Note: Descriptions are shown in the official language in which they were submitted.
PUMPING SYSTEM SHAFT CONVERSION ADAPTER
RELATED APPLICATIONS
[001] This application claims the benefit of United States Provisional Patent
Application Serial No.
62/535,224 filed July 20, 2017 entitled "Pumping System Shaft Conversion
Adapter."
FIELD OF THE INVENTION
[002] This invention relates generally to the field of submersible pumping
systems, and more
particularly, but not by way of limitation, to a mechanism for converting
shafts used in multistage
centrifugal pumps.
BACKGROUND
[003] Multistage centrifugal pumps are used in a variety of submersible and
surface-based
applications. In these pumps, each "stage" includes a rotating impeller and a
stationary diffuser. A
shaft keyed only to the impellers transfers mechanical energy from the motor.
During use, the
rotating impeller imparts kinetic energy to the fluid. A portion of the
kinetic energy is converted to
pressure as the fluid passes through the downstream diffuser. As the fluid is
pressurized and moved
through the pump, force pushes against the impellers in the opposite
direction. This force is generally
referred to as "down thrust." "Up-thrust" occurs as fluid moving through the
impeller pushes the
impeller upward. Centrifugal pumps have a flow rate equilibrium point where
the up thrust and
down thrust generated by the impellers are balanced. Lower flow rates cause
excess down thrust,
while higher flow rates may cause excess up thrust. To prevent damage to the
pump, the up thrust
and down thrust must be controlled using one or more thrust bearings.
[004] In many multistage pumps, the impellers are placed onto the pump shaft
and compressed
between a pair of two-piece rings located at opposite ends of the pump shaft.
This design is often
referred to as a "fixed impeller" pump and the thrust generated by the
collection of impellers is
transferred to the "compression shaft" through the lower two-piece ring. The
thrust is carried by the
compression shaft into a large thrust bearing that is often located in a seal
section that is adjacent to
the pump.
[005] In some cases, it is desirable to use a "floating impeller" design in
which the impellers are not
all linked together under compression. In a floating impeller design, the
impellers are allowed to
move in an axial direction along the shaft during operation and the down
thrust generated by the
impellers is not transferred through the shaft to a dedicated thrust bearing.
Instead, the down thrust
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created by the impellers is offset by "bearing stages" positioned at intervals
within the pump. The
impellers must be free to move independently between bearing stages to
transfer the thrust to the
bearing stages.
[006] A standard "floater" shaft utilizes snap rings to hold the impellers,
spacers and other
components to the shaft and allow for free axial movement of the impellers.
Existing floater shafts
thus include specific grooves at specified locations on the shaft to
accommodate the snap rings.
These grooves are not typically present on a compression shaft. Efforts to
retrofit compression shafts
to accommodate a floating impeller design are expensive and time consuming
because the snap ring
grooves must be added to the compression shaft. There is, therefore, a need to
develop an adapter
system that permits the facilitated conversion of a compression shaft into a
floater shaft. It is to these
and other objects that the present invention is directed.
SUMMARY OF THE INVENTION
[007] In one aspect, embodiments of the present invention include a pump for
use in a motorized
pumping system. The pump includes a shaft that has a lower ring groove and an
upper ring groove.
The pump also includes a lower adapter and an upper adapter. The lower adapter
has a pair of lower
ring halves configured to fit within the lower ring groove and the upper
adapter has a pair of upper
ring halves configured to fit within the upper ring groove. The pump further
includes a plurality of
stages that each have a stationary diffuser and a rotating impeller. The
rotating impellers are
connected to the shaft with a keyed connection that permits the impeller to
axially travel along the
shaft.
[008] In another aspect, an embodiment of the invention includes a method for
converting a
compression shaft to a floater shaft, where the compression shaft includes an
upper ring groove and a
lower ring groove that are respectively capable of holding an upper two-piece
ring and a lower two-
piece ring to apply compression to an impeller stack disposed along the
compression shaft. The
method includes the steps of placing an upper adapter into the upper ring
groove, placing one or
more impellers on the shaft, placing one or more standard spacers on the shaft
and placing a lower
adapter into the lower ring groove.
BRIEF DESCRIPTION OF THE DRAWINGS
[009] FIG. 1 is an elevational view of a submersible pumping system.
[010] FIG. 2 is a cross-sectional view of the pump from the submersible
pumping system of FIG. 1.
[011] FIG. 3 is a close-up, cross-sectional view of several stages from the
pump of FIG. 2.
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[012] FIG. 4 is a close-up, perspective, cross-sectional view of the upper
adapter near the head of
the pump.
[013] FIG. 5 is a cross-sectional view of the head of the pump with upper
adapter.
[014] FIG. 6 is a close-up, perspective, cross-sectional view of the lower
adapter in the base of the
pump.
[015] FIG. 7 is a cross-sectional view of the base of the pump with the lower
adapter.
[016] FIG. 8 is a close-up, cross-sectional view of the upper adapter.
[017] FIG. 9 is a close-up, cross-sectional view of the lower adapter.
[018] FIG. 10 is a perspective view of the lower adapter.
WRITTEN DESCRIPTION
[019] FIG. 1 shows an elevational view of a pumping system 100 attached to
production tubing
102. The pumping system 100 and production tubing 102 are disposed in a
wellbore 104, which is
drilled for the production of a fluid such as water or petroleum. As used
herein, the term
"petroleum" refers broadly to all mineral hydrocarbons, such as crude oil, gas
and combinations of
oil and gas. The production tubing 102 connects the pumping system 100 to a
wellhead 106 located
on the surface. Although the pumping system 100 is primarily designed to pump
petroleum
products, it will be understood that the present invention can also be used to
move other fluids. It
will also be understood that, although each of the components of the pumping
system are primarily
disclosed in a submersible application, some or all of these components can
also be used in surface
pumping operations.
[020] It will be noted that although the pumping system 100 is depicted in a
vertical deployment in
FIG. 1, the pumping system 100 can also be used in non-vertical applications,
including in horizontal
and non-vertical wellbores 104. Accordingly, references to "upper" and 'lower"
within this
disclosure are merely used to describe the relative positions of components
within the pumping
system 100 and should not be construed as an indication that the pumping
system 100 must be
deployed in a vertical orientation.
[021] The pumping system 100 includes a pump 108, a motor 110 and a seal
section 112. In some
embodiments, the motor 110 is an electrical motor that receives power from a
surface-mounted
motor control unit (not shown). When energized, the motor 110 drives a shaft
that causes the pump
108 to operate. The seal section 112 provides for the expansion of motor
lubricants during operation
while isolating the motor 110 from the wellbore fluids passing through the
pump 108. Although
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only one of each component is shown, it will be understood that more can be
connected when
appropriate. It may be desirable to use tandem-motor combinations, multiple
seal sections, multiple
pump assemblies or other downhole components not shown in FIG. 1. For example,
in certain
applications it may be desirable to place a seal section 112 below the motor
110.
[022] Turning to FIG. 2, shown therein is a cross-sectional view of the pump
108. The pump 108
includes a pump housing 114, a head 116, a base 118, a shaft 120, and a
plurality of stages 122. As
shown in the close-up view of FIG. 3, each of the plurality of stages 122
includes a diffuser 124 and
an impeller 126. The impellers 126 are connected to the shaft 120 with a keyed
connection that
permits axial movement of the impeller 126 along the shaft 120. In this way,
the impellers 126 are
permitted a limited amount of axial "float" between adjacent diffusers 124.
[023] As illustrated in FIG. 3, the stages 122 in the pump 108 are configured
as either floating
stages 128 or bearing stages 130. In each floating stage 128, the impeller 126
transfers hydraulic
load to the lower or upstream impeller 126 through a standard spacer 132 that
passes through the
diffuser 124 without interference or contact. In each bearing stage 130, the
impeller 126 transfers
down thrust through a spacer 132 to a bearing spacer 136 by contact with a
bearing pad 134 in the
adjacent diffuser 124. In this way, the hydraulic load created by a collection
of impellers 126 is
transferred into a diffuser 124 in a bearing stage 130. It will be appreciated
that some or all of the
stages 122 can be configured as a bearing stage 130. As illustrated in FIGS.
2, 6, and 7, the pump
108 may also include a separate lower bearing support 138 that includes a
bearing pad 134 that
offsets thrust carried through a bearing spacer 136.
[024] Turning to FIGS. 4 and 5, shown therein are close-up, cross-sectional
views of a portion of
the upper end of the pump 108. The shaft 120 includes a standard upper ring
groove 140 that is
configured to accept a conventional two-piece ring (not shown), which would be
used in a fixed
impeller pump to capture the compression within the impeller stack. The two-
piece ring has been
replaced with an upper adapter 142 for the floating impeller design of the
pump 108. A close-up,
cross-sectional view of upper adapter 142 is shown in FIG. 8. The upper
adapter 142 includes two
upper ring halves 144a, 144b. Each of the two upper ring halves 144a, 144b has
a width that is
configured to fit tightly within the upper ring groove 140. Each of the upper
ring halves 144a, 144b
further includes an upper adapter snap ring groove 146 and an upper adapter
shoulder 148.
[025] During assembly, the two upper ring halves 144a, 144b are placed into
the upper ring groove
140 and approximated. An upper adapter snap ring 150 can then be placed into
the upper adapter
snap ring groove 146 to hold the two upper ring halves 144a, 144b together
within the upper ring
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groove 140. In other embodiments, set screws or clamps are used to hold the
two upper ring halves
144a, 144b together. Once assembled, the upper adapter 142 remains fixed with
the shaft 120 to
contain and position the standard spacers 132 and impellers 126 as they are
allowed to move axially
along the shaft 120. The upper adapter 142 provides a stop and upper limit for
the upward,
downstream displacement of the top impeller 126 and spacers 132.
[026] Turning to FIGS. 6 and 7, shown therein are close-up, cross-sectional
views of the lower end
of the pump 108. The shaft 120 includes a lower ring groove 152 that is
configured to accept a
conventional two-piece ring (not shown) that would be used in a fixed impeller
pump to capture the
compression within the impeller stack. The two-piece ring has been replaced
with a lower adapter
154 for the floating impeller design of the pump 108. Cross-sectional and
perspective views of
lower adapter 154 are shown in FIGS. 9 and 10, respectively. The lower adapter
154 includes two
lower ring halves 156a, 156b. Each of the two lower ring halves 156a, 156b has
a width that is
configured to fit tightly within the lower ring groove 152. Each of the lower
ring halves 156a, 156b
further includes a lower adapter snap ring groove 158 and a lower adapter
shoulder 160.
[027] During assembly, the two lower ring halves 156a, 156b are placed into
the lower ring groove
152 and approximated. A lower adapter snap ring 162 can then be placed into
the lower adapter snap
ring groove 158 to hold the two lower ring halves 156a, 156b together within
the lower ring groove
152. In other embodiments, set screws or clamps are used to hold the two lower
ring halves 156a,
156b together. Once assembled, the lower adapter 154 remains fixed with the
shaft 120 to contain
and position the standard spacers 132 and impellers 126 as they are allowed to
move axially along
the shaft 120.
[028] As best illustrated in FIG. 6, the lower adapter 154 can be used in
combination with the lower
bearing support 138 to offset down thrust carried along the shaft 120 while
permitting the shaft 120
to lift downstream in the event the up thrust forces exceed the down thrust
forces. The outer
diameter of the lower adapter 154 is smaller than the inner diameter of the
lower bearing support
138. This clearance allows the lower adapter 154 to move inside the lower
bearing support 138,
where the lower adapter should 160 can push the bearing spacer 136 and any
standard spacers 132
downstream along the shaft 120 within the tolerances provided by the spaces
between the various
components connected to the shaft 120.
[029] Thus, the upper adapter 142 and lower adapter 154 provide an efficient
mechanism for
positioning and retaining the standard spacers 132, bearing spacers 136,
impellers 126 and other
components disposed along the outside of the shaft 120. The upper adapter 142
and lower adapter
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154 permit the conversion of a conventional compression shaft into a "floater"
shaft without
additional machining operations to the shaft 120. The ability to quickly and
easily convert a
compression shaft into a floater shaft reduces inventory demands and improves
part
interchangeability. Shafts removed from older fixed impeller pumps can be
easily reclaimed,
converted and installed in a floating impeller pump with the upper and lower
adapters 142, 154.
[030] It is to be understood that even though numerous characteristics and
advantages of various
embodiments of the present invention have been set forth in the foregoing
description, together with
details of the structure and functions of various embodiments of the
invention, this disclosure is
illustrative only, and changes may be made in detail, especially in matters of
structure and
arrangement of parts within the principles of the present invention to the
full extent indicated by the
broad general meaning of the terms in which the appended claims are expressed.
It will be
appreciated by those skilled in the art that the teachings of the present
invention can be applied to
other systems without departing from the scope and spirit of the present
invention.
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