Note: Descriptions are shown in the official language in which they were submitted.
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~ydraulic oil pump
Background of the invention
I. Field of the Invention
This invention relates to jack pumps of the type used
to pump crude oil from oil wells.
II. Description of the Prior Art
When an oil well has insufficient pressure to force
the oil to the surface, pumping equipment is used to raise
the oil. The conventional method of lifting oil from the
bottom of an oil well employs a reciprocating rod
connected to a device at the surface which causes the rod
to move up and down. At its lower end, the reciprocating
rod is connected to a displacement pump positioned below
the fluid level within the oil well.
The most common type of surface device for
reciprocating the rod takes the form of a walking beam
supported on a vertical post. The beam is attached to the
supporting vertical post by means of an interposed
oscillating journal assembly connected to the centre of the
beam in the conventional rockinghorse style configuration,
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or at one end of the beam in the unitorque and the air
balance style of units. A rotating eccentric connected to
one end of the rocking beam, or connected to a mid position
of the end supported beams, causes the free end of the
beam to move up and down. This end,being connected to the
oilwell rods,causes the reciprocating pumping action.
This form of device has many well known advantages and
disadvantages.
A second form of surface device consists of a verti-
cally mounted hydraulic ram connected at its lower end to
the reciprocating rod extending Erom the surface of the
yroundO Examples of this type of surEace device are
disclosed in Canadian patent 1l032,064 issued on May 30,
1978 to Canadian Foremost Ltd. ; Canadian patent 1,076,926
issued on May 6, 1980 to Canadian Foremost Ltc~. ; U.S.
patent 3~491,538 issued on January 27, 1970 to Driltrol;
and U.S. patent 4,249,376 issued on February 10, 19~1 to
Weckerly.
There are numerous forms of hydraulically activated
oilwell pumping units that make use of hydraulic energy to
lift the sucker rods. In most instances devices and
arrangments are not incorporated whereby the energy
created by the downward action of the sucker rods is
accumulated for reuse in support of the upward stroke
action. The patents mentioned above attempt to accumulate
a portion of the energy that is expended by the downward
action of the sucker rods. This mav take the form of a
pressurized reservoir which will contain the fluid expelled
from the cylinder of the hydraulic ram or motor together
with a pressuri~ed gas. On the downstroke of the piston
in the cylinder the weight of the reciprocating rods is
used to drlve hydraulic fluid from the cylinder into
the accumulator that contains a head of pressurized
qas, urther compressing the gas within ~he accumula-
tor. The hwdraulic pump used to operate the hydraulicram is efEectively idling during this phase of the
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cycle. In the case of the closed loop hydraulic system
the pressurized hydraulic fluid from the cylinder is
directed into the suction port oE the hydraulic pump which
controls the movement of the fluid during the downstroke.
During the upstroke the fluid from the accumulator is fed
to the hydraulic pump where the pressure is boosted and
then supplied to the hydraulic cylinder. In another form
of device the gas being compressed is contained in a dry
accumulator (does not contain oil). The action of the
falling rods causes a piston in the gas cyclinder to
compress the gasO ~he oil from the hydraulic oil cylinder
is directed to the suction port of the pump and is
directed to atmospheric vented storage. The pump controls
the downward movement of the piston. The pump does little
or no work on the downstroke. The pressurized gas
exerting upward pressure within the independent cylinder
forces an independent piston, that is connected by the
device to the hydraulic piston, upwardly and in this way
augments the lifting force of the hydraulic motor system.
Accordingly the accumulator acts to counterbalance the
weight of the reciprocating ~ods so that less work has to
be carried out by the hydraulic pump during the upstroke
action. Because the hydraulic pump operates at no load or
partial load during the downstroke of the jack pump, only
half or a reduced portion of the power available to the
unit during the cycle of operation is made use of. As
most power supply is charged for on a maximum-use basis
this results in excess ca~ital costs and o~erating
cllarges .
In the patents mentioned above the speed of the piston
motor action is controlled directly by the capacity of the
hydraulic pump~
Summary of the Invention
It is an object of the present invention to make full
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use oE the hydraulic pump and power source equipment
(energizing motor) throughout the complete cycle of
operation of the hydraulic jack pumpO
It is a further object of the invention, at least in
preferred forms, to incorporate an adjustable facility
that allows for the accumulation of a portion of the
energy by the pump assembly during the downs~roke of the
pumping cycleO
According to one aspect of the invention there
is provided a jack pump comprising: a reciprocating
hydraulic motor having a power stroke and a dissipating
stroke; a hydraulic pump having an inlet and an outlet
for hydraulic fluid; at least one pressurized accumulator;
a reservoir for hydraulic fluid; and a hydraulic flow con-
trol circuit interconnecting said motor, pump, accumulator
and reservoir, said flow control circuit comprising: first
pipe means interconnecting said reservoir and the inlet
of said pump for enabling the pump to draw hydraulic fluid
from said reservoir second pipe means directly connecting
the outlet of said pump to said at least one pressurized
accumulator so that hydraulic fluid may be pumped on a
continuous basis to said at least one accumulator; third
pipe means connecting said at least one accumulator to
said hydraulic motor to enable pressurized hydraulic fluid
to pass from said accumulator to said motor to cause said
power stroke; fourth pipe means connecting said hydraulic
motor to said reservoir to enable hydraulic fluid from
said motor to pass directly to said reservoir during said
dissipating stroke; sensor means to d~termine when said motor
has terminated its power stroke and its dissipating stroke
respectively; and valve means controlled by said sensor
means and acting on sa.id third and fourth pipe means to
permit pressurized fluid to pass through said third pipe
means ~or said Power stroke and through said fourth
pipe means during said dissinating stroke without
restrictiny the flow of fluid through said ~irst and
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second pipe means caused by continuous operation of said
pump.
According to another aspect of the invention there
is provided a method of operating a jack pump including a
reciprocating hydraulic motor having a power stroke and a
dis.sipating stroke, at least one pressurized accumulator,
a hydraulic pump, a reservoir for hydraulic fluid and a
hydraulic flow circuit interconnecting said motor, pump,
accumulator and reservoir; said me~hod comprising: operat-
ing said pump ,continuously throughout each cycle comprising
a power stroke and a dissipating stroke of said motor
to continuously charge said pressurizedaccumulator with
hydraulic fluid from said reservoir; directing fluid from
said accumulator to said motor during said power stroke in
order to actuate said motor; and directing fluid from said
motor directly to said reservoir during said dissipating
stroke.
In a preferred form of the invention, the reservoir is
maintained under a superatmospheric pressure.
An advantage of the invention, at least in its
preferred forms, is that it can utilize a minimum power
source at a level rate of usage throughout the full cycle
period and that it can conserve a reasonably large portion
of the energy that is expended by the downward action of
the sucker rods; this conserved or accumulated energy to
be used in support of the hydraulic pump, reducing the
power required to charge the power accumulators inter-
posed between the hydraulic pump and the hydraulic
motor. The invention can also provide a means of
raising the sucker rods at a rate of speed greater
than that which would be possible if the pump acted
directly to supply the oil volume required to move the
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piston upwardly in ~he mo-tor, and ~rovldes a means
of allowing the sucker rods to return to their lower
position unimpeded by mechanical constraints inherent
within the jack pump.
It is a further advantage of the present invention, at
least in preferred forms, that it can divide the upstroke
action and the downstroke action of the hydraulic jack
pump in order to control and maximize independently the
functions of lift (upstroke) and the function of freefall
(downstroke)~
The described invention, at least in the pre-
ferred forms, maximizes the speed of rise of the
sucker rods consistent with the capacity of the oil-
well e~uipment, and maximizes the rate of fall by a
self-regulating system of the sucker rods consistent with
the oilwell production characteristics, and conserves the
maximum amount of expended energy during the downward
movement of the sucker rods, the maximum being determined
by the production characteristics of the oilwell; and
further utilizes the power available on a 60 second per
minute basis.
This invention is designed in particular to deal with
and satisfy the very difficult production problems of
heavy viscous oil production.
Heavy viscous oil is produced by different methods
ranging from what is termed as primary production which,
in so far as jack pumps are concerned, is the pumping of
the oil by a conventional downhole pump without the
assistance of pressurization of the formation or heating
3~ of the oil to cause it to be less viscous; to tertiary
production systems which may involve pressurizing the
formation reservoir and heating the oil in ~ . In order
to maximize production it is necessary to raise the pump
plunger as rapidly as possible consistent with downhole
considerations and eqoipment constraints and then to allow
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the sucker rods together with the pump plunger to return to
the bottom position as rapidly as possibleO During a ter~iary
pxoduction cycle that employs a method of heating the oil bear-
ing formation, the oil originally produced is warm and flows
reasonably freely. As the cycle proqresses to its final
phase, the oil becomes cooler and more viscousO As the
oil becomes more viscous the oil in the production tubing
tends to restrict the action of the sucker rods when
falling to their bottom posit:ion. This change in rate of
speed is gradual and progresC;ive. In order to allow the
pump to function to permit the return of the sucker rods
to the lower position as rapidly as possible throughout
the changing cycle, ;t is necessary to permit a maximum
degree of freefall action. In one form of the invention
later described this is accomplished by accumulating a
maximum amount of the energy expended by the sucker rods
returniny to the lower position consistent with allowing
sufficient downward force due to gravity in order to cause
the rods to fall at their maximum rate of fall. This form
of the invention further allows the maximization of the
above action by virtue of having the energy accumulation
system pursuant to the upward thrust of the piston
incorporated with;n the system in such a manner as to not
restrict the freefall action of the rods in any way; and
by virtue of having the downthrust energy accumulation
system operate entirely independent of the upward thrust
system which allows for independent regulation of the
downward thrust energy accumulation~ makin~ it possible to
use any portion of the rod fall energy to force the
downward movement of the sucker rods within the shortest
possible time. The time period will adjust automatically
in accordance with the change in viscosity of the crude
oil within the production column.
During the period of the downward movement of the
sucker rods, the hydraulic pump forces oil into the
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accumulator positioned downstream from the hydraulic pump,
recharging the oil volume that was allowed to move into
the cylinder during the upstroke of the 3ack pump. During
the upstroke period the hydraulic pump continues to charge
the accumulator. This allows full cycle utilization of
pump capacity and power provided.
The upstroke action is governed by the capacity of the
accumulators positioned between the hydraulic pump and the
cylinder to deliver pressurized fluid to the cylinder.
10 This is regulated independently from the pump's volume
capacity. This technique maximizes the speed of the
upstroke~ However, the volume of fluid supplied by the
pump over a full cycle is equal to that required by the
cylinder during the upstroke.
The system allows:
1. the maximum upward speed of the sucker rods that
their design and other production considerations will
permit;
2. the full use of the time involved in the downward
movement of the rods to maximize the use of hydraulic pump
and power supply capacity in the process of recharging the
accumulators;
3. the freedom to maximize the downward movement of
the sucker rods by allowing use of that amount of downward
force that is required to move the rods to their lowest
position as rapidly as possible; and
4. to conserve any energy generated by the freefall of
the rods that is excessive to that force required to
return the rods to their lowest position within the time
frame dictated by production program considerations.
The accumulators as used in this present invention are
rreferably of the closed chamber form. The charged gas can-
not escape without a conscious action of bleeding off.
Description o~ the Drawings
Figure 1 is a diagram of the hydraulic circuit of one
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embodiment of the invention showing the operation during
the start~p of the unit;
Figure 2 is a diagram of the same hydraulic circuit
showing the operation during the upstroke of the cycle;
Figure 3 is a diagram of the same hydraulic circuit
showing the operation during the downstroke of the cycle;
and
Figure 4 is a perspective diagram showing various
parts of the pump jack e~uipment used in the circuit of
Figures 1-3 but omitting connecting tubing.
Description of the Preferred Embodiments
Figures 1 to 3 shou the same hydraulic pumping unit,
which is an embodiment of the present invention, in three
different phases of operation, as described below.
The main parts of the hydraulic pumping unit are as
follows. A cylinder 7 is mounted vertically above a well
head (not shown). The cylinder contains a hydraulically
activated piston 45 connected to a piston rod 46. The
piston rod 46 is connected to a polish rod (not shown) at
the well head, and the polish rod is in turn connected to
sucker rods (not shown) connected to a pump at the bottom
of the well. Repeated raising of the piston 45 in
cylinder 7 by the pressure of hydraulic fluid under the
piston, and lowering of the piston under the weight of the
sucker rods, causes oil to be pumped from the well.
Hydraulic fluid is supplied through first pipe means
~line D) from a reservoir 28 to the inlet of pump 2 and thence
through second pipe means to accumulators 3 for use in
operating the piston 45. Third pipe means connect the
accumulators 3 to the cylinder 7 and ~ourth pipe means
connect the cylinder 7 to ~he reservoir 28. The flow
of hydraulic fluid is governed by a cîrcuit which
includes sensors in the Eorm of limit control valves
8 and 9 operated in turn by an actuator in the form
of a projection 100 on piston rod 46. The drawings
show a space between projection 100 and limit control
valves ~ and 9 but in reality the limit control
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valves are of course positioned to contactl and thus to be
operated by, ~he projection 100.
Figure 1 shows the start up procedure necessary for
preparing the unit for normal operation. A predetermined
5 quantity of oil is charged to reservoir 28 and the
reservoir 28 is charged with pressurized gas (e.g.
nitrogen3 to a minimum of 10 p.s.i. Gas is charged to
accumulators 3 up to a p.s.i. equal to the amount of
lifting pressure that is to be required below piston 45.
Low pressure acc~ulators 10 and 21 are charged with
a suitable amount of gas. Valve 22 is closed. The
projection 100 on the lower position of piston rod 46
impinges against a plunger of limit control valve 9O
Valve 9 will move to the open position as soon as
pressurized fluid is received from line A~
Electric motor 1 is started causing variable speed
hydraulic pump 2 to operate. Oil is drawn through first
pipe means from reservoir 28 by the pump through valve 30
and filter 29, and the fluid is directed through second
pipe means to accumulators 3 through check valve 37 and
shutoff valves 38 and 39 that are in the open positions.
A pump discharge pressure of approximately 110% of the
lifting pressure within cylinder 7 is employed. When
this pressure is reached, the pump 2 pressure is main-
tained by means of a pressure compensating device.
The operation of the pump 2 pressurizes lLne A causing
fluid to flow through valve 9 Erom port P to B and thence
to port A of valve 11. This opens valve 11 so that fluid
flows from line A to valve 4, causing valve 4 to open.
Needle valve 23 is opened manually allowing fluid to pass
through line E to a position within the cylinder 7 below
piston 45. Pressurization of line E causes oil to flow to
valve 5, thus opening valve 5. Valve 23 is now manually
closed. Manual operation of valve 23 is required at this
stage because, during initial startup, the total system is
not pressurized. A predetermined amount of oil is let
into accumulators 10 and 21 through valve 49. Valve 49 is
then closed and the unit is ready for operation.
Figure 2 shows the operation of the unit during the
upstroke. Valve 22 is opened sufficiently and acts as a
flow control valveO Oil frc,m accumulators 3 is forced
into line B, through valve 22 to cylinder 7 via vaLves 4,
5 and 6, (i.e. the third pipe means) causing the piston 45
~o begin to rise to its uppermost position. The rate of
rise oE the piston that is desired is converted into oil
volume per second at a desired pressure adequate to lift
the weight attached to piston rod 46. The desired rate
of flow is set on valve 22. The desired pressure is set on
the pump pressure control. The pump volume control is set
to provide a volume of oil slightly in excess of that set
on valve 22. Valve 4 is kept in the open position because
of the pressurized fluid it receives from valve 11 which
in turn is kept open by the pressurized ~luid it receives
from valve 9. Valve 5 is kept open by the pressurized
fluid it receives from line ~. The piston 45 continues
to rise at the desired rate until projection 100 on piston
rod 46 contacts a plunger of limit control valve 8.
Figure 3 shows the operation of the pumping unit
during the downstroke. Depression of the plunger of limit
control valve 8 by projection 100 causes oil to flow from
line A to ports P and B and then to port B of valve 11.
Valve 11 then directs pressurized fluid from line A to
valve 12, opening it. Valve 4 is vented through valve
11 to a sump reservoir 33 via valve 17, thus allowing
valve 4 to assume the closed position. Valve 5 remains in
the open position. Oil flows from cylinder 7 through line
~, through flow control valve 6, line C and valve 12 to
the reservoir 28 (i.e. the fourth pipe means),
Because of the gas pressure in reservoir 28, the weight
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of the sucker rods attached to piston rod 46 is counter-
balanced to some extent. The gas pressuxe is selected to
be compatible with production characteristics and a normal
setting is about one halE of the cylinder lifting pressure.
In the event that the restric:tions within the oil produc-
tion column in the well are not adequate to retard the rate
of downward movement of the sucker rods to a sufficient
extent, the rate of downward movement can be controlled by
valve 6. This valve can be adjusted manually.
Accumulators 10 and 21 together with needle control
valves 13, 15, 17 and 19 serve the purpose of dampening
the change in force at the top and bottom of the piston
stroke.
Oil from the A piston of valve 11 can escape through
valve 9 to be vented to tank 33. The small amount of
bypass oil from pump 2 is vente~ into tank 33. Tank 33
~lso receives oil from valves 5, 4, 12, 8 and 9 during
operation of these valves. The pipes conveying the fluid
to tank 33 act as Eifth pipe means~ The level of oil in
tank 33 is controlled by float switch 31. when the switch
is operated, oil is drawn from tank 33 by pump 34 oper-
ated by electric motor 35 and transferred to reservoir 28
(through sixth pipe means). The pressure setting on pump
34 is controlled by pressure relief valve 36, which is set
at a p.s.i. somewhat greater than the maximum in reservoir
28.
Valve 5 is an emergency control valve to shut off
fluid to the cylinder. If the sucker rod attached to
piston rod 46 should break, piston 45 would have free
upward movement and the pressure within cylinder 7 would
be rapidly reduced. Valve S is held in the open position
by pressure from line E which has the same pressure as the
fluid in the cylinder. If the pressure falls in line E,
valve S closes~ shutting ofE the flow of oil to line E and
the cylinder.
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During the period of discharge of oil from cylinder 7,
i.e. the downstroke, the hydraulic pump 2 continues to
draw oil from reservoir 28, pressurize it and charge
it to accumulators 3, thus replenishing the charge of
pressurized oil in the accumulators 3. Pump 2 operates
continuously under load during the full cycle of operation
of the pumping unit, thus putting the pump to maximum use
for efficiency.
It can be seen that the rate at which the piston rises
within the cylinder is determined by the load suspended
from the piston rod, the pressure maintained in accumulators 3
and the amount of fluid that is allowed to pass through
valve 22. For example, the gallons per minute of fluid
that can be charged to cylinder 7 from the accumulators 3
can be considerably greater than the gallons per minute
output of the pump. The pump can utilize the longer
period of downstroke to recharge the accumulators 3 with
sufficient hydraulic oil for the upstroke. For example, if
t.he piston rises in 15 seconds and falls in 45 seconds,
the system allows three times as long for the pump to
accumulate the pressurized fluid in the accumulators, than
is required for the discharge of the pr~ssurized oil from
the accumulators. In this case, the power requirement of
the motor 1 that operates pump 2 may be 1/3 of that
required to raise the piston in a system employing a
direct pump to cylinder connection. Thus by charging
accumulators 3 with a pressure related to the lift
required by piston 45, by setting valve 22 to minimize the
period of the upstroke, and by setting the pump pressure
and volume in proper relationship with the maximum
pressure and volume required in accumulators 3,
the action of the hydraulic pump can be set to use the
minimum amount of power consistent with the time available
(~ull cycle period) to adequately charge accumulators 3
to provide the necessary energy for raising the piston.
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The system also all.ows for flexible control of the
downward action of the sucker rods when the fluidity of
the produced oil is sufficlent to allow the sucker rods to
fall freely, the rate of fall can be conkrolled by valve 6
and the restrictive pressure maintained ih reservoir 28.
It is necessary ~o leave sufficient difference between the
pressure below the piston in the cylinder and the pressure
within the reservoir 28 to permit as rapid a fall of the
sucker rods as production conditions allow. The rate of
rod all is governed by production constraints and not by
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limitations within the pumping unit structure, As was the
case with the upstroke so it is with the case of the
downstroke, i.e, the system allows for optimization of the
respective movements. Both the upstroke and the down-
stroke are dealt with as individual components of thetotal cycle. It is thus possible to balance the time
ratios and ~he power factors within the widest possible
ranges~
~eservoir 28 reclaims energy generated by the downward
fall of the sucker rods that is not required to return the
sucker rods to their lower position. The pressurized fluid
from reservoir 28 is fed to the inlet of pump 2 where the
pressure is further boosted for delivery to accumulators
3. The pressurization of the fluid in reservoir 28 thus
reduces the power requirement of the pump for delivering
pressuri~ed ~luid to the accumulators 3.
As an example, the pump pressure may be 2000 p.s.i.
and the pressure in the reservoir may be 1000 p.s.i~
Figure 4 show~ the various components of the equipment
described in connection with Figures 1, 2 and 3, inter-
connecting conduits having been omitted for the sake of
clarity.
The accumulators 3, combined hydraulic pump 2 and
motor 1, the oil accumulator reservoir 28 and a cooler 66
for the hydraulic fluid are mounted on a supporting plate
80.
The cylinder 7 containing the piStOIl 45 with dependent
piston rod 46, is mounted on a triangular cage 81 formed
by triangular end plates 82 and 83 separated by support
rods 84, 85, and 86. The cage 81 is located above a well
head, from which a polish rod 89 extends. The polish rod
89 is connected to the lower end of the piston rod 46 by a
screw coupling 90. Projection 100 is located at the upper
end of the polish rod (or alternatively at the lower end of
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the piston rod) for actuation of limit control valves 8
and g.
The pcsitions of limit controls 8 and 9 limit the
length of the stroke of the piston 45 in the cylinder 7,
since reversal of the piston takes place when the control
8 or 9 is actuated by the pro~ection 100. To enable
the length of the stroke of ~he piston to be varied,
the positions of the limit controls 8 and 9 are variable.
Each of these controls is slidably mounted on a vertical
rod 91~ The rod is triangular in cross-section so that
the limit controls 8 and 9 cannot rotate on the rod, but
only move upwardly or downwardly. Vertical adjustment of
the limit controls is controlled by a second vertical rod
92 extending through the limit control casings. This rod
has an outer helical thread which engages with an internal
thread (not shown~ in the limit control casings~ Rotation
of the rod 92 in one direction or the other thus raises or
lowers the limit controls 8 and 9. Rotation of the ro~ 92
can be controlled by a pulley arrangement 93.
The system of this invention allows the energy
generated by the prime mover to be used at a uniform and
steady rate throughout the full cycle of operation, by
accumulating fluid under pressure during the full cycle
period.
This is achieved by accumulating energy at an even
rate throughout the full cycle period and using it for a
portion of the cycle period that is less than 1/2 of the
total cycle time.
Power requirements are further reduced by accumulating
any surplus energy generated by the downward pull of the
sucker rod and feeding this energy to the hydraulic pump
on a continuous basis, thus augmenting the pump's action of
storing energy in accumulators 3.
The above represents a preferred form of the invention.
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Other forms of the invention falling within the scope of
the following claims are possible, as will be apparent to
a person skilled in the art. For example, resevoir 28 may
be vented to the atmosphere so ~hat none of the energy of
the free fall of the piston 45 together with the sucker
rod string is recovered in reservoir 28 and by pass oil
from the pump and regulating valves can be fed directly to
reservoir 28 thus by-passing tank 33. This may be desir-
able when no restriction on the free kall action of the
10 sucker rod string is requiredl. Further methods of counter
balancing the weigh~ o~ the sucker rod string may be
employed without affecting the basic action of this
invention. This may be desirable when the diffeLence
between the weight of the sucker rod s~ring and that of
15 the fluid column in the well is very great.
