Note: Descriptions are shown in the official language in which they were submitted.
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RECIPROCATING PUMP DRIVE ASSEMBLY
FIELD OF THE INVENTION
The present invention relates to a drive assembly for a pump of the type
comprising a polish rod reciprocating relative to a wellhead, and more
particularly the
present invention relates to a drive assembly including a linear actuator a
plurality of
lengths of cable connected between the linear actuator and the polish rod by
direction
altering cable guides.
BACKGROUND
As disclosed in Canadian Patent Application 2,514,916 and
corresponding issued US Patent 8,082,734 by St. Denis reciprocating pumps are
extensively used on oil wells and they generally consist of a polish rod with
cooperating valves that serve to pump liquids to surface as the polish rod is
reciprocated in the well. According to St. Denis a drive assembly is provided
for a
reciprocating pump which includes a support structure and a linear actuator
mounted
on the support structure. The linear actuator has a stationary portion and a
movable
ram portion. At least one direction altering cable guide is mounted to the
movable ram
portion of the linear actuator. At least one cable is provided having a first
end and a
second end. The first end is anchored to one of the support structure or the
stationary
portion of the linear actuator. The second end is adapted for attachment to a
polish
rod of a reciprocating pump. As the movable ram portion moves, the cable and
cable
guide configuration provide a mechanical advantage which results in the polish
rod
reciprocally moving a multiple of the distance travelled by the movable ram
portion of
the linear actuator. The movable ram portion is driven by a rotating screw
with a
travelling nut; however, the mechanism requires use of additional shock
absorbers to
slow the movement of the travelling nut in the event of a power loss such that
the
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resulting mechanism is complex and may require considerable maintenance to
operate.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a drive
assembly for a reciprocating pump including a polish rod arranged to be
supported for
reciprocating movement relative to a wellhead, the drive assembly comprising:
a support frame arranged to be supported in proximity to the wellhead;
a linear actuator including a lower portion arranged to be fixed to the
support frame and an upper portion supported on the lower portion for linear
reciprocating movement between a lowered position and a raised position;
a pump bracket arranged to= be coupled to the polish rod of the
reciprocating pump;
an anchor bracket arranged to be fixed to the support frame;
two pairs of direction altering cable guides supported on the upper
portion of the linear actuator; and
four lengths of cable in which each length of cable comprises:
a first portion substantially anchored to the pump bracket;
a second portion substantially anchored to the anchor bracket;
and
an intermediate portion extending through a respective one of the
direction altering cable guides on the upper portion of the linear actuator
between the
first portion and the second portion.
The arrangement of two pairs of cable guides on the actuator together
with four lengths of cable provides a considerable factor of safety in
connecting the
linear actuator to the polish rod to ensure minimal damage to the drive
assembly
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would occur in the event of a cable failure as the linear actuator remains
substantially
balanced between the first portion anchored to the polish rod and the second
portion
anchored to the support frame. Preferably the lengths of cable are joined in
series
with one another so as to comprise a single, integral, and continuous strand
of cable
extending between two opposing ends. In this instance additional cable guides
can
be used at the connection to the support frame and the polish rod.
Preferably the continuous strand is coupled at each of the two opposing
ends on the pump bracket. Preferably a junction between each adjacent pair of
lengths of cable joined in series with one another is substantially anchored
to the
respective bracket by a direction altering cable guide fixed on said bracket.
Preferably the cable is supported on each cable guide so as to be
relatively slidable in a longitudinal direction of the cable.
When two lengths of cable are joined integrally in series with one
another at the pump bracket, the pump bracket preferably includes a direction
altering
cable guide fixed thereon upon which the integrally joined lengths of cable
are
substantially anchored.
Preferably the anchor bracket includes two direction altering cable
guides fixed thereon in which each cable guide of the anchor bracket is
associated
with two lengths of cable which are integrally joined in series with one
another at the
respective cable guide upon which the integrally joined lengths of cable are
substantially anchored.
When the direction altering cable guides of a first pair on the upper
portion of the linear actuator each correspond to a first radius of curvature
between
the first portion and the second portion of the respective length of cable,
preferably
the direction altering cable guides of a second pair on the upper portion of
the linear
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actuator correspond to a second radius of curvature between the first portion
and the
second portion of the respective length cable which is different from the
first radius of
curvature.
When the cable received in the cable guide at the pump bracket lies in a
first plane, preferably the cable guides at the anchor bracket are oriented in
a fixed
angular relationship relative to one another such that the cable received in
the cable
guides at the anchor bracket each lie in a respective plane oriented
transversely to
said first plane.
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevational view of the drive assembly.
Figure 2 is a front elevational view of the drive assembly.
Figure 3 is a perspective view of the support frame and the anchor
(supported thereon).
Figure 4 is a top plan view of the support frame and anchor (supported
thereon).
Figure 5 is a side elevational view of the support frame and anchor
(supported thereon).
Figure 6 is a perspective view of the pump bracket.
Figure 7 is a bottom plan view of the pump bracket.
In the drawings like characters of reference indicate corresponding parts
in the different figures.
DETAILED DESCRIPTION
Referring to the accompanying figures, there is illustrated a
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reciprocating pump drive assembly generally indicated by reference numeral 10.
The
assembly 10 is particularly suited for use with a reciprocating pump 12 of the
type
commonly used in the oil industry. Typically, the pump comprises a polish rod
14
slidably received through the seals of a stuffing box 16 at the well head of a
well such
5 that the rod is vertically slidable in a longitudinal direction relative
to the well bore.
The drive assembly 10 includes a support frame 18 arranged to be fixed
in relation to the well head. The frame includes a base plate 20 supported in
a
horizontal orientation. The base plate is a flat plate which is generally U-
shaped
about an interior opening 22 through which the polish rod is arranged to be
received.
The opening 22 is open to a first side 24 of the base plate to define the U-
shape of the
base plate about the opening. Fastener apertures 26 are located at
circumferentially
spaced positions about a perimeter of the interior opening in a generally U-
shaped
pattern to accommodate fasteners for fastening to the well head about the
polish rod
through an arc of greater than 180 degrees about the periphery of the well
head.
The frame 18 further comprises two uprights 28 comprising posts of
rectangular cross section of tubular steel material which are parallel and
spaced apart
from one another along one edge of the base plate at the second side 30
opposite
from the first side 24. The two uprights lie in a generally common center
plane of the
drive assembly as described in further detail below.
The frame further includes two gussets 30 joined between the uprights
28 respectively and the base plate such that each gusset spans from the
upright to
the base plate towards the opposing first side 24 thereof. The gussets are
supported
along opposing sides of the base plate for locating the interior opening and
the polish
rod received therethrough centrally therebetween.
A mounting plate 32 is joined between the two uprights at the top end
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thereof to span horizontally and locate fastener apertures therein to define a
mounting
surface for the bottom end of a linear actuator 34 mounted thereon. The linear
actuator 34 is a hydraulic piston cylinder configuration mounted for vertical
extension
and retraction above the uprights 28 at a laterally central location between
the two
uprights within the common central plane thereof.
The actuator includes a lower portion 36 defining a hollow chamber
functioning as the cylinder portion of the actuator which remains stationery
and fixed
relative to the support frame 18 and the wellhead. An upper portion 38 is
supported
on the lower portion in the form of a ram which is vertically slidable and
moveable
relative to the lower portion. The upper portion includes a piston at the
bottom end
thereof which is received within the cylinder portion of the lower portion 36
so as to
vary the chamber size between the piston and the bottom end of the lower
portion as
the upper portion is linearly displaced relative to the lower portion.
Suitable hydraulic
control lines communicate with the interior of the hollow chamber of the lower
portion
adjacent the bottom side thereof such that the upper portion can be displaced
between a lowered position and an extended raised position by controlling the
amount
of hydraulic fluid introduced into the hollow chamber in a conventional
manner.
A mounting frame 40 is supported at the top end of the linear actuator
for movement with the upper portion relative to the lower portion. The
mounting frame
generally comprises a shaft mounted horizontally within the central plane of
the
uprights 28 to span laterally outward in two opposing directions towards
opposing
ends of the shaft, locating the linear actuator centrally therebetween.
The mounting frame supports a pair of first cable guides 42 thereon at
the respective opposing ends of the shaft such that the first cable guides 42
are
laterally spaced apart in the axial direction of the shaft at equal distances
at opposing
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sides from the linear actuator centered therebetween. Each first cable guide
42
comprises a pulley wheel mounted coaxially with the shaft such that an outer
periphery of the pulley wheel includes a circumferential groove receiving a
cable
therethrough to change the direction of the cable in a generally U-shaped
pattern
when extending over top of the pulley wheel between two opposing sides of the
central plane of the uprights as described in further detail below. The radius
of the
pulley wheels defines a first radius of curvature of the change in cable
orientation as it
passes through the cable guide.
The mounting frame further supports a pair of second cable guides 44
also coaxially on the shaft so as to be coaxial with the first cable guides
but at a
narrower lateral spacing in the axial direction of the shaft. The second
guides are
similarly laterally spaced in equal distances on opposite sides of the linear
actuator
received centrally therebetween such that the second cable guides 44 are
located at
intermediate positions between the two first cable guides. The second cable
guides
similarly comprise pulley wheels with a circumferential groove for receiving a
cable
therein to change the direction of the cable passing therethrough in a
generally U-
shaped pattern overtop of the cable guide between opposing sides of the
central
plane of the uprights.
The cable in this instance comprises a single, continuous and integral
strand of steel cable which is comprised of four cable lengths 46 connected in
series
with one another and each substantially anchored between the support rod and
the
polish rod at opposing sides of the central plane by extending back and forth
overtop
of the cable guides on the mounting frame 40. The multiple lengths of cable
anchored
between the support frame on one side of the common plane and the polish rod
on
the other side of the common central plane provide a mechanical advantage for
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reciprocating the polish rod in response to reciprocation of the linear
actuator while
also multiplying the stroke length of the actuator.
In the illustrated drive assembly, four lengths of cable 46 are provided
integrally in series with one another such that each length of cable includes
a first
portion 48, an intermediate portion 50 and a second portion 52. In each
instance, the
first portion 48 is substantially anchored at a pump bracket 54 which connects
the
cables to the top end of the polish rod and extends substantially vertically
upward
towards the cable guides on the top of the mounting frame of the linear
actuator
spaced outwardly from a first side of the central plane.
Each intermediate portion 50 alters in direction as it extends over the
respective cable guide among the first and second cable guides 42 and 44 so as
to be
generally U-shaped as it crosses over from the first portion 48 spaced outward
from a
first side of a central plane to the respective second portion 52. The second
portion
52 is spaced outwardly from the opposing second side of the central plane by
an
equal amount as the respective first portion due to the cable guides being
coaxial with
the shaft located in alignment with the common central plane of the uprights.
Each second portion 52 extends substantially vertically downward from
the intermediate portion before being anchored at the bottom end to an anchor
bracket 56 supported in fixed relation on the support frame 10 such that the
second
portion spans substantially vertically.
The pump bracket 54 includes a mounting plate 58 which is generally
horizontal in use and is elongate in a lateral direction such that two
opposing sides 60
span in the lateral direction between two opposing ends 62. A central opening
64 is
located through the mounting plate at a central location between the two sides
60 and
the two ends 62 for receiving suitable fastening members for securement to the
top
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end of the polish rod such that the mounting plate is fixed in relation to the
polish rod
in use.
The mounting plate 58 further includes two mounting apertures 66
spaced apart laterally at opposing ends 62 to locate the central opening
centrally
therebetween in the lateral direction, however, the mounting apertures are
offset
along one of the side edges 60 in the other direction. The two mounting
apertures are
arranged for receiving the two opposing ends of the continuous strand of cable
or
suitable fasteners for fastening the two cable ends 68 thereto. The two
mounting
apertures are spaced apart in the lateral direction by a distance
corresponding to the
lateral distance between the two first cable guides at opposing ends of the
shaft such
that respective second portions of the cable lengths extending from the first
cable
guides are aligned with the two mounting apertures 66 in the assembled
configuration
when the respective second portions of the lengths of cable extend
substantially
vertically therebetween.
The pump bracket further includes a cable guide 70 at the second side
of the mounting plate opposite from the first side locating the two mounting
apertures
therein such that the central opening is substantially centered between the
mounting
apertures at the first side and the cable guide at the second side. The cable
guide 70
on the pump bracket defines a generally U-shaped channel 72 for receiving a
respective portion of cable therein to alter the direction of the cable
through an arc of
approximately 180 degrees.
The channel 72 includes two opposing ends 74 and a curved portion
therebetween which curves downwardly and inwardly from both ends 74 to a
central
apex defining a lowest portion of the channel. The two opposing ends 74 are
spaced
apart by a distance corresponding to the lateral or axial space between the
two
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second cable guides on the actuator for alignment with the respective second
portions
of the respective lengths of cable extending downwardly therefrom. The cable
guide
70 on the pump bracket receives a junction between two lengths 46 of cable
where
two of the lengths connected in series are integrally joined with one another
and
5 change of direction through the cable guide. The junction between adjacent
cable
lengths received within the cable guide on the pump bracket corresponds to the
center of the continuous strand of cable.
The two portions of cable substantially anchored to the cable guide at
the second side of the mounting plate 58 are thus balanced in one direction
with the
10 two additional portions of cable anchored at spaced positions at the
opposing first
side of the mounting plate 58. Furthermore the cables at each respective side
of the
mounting plate are laterally balanced with the polish rod connection being
laterally
centered therebetween. The cables thus provide a substantially even and
balance
lifting force to the polish rod as the linear actuator is extended and
substantially equal
tension is applied to the cables.
The anchor bracket 56 is mounted on the uprights 28 of the support
frame in fixed relation therewith at the first side of the central plane
opposite from the
pump bracket. The anchor bracket generally includes a base plate 76 which is
mounted vertically on the uprights parallel and adjacent to the central plane
thereof.
The base plate 76 supports an upper cable guide 78 and a lower cable guide 80
thereon in which both cable guides are configured generally similarly to the
cable
guide 70 of the pump bracket so as to comprise a generally U-shaped channel 72
which is curved downwardly and inwardly from both ends 74 to a central apex
defining
the lowest portion of channel.
Although the plane of the cable received through the cable guide 70 of
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the pump bracket is parallel to the central plane of the uprights, the plane
of the cable
received within each of the upper and lower cable guides 78 and 80 are
oriented in
upright planes at respective fixed angular orientations transversely to the
first plane of
the pump bracket cable guide 70 and the central plane of the uprights.
More particularly, each of the upper cable guide 78 and the lower cable
guide 80 is generally semi-circular between the two opposing ends 74 thereof
to
define a respective radius of curvature for altering the direction of the
cable received
therethrough. The radius of curvature of the upper and lower guides is
substantially
equal to one another as each spans a distance between the two opposing ends 74
thereof which corresponds approximately to the distance from one of the first
cable
guides at one side of the linear actuator to a corresponding second cable
guide at the
opposing side of the linear actuator.
Each of the channels 72 of the respective cable guides are supported in
this arrangement such that one end is in vertical alignment directly below the
outermost peripheral edge of the respective first cable guide of the linear
actuator
while the other end is aligned vertically below the corresponding outermost
peripheral
edge of the respective second cable guide so that the respective first
portions of cable
spanning therebetween are substantially vertical in orientation. As with the
other
cable guides, each of the upper cable guide 78 and lower cable guide 80
receives a
portion of the cable therethrough which corresponds to an integral junction
between
two adjacent lengths of the cable connected in series with one another to form
the
continuous cable strand.
The channel 72 of each of the upper cable guide and the lower cable
guide is defined as a circumferential groove about the periphery of an upright
semi-
circular plate 82. Each of the plates 82 is supported by a support member 84
fixed at
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an inner end to the base plate 76 to extend outward from the central plane
towards an
outer end fixing the respective plate 82 thereon such that the upper guide is
located
spaced above the lower guide. An additional support plate 86 spans vertically
between the support members of the upper and lower cable guides and is joined
at an
inner edge to the base plate to function as a gusset to provide additional
support to
each plate 82.
By providing the configuration of anchor bracket and pump bracket as
disclosed herein, a single strand of cable can be wound about the cable guides
to
define four individual lengths 46 of cable, each substantially anchored at a
first portion
to the anchor bracket, extending over a respective cable guide on the linear
actuator
at an intermediate portion, and being anchored to the pump bracket at an
opposing
end. The cable guides may receive the cables therethrough such that the cable
is
relatively slidable in relation to the cable guides and the channels or
grooves receiving
the cable therethrough such that as the linear actuator is extended and
retracted,
minor imbalances resulting from the different radius of curvatures of the
different
cable guides can be accommodated for to maintain an even tension on the
cables. At
some cable guides however, additional fasteners or clamping assemblies may be
used to clamp respective sections of the cable within the cable guides so as
to be
substantially fixed relative to one another.
The arrangement of the pump bracket and the anchor bracket of the
present invention is most distinguished from the prior art and most
advantageous in
that it permits four lengths of cable to be connected in a manner which
maintains
balance between the forces of tension pulling upwardly on the polish rod with
each
reciprocation to minimize any unnecessary wear on the polish rod which can
otherwise occur due to imbalanced lifting forces. The four lengths of cable
also
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provide a considerable factor of safety for transferring lifting force from
the linear actuator
to a corresponding lifting force on the polish rod during up and down
reciprocation of the
reciprocating pump.
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.
