of the tubular housing. The bypass ports 38 are circumferentially spaced from one another about the circumference of the tubular housing.
A sleeve 40 is mounted so as to be slidable longitudinally along the lower portion of the tubular housing between a closed position preventing escape of fluid through the bypass ports 38 and an open position in which fluid is permitted to escape through the bypass ports from the longitudinal passage to the exterior of the tubular housing. The sleeve 40 has an outer diameter along the length thereof which is approximately equal to the outer diameter of the collar 34 at the top end of the tubular housing. The interior diameter of the sleeve is stepped in profile to define (i) an upper portion 42 having an interior diameter which is greater than the outer diameter of the housing to define an annular gap therebetween and (ii) a lower portion 44 below the upper portion which is reduced in interior diameter relative to the upper portion so that the interior diameter of the lower portion is very close to the outer diameter of the lower portion of the tubular housing.
A top end of the sleeve 40 defines an annular end face 46 which forms a second metal sealing face thereon which is also annular about the circumference of the tubular housing. The annular end face 46 forms an annular protrusion having a V-shaped profile in the radial direction which mates with the profile of the end face 36 of the collar 34.
An O-ring 48 is received within an annular groove within the inner cylindrical surface of the lower portion 44 of the sleeve 40. The O-ring spans a radial gap between the sleeve 40 and the tubular housing 30 to form a first sealing interface between the sliding sleeve and the tubular housing. The O-ring 48 forming the first sealing interface is engaged between longitudinally oriented faces of the sleeve and the tubular housing respectively so as to maintain a fluid seal at the first sealing interface throughout sliding movement of the sleeve 40 longitudinally along the tubular housing 30.
In further embodiments, the O-ring may be replaced with a variety of other sealing materials, for example including a hard coat on the axially oriented surfaces to define a first sealing interface that maintains relative sealing between the sleeve 40 and the housing 30 throughout sliding movement of the sleeve relative to the housing.
In the closed position of the bypass valve assembly, the sleeve 40 is located at the uppermost position so that the end face 46 thereof abuts the end face 36 of the collar 34 of the tubular housing so that the corresponding metal sealing faces of the sleeve and the tubular housing define a second sealing interface between surfaces oriented transversely to the longitudinal sliding direction. In this manner the sealing faces of the second sealing interface only provide a fluid seal when the sleeve is in the closed position directly abutted against the collar; however, the fluid seal is immediately broken as soon as the sealing faces become separated from one another upon any slight movement of the sleeve away from the collar and away from the closed position.
In further embodiments, the metal sealing faces on the sleeve 40 and on the collar of the housing 30 may be coated with a variety of different materials which provide a seal against liquid penetration therebetween when the valve is closed.
A coil spring 50 is used for biasing the sleeve towards the closed position. The spring 50 is helical about a longitudinal axis oriented in the longitudinal direction of the tubular housing so that the spring is compressed axially to produce biasing of the sleeve in the longitudinal direction towards the closed position.
A lower collar 52 is mounted onto the lower portion of the tubular housing below the sliding sleeve 40 and the coil spring 50 at a location which causes axial compression of the coil spring 50 between the lower collar 52 and the sliding sleeve. The lower collar 52 has an interior diameter which is approximately equal to the outer diameter of the housing at the lower portion thereof, however no sealing function is required across the lower collar. An annular groove 54 is formed in the exterior of the lower portion of the tubular housing at the location of the lower collar such that a plurality of locking screws 56 can be threaded radially into the lower collar 52 so that the inner ends of the screws align with and are received into the annular groove 54. The locking screws are provided at evenly spaced apart positions about the full circumference of the lower collar to secure the lower collar against axial displacement relative to the tubular housing.
In order to assemble the bypass valve assembly, the O-ring 48 of the sliding sleeve is received within the groove thereof and the sleeve is then longitudinally and slidably mounted over the bottom end of the tubular housing. The coil spring 50 is then mounted onto the lower portion of the housing below the sliding sleeve followed by the locking lower collar 52 being mounted onto the lower portion of the housing below the coil spring. The lock screws are used to set the lock collar in fixed position along the tubular housing with the coil spring compressed between the lower collar and the sliding sleeve.
The bypass valve assembly is mounted in series with the tubing string adjacent the top end thereof using the threaded connections between adjacent sections of pipe 22 of the tubing string. The location of the bypass valve assembly ensures that the valve opens when pressure within the tubing string exceeds the threshold pressure determined by the compression of the coiled spring in order to protect surface equipment that receives the pressure flow from the tubing string in operation.
A suitable spring is selected and suitably compressed by the lower collar 52 such that the compression of the spring generates a sufficient biasing force to urge the sleeve into the closed position and retain the sleeve in the closed position until pressure within the tubular housing exceeds the pressure threshold of the valve assembly. When the pressure exceeds the pressure threshold, pressurized fluid will flow through the ports into the annular gap between the tubular housing and the sliding sleeve so that the pressure of the fluid will push downwardly on the O-ring 48 for urging the sliding sleeve downwardly against the biasing force of the spring 50. Immediately upon displacement of the sliding sleeve away from the closed position, the excess pressure will cause fluid to escape through the second sealing interface by the separation of the metal sealing faces on the sliding sleeve and the collar of the tubular housing respectively such that the escaping fluid causes a pressure reduction within the tubing string. When the pressure within the tubing string returns below the pressure threshold, the biasing force of the coil spring will overcome the force of the pressurized fluid within the tubing string such that the bypass valve assembly will immediately return to the closed position thereof. The process repeats automatically each time the pressure increases above the pressure threshold of the valve assembly as determined by the coil spring.
Turning now to the second embodiment shown in
The insert pump is represented schematically in
The working barrel 102 defines a hollow pumping chamber 105 therein which is enclosed at the top end by a top wall 106 having a plurality of outlet ports 108 communicating therethrough. The top wall 106 also includes a central sucker rod passage 110 for receiving a sucker rod 112 longitudinally slidable therethrough. The pumping chamber is also enclosed at a bottom wall 114 locating a central inlet port 116 therein. A standing valve is defined within the working barrel by a ball 118 which can be seated on the inlet port 116 for closing the inlet port. The ball 118 on the inlet port 116 can be opened by a fluid pressure below the inlet port which exceeds the fluid pressure in the pumping chamber to lift the ball 118 upwardly off of the inlet port seat.
A plunger body 120 is received within the pumping chamber 105 while being coupled to the bottom end of the sucker rod 112 for longitudinal displacement relative to the tubing string and the working barrel 102 together with reciprocating movement of the sucker rod within the tubing string. The plunger body includes an outer diameter which closely fits within the inner diameter of the pumping chamber and which supports a plurality of inner seals 122 about the circumference thereof to maintain a sealing interface with the inner wall of the pump chamber so as to maintain a pressure differential across the plunger body within the pumping chamber while enabling the plunger body to be reciprocated longitudinally along the length of the pumping chamber. The plunger body includes a hollow plunger chamber 124 therein which communicates openly with the upper portion of the pumping chamber 105 above the plunger body through outlet ports 126. An inlet port 128 is provided through a bottom wall of the plunger body at a central location for communication of the plunger chamber with the lower portion of the pumping chamber below the plunger body. A travelling valve is defined by a ball 130 arranged to be seated on the inlet port 128 within the plunger chamber. Similarly to the standing valve, the travelling valve remains closed when pressure above the ball within the plunger chamber exceeds pressure below the ball within the lower portion of the pumping chamber; however, a greater pressure in the lower pumping chamber causes the ball 130 to be lifted from the inlet port 128 to allow upward flow from the lower pumping chamber into the inner plunger chamber.
The bypass valve 10 according to the second embodiment is substantially identical to the bypass valve described above with regard to the first embodiment with the exception of a gate member 140 being provided within the interior of the tubular housing. The gate member 140 comprises an inner sleeve having an outer diameter closely matching the inner diameter of the tubular housing 30 of the bypass valve while the inner diameter of the gate member corresponds approximately to the inner diameter of the tubing string along the main portion of the inner sleeve. The gate member further includes a seat portion 142 toward the bottom end of the inner sleeve in which the interior diameter is reduced from the first interior diameter of the main portion to a second interior diameter that corresponds approximately to the outer diameter of the working barrel 102 of the insert pump 100. More particularly the outer diameter of the working barrel is received within the seat portion of the gate member 140 by interference fit to frictionally couple the pump with the gate member. The stop flange 104 on the working barrel of the insert pump ensures that the pump cannot be pushed through and below the seat portion 142 of the gate member.
The gate member is longitudinally slidable within the tubular housing 30 of the bypass valve between an open position shown in
The gate member 140 further includes a lock portion in the form of a plurality of lock fingers 146. The lock fingers 146 are defined at an end portion of the gate member extending axially outward beyond the main portion of the gate member at the bottom end thereof. The lock fingers each extend longitudinally outward to respective free ends at circumferentially spaced locations about the circumference of the gate member. Each lock finger 146 defines a radial protrusion 148 at the free ends thereof which extend radially outward beyond the outer diameter of the inner sleeve of the gate member in a relaxed and un-flexed position of the lock fingers. In the open position of the gate member, the radial protrusions 148 of the lock fingers are aligned with an annular groove 150 formed in the interior wall of the tubular housing which receives the radial protrusions therein. In order to displace the gate member toward the closed position, sufficient axial force must be applied to cause the free ends of the fingers to be displaced inwardly until the radial protrusions 148 are contained within a boundary defined by the outer diameter of the remainder of the inner sleeve of the gate member. The fingers remain biased to an unflexed and unlocked position to effectively retain the gate member in the open position thereof. By applying sufficient axial force to flex the fingers against their outward bias, the protrusions can be released from the annular groove as the gate member is displaced to the closed position.
In use, the insert pump 100 is supported on the end of a sucker rod 112 and is lowered into the tubing string with the sucker rod. Urging the sucker rod downwardly once the pump reaches the bypass valve is sufficient to seat the working barrel 102 into the seat portion 142 within the interior of the gate member 140. The resulting interference fit therebetween enables the gate member to be displaced between the open and closed positions thereof by raising and lowering the working barrel of the insert pump relative to the tubing string under control of the positioning of the sucker rod 112. Once the pump has been seated and the gate member is displaced to the open position, the lock fingers 146 will retain the gate member in the open position while the sucker rod is further longitudinally displaced to reciprocate the plunger body 120 along the full length of the pumping chamber to effect pumping of fluid up the tubing string during normal operation of the pump. As the plunger body is displaced downwardly, pressure buildup in the lower pumping chamber due to the closed standing valve 118 causes fluid to be forced upwardly through the plunger body into the upper portion of the pumping chamber. As the plunger body returns upwardly to the top of the pumping chamber, fluid in the upper pumping chamber is forced up the tubing string due to the closing of the travelling valve. Simultaneously, a low-pressure zone is defined within the lower pumping chamber below the plunger so that fluid pressure below the insert pump induces upward flow through the standing valve into the lower pumping chamber. The pump continues to reciprocate to pump fluid up the tubing string. The bypass valve in this instance operates in the usual manner as described above to relieve any excess pressure above a prescribed threshold pressure of the bypass valve 10. If servicing is required, an operator can pull upwardly on the sucker rod to unseat the pump from the seat portion 42; however, the gate member will be displaced upwardly into the closed position with the upward movement of the sucker rod prior to unseating of the insert pump from the seat portion of the gate member 140. In the event that the pump cannot be released from the seat portion 142, upward displacement of the sucker rod still enables displacement of the gate member into the closed position. Once the gate member is closed, fluid can be pumped into the tubing string to raise the pressure within the tubing string above the shearing threshold of the tubing drain to shear the tubing drain open. The annular seals between the gate member and the surrounding tubular housing 30 of the bypass valve isolate the sliding sleeve 40 of the bypass valve from the pressure within the tubular housing so as to enable sharing of the tubing drain open even if the bypass valve normally functions to relieve pressure at a lower threshold than the shearing threshold of the tubing drain. Once the tubing drain has been opened and the tubing string has been drained through the tubing drain, the drained tubing string can be more readily pulled up for servicing.
Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.
This application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 62/844,938 filed May 8, 2019 and U.S. provisional application Ser. No. 62/731,377, filed Sep. 14, 2018.
| Number | Date | Country | |
|---|---|---|---|
| 62844938 | May 2019 | US | |
| 62731377 | Sep 2018 | US |
