Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a pump jack drive apparatus, and
in particular to an apparatus for driving and controlling the speed of
operation of a pump jack.
There are presently available a number of alternative forms
of pump for pumping oil. Because of their unreliability and expense,
such pumps have not replaced the conventional pump jack in oilfields.
The pumping of heavy oils presents certain problems. If such problems
can be overcome, the production of heavy oils can be substantially
increased.
The motion of the walking beam of a conventional pump jack
is derived from a rotating eccentric. The stroke cycle is normally fixed
and resembles a sine wave. In order to pump efficiently, the pumping
cycle cannot be changed. When pumping heavy oil, the pumping cycle may
be altered which is one of the problems referred to above. In the pro-
duction of heavy oils, it is advantageous ~1) to be able to change the
rate of pumping and stroling profile, or (2~ to be able to maintain the
rate of pumping constant at a predetermined level.
Because of the relatively low production rates of heavy oil,
the equipment used to control pumping with a pump jack should be in-
expensive and reliable. The object of the present invention is to meet
such demands by providing a relatively simple, inexpensive apparatus
for driving and controlling operation of a pump jack.
Accordingly, the present invention relates to a driving ap-
paratus for a pump jack of the type including a samson post, a walking
beam plvotally mounted on the samson post for rotation around a horizon-
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tal axis, a horsehead on one end oF the walking beam for driviny
connection to a pump mechanism, said apparatus compris~ng first cylinder
means pivotally mounted on said samson post, first piston rod means
associated with said first cylinder means and pivo~ally connected to
said walking beam on one side of said horizontal axis for moving said
one end of said walking beam upwardly; second cylindQr means pivotally
mounted on said samson post; second piston rod means associated with said
second cylinder means and pivotally connected to said walking beam on
the other side of said horizontal axis for moving said one end of said
walking beam downwardly, and control means for alternately operating said
first and second cylinder means independently of each other, whereby said
one end of the walking beam and said horsehead are reciprocated upwardly
and downwardly, the upward and downward movements being at the same or
different speeds.
The invention will now be described in greater detail with
reference to the accompanying drawings, which illustrate a preferred
embodiment of the invention, and wherein:
Figure 1 is a side elevation view of a pump jack and drive
apparatus in accordance with the present invention;
Figure 2 is a cross-sectional view taken generally along
line II-II of Figure l;
Figure 3 is a schematic block diagram of the basic elements
of the pump jack and drive apparatus of Figures 1 and 2;
Figure 4 is a schematic block diagram of a control system
used in the drive apparatus of the present invention,
Figure 5 -is a schematic block diagram of an electrical cir-
cuit used in the apparatus of Figures 1 to 4; and
Figure 6 is a block diagram of a second form of control
system for use in the apparatus of Figures 1 to 3.
With reference to Figures 1 and 2, the apparatus of the
present invention is intended for use with a conventional pump jack of
the type including a walking beam 1, pivotally mounted on the top of a
samson post 2 for rotation around a horizontal axis defined by a saddle
bearing 3. The samson post 2 includes four inclined legs 4 extending
upwardly from a base 5, a top plate 6 and crossbars 7 extending between
the legs 4 at the front and rear ends of the post 2. A counterweight 8
is mounted on rear end 9 of the walking beam 1, and a horsehead 10 is
mounted on the front end 11 of such beam. A wire line assembly or wire
rope bridel 12 is connected at one end to the horsehead 10, and at the
other end to a pump mechanism, including a polished rod 13. The bail
12 and rod 13 are connected by a connector 14. Usually, the polished
rod 13 reciprocates a sucker pod or pump rod associated with a downhole
pump (not shown).
In conventional pump jackes, the walking beam is caused to
rotate around the samson post 2 by means of a pitman assembly (not
shown) connected to the rear end 9 of the beam. In the case o-f the
present invention, the walking beam 1 is driven by means of hydraulic
cylinders 15 and 16 connected to the rear end front ends 9 and 11,
respèctively of the walking beam. The bottom ends of the hydraulic
cyliaders lS and 16 are pivotally connected to an I-beam 17 by clevises
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18. The I-beam 17 is supported by the crossbars 7 Piston rods 19
extend upwardly from the top ends of the cylinders 15 and 16 to the
walking beam 1. The top ends of the piston rods 19 are pivotally con-
nected to the walking beam 1 by clevises 20.
The hydraulic cylinders 15 and 16 are operated by a hydraulic
pump 21, which is driven by a prime mover in the ~orm of motor 22.
Hydraulic fluid is stored in hydraulic fluid reservoir 23, The pump 22,
the motor 21, and the reservoir 23 are mounted on the rear end of the
base 5. A V-belt 24 passes around pulleys 25 on the motor 22 and the
pump 21, respectivel~v.
With reference to Figure 3, the hydraulic circuit for
operating the cylinders 15 and 16 includes ~he reservoir 23, which is
connected to a control and pump unit 26 by a line 27, lines 28 and 29
for supplying hydraullc fluid to the cylinders 15 and 16, respectively,
and sumps 30. The upper and lower limits of travel of the front end 11
of the walking beam 1 are de~ermined by microswitches or proximity
switches 31 and 32, respectively. The switches 31 and 32 are mounted
on an arm (not shown) extending upwardly from the samson post 2 in
positions such that they are closed by the walking beam 1 or by a lug
or magnet (not shown) projecting outwardly therefrom, By ad,justing the
positions of the switches 31 and 32, the vertical travel of the ends of
the walking beam 1 and of the horsehead 10 can be changed.
Referring now to Figure 4, in one form of control system of
the aparatus of Figures 1 to 3~ the pump 21 is a variable displacement
pump, which is used in conjunction with a fixed displacement pump 34.
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The pressure of hydraulic fluid (oil) pumped from the reservoir 23 by
the pump 34 is kept at constant pressure, normally approxlmately 250
psi, by a relieF valve 35 which is connected to line 36 between the
pumps 21 and 34, and to sump 37. Fluid from the pump 34 supplies the
main pump 21 and the control system. Control of the pump 21 and thus
of movements of the rods 19 and the walking beam 1 is achieved by means
of solenoid operated valves 38 and 39, which receive fluid from the
pump 34 via lines 40 and 41, respectively, and needle valves 42 and 43,
respectively. The valves 38 and 39 and lines 44 and 45 connect top end
46 or bottom end 47, respectively of a hydraulic control cylinder 48 to
the pump 34 or to a sump 49. Piston rod 50 of the cylinder 48 is con-~
nected to the pump 21 for controlling operation thereof. The limits of
movement bf the rod 50 are contro~lled by stops 51 and 52 movably mounted
on an arm 53 connected to the cylinder 48. Screws 54 are used to fix
the positions of the stops 51 and 52 on the arm 53. The stops 51 and
52 are contacted by a lug 55 on the outer end of the piston rod 50.
Damage to the apparatus is prevented by a relief valve 56 between the
lines 28 and 29.
In operation, the motor 21 is started to also start the
pumps 21 and 34. The pump 34, which is a fixed displacement pump, is
connected to the motor 21 by drive shaft 57. With the motor 22 running,
the pump 34 be~ins to deliver fluid to the pump 21 and the remainder of
the control system. Fluid is delivered to the solenoid valves 38 and
39 under charge pressure. With starting switch 58 (Figure 5) open,
fluid is stopped at the valves 38 and 39. When the starting switch 58
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is closed, current flows through lines 5g and 60, and terminals 61, 62,
63, and 64 to energize solenoid 65 of the switch 38. The lines 59 and
60 are connected to a 110 volt AC source of power. Thus, flu;d from the
pump 34 flows through lines 40 and 44 to the top end 46 of the control
cylinder 48. The rod 50 is retracted and hydraulic fluid is delivered
from the cylinder 16 via line 29 to the pump 21, while fluid is pumped
through the line 28 to the cylinder 15. This causes the horsehead 10
to move upwardly.
At the top of the stroke of the walking beam 1~ the micro-
switch 31 is closed which energized relay 66, breaking contact 67 and
causing an interruption in power to the coil of the relay 68. Such
interruption closes a contact 69 and energizes relay 70 which flips
contact 71 from closing terminals 63 - 64 to closing terminals 72 - 63.
Thus, solenoid 73 of the microswitch 39 is energized and the solenoid
65 is de-energized. Hydraulic fluid then flows through the valve 39 and
lines 41 and 45 to the bottom 47 of the cylinder 48, while fluid from
the top 46 of the cylinder passes through line 44 and the valve 38 to
sump 49. The pump 21 operates to pump hydraulic fluid through the line
29 to the top of the cylinder 16 while fluid is withdrawn from the top
of the cylinder 15 through the line 28. The horsehead 10 then travels
downwardly. ~Ihen the bottom limit of travel of the horsehead 10 is
reached, the microswitch 32 is closed to reverse the power to the
solenoids 65 and 75 using contacts 74, 75, and 76. It will be noted that
the relays 66, 68, and 70 are powered by a 12 volt DC battery 77.
The speed of movement of the rods 19 in the cylinders 15 and
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16 is controlled by the spacing of khe stops 5l and 52. If ~he stops
51 and 52 are placed farther apart, then fluid is pumped more rapidly
into the top of the cylinder 15 or 16 and withdrawn more rapidly from
the top of the other cylinder. Thus, the stop 52 controls the speed oF
the pump jack, I.E., of the horsehead 10 upwardly, and the stop 51 con-
trols the speed downwardly. Acceleration of the pump jack is effected
by increasing the rate of travel of the rod 50 in the cylinder 48. The
needle valves 42 and 43 control the rate of feed of hydraulic fluid to
the cylinder 48, and thus control the rate of movement of the rod 50,
which in turn controls the rate of change of fluid displacement through
the pump 21. The valve 42 controls acceleration at the bo~tom of the
stroke and the valve 43 controls acceleration at the top of the stroke
of the pump jack~
Referring now to Figure 6, a control system utilizing a
fixed displacement pump will now be described. In situations where
there is no need for easy adjustment of the speed of operation of the
pump jack, a fixed displacement pump 78 can be used, with a resulting
saving in costs. The ratio of the speed of movement of the rods 19 up-
wardly and downwardly and thus the speed of the horsehead 10 can be
adjusted by chan~ing the diameter of the cylinders 15 and 16. For
example, since the hydraulic fluid is supplied at a constant rate, if
the diameter of the cylinder 15 is twice that of the cylinder 16, the
pump jack will move downwardly four times more quickly than upwardly.
The overall speed of the pump jack is determined by the size and speed
of operation of the pump 78.
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The control system of Figure 6 is essentially the same as
that of Figure 4, and wherever possible the same reference numerals have
been used to identify the same or similar elements.
The operation of the control system of Figure 6 is the same
as that of Figure 4, except that the outer end of the piston rod 50 of
the cylinder 48 is connected to a valve 79, which is connected directly
to the pump 78 by a line 80 and to the lines 28 and 29 for carrying
hydraulic fluid to the cylinders 15 and 16, or to sump 81. A relief
valve 82 is connected to the line 80. Movement o-f the rod 50 following
opening of one of the valves 38 and 39 results in movement of the valve
79 to a position in which fluid flows to cylinder 15 or 16, and fluid
is returned to sump 81 from the other cylinder.
The advantages of the apparatus described hereinbefore are
many. By eliminating the conventional drive assembly, ~Ihich includes a
gearbox, the horsehead can be driven upwardly and downwardly at different
rates, i.e., the horsehead can ascend more quickly than it descends.
The speed of operation of the pump jack is relatively easy to adjust with
the apparatus of the present invention. Because the stroke pattern is
not necessarily sinusoidal, forces and peak velocities are reduced
which 1ncreases efficiency.
By locating the drive cylinders close to the fulcrum of the
walking beam, piston rod movement is decreased, and thus cylinder life
is increased. Hydraulic pumps presently in use require a ratio of cyl-
inder rod movement to polished rod movement of 1:1.
Further modifications and alternative embodiments of the
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invention will be apparent to those skilled in the art in view of the
foregoing description. Accordingly, this description is -to be construed
as illustratlve only and is for the purpose of teachiny those skilled
in the art, the manner of carrying out the invention. It is further
understood that the form of the invention herewith shown and described
is to be taken as the presently preferred embodiment. Various changes
may be made ln the shape3 size and generaly arrangement of components,
for example, equivalent elements may be substituted for those illustrated
and described herein, parts may be used independently of the use of other
features, all as will be apparent to one skilled in the art after having
the benefits of the description of the invention.
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