Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
,
The present invention relates generally to high
pressure fluid choke valve devices, and more particularly
to choke valve devices designed for use on oil and gas
wells.
One of the most potentially dangerous and expensive
occurrences confronting the petrochemical industry is well
blowouts. One device for preventing blowouts is the
hydraulic choke valve invented by Wesley F. Renfro, which
is the subject of Canadian Letters Patent No. 1,170,384,
issuPd July 17, 1984.
The Renfro device comprises a choke valve housing
that includes a high pressure fluid passageway extending
therethrough. A choke plug, adapted to fit sealingly
against a valve seat in the passageway in order to close
the passageway, is rigidly and non-rotatably affixed to
one end of a choke actuator assembly which extends
longitudinally within the choke valve housing. A worm
gear assembly rotates the actuator assembly, which drives
a ball screw and causes the actuator assembly and the plug
to move longitudinally within the choke housing in
alignment with the valve seat to open and close the valve.
Since the ball screw of the actuator assembly must rotate
to move longitudinally within the housing, the choke plug
is also rotated until it is tightly seated against the
valve seat in the high pressure fluid passageway.
When the choke valve is closed, the high pressure in
the upstream portion of the choke valve tends to hold the
plug against the valve seat with a tremendous force. To
retract the plug from the seat, the plug must rotate
relative to the ....... ~
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valve seat through a substantial angular displacemen-t while it
is in contact with the se~t beEore it is actually separated
from the seat. The forces holding the plug against the ~eat,
combined with a high coefficient of friction between the plug
and valve seat, create a high torsional resistance to the
rotational opening motion of the valve~ It has been found
that under especially high pressure conditions such torsional
resistance can strain or stall the motor operating the valve,
causing the valve to remain closed. Such high torsional
resistance can also cause premature wear and possibly breakage
of the plug wear material, damage to the means for mounting
the plug to the choke actuatox assembly and a tendency to
unscrew the valve seat. The torsional resistance to rotation
is also present when closing the valve.
SU~ARY A~D OBJECTS OF TH~ INVE~TION
In view of the foregoing limitations and shortcomings
of the prior art devices, as well as other disadvantages not
specifically ~entioned above, it should be apparent that there
still exists a need in the art for a means for opening and
closing a choke valve that does not create potentially
damaging and dangerous torsional resistance between the plug
and valve seat, especially during unusually high pressure
conditions. It is, therefore, a primary object of this
invention to fulfill that need by providing a choke device
wherein the choke valve operates with a significantly reduced
amount of torsional resistance between the plug and the valve
seat.
More particularly, it is an important object of this
invention to provide a high pressure choke valve wherein the
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choke plug can be separated from the valve seat with no or a
minimal amount of relative rotational motion between the plug
and the valve seat.
It is another object of this invention to provide a
high pressure choke valve wherein the choke plug is axially
driven into seating engagement with its seat with a reduced
amount of torsional resistance.
It is still another ob~ect of this invention to
provide a high pxessure choke valve having a rotating actuator
means engaged to a choke plug means in a substantially
rotationally independent manner.
Briefly described, the aforementioned objects are
accomplished according to the invention by providing a high
pressure choke valve wherein the choke valve plug is adapted
to translate into and out of contact with the valve seat in a
substantially non-rotational manner.
The device comprises a choke housing that includes a
high pressure fluid pa~sageway extending therethrough. A
choke valve plug, adapted to fit sealingly against a valve
seat in the passageway in order to close the passageway, is
aEfixed to one end of a choXe actuator assembly in a
substantially rotationally independent manner. The
non-rotational connection between the plug and actuator
assembly is provided axially by engaging an annular flange of
the actuator assembly between a thrust bearing and a split
bushing disposed within a blind bore located at one end of the
plug assembly. A drive means including a worm gear assembly
rotates the ball screw actuator assembly, which causes the
actuator assembly and the attached plug assembly to move
longitudinally within ~he choke valve housing in alignment
with the valve seat to open or close the valve. Because the
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plug and the actuator assembly are substantially rotationally
independent, the plug engages the valve seat with mini~al
relative rotational movement, thus eliminating the potentially
harmful torsional resistance present in the prior art choke
valve described above.
With the foregoing and other objects, advantages and
features of the invention that will become hereinafter
apparent, the nature of the invention may be more clearly
understood by reference to the following detailed description
of the invention, the appended claims and to the several views
illustrated in the attached drawings.
BRIEF DESCRIPTION OF TEIE DR~WINGS
Figure 1 is a cross-sectional perspective view of the
choke valve device of the present invention;
F gure 2 is a side elevation view, partly in section,
of the valve plug and actuator assembly of the present
invention shown mounted within the actuator assembly housing;
Figure 3 is a cross-sectional detail view of the
actuator assembly and end cover taken along line 3-3 of Figure
2; and
Figure 4 is an exploded side elevation view, partly
in section, of the means for connecting the actuator assembly
to the plug assembly.
DETAILED DESCRIPTION OF A PREFERRED EMBODIME~T
-
Referring now in detail to the drawings wherein like
parts are designated by like reference numerals throughout,
there is illustrated in Figure 1 a choke valve device 10.
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Fluids under high pressure enter the device 10 through
passagewa~ 12 and exit via passageway 14. Flanges 16 and 18
are adapted to inter-face with a gas well flow line (not
shown). A plug 20 moves longitudinally within the device 10
in alignment with passageway 14. Plug surface 22 fits
sealingly against the valve seat surface 24 in passageway 14
in order to close off the passageway.
The housing and body elements of the inventive
device, as seen in Figure~ 1-3, will now be described in
detail. A choke nut 26 secures an actuator assembly body 28
within the main choke body housing 32. A center housing 34 is
attached to the actuator asse~lbly body 28 by set screws 36 and
is further attached to an aft ball screw housing 38 by cap
screws 40. A bearing housing 29 is ~hreaded to the actuator
assembly body 28, and an inner housing 42 is rotatably mounted
within the aft screw housing 38 by bearings 44. Integrated
worm 48 and gear 50 are mounted within a gear case housing 52,
which is bolted to the aft ball screw housing 38 by socket
screws 54~
The portion of the inner housing 42 extending to the
right of the gear casing 52 (as seen in Figures 1 and 2) has
two opposing longitudinal slots 79 formed therethrough, and
high pressure-re~istant sight glass 58 is sealingly mounted
over each slot 79. A rear outer cover 56 is mounted over the
sight glasses 58 and the slotted portion of the inner housing
42. Corresponding slots 82 in the outer cover 56 are aligned
with the siyht glass 58 and slots 79 such that the slots 79
are visible from without the outer cover 56.
A stop plug 60 is threaded into a bore in the
right-hand end of the housing 42 and is secured within the
outer cover 56 by an end cap 62 which is bolted to the outer
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cover 56 by screws (not shown). The end cap 62 is provided
with an orifice 64 through which clear lubricating oil may be
added. ~ plug (not shown) fits in and seals the orifice 64.
Seals 46 are provided where needed between the various housing
elements as seen in E'igures 1 and 2.
Having now described the housing and body elements,
the interior elements and their relationship with the housing
and body will now be described in detail. A ball screw 66~
having helical grooves 68 formed therein, is mounted within
the bearing housing 29 and the inner housing 42.
Complementary helical grooves 70 are formed in the bearing
housing 29 and are aligned with the ball screw grooves 68 so
as to form a helical passageway in which ball bearings 72 are
located.
~ key 74 operatively engages the gear 50 to the inner
housing 42, such that rotation of the worm 48 and gear 50
causes the inner housing 42 to rotate within bearings 44. A
pin 76 extends through an opening in the ball screw 66 and is
secured by set screws (not shown). The ends of pin 76 extend
into slots 79 of the inner housing 42, and are visible from
without the outer cover 56 through sight glass 58 and outer
cover slots 82. The rotational motion of the inner housing 42
is transmitted to the ball screw 66 via the pin 76 and rotates
the ball screw within the bearing housing 29. When the ball
screw 66 rotates, the ball bearing and helical groove
arrangement between the bearing housing 29 and the ball screw
66 causes the ball screw to translate longitudinally within
the inner housing 42.
As the ball screw 66 moves through the inner housing
42, the pin 76 likewise moves through the slots 79. The
location of the pin 76 within slots 79 corresponds to the
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operating position of the choke valve, i.e., when the pin 76
is at the right end (as seen in Figures 1 and 2) of the slots
79, the valve is openl and when the pin 76 is at the left end
of the slots 79, the valve is closed.
The plug 20 is rigidly affixed to a plug assembly 78
in a conventional manner, such as a threaded engagement (not
shown). The plug assembly 78 is attached to the ball screw 66
by shaft 80 in a rotationally independent manner as described
in detail hereinafter. A set screw 94 reinforces the threaded
attachment means.
In the prior art Renfro device, the plug assembly 78
would be rigidly connected to the ball screw 66 by a shaft
similar to shaft 80, which would be integral with both the
plug assembly and the ball screw. Rotating the ball screw in
the appropriate direction in the Renfro device causes the ball
screw and plug assembly to rotate and move axially within the
choke device until the plug sealingly engages with the valve
seat to close off the passageway. To retract the plug from
the seat in the Renfro device, it was necessary that the plug
rotate against the seat while it was in contact therewith for
a certain angular displacement before it actually separated
from the seat. The forces holding the plug against the seat,
combined with the high coefficient of friction between the
plug and valve seat, created a high torsional resistance to
the operating motion of the valve. The torsional resistance
can strain or stall the motor operating the valve, causing the
valve to remain closed. The resistance can also cause
premature wear or breakage of wear material of the plug,
and/or damage to the means connecting the plug 20 to the plug
assembly 78.
The present invention is an improvement of the
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above-described Renfro device, in that it advantageously
includes means for driving the plug assembly axially wi-thin
the choke device without creating the potentially harmful
torsional resistance of the prior art device.
Referring now to Figure 4, an exploded view of a
means for connecting the ball screw 66 to the plug assembly 78
in a substantially rotationally independent relationship in
accordance with the present invention is illustrated. The
plug assembly 78 has a blind bore 82 formed at the right-hand
end thereof opposite the plug 20. A thrust bearing 84 is
located at the bottom of the bore 82. Shaft 80 is integrally
connected to the ball screw 66 and has an integral, outwardly
extending, circumferential flange 86 located at the end
thereof. The diameter of the flange 86 is slightly less than
the inside diameter of the bore 82 but is greater than the
diameter of the shaft 80. A split bushing 88 with a
circumferential flange 92 is placed around the shaft 80
between the shaft flange 86 and the ball screw 66. The
bushing 88 is then inserted with shaft 80 into the bore 82 and
the bushing flange 92 is bolted to the end surface of the plug
assembly 78 with screws 90. The flange 86 of shaft 80 is thus
interposed between the thrust bearing 84 and the split bushing
88, with minima] axial gaps between each bearing 84, 88 and
the bearing surfaces of flanye 86, as can be seen from the
broken portion of the plug assembly in Figure 2.
As will be appreciated by those skilled in the art,
the arrangement of Figure 4 may be reversed, that is, the
shaft 80 may be integrally formed with the plug assembly 78
and the bore 82 and thrust bearing 84 may be provided in the
end of the ball screw 66, confronting the plug assembly 78.
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Operation
To operate the device of the present invention, a
drive means (not shown) is used to drive worm 48, which in
turn drives worm gear 50. Gear 50, is secured to the inner
housing 42 by key 74, and accordingly rotates the inner
housing 42. The rotational movement of the inner housing 42
is imparted to the ball screw 66 by the walls of slots 79
through the pin 76. Accordingly, rotation of worm 48 results
in rotation of the ball screw 66.
Since the bearing housing 29 is stationary and does
not rotate with the ball screw 66, the ball bearings 72 in the
helical passageways formed between the bearing housing 2~ and
the ball screw 66 cause the ball screw 66 to move
longitudinally with respect to the bearing housing 29 and the
inner housing 42.
When the ball screw 66 moves to the left, as viewed
with respect to Figure 2, the flanga 86 on the end of shaft 80
abuts the thrust bearing 84 mounted in the blind bore 82 of
the plug assembly 78. The ~lange 86 rotates as it moves
longitudinally, engages the thrust bearing 84 and transmits
the axial component of the flange 86 motion with minimal
rotational motion. Thus, the ball screw imparts an axial
force to the plug assembly without causing substantial
rotation of the plug assembly. The minimal rotational force
transmitted to the plug assembly through the bearing 84
advantageously improves the seating of the plug 20 with the
valve seat 24.
When the ball screw 66 is rotated in the opposite
direction it will translate axially to the right, as viewed
with respect to Figure 2. The right-hand annular surface of
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flange ~6 abuts the left-hand end of split bearing 88 which is
bolted to the plug assembly 78. Bearing 88 likewise transmits
primarily the axiaL component of the movement of flange 86 and
retracts the plug assembly 78 from the valve seat 24 without
causing rotation of the plug 200 Accordingly, the torsional
resistance between the plug 20 and the valve seat 24 is also
avoided when the plug is unseated.
Although only a preferred embodiment is specifically
illustrated and described herein, it will be appreciated that
many modifications and variations of the present invention are
possible in light of the above teachings and within the
purview of the appended claims without departing from the
spirit and intended scope of the invention.
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