Note: Descriptions are shown in the official language in which they were submitted.
1
ZERO RESTRICTION BALL VALVE INSERT, ONE-PIECE CAGE AND
ASSEMBLY
FIELD OF THE INVENTION
[0001] The
present invention relates generally to a ball check valve of the
type used in downhole reciprocating pumps of the artificial lift system. More
particularly, relates to an improved insert, a one-piece cage and their
assembly
for ball check valve.
BACKGROUND
[0002] In
hydrocarbon recovery operations, an artificial lift system is
typically used to recover fluids from a well in a subterranean earth
formation.
Common artificial lift systems include positive displacement reciprocating
pumps such as "sucker rod pump". The pump comprises a plunger positioned
within a barrel. The plunger is coupled to a lower end of a reciprocating rod
or
rod string, which may be referred to as "sucker rods" or "rod string". Plunger
is a
part of the traveling assembly and the barrel is a part of the standing
assembly.
A traveling valve is located either above or below the plunger and a standing
valve is located at the bottom of the barrel. The standing valve and the
traveling
valve each include a ball check valve. The traveling valve moves up and down
under the action of a pumping unit. The movement of the traveling valve within
the barrel draws the fluid to the surface.
[0003] The
upward travel of the traveling valve may be referred to as
"upstroke" and the downward travel may be referred to as "downstroke". On the
upstroke the ball check valve in the traveling valve closes thereby causing
the
fluid situated above the traveling valve to be moved upward. Simultaneously,
the ball check valve of the standing valve opens there by allowing fluid to
enter
the portion of the pump barrel located between the traveling valve and the
standing valve. This portion of the pump barrel located between the traveling
valve and the standing valve may be referred to as "pump intake". On the
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downstroke, the ball check valve opens thereby allowing fluid to pass through
the traveling valve so that it can be lifted upward upon the next
reciprocation
thereof. Meanwhile, the ball check valve of the standing valve closes,
preventing downward movement of fluid therethrough.
[0004] In general, ball check valves comprise a vertically oriented
cylindrical cage/housing and a ball positioned in the cage allowing continuous
opening and closing of the valve. The cage comprises of ball guides and ball
stop to keep the ball inside the cage. In other cases, the ball is positioned
in an
insert and the insert is securely held inside the cage. A seat is positioned
below
the ball which provides a seal surface for the ball to sit while providing a
fluid
seal. The seat is held in its place with a seat plug screwed and torqued
against
the seat underneath. It has been found that in either of the scenarios where
the
ball is received inside, they do not provide a full open flow. This causes
restriction in the flow area compared to the fluid flow area available through
the
seat underneath. Any such restriction in the fluid flow causes pressure drop,
loss of production and inefficiency. Such fluid flow restriction also causes
sucker
rods to buckle in the downstroke. Such buckling causes sucker rods to break
and rub against the well tubing. Which leads to holes in the well tubing and
increases wear and tear in the entire pumping system causing premature
failures.
[0005] Further more, referring to the prior art CA2435601C and general
practice, a diametrical clearance of 0.762 mm [0.03 in] or greater is
maintained
between the ball and the inside bore of the insert, this causes the ball to
rattle
rapidly during the fluid flow through the valve. Such rattling action of the
ball
leads to premature failure either by cracking or wearing off the insert and
the
cage.
[0006] Traditionally the insert is securely held inside the cage using
interference or shrink fit and friction welding methods. Two pieces of
cage/housing is friction welded around the insert as shown in the prior art US
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patent 6,029,685A. An interference or shrink fit between ball receiving insert
and cage is formed by making the outside diameter of the insert equal to or
bigger than the inside diameter of the cage cavity. Interference fit causes
fluid
restriction by restricting the fluid flow area around the ball. Interference
fit also
causes radial stress on the insert. Friction welding process subjects insert
to
undergo high axial compression stress. Such pre-stress causes the insert to
crack while in service or during the assembly process. It is found that the
friction
welded cage breaks apart at the welded region when installed in high pressure
deeper well bores causing the ball check valves to fail inside the pump.
[0007] Another way of holding the insert inside the cage is by
multiple
pieces of cage/housing with threaded connections are screwed together with a
rubber gasket to provide a fluid seal. It has been found that the gasket leaks
when in service, and the assembly of threaded connections are prone to
premature failure under the stresses imposed by pumping operation. The
assembly of multiple pieces of cage/housing with threaded connection is
referred in US patent 2,294,568A.
[0008] Any such failure requires the removal of the down hole pump
incorporating the ball check valve to the surface for disassembly and repair,
a
costly and time-consuming operation. The use of the traditional ball receiving
insert and the use of friction welding, conventional welding techniques or the
threaded connections to join the component parts of the cage assembly of a
ball
check valve leads to similar problems.
SUMMARY OF INVENTION
[0009] The present invention comprises an improved insert, a one-piece
cage and their assembly method for ball check valves which overcomes the
foregoing and other problems long since associated with the prior art. The
improved insert assembled in the one-piece cage provides an open flow without
causing fluid restriction in comparison with the fluid flow area available
through
the seat. The improved insert keeps the ball received inside from rattling
during
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reciprocating pump action there by preventing premature failure of the insert.
The improved insert is positioned inside the cage cavity whose inside diameter
is bigger than the outside diameter of the insert there by creating a more
fluid
flow area. The ball receiving insert is retained in place within the one-piece
cage
by a fluid seal screw thread connection there by preventing the insert from
undergoing pre-stress caused by other assembly processes. The improved
cage comprises a unitary, i.e., one-piece construction eliminating the need
for
assembling multiple pieces of cage/housing together.
[0010] In
accordance with more specific aspects of the invention, the
insert preferably comprises a unitary, i.e., a one-piece construction. The
insert
may be formed from hard, tough, wear and corrosion resistant material sold
under the trademark STELLITE , however, other, similar materials may be
used in the practice of the invention, if desired. Similarly, the improved
cage
comprises a unitary, i.e., a one-piece construction that may be formed with a
high strength and high corrosion resistant materials.
[0011] Other
aspects and features of the present disclosure will become
apparent to those ordinarily skilled in the art, upon review of the following
description of the specific embodiments of the disclosure.
[0012] The
present disclosure will be better understood having regard to
the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG.
1 is a side cross-sectional view showing an insert and a
cage/housing assembly in accordance with the prior art;
[0014] FIG.
2 is an exploded side cross-sectional view of FIG. 1 showing
an insert, two pieces of cage/housing, ball, seat and seat plug in accordance
with the prior art;
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[0015] FIG. 3 is a perspective view of the insert used in accordance
with
the prior art;
[0016] FIG. 4 is a top view of the insert of FIG. 3;
[0017] FIG. 5 is a side cross-sectional view of a four-piece insert
guided
cage assembly in accordance with the prior art;
[0018] FIG. 6 represents exploded side cross-sectional view of FIG. 5
showing an insert, two pieces of cage/housing, ball, seat and seat plug in
accordance with the prior art;
[0019] FIG. 7 is a side cross-sectional view of a sucker rod pump
assembly used to recover fluids from a well in a subterranean earth formation.
Traveling assembly is shown positioned inside the standing assembly;
[0020] FIG. 8 is an exploded side cross-sectional view of a sucker rod
pump assembly of FIG. 7 in accordance with the prior art;
[0021] FIG. 9 is a side cross-sectional view of the ball check valve
assembly showing the insert, one-piece cage and their assembly with the ball
unseated and in contact with the stop, incorporating the preferred embodiments
of the present invention; and
[0022] FIG. 10 is a side cross-sectional view like FIG. 9, showing the
ball
seated in the seat;
[0023] FIG. 11 is an exploded view illustrating the ball check valve
assembly shown in FIG. 9 and FIG. 10, comprising of a side sectional-view of
the one-piece cage and side view of the insert, ball, seat and seat plug in
accordance with the preferred embodiments of the present invention;
[0024] FIG. 12 is a side view of the insert of FIG. 9 with the
ribs/ball
guides shown perpendicularly inclined with respect to the base of the insert;
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[0025] FIG. 13 is a top view of the insert of FIG. 12;
[0026] FIG. 14 is a perspective view of the insert of FIG. 12 in
accordance with the present invention;
[0027] FIG. 15 is a perspective view of the insert of FIG. 12 with a
ball
valve seated in place; and
[0028] FIG. 16 is a perspective view like FIG. 15, showing the ball
valve
unseated and in contact with the stop.
[0029] FIG. 17 is a bottom perspective view of the insert of FIG. 12;
[0030] FIG. 18 represents a variation of the bottom perspective view
of
the insert of FIG. 12; showing clutches on the bottom side of the insert;
[0031] FIG. 19 is a perspective view of the insert with its ribs/ball
guides
helically inclined in accordance with the present invention; FIG. 19
represents a
variation of the features of the insert of FIG. 14;
DESCRIPTION
[0032] In an artificial lift system, a sucker rod pump 45 is used to
draw
fluid to the surface using a reciprocating pump action. A sucker rod pump in
general comprises of a standing assembly 50 and a traveling assembly 40 of
FIG. 7 and FIG. 8. Referring to FIG. 7, traveling assembly 40 is securely
positioned inside the standing assembly 50. The upper end of the traveling
assembly 34 is connected to the sucker rod string. The rod string in turn is
connected to a surface unit that provides a reciprocating pump action. The
reciprocating action of the pumping unit causes the traveling assembly 40 to
move upward and downward thereof. A traveling ball check valve 32 is located
either above or below the traveling assembly 40 and a standing ball check
valve
44 is located at the lower portion of the standing assembly 50. The upward and
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downward movement of the traveling valve 32 inside the pump intake chamber
42 draws fluid to the surface.
[0033] Further detailing, on the upstroke the ball check valve in the
traveling valve 32 closes thereby causing fluid situated above the traveling
valve
32 to be moved upward. Simultaneously, the ball check valve of the standing
valve 44 opens there by allowing fluid to enter the portion of the pump barrel
located between traveling valve and the standing valve. This portion of the
pump barrel located between the traveling valve and the standing valve may be
referred to as "pump intake" 42 of FIG. 7. On the downstroke, the ball check
valve 32 of the traveling assembly 40 opens thereby allowing fluid to pass
through the traveling valve so that it can be lifted upwardly upon the next
reciprocation thereof. Meanwhile, the ball check valve 44 of the standing
assembly 50 closes thereby preventing downward movement of fluid
therethrough.
[0034] In general, ball check valves comprise a vertically oriented
cylindrical cage and a ball positioned in the cage for reciprocation to open
and
close the valve, the cage comprises of ball guides and ball stop to keep the
ball
inside the cage. In other cases and according to prior art, as referred to in
FIG.
1 the ball 18 is positioned in an insert 14 and the insert is securely held
inside
the cage/housing 16. A seat 20 is positioned below the ball which provides a
seating surface for the ball to sit while providing a fluid seal. The seat 20
is held
in its place with a seat plug 22 screwed and torqued against the seat
underneath using a screw thread connection 26. The insert 14 is held inside
cavity 17 of the cage 16 using interference or shrink fit. A shrink fit 8 is
formed
by making the outside diameter of the insert equal to or slightly bigger than
the
inside diameter of the cage/housing cavity 17 of FIG. 2. Interference fit
causes
radial stress on the ball receiving insert. It is found that these radial
compression stresses cause the insert to crack. After the insert is secured in
the
cage 16 the rest of the cage assembly is done by friction welding 24 cage 12
to
cage 16 as referred in Fig 1. The friction welding prevents the insert from
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moving upward during the movement of the ball inside the insert. It is found
that
the friction welded cage breaks apart at the welded region when installed in
high
pressure deeper well bores causing the ball check valves to fail inside the
pump.
[0035] FIG. 5 refers to an alternate method for insert and cage
assembly
according to prior art. The insert 14 is dropped inside the cage 16 against a
shoulder 6. The shoulder 6 prevents the insert from moving further down. Cage
12 is screwed and torqued into cage 16 by keeping a gasket 24 in between the
top ring face 7 of the insert and bottom face 9 of the cage 12. The assembly
of
cage 12 and cage 16 is formed by the screw threads 28 keeping the insert 14
from moving upwards during the movement of the ball inside the insert bore 19.
It has been found that the gasket leaks when in service, and the assembly of
threaded connections are prone to premature failure under the stresses
imposed by the pumping operation.
DESCRIPTION OF THE PREFERRED EMBODIENT
[0036] Referring now to the drawings, and particularly to FIG. 9,
there of,
there is shown a ball check valve assembly 100 comprising the preferred
embodiment of the present invention. The ball check valve 100 comprises an
improved insert 120 and an improved one-piece cage 110 for the ball check
valves. The improved cage comprises a unitary, i.e., a one-piece construction
eliminating the need for assembling multiple pieces of cage together. The one-
piece cage 110 has an insert receiving cavity 111 formed at the top end of the
fluid seal thread 113 and there by extended upwards as also shown in FIG. 11.
[0037] The cage assembly 100 includes an insert 120 which is formed
from a hard, tough, wear resistant material. Preferably, the insert 120 is
formed
from a material sold under the trademark STELLITE , however other suitable
materials may be used in the practice of invention, if desired. Importantly
the
insert 120 comprises a unitary, i.e., a one-piece construction.
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[0038] Referring to FIG. 12 and FIG. 14, The unitary insert 120
comprises
a bottom ring 132 at the lower end thereof which extends upwards to form a
fluid seal threads 131. The end of threads 131 extends to form a top ring 127
from which vertically spaced ribs 124 are formed extending upwards. The ribs
124 extend upwards and converge at the top towards the longitudinal axis
forming a dome shaped ball stop 122. The converged ribs form circumferentially
spaced arched side openings 138. The side openings 138 span from the top
face 125 of the top ring 127 to the point of convergence 129 of the insert.
[0039] As best shown in FIG. 14, 17 and 19, the ribs 124 extend
upwards
either perpendicularly or inclined helically to the base 126. The extended
ribs
converge at the insert's longitudinal axis forming a dome shaped cavity. As
shown in FIG. 17 the ribs 124 extend upward forming an inward arch 122 is
referred to as the ball stop. The bottom surface 123 of the ribs 124 are
converged at longitudinal axis to provide a smooth hemi-spherical stop surface
122 for engaging and restraining upward movement of the ball 140 as shown in
FIG. 16. The convergence of the ribs as explained form circumferentially
spaced, full open arched windows for the fluid to exit outwardly and upwards
there by eliminating obstruction in the fluid flow. An upwardly directed
conical
protrusion 121 is formed and extended from the point of convergence 134 of the
ribs 124. This conical protrusion 121 directs the fluid upwards and reduces
the
formation of eddies or vortices in the fluid flow and there by lowering
pressure
drop.
[0040] As best shown in FIG. 12 and FIG. 14 the base 126 of the insert
is
formed in the shape of a ring to provide a cylindrical passageway 133 along
the
insert bore 128. The insert bore 128 receives a ball valve 140 that can move
upwards and downwards inside the insert. The valve ball 140 can sit on the
annular seat 150 to close the passageway 133 as shown in FIG. 15, or it can be
displaced upwards by the fluid pressure from below as shown in FIG. 16. When
the ball 140 is unseated, fluid in the passageway 133 flows outwardly through
the side openings 138 and around the ball 140 thereby moving upwardly. The
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diametrical clearance between the valve ball 140 and the inside diameter of
the
insert bore 128 may be less than .381mm [0.015 in]. Such small clearance
prevents the ball from rattling inside the insert bore when fluid flows
through the
passageway 133, thereby reducing the failure of the insert, due to the ball
beating the ball guides 123.
[0041] As
best shown in FIG. 11, the unitary cage 110, i.e., a one-piece
in construction, has a cavity 111 that receives the unitary insert 120. The
cage
cavity according to an aspect of the disclosure may begin at the top end of
the
thread feature 113 and there by extended upwards. The screw threads 113 in
the cage correspond to the screw threads 131 on the insert 120. These screw
threads 113 and 131 are of primarily taper thread form that can hold the
insert in
place simultaneously forming a fluid seal connection between the cage and the
insert. However, other thread forms and any suitable means may be used
including, but not limited to threaded connection in the practice of
invention, if
desired.
[0042] As
represented in FIG. 9 and FIG. 11, the insert when screwed
into the corresponding cage thread 113, the ribs, ball stop, conical
protrusion
forming section 139 of the insert is received in the cage cavity 111. The
outside
diameter 136 of the insert ribs 124 will remain smaller than the inside
diameter
112 of the cavity 111. There by creating an annular region 135 for the fluid
to
flow around the ball outwardly and there by exiting upwardly. This annular
region 135 corresponds and supplements to the fluid flow area to provide a
full
open zero restriction fluid flow around the ball valve. Thereby promoting high
volumetric fluid flow therethrough.
[0043] The
one-piece cage 110 as described earlier supports a
cylindrical seat 150 positioned underneath the insert 120, allowing the ball
valve
140 to seat thereby providing a fluid seal. The seat 150 is held in place by a
seat plug 160 screwed and torqued against the seat forming a threaded
connection between seat plug thread 161 and cage thread 115.
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[0044] As
best shown in FIG. 18 there are clutches 143 formed on the
bottom of the base ring 137 extending downwards. These clutches 143 can be
engaged with a torqueing tool to screw and torque the insert 140 into cage
110.
However, various modifications and variations of these features may also be
implemented. These clutches 143 are removed by machining process to form a
smooth seal face 137 on the bottom of the insert. The process of removing
clutches is carried out after the establishment of secure fluid seal threaded
connection 113 between the insert 120 and one-piece cage 110.
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