Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PATENT APPLICATION
SUCTION PORT LOCK NUT WITH STUB BUTTRESS THREADS
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of co-pending U.S.
Provisional
Application Ser. No. 61/138,776, filed December 18th, 2008, the full
disclosure of which is
hereby incorporated by reference herein.
1. Field of the Invention:
[00021 The present invention relates in general to reciprocating pumps and, in
particular, to an
improved apparatus for a locking nut in a reciprocating pump.
2. Description of Related Art
[00031 In oil field operations, reciprocating pumps are often used for various
purposes. Some
reciprocating pumps, generally known as "service pumps," typically pump
service fluids used for
downhole operations such as cementing, acidizing, or fracing a well. These
service pumps may
typically operate for relatively short periods of time, but on a frequent
basis such as several times
a week. Often they are mounted to a truck or a skid for transport to various
well sites.
[00041 The oil field reciprocating pumps typically include a plunger that
reciprocates within a
cylinder for pumping fluid through a cylinder. The cylinder generally includes
a fluid inlet and a
fluid outlet. An opening in the pump provides access to an interior of the
cylinder. The opening
is typically sealed with a threaded suction cover that can be removed from the
cylinder.
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Summary of the Invention
[0005] Disclosed herein is reciprocating pump assembly that includes a block
body, a cylinder
chamber in the block body, a plunger reciprocatingly disposed in the block
body, an opening in
the block body adjacent the cylinder chamber, threads formed in the opening, a
cover plate in the
opening, and a threaded surface on the outer periphery of the cover plate
engaging the threads
formed within the opening and projecting within the block body past the
threads on the opening.
The threaded surface on the cover plate may include at least two unloaded
threads that project
within the block body past the threads in the opening. The threaded surfaces
on the cover plate
can have a length of loaded threads that engage the threads in the opening,
and a length of
unloaded threads that project within the block body past the threads in the
opening and the length
of loaded threads is greater that the length of the unloaded threads. The
threaded surface on the
outer periphery of the cover plate can include threads having a root portion
with a curved profile.
The threaded surface on the outer periphery of the cover plate may have
British Butt threads.
The threaded surface on the outer periphery of the cover plate can include
threads having a thread
depth that is from about 60% to about 70% of the thread pitch. The threaded
surface on the outer
periphery of the cover plate can include threads having a truncated crest. At
least some of the
unloaded threads can be substantially identical to the loaded threads. The
threaded surface on the
outer periphery of the cover plate may include threads having a rear flank
disposed along a path
oriented at an angle of about 45 with respect to the angle of the cover plate
axis.
[0006] Also described is a reciprocating pump assembly that includes a
cylinder block, cylinder
chambers formed in the block, a plunger reciprocatingly disposed in each
cylinder chamber,
circular openings in the block at an end of each chamber, a thread formed in
the openings, and
cover plates. Where each cover plate has a thread formed on its outer
circumference, at least a
portion of the length of the thread being fully formed and at a maximum depth,
the cover plates
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coaxially coupled into each opening so that the maximum depth portion of each
cover plate
thread engages the portion of each thread in the openings proximate the ends
of each chamber.
Part of the maximum depth portion of each cover plate thread can be out of
engagement with and
further inward from the thread in the opening.
[0007] In an optional embodiment, a pump assembly is described having, a block
body, a
cylinder chamber in the block body, a plunger reciprocatingly disposed in the
block body, an
opening in the block body adjacent the cylinder chamber, threads formed in the
opening, a cover
plate in the opening, a threaded surface on the outer periphery of the cover
plate engaging the
threads formed within the opening and having at least two unloaded threads
projecting within the
block body past the threads on the opening, and a length of loaded threads
that exceeds the length
of the unloaded threads.
Brief Description of the Drawings:
[0008] Figure 1 is a side perspective view of a reciprocating pump in
accordance with the
present disclosure.
[0009] Figure 2 is a side partial sectional view of the pump of Figure 1.
[0010] Figure 3 is an enlarged side sectional view of a portion of the valve
stop assembly of
Figure 2.
[0011] Figure 4 is a side sectional view of a retainer nut of the valve stop
assembly of Figure
3.
[0012] Figure 5 is an enlarged sectional view of a threaded portion of the
retainer nut.
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Detailed Description of the Invention:
[0013] The apparatus and method of the present disclosure will now be
described more fully
hereinafter with reference to the accompanying drawings in which embodiments
are shown. This
subject of the present disclosure may, however, be embodied in many different
forms and should
not be construed as limited to the illustrated embodiments set forth herein;
rather, these
embodiments are provided so that this disclosure will be thorough and
complete, and will fully
convey the scope of the invention to those skilled in the art. Like numbers
refer to like elements
throughout. For the convenience in referring to the accompanying figures,
directional terms are
used for reference and illustration only. For example, the directional terms
such as "upper",
"lower", "above", "below", and the like are being used to illustrate a
relational location.
[0014] It is to be understood that the subject of the present disclosure is
not limited to the
exact details of construction, operation, exact materials, or embodiments
shown and described, as
modifications and equivalents will be apparent to one skilled in the art. In
the drawings and
specification, there have been disclosed illustrative embodiments of the
subject disclosure and,
although specific terms are employed, they are used in a generic and
descriptive sense only and
not for the purpose of limitation.
[0015] A reciprocating pump assembly 10 is illustrated in FIG. 1 in a side
perspective view.
The assembly 10 includes a pump section 12 coupled to a fluid cylinder portion
11. A crankshaft
housing 13 is shown covering the pump section 12 and shielding its components.
A plunger or
plunger rod 16 assembly is shown projecting from a side of crankshaft housing
13 to the cylinder
section 11. Stay rods 15 adjacent the rod assembly 16 anchor the cylinder
section 11 to the pump
section 10. The cylinder section 11 includes a cylinder block 17 having
multiple cylinder
chambers 39 (shown in dashed outline). Each cylinder chamber 39 is shown
herein in alternating
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fluid communication with a fluid inlet 19 and a fluid outlet 21. Each cylinder
chamber 39 end is
capped with a suction cover plate 22. An opening 18 is formed in the cylinder
block 17
configured to receive a cover plate 22. The pump assembly 10 can easily be
mounted to a trailer
that can be towed between operational sites, or to a skid such as for offshore
operations.
[0016] Referring now to FIG. 2, an example of the pump assembly 10 is
illustrated in a side
sectional view, In this example, a plunger 35 is shown reciprocatingly
disposed within one of the
cylinder chambers 39. Although a single plunger 35 is illustrated, each
cylinder chamber 39 may
include a corresponding plunger 35. Each cylinder chamber 39 and plunger 35
comprise what
may be referred to as a plunger throw, thus the pump assembly 10 of FIG. 1
comprises three
plunger throws. Pump assembly 10 embodiments exist having other than three
plunger throws
(i.e. a triplex), such as pump assemblies having four or more plunger throws.
[0017] A rotatable crankshaft 25 is shown within the crankshaft housing 13 and
as will be
described in more detail below, reciprocates the plunger 35 within the
cylinder chamber 39 when
it is rotated. The crankshaft 25 includes a main shaft 30 that connects to and
is rotated by a
motor (not shown). In one embodiment, a flywheel gear 24 is illustrated
mechanically
connecting to the crankshaft 25. Teeth on the flywheel gear 24 mesh with teeth
on a drive gear
26, and the drive gear 26 is attached to the motor. A crank pin 28 attaches to
the main shaft 30,
shown offset from and substantially parallel to the axis Ax of the crankshaft
25. An elongated
connector rod 27 is depicted having an end anchored around the crank pin 28
with a bearing
surface therebetween enabling the crank pin 28 to rotate with respect to the
connector rod 27. In
the embodiment of FIG. 2, the crank pin 28 is offset from the axis Ax of the
crankshaft 25, so
when the crankshaft 25 rotates, the crank pin 28 orbits the axis Ax of the
crankshaft 25. The
rotatable connection between the end of the connector rod 27 and crank pin 28
causes the
connector rod 27 to reciprocate.
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[00181 A cross head pin 31 attaches the connector rod 27 to a cross head 29 on
the end of the
connector rod 27 opposite where it attaches to the crank pin 28. As shown in
FIG. 2, the
connector rod 27 is substantially horizontally oriented; as the crankshaft 25
rotates, the connector
rod 27 will be oblique to horizontal. The cross head pin 31 allows the
connector rod 27 to pivot
with respect to the crosshead 29. The crosshead 29 is shown disposed within a
horizontally
oriented crosshead housing 32. Thus as the crank pin 28 orbits with crankshaft
25 rotation, the
attached connector rod 27 pivots and moves laterally back and forth within the
housing 13 to
reciprocate the crosshead 29 within the crosshead housing 32. A plunger rod 33
is illustrated
connected between the crosshead 29 and the plunger 35, thus when the crosshead
29 is
reciprocated by the rotation of the crankshaft 25, the plunger 35 is also
reciprocated within the
cylinder chamber 39.
[0019] An example of an inlet valve 41 is depicted within the cylinder block
17 and controls
fluid from the fluid inlet 19 into the cylinder chamber 39. The inlet valve 41
can open as the
plunger.35 reciprocates out of the chamber 39 to introduce fluid into the
chamber 39, and as the
plunger 35 reciprocates back into the chamber 39, the inlet valve 41 closes to
isolate the chamber
39 from the fluid inlet 19. As plunger 35 moves longitudinally away from
cylinder chamber 39,
the pressure of the fluid inside chamber 39 decreases creating a differential
pressure across inlet
valve 41, which actuates valve 41 and allows the fluid to enter cylinder
chamber 39 from fluid
inlet 19. The fluid being pumped enters cylinder chamber 39 as plunger 35
continues to move
longitudinally away from cylinder block 17 until the pressure difference
between the fluid inside
chamber 39 and the fluid in fluid inlet 19 is small enough for inlet valve 41
to actuate to its
closed position.
[0020] Fluid in the chamber 39 pressurized by the inwardly reciprocating
plunger 35 is
directed to a fluid outlet 21 shown formed within the cylinder block 17 and
adjacent the cylinder
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chamber 39. An outlet valve 43 is also shown in the cylinder block 17 set
between the fluid
outlet 21 and a cylinder block discharge 44. The outlet valve 43 controls
fluid from the fluid
outlet 21 to the cylinder block discharge 44. As plunger 35 begins to move
longitudinally
towards cylinder block 17, the pressure on the fluid inside of cylinder
chamber 39 begins to
increase, and continues to increase until the differential pressure across
outlet valve 43 exceeds a
set point. When the set point is exceeded, the outlet valve 43 opens to allow
the fluid to exit
cylinder block 17 through fluid outlet 21. In one embodiment, fluid is only
pumped across one
side of plunger 35, therefore pump assembly 10 is a single-acting
reciprocating pump. Valves 41
and 43 can be spring-loaded valves actuated by a predetermined differential
pressure.
[0021] A suction valve stop assembly 51 is illustrated in the cylinder block
17 adjacent the
suction cover plate 22. The suction valve stop assembly 51 comprises two
primary components:
a suction valve stop 53 and suction cover 55. The suction cover 55 is
generally cylindrical in
shape and is designed to be mounted sealingly in opening 18 in the cylinder
block 17.
[0022] Additional crank pins 28 may optionally be provided that are shown
illustrated offset
from the crankshaft axis Ax and at different locations around the
circumference of the crankshaft
25. This alternates when fluid is pumped from each cylinder chamber 39 within
the cylinder
block 17. As is readily appreciable by those skilled in the art, alternating
the cycles of pumping
fluid from each of cylinder chambers 39 helps minimize the primary, secondary,
and tertiary (et
al.) forces associated with pump assembly 10.
[0023] Referring now to FIG. 3, illustrated is an enlarged side sectional view
of the suction
cover plate 22 coupled to the opening 18 within the cylinder block 17. The
suction cover plate
22 includes threads 222 on its outer periphery shown mated with
correspondingly formed threads
172 on the opening 18 circumference. As shown, the threads 222 extend the
entire width of the
suction cover plate 22 and exceed the axial distance of the threads 172 of the
opening 18.
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Accordingly, some portion of the threads 222 on the cover plate 22 do not
engage threads 172 on
the opening 18. Pressure within the cylinder chamber 39 exerts a force against
an inner surface
23 of the cover plate 22, which transmits from cover plate threads 222 to the
opening threads
172. The threads 222 that do not engage the opening threads 172 will not
receive/transfer a load
to the threads 172, and thus are referred to herein as unloaded threads 224.
The threads 222
engaged with threads 172 can undergo a load and are referred to as loaded
threads 223.
100241 An arrow F illustrates the direction of the force applied to the cover
plate 22 by the
cylinder 39 pressure, Most of a load transferred between engaged threads
concentrates on the
first 2-3 threads adjacent the applied load; which in the example of FIG. 3
are the loaded threads
223 adjacent the unloaded threads 224. Since the first 2-3 of the loaded
threads 223 are in
roughly the middle portion of the plate threads 222, the thread depth is
substantially constant,
unlike the thread depth at either terminal end of the plate threads 222. The
process by which
threads are formed results in a thread depth typically being less at the
terminal ends of a thread
than at the thread middle portion. Thread depth is typically minimal at the
terminal ends of the
thread and increases to a fully formed thread having a maximum depth until
reaching the opposite
terminal end. In one exemplary embodiment, the loaded threads 223 transferring
the load from
the cover plate 22 to the cylinder block 17 are fully formed and at
substantially the maximum
depth. This minimizes a stress concentration within the threads 222 that might
occur if the
portion of the threads 222 directly adjacent the inner surface 23 were engaged
with the opening
threads 172. FIG. 3 provides an example of engaging threads in the inner
portion of the thread
222 length to prevent loading on an end of the thread 222 length where the
thread may not be
fully formed. Preferably, unloaded threads 224 comprise at least the first two
threads of the
combined set of threads 223, 224. Unloaded threads 224 have the same form as
loaded threads
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223. The length of the loaded threads 223 is greater than the length of
unloaded threads 224,
preferably at least twice.
[0025] The diameter of the opening 18 reduces along a curved profile 174 or
fillet past the
inner surface 23 of the suction cover plate 22 adjacent to the suction cover
55, where the profile
174 has a defined radius. In one embodiment the radius ranges from about 10%
to about 30% of
the distance between the opening 18 front and the shoulder formed by the
profile 174. An
advantage provided by the profile 174 is it better distributes stress loading
in the area of the
cylinder block 17 where the opening 18 necks down to the suction cover 55.
Unloaded threads
224 are located within a smooth cylindrical portion of opening 18 and do not
touch the wall of
opening 18
[0026] FIG. 4 provides a side sectional view of an example of the suction
cover plate 22. The
cover plate 22 is shown with threads 222 on its outer periphery and a socket
224 formed into the
cover plate 22. The socket 224 is shown coaxial with the cover plate axis Ap;
the socket 224 can
be profiled to receive a wrench for installing the cover plate 224 into the
opening 18.
[0027] An example of the threads 222 is depicted in a side cross sectional
view in FIG. 5. As
shown, the threads 222 each include a root portion 226 that is curved for
distributing forces along
the curve rather than allowing a stress concentration that can occur if the
cross section of the
thread root defined an angle. The threads 222 include a load flank 228, shown
optionally
disposed angled at about 70 with respect to the cover plate axis Ap and a
crest 230 that is
truncated rather than elongated. Crest 230 appears flat in a sectional view.
The rear flank 232 of
the threads 222 extends from the crest 230 to the root 226 along a path that
is at an angle oblique
to the cover plate axis A. The angle between the rear flank 232 and cover
plate axis Ap can be
around 45 in one exemplary example. In one embodiment, the threads 172 on the
opening 18
may be shaped and profiled as described in the embodiment of FIG. 5, and may
be described as a
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British Butt Thread. An advantage of employing the threads as depicted in FIG.
5 for use with
the present device is reduced stress concentrations at the thread root,
thereby reducing fatigue and
enhancing component useful life.
10028] While the invention has been shown in only one of its forms, it should
be apparent to
those skilled in the art that it is not so limited, but is susceptible to
various changes without
departing from the scope of the invention.
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