U.S. patent number 3,802,803 [Application Number 05/321,280] was granted by the patent office on 1974-04-09 for submersible screw pump.
Invention is credited to Alexandr Antonovich Bogdanov, Andrei Mikhailovich Ratov.
United States Patent |
3,802,803 |
Bogdanov , et al. |
April 9, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
SUBMERSIBLE SCREW PUMP
Abstract
Submersible screw pumps for transferring liquids, substantially
viscous liquid containing gas under a high pressure, for example in
the process of oil pumpage from deep oil wells or when pumping oil
products from reservoirs in which there is provided a drive with a
seal and a starting device, coaxially secured stators formed by
rigid casings, housing coaxially disposed elastic bushings having
inner threads and protected by a safety valve; twin screw rotors of
which one has a right-hand thread and the other a left-hand thread
and which are connected to the drive shaft and to each other
through a flexible coupling with, each screw rotor being
eccentrically disposed in the corresponding stator having an extra
thread start as compared with the rotor, so that between the
threads of the rotor and the stator there are defined closed spaces
disposed along the axis of the stator from the intake chamber of
each rotor to the common delivery chamber; the length of the
elastic bushing of each stator being at least 20 times the cross
sectional diameter of the corresponding screw rotor; the oblong
elastic bushings being protected from dry friction and excess
pressure owing to the fact that the delivery chamber is
automatically connected to and disconnected from the intake
chambers of the screw rotors by means of a gate and a pilot valve,
disposed coaxially in the safety valve, depending on the output of
the screw rotors and the pressure within the delivery chamber, in
which case the centers of the extreme closed spaces of each rotor
adjoining the delivery chamber are located on a common line
extending through the axis of the stators and the axis of the rigid
member connecting the two heads of universal joints serving as a
flexible coupling between the rotors and transmitting torque from
one rotor to the other.
Inventors: |
Bogdanov; Alexandr Antonovich
(Moscow, SU), Ratov; Andrei Mikhailovich (Moscow,
SU) |
Family
ID: |
26884414 |
Appl.
No.: |
05/321,280 |
Filed: |
January 5, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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188729 |
Oct 13, 1971 |
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Current U.S.
Class: |
417/211.5;
418/48 |
Current CPC
Class: |
F04C
2/1073 (20130101); F04B 47/06 (20130101) |
Current International
Class: |
F04B
47/00 (20060101); F04B 47/06 (20060101); F04C
2/00 (20060101); F04C 2/107 (20060101); F01c
005/04 (); F04c 011/00 (); F04c 017/12 () |
Field of
Search: |
;417/200,435,211.5
;418/48 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Sher; Richard
Attorney, Agent or Firm: Holman & Stern
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a continuation of application Ser. No. 188,729
filed Oct. 13, 1971, now abandoned.
Claims
We claim:
1. A submersible screw pump adapted for operation in an oil well
for pumping oil therefrom comprising in combination: a drive
provided with a shaft; a starting device mounted on the shaft of
said drive; first and second stators mounted in a co-axial
relationship with said drive, each of said stators having elastic
bushings mounted within a rigid casing; a first screw rotor
arranged eccentrically in said first stator, said first stator
having an inner screw surface with an extra screw thread as
compared to the screw surface of said first screw rotor; a first
double universal joint for connecting said starting device with
said first screw rotor and transmitting a turning moment; a second
screw rotor arranged eccentrically in said second stator, said
second stator having an inner screw surface with an extra screw
thread compared to the screw surface of said second screw rotor;
the direction of the screw surfaces of said second stator and screw
rotor being opposite to the direction of the screw surfaces of said
first stator and screw rotor; said screw surfaces of said first and
second stators and screw rotors being in contact with each other
and forming closed spaces disposed along the axes of the stators,
the closed spaces to be filled with liquid being pumped; a second
double universal joint for coupling said first and second screw
rotors, transmitting a turning moment and carrying axial loads due
to the pressure of the liquid; at least two intake chambers, one
chamber being located at the extreme end of each of said first and
second screw rotors and being connected with the space of said oil
well; a delivery chamber located between the two other ends of said
first and second screw rotors, said second double universal joint
being located in this delivery chamber; a safety valve
communicating through a channel with said delivery chamber and with
the space of the tubing serving for lowering said pump into said
well where said pump operates and protecting said pairs of rotors
and stators from dry friction and excessive pressure by admitting
the oil from the space of said tubing into the space of said well;
the length of the bushings of each of the first and second stators
being at least 20 times the cross-sectional diameter of the
corresponding screw rotor.
2. The submersible screw pump of claim 1, wherein said first and
second stators are formed by rigid sleeves and elastic bushings
secured inside said rigid sleeves, the centers of the extreme
closed spaces of each screw rotor adjoining said delivery chamber
being located along a single line passing through the axis of said
first and second stators and the axis of said double universal
joint located in the delivery chamber. the
3. The submersible screw pump of claim 1 wherein each of said first
and second double universal joints comprises: two heads, a rigid
member interconnecting said heads, an internal and external cover
for accommodating said heads therebetween, at least two pairs of
rollers for pivot connection of said heads with said covers, the
pair of said external covers being secured to the adjacent ends of
said screw rotors.
4. The submersible screw pump of claim 3 wherein each said head of
said double universal joints comprises two part-spherical surfaces,
two symmetrically located truncated cones with their bases
adjoining one another and having a taper angle corresponding to the
angle of deviation of the axis of said rigid member from the axes
of said screw rotors; at least two longitudinal semicylindrical
slots on said truncated cones, each said cover accommodating said
heads having a part-spherical surface, and at least two
longitudinal semicylindrical slots located correspondingly to said
longitudinal semicylindrical slots on said heads, said rollers
being arranged freely and with a gap in said longitudinal
semicylindrical slots of said heads and said covers and having
linear contact with the lines of intersection of the surfaces of
said truncated cones with the surfaces of said semicylindrical
slots of said heads to ensure transmission of the turning moment
between said heads and said covers at an angle to the axes of said
rigid member and said screw rotors.
5. The submersible screw pump of claim 3 wherein one pair of said
internal or external covers is made integral with the casing of
said cover, thus forming a single member.
6. The submersible screw pump of claim 3 wherein said heads are
secured at the ends of said screw rotors and said driving shaft,
two of said adjacent internal covers of said double universal joint
being interconnected through a bridge to form an integral
member.
7. The submersible screw pump of claim 4 wherein said
part-spherical surfaces of said heads and covers are made in the
form of changeable inserts.
8. The submersible screw pump of claim 3 wherein said covers have
an opening for mounting said rigid member which is sealed by a
sealing cup, the end face of the sealing cup conforming to the end
face shape of said cover.
9. The submersible screw pump of claim 8 wherein the opening in the
cover is sealed by an undulated pipe, and inlet and outlet valves
are mounted on said cover.
10. The submersible screw pump of claim 2 wherein said rigid
sleeves of the stators are made of metal and have at least two rows
of uniformly arranged orifices and grooves on the inner surface and
on the end faces of said flexible bushing.
11. The submersible screw pump of claim 1 wherein said safety valve
includes a gate and a guide bushing, a pilot valve bushing having
channels for connection with the space of said well, a pilot valve
having two transverse diameters for disconnecting the space of said
tubing from the space of said well, a hydraulic buffer having a
bushing which is provided with a calibrated hole with a gentle
transition along a tapered surface from said hole to said pilot
valve, said pilot valve moving together with said gate in one
direction under the effect of the difference of the forces of the
accelerated flows of liquid in said guide bushing and in said
buffer bushing and moving in the other direction under the effect
of the liquid pressure in the space of said tubing.
12. The submersible screw pump of claim 11 wherein said hydraulic
buffer is disposed on the side opposite to said gate and serves as
a limiter restricting the movement of said pilot valve in the
direction of motion of the flow of pumped fluid.
13. The submersible screw pump of claim 12 wherein, in order to
prevent a pressure drop within said buffer bushing compared to the
pressure in the space of said tubing, between the adjacent end
faces of said pilot valve bushing and said buffer bushing there are
located symmetrical channels having a cross sectional area equal to
a double cross sectional area of said maximum diameter of the pilot
valve.
14. The submersible screw pump of claim 11 wherein, for reducing
the effect of the velocity flow of liquid on the velocity of motion
of said gate and said pilot valve during the process of starting
said pump, said guide bushing has at least two symmetrical slots
the dimension of which along the axis of said valve exceeds the
length of the generating line of the cylinder of said gate, while
the lower step of said slots is spaced from said seat by a distance
at least twice as great as said length of the generating line of
the cylinder of said gate.
15. The submersible screw pump of claim 1 wherein said starting
device is made in the form of a starting clutch disposed between
said drive and said driving shaft and comprising a collar as a
driven member, two inner teeth, the end face of said collar on the
side of said drive having annular bridges interconnecting the faces
of said teeth, and a driving member in the form of two claws and a
spring for resetting said claws when said drive is stopped.
16. The submersible screw pump of claim 15 wherein said bushing of
said driven member has apertures located symmetrically relative to
each other along the entire length of said teeth and an oblique
portion on the inner surface of said collar opposite to said tooth
along said aperture.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the pump-making industry and, more
particularly, to submersible screw pumps for transferring fluids,
substantially viscous fluids containing gases at a high pressure,
for example, in oil pumpage from deep oil wells or in transferring
oil products from oil reservoirs.
PRIOR ART
Known in the art are submersible pumps of this type. A screw pump
has been proposed heretofore, comprising a drive with a starting
device, coaxially secured stators formed by rigid casings with
elastic bushings fixed within the casings coaxially therewith, with
the elastic having inner screw threads and being protected by a
safety valve with a piston and a pilot valve, and twin screw
rotors.
One of the rotors has a right-hand screw thread and the other rotor
a left-hand screw thread, with each screw rotor being disposed
inside the corresponding stator having a number of starts of the
thread exceeding that of the rotor by one. In principle, both
rotors can rotate in opposite directions. Provided between the
screw threads of the rotor and stator are closed spaces disposed
along the stator axis from the intake chamber of each rotor to the
common delivery chamber.
The screw rotors are usually connected to the driving shaft and to
each other through double universal joints in which both heads are
interconnected by an elastic member.
In the stators of the known screw pumps, the length of the elastic
bushing is only 5 to 10 times the diameter of the screw rotor cross
section. Such pumps can operate during a long period at a pressure
not exceeding a 200-meter column of the liquid pumped.
The double universal joints employed in such pumps for connecting
the screw rotors, are provided with two heads interconnected
through a flexible member, for example, a steel rope.
The coupling elements transmitting the torque are made defined as
balls located within the slots. The pump is provided with a
protective device made as a safety valve, in which the travel of
the pilot valve in the direction of flow of the liquid being pumped
is by virtue of the velocity pressure of the flow, and in the
opposite direction due to the pressure of liquid in the delivery
chamber.
The known screw pumps are disadvantageous in that they fail to
develop a pressure exceeding a 1,000-m column of the liquid pumped
and cannot operate under such conditions during several months
continuously and without repair.
In the known pumps operating at a pressure of a 1,000-m column of
liquid the elastic bushings of the stators are liable to break and
fail, the flexible member, viz., the steel rope interconnecting the
heads of the joints breaks down, the pilot valve of the safety
valve and the driven collar of the starting clutch are apt to get
damaged during the start of the rotors.
The known screw pumps are inefficient when employed for oil pumpage
from deep wells and, sometimes, they are absolutely useless under
such operating conditions; therefore, a new engineering solution of
the problem is made necessary. This solution should be suitable not
only for oil pumpage from a well but also for transferring viscous
oil products from underwater reservoirs.
The known screw pumps are equipped with safety valves having guide
sleeves of the gates which are slotted in their upper portion. The
purpose of these slots is to reduce the effort of the velocity
pressure applied to the gate at the end of its rise. This purpose,
however, can be met only at a definite ratio between the length of
these slots and the distance from the seating of the valve guide
sleeve to the nearest step of the slots, and the length of the
valve gate cylinder generatrix.
An object of the present invention is to eliminate the
above-mentioned disadvantages.
SUMMARY OF THE INVENTION
The specific object of the invention is to provide a high-pressure
and long-life submersible screw pump for oil pumpage from deep oil
wells, in which there are provided definite ratios between the
sizes determining the hydraulic and mechanical characteristics of
the screw rotors and stators of the pump. This necessitates to
combine the great length of the elastic bushings of the stator
capable of creating high heads, with the strength of the balanced
screw rotors, pivot joints, pilot valve, and the components of the
starting clutch to provide a reliable start of at least two
substantially long screw rotors. Such a pump intended for
oil-production industry, must operate in a well continously during
6-12 months without repair.
The elastic bushings must be reliably fixed to the rigid casings of
the stators and protected against dry friction and destruction by
excess pressure.
The pilot valve with a gate should automatically travel in its
bushings in one direction not only under the action of the velocity
pressure of the liquid at the stator outlet but also due to the
hydraulic resistance of the buffer at the end of the upward motion
of the pilot valve, and in the opposite direction under the
pressure of the liquid effective in the delivery chamber.
High pressure developed by the pump results in heavy axial loads
and torques which are particularly increased during starting.
Therefore, the double universal joints should be free of any weak
links such as a flexible member interconnecting the heads of the
joints and balls transmitting torque through a point contact of the
surfaces.
In addition, it is necessary to strengthen the starting device by
eliminating breakdowns of the driven collars of the starting
clutch.
According to the invention, these and other objects are attained
owing to the fact that in the submersible screw pump, the length of
the elastic bushing of each stator is at least 20 times the
cross-sectional diameter of the corresponding screw rotor, while
the oblong elastic bushings are protected against dry friction and
excess pressure by automatically connecting the delivery chamber to
or disconnecting it from the intake chambers of the rotors by means
of a gate and a pilot valve, located coaxially within the safety
valve, depending on the output of the rotors and the pressure
effective in the pump delivery chamber, in which case the centers
of the extreme closed spaces of each rotor adjacent to the delivery
chamber are located on a common line passing through the axis of
the stators and the axis of the rigid member interconnecting the
two heads of the joints transmitting torque from one rotor to the
other.
Each head of the double universal joints is preferably formed by
two part-spherical surfaces partitioned by two symmetrically
arranged truncated cones adjoining each other with their bases and
having an angle of taper corresponding to the angle of deviation of
the axis of the rigid member interconnecting the heads, from the
axis of the stators, the surface of these cones being provided with
longitudinal part-cylindrical slots which correspond to the slots
of the head cap bushings encompassing the heads and accommodating
loosely set rollers which are in a linear contact with the lines of
intersection of the truncated cones of the heads with the
part-cylindrical slots to form an engagement of the heads with the
bushings of the head caps capable of transmitting torque at an
angle to the axis of the universal joint rigid member and to that
of the screw rotor.
One of the head caps of each universal joint is preferably made
integral with the cap bushing, thus forming a single member.
The heads of the double universal joint are preferably secured to
the ends of the screw rotors and the driving shaft and each head is
slidably encompassed by two caps through part-spherical surfaces
and with a gap, in which case the two adjacent caps of one joint
are preferably interconnected by a bridge to form a single
member.
It is desirable to make the part-spherical surfaces in the form of
changeable inserts.
According to the specific object of the invention, one of the caps
of the joint head is preferably provided with an opening which is
sealed by an elastic cup which follows the shape of the head cap
end face.
It is also advantageous to make the seal of the opening in the head
cap as an undulated pipe and to provide inlet and outlet valves on
the head caps of the universal joints.
Advantageously, the rigid casings of the stators of metal are
preferably provided with at least two rows of equally spaced
orifices while grooves are on the inner surfaces and end faces of
the rigid casings of the stator.
Then, in the safety valve protecting the elastic bushings of the
stators against dry friction and excess pressure, the valve being
located in the delivery chamber and consisting of a guide sleeve
provided with a seating and slots, a gate disposed in the sleeve, a
pilot valve arranged in its bushing whose hollow space is
communicated through channels with the intake chambers of the screw
rotors, the pilot valve being adapted to cut off these channels
from the delivery chamber, it is advisable to locate coaxially to
the gate and the pilot valve, a hydraulic buffer having, in its
sleeve, a calibrated hole with a gentle transition along an oblique
surface from the hole to the pilot valve which, together with the
gate, moves in one direction under the action of the differential
pressure created by the flows of liquid within the guide and buffer
sleeves and moves in the opposite direction under the pressure of
the liquid effective in the delivery chamber. Advantageously, the
safety valve is provided with a limiter of the pilot valve travel
in the direction of flow of the liquid being pumped which limiter
is constituted as a hydraulic buffer disposed on the side opposite
to the gate. To prevent a pressure drop within the buffer sleeve as
against the pressure within the delivery chamber, it is expedient
to make symmetrical channels between the adjacent end faces of the
pilot valve bushing and the buffer sleeve, with the cross-sectional
area of channels being equal to at least a doubled cross-sectional
area of the pilot valve.
The guide sleeve of the safety valve is preferably provided with at
least two symmetrical slots whose size along the axis of the valve
exceeds the length of the gate cylinder generatrix, the lower step
of the slots being spaced from the gate seating for a distance at
least twice as large as the length of the gate cylinder generatrix.
Furthermore, advantageously the starting device is defined as a
starting clutch disposed between the drive and the drive shaft and
having a driven member constituted by a collar with two inner claws
which during rotation of the driving member, located inside of the
driven member, mesh with spring-interconnected pawls, in which case
the end face of the collar of the clutch driven member on the drive
side is preferably defined by annular bridges interconnecting the
end faces of the claws.
The collar of the starting clutch driven member is preferably
provided with apertures disposed symmetrically to each other on one
side throughout length of each claw, with an oblique surface being
near each aperture on the collar inner side opposite to the
claw.
The proposed novel combination of the components of a submersible
screw pump makes it possible to considerably increase the
efficiency of such a pump when pumping oil from deep wells.
The submersible screw pump is of the volume type and combines the
advantageous features of centrifugal and piston pumps.
The proposed pump provides for a continuous flow of liquid in a
system oil bed - well - casing head with minimum emulsification of
the liquid without pulsation due to the principal operating
characteristics of the pump and due to the absence of suction and
discharge valves and also provides for a high head and delivery of
fluid at a low cross section and a small weight of the pump (the
head may be as high as 1,500-2,000 m and even higher).
The pump has a high efficiency which only slightly changes within a
wide range of pressures and reaching 70-80 percent when pumping a
viscous liquid.
The simple construction of the pump facilitates its mounting and
repair. The starting clutch facilitates the start of the pump with
a standard submersible electric motor equipped with a hydraulic
protection system, while the presence of a safety valve provides
for filling the pumping tubes with liquid when lowering the pump
into a well and discharge of the liquid therefrom when the pump is
withdrawn from the well, and prevents dry friction of the rubber of
the elastic bushings of the pump stators when the gate is closed or
in the case of clogging, the discharge pipeline or absence of
liquid in the intake chambers of the rotors. The provision of such
a valve makes it possible to wash the pumping tubes with a hot
liquid to remove paraffin deposits and to pump a thick liquid into
a flowing well through the central string prior to raising the
pump. The valve operates automatically depending on whether the
liquid is present in the well.
An unexpected technical effect has been obtained during pumpage of
oil wells with a yield below the rated output of the pump. Due to
the automatic operation of the safety valve which controls the
cooling and lubrication of the oblong elastic bushings of the
stators, the dynamic level of the oil reservoir in the well with
inadequate oil yield is subjected to rhythmical oscillations and
this increases the oil inflow from the reservoir into the well. The
yield of the well, as well as the production of oil are
increased.
The use of the present invention makes it possible to considerably
widen the field of application of the screw pumps in the oil
production industry. The pump can also be effectively employed as a
reservoir pump, for example for transferring viscous oil products
from underwater reservoirs into tankers.
The present invention will be better understood from the following
detailed description of an embodiment thereof with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal section of the submersible screw pump
according to the invention having a pair of screw rotors with
right-hand and left-hand threads;
2 shows an embodiment of the submersible screw pump comprising
several pairs of twin screw rotors interconnected in pairs and
coupled to both ends of the drive shaft;
FIG. 3 the view looking in the direction of the arrows is a
longitudinal section of the screw rotor and stator, taken on an
enlarged scale;
FIG. 4 is a sectional view taken along the line IV--IV in FIG. 3
the view looking in the direction of the arrows;
FIG. 5 is a fragmentary longitudinal section of the stator with a
left-hand two-start screw thread, taken on an enlarged scale;
FIG. 6 is a sectional view taken along the line VI--VI in FIG. 5
the view looking in the direction of the arrows;
FIG. 7 is an enlarged-scale view of a longitudinal section of the
double universal joint;
FIG. 8 is a sectional view taken along the line VIII--VIII in FIG.
7 the view looking in the direction of the arrows;
FIG. 9 is an enlarged-scale fragmentary longitudinal section of a
modification of the universal joint head;
FIG. 10 is an enlarged-scale fragmentary sectional view of a
modification of the universal joint head;
FIG. 11 is an enlarged-scale fragmentary longitudinal section of a
modification of the universal joint head secured to the end of the
screw rotor;
FIG. 12 is an enlarged-scale fragmentary longitudinal section view
of still another modification of the universal joint head;
FIG. 13 is an enlarged-scale fragmentary longitudinal section view
of a portion of the pump with a safety valve and a hydraulic
buffer;
FIG. 14 is a cross section taken along the line XIV--XIV in FIG. 13
the view looking in the direction of the arrows;
FIG. 15 is a longitudinal section on an enlarged scale of the
driven portion of the starting clutch, and
FIG. 16 is a sectional view taken along the line XVI--XVI in FIG.
15 the view looking in the direction of the arrows.
DETAILED DESCRIPTION OF THE INVENTION
The following terms will be used in the description of the present
disclosure.
The term "submersible screw pump" is applied to a pump of an
eccentric-screw or rotary type immersed into a well under the
liquid level to pump this liquid to the daylight surface.
The "drive" is a motor, preferably a submersible electric
motor.
The "starting clutch" is a clutch adapted for unidirectional
working rotation of the unit, for example a claw or centrifugal
clutch, which places the pump into operation after the motor rotor
has been accelerated to a predetermined speed.
The "flexible coupling" is a device interconnecting two shafts of
which at least one performs planetary motion and transmits torque
and axial loads from one shaft to the other. The flexible coupling
can be a double universal joint or a double axially movable
coupling transmitting torque at an angularity of the driving and
driven shafts and designed for loads corresponding to the pump
parameters.
The "universal joint" is a device capable of transmitting torque,
tensile and compressive loads, or power from one shaft to the other
whose axis is coplanar with that of the former shaft and makes an
angle therewith variable during operation.
The "double universal joint" is a device consisting of two
universal joints.
The "screw rotor" is a rotor with a screw thread, for example
one-start thread, which in its cross section is a circle, the
centers of all the cross sections being regularly arranged on a
screw line about the axis of the screw rotor.
The "twin screw rotors" are two screw rotors, one having a
right-hand thread and another having a left-hand thread,
interconnected, for example, through a double universal joint.
The "elastic bushings" of the stators are usually of oil-resistant
rubber which is cured onto a rigid, preferably metal, stator
sleeve. The inner screw surface of these bushings corresponds to
the screw surface of the rotor and has one extra start of the
thread as compared to the screw surface of the rotor.
The "closed spaces" are spaces between the screw rotor and the
elastic bushing of the stator formed due to the provision of an
"extra" start of the screw surface of the elastic bushing of the
stator, with such spaces being filled with liquid. Due to the
interference between the rotor and the stator bushing, these closed
spaces have an indefinite spiral shape formed by two screw
surfaces, i.e. by the surfaces of the stator and rotor and the
contact line, that is the line of intersection of these
surfaces.
The submersible screw pump (FIGS. 1 and 2) comprises a drive 1, for
example an electric motor powered through a cable 2. Mounted on a
shaft 3 of the drive 1 is a starting device constituted by a
starting clutch 4 consisting of a driving member 5 and a driven
member 6 interconnected through two pawls 7. The driven member 6 is
mounted on a driving shaft 8 of the pump rotating in bearings 9 and
10 with shock absorbers 11 and having a seal 12. Mounted on the
other end of the driving shaft 8 is a double universal joint 13
connecting the shaft 8 to one of two screw rotors 14 positioned
into an elastic bushing 16 (FIGS. 1, 2, 3 and 4) of a stator 15
which, in turn, is coaxially fixed in a rigid casing 17.
The other end of the screw rotor 14 projecting from the elastic
bushing 16, mounts another universal joint 13 connecting the second
screw rotor 14 with the first rotor. One of the rotors 14 has a
right-hand thread while the other has a left-hand thread.
Each screw rotor 14 is located within a corresponding elastic
bushing 16 of the stator 15 having a thread with an extra start as
compared to that of the rotor 14 so that between the screw threads
of the rotor 14 and the elastic bushing 16 of the stator 15, there
are formed closed spaces 18 disposed along the pump axis from an
intake chamber 19 of each rotor 14 to a common delivery chamber 20.
In this case, the centers of the closed spaces 18 of each rotor 14,
which are the closest to the delivery chamber 20 are disposed on a
common line passing through the axis of the stators 15 and the axis
of the double universal joint 13 connecting the two rotors 14.
Located within the delivery chamber 20 is a safety valve 21
provided with a hydraulic buffer 22.
The rigid casings 17 of the stators 15 (FIGS. 5 and 6) are of metal
and provided with three rows of uniformly disposed orifices 23,
while V-shaped or rectangular grooves 25 are provided inside each
rigid casing 17 and at its end faces 24.
Each double universal joint 13 (FIG. 7) consists of two heads 26
interconnected through a ridid member 27, for example a shaft or
bridge (FIG. 11). Each of the heads 26 (FIG. 7) is formed by two
part-spherical surfaces 28 divided by two symetrically located
truncated cones 29 whose bases adjoin each other (FIGS. 7, 9-12).
The angles of the truncated cones 29 are equal by magnitude to the
angle of deviation of the axis of the rigid member 27 from the axes
of the screw rotors 14 (FIGS. 1 and 2). The cones 29 (FIG.8) are
intersected by longitudinal part-cylindrical slots 30 corresponding
to longitudinal part-cylindrical slots 31 of busings 32 (FIGS.
7-12) of caps 33 encompassing the heads 26. Loosely set in the
slots 30 and 31 (FIG. 8) are rollers 34 (FIG. 7) adapted for
engagement of the heads 26 with the bushings 32 through the linear
contact of the truncated cones 29 with the rollers 34.
Each head 26 is embraced by two caps 33 having part-spherical
surfaces 28 corresponding to the heads 26. One of the caps 33 of
the heads 26 of each universal joint 13 is integral with the
bushing 32, thereby forming a single member 35 (FIGS. 10 and 12),
in which case, the caps 33 may be located both on the inner side of
the double universal joint 13 (FIGS. 7, 10 and 12) and on the outer
side thereof FIG. 11. FIG. 9 shows an exemplary embodiment of one
member of the double universal joint 13 made as two caps 33, inner
and outer, thread-joined to the bushing 32.
FIGS. 7, 9 and 12 show exemplary embodiments of the part-spherical
surfaces 28 of the head 26 and the caps 33 made as changeable
inserts 36 or 37.
One of the caps 33 of the head 26 has an opening 38 (FIG. 10) which
is sealed with an elastic cup 39 whose sealing flange 40 follows
the shape of the face of the cap 33 of the head 26. The cup can be
pressed to the cap 33 by a spring 41.
FIG. 12 shows an exemplary embodiment of the seal of the opening 38
of the cap 33 by means of an undulated pipe 42, in which case an
inlet valve 43 and an outlet valve 44 are disposed on the caps 33
of the heads 26.
The safety valve 21 (FIG. 1) is located in the chamber 20 and
comprises a guide sleeve 45 (FIG. 13) provided with a seating 46
and at least two slots 47 in which is slidably mounted a gate 48 of
a pilot valve 49 arranged in a bushing 50 of the pilot valve 49. A
cavity 51 of the bushing 50 through channels 52 and ports 53
communicates with the intake chambers 19 (FIG. 1) of the screw
rotors 14 and are shut off from the delivery chamber 20 by the
pilot valve 49.
Located coaxially with the gate 48 (FIG. 13) and the pilot valve 49
on the side opposite to the gate 48, is a hydraulic buffer 22
having in a sleeve 54 a calibrated hole 55 featuring a gentle
transition along an oblique surface 56 from the hole 55 to that
portion of the sleeve 54 in which moves the end of the pilot valve
49 after it has left the bushing 50.
Provided between the adjacent faces of the bushing 50 of the pilot
valve and the sleeve 54 of the buffer 22 are symmetrical channels
57, whose cross-sectional area is at least equal to the double
cross-sectional area of the pilot valve 49. The channels 57 may
have either annular or rectangular shape as shown in FIG. 13.
The length of the symmetrical slots 47 of the guide sleeve 45 along
the axis of the valve 21 from a lower step 58 of the slots 47 to a
upper step 59 exceeds the length of the generatrix of the cylinder
of the gate 48.
The lower step 58 is spaced from the seating 46 for a distance
which is at least twice as large as the length of the generatrix of
the gate 48.
The driven member 6 (FIGS. 1 and 2) of the starting clutch 4 of the
pump is defined by a collar 60 (FIG. 15) provided with two internal
claws 61. A face 62 of the collar 60 at the side of the drive 1 is
constituted as annular bridges 63 connecting the faces of the claws
61. These bridges 63 form apertures 64 in the collar 60 (FIG. 16),
with the apertures being arranged symmetrically relative to each
other on one side of each claw 61 along the entire length thereof.
Near each aperture 64, the inner side of the collar 60 opposite to
the claw 61 has an oblique surface 65.
A sludge pipe 66 is located above the safety valve 21 (FIG. 1)
forming a gap between its walls and pumping tubes 67 which serves
as a settler for large solids of mechanical impurities.
OPERATION
The present submersible screw pump operates as follows.
The pumping unit is sunk into an oil well by means of tubes 67
(FIG. 1) and the electric motor 1 of the drive is powered from the
daylight surface through the cable 2.
The torque of the electric drive 1 during its operation is
transmitted to the driving member 5 of the starting clutch 4
mounted on the shaft 3. The driving member is located within the
collar 60 (FIG. 15) of the driven member 6 (FIG.1) of the starting
clutch 4. Under the effect of centrifugal force the pawls 7 located
in the driving member 5 overcome the action of the return spring
and mesh with the claw 61 (FIGS. 15 16) of the collar 60 (FIG. 1).
Upon deactivating the electric motor of the drive 1, the pawls 7
under the action of the non-return spring are attracted to each
other, and the driven member 6 is disengaged from the driving
member 5. The driven member 6 is mounted on the drive shaft
rotating in the bearings 9 and 10. The bearings 10 may be
radial-thrust bearings provided with rubber-metal shock absorbers
11 which increase the life of these bearings.
From the driving shaft 8, the torque through the two double
universal joints 13 is transmitted first to one and then to the
other screw rotor 14.
The screw rotors 14 rotate in the elastic bushings 16 of the
stators 15 eccentrically and execute planetary motion. Since the
rotors 14 are arranged in the bushings 16 with a negative
allowance, they can be started with the standard submersible pump 1
only through an impact by means of the starting clutch 4.
In principle, the present screw rotors 14 can rotate in both
directions. However, the direction of rotation must be strictly
definite at a predetermined arrangement of the intake chambers 19
and the delivery chamber 20 with a safety valve 21. The opposite
direction of rotation would be unsuitable since the pump cannot
operate without being primed. The starting clutch 4 serves as a
non-return coupling to avoid such a possibility.
During undesirable reverse rotation, the pawls 7 do not engage the
claws 61 (FIG. 15, 16) of the collar 60 due to the presence of the
apertures 64 and the oblique surface 65 on the inner side of the
collar 60 (FIG. 1).
In the case of emergency axial displacement of the driven member 6
of the starting clutch 54 downwards or upwards, the pawls 7
disengage the claws 61 (FIGS. 15, 16) and the starting clutch 4
(FIG. 1) disconnects the electric drive 1 from the pump, thus
serving as a safety device.
In order to balance the axial loads due to the pressure developed
by the pump in the delivery chamber 20 and to unload the radial
thrust bearings 10, the pump is equipped with double screw rotors
14, one having a right-hand thread and the other a left-hand
thread. During the rotation of the rotors 14, the liquid from the
intake chambers 19 fills the closed spaces 18 between the rotors 14
and the elastic bushings 16 of the stators 15, and the flows of
liquid move in these spaces 18 along the axis of the stators 15
towards each other into the delivery chamber 20 housing the double
universal joint 13.
The combined flow of liquid from the two rotors 14 washes the
stator 15 which is more distant from the drive 1 and is fed first
into the safety valve 21 and then through the sludge pipe 66 into
the tubing 67 through which the liquid is pumped to the daylight
surface.
The connection of the screw rotors 14 through the double universal
joints 13 permits the rotors 14 to be self-aligning units occupying
the optimum position within the elastic bushings 16 of the stators
15, thus compensating for the technological errors associated with
the process of manufacture and assembly of the pump. Owing to the
fact that the rotors 14 rotate eccentrically about the axis of the
stators 15, to balance the centrifugal forces appearing during
rotation, the rotors 14 are displaced from the axis of the stators
15 in diametrically opposite directions, while the centers of the
extreme closed spaces 18 adjacent to the delivery chamber 20 are
located on a common line passing through the axis of the rigid
member 27 of the double universal joint 13.
The remaining unbalanced moment due to the pair of contrifugal
forces acting in opposite directions, creates a certain vibration
of the pump which improves filling of the intake chambers 19 and
the adjacent closed spaces 18 of the screw rotors. This effect is
particularly important during pumping of viscous liquids.
In this case, the suction capacity of the pump is of up to 8.5 m of
the column of liquid.
In addition, the vibration of the pump, which does not reduces the
strength of its components, effectively acts upon the oil flow
passing from the oil-bearing bed into the well and this also is an
advantage of the present submersible pump.
In order to provide for high heads of 1,000-2,000 meters of the
liquid column which are necessary for pumping oil from deep wells
and to meet the requirements of the strength of the pump
components, the elastic bushings 16 of the stators 15 are oblong,
in which case their length is at least 20 times the cross-sectional
diameter of the corresponding rotor 14.
In order to provide for a reliable coupling of the elastic bushings
16 with the rigid, for example metal casings 17 of the stators 15,
the inner surface of the casings 17 and the end faces 24 are
provided with grooves such as thread or rectangular cuts. The three
rows of uniformly disposed orifices 23 are used for the same
purpose.
The torque from the driving shaft 8 to the screw rotors 14 is
transmitted through the rollers 34 (FIGS. 7-12) of the double
universal joints 13. The truncated cones 29 of the heads 26 have an
angle of taper corresponding to the angle of deviation of the axis
of the rigid member 27 of the joint 13 from the axes of the rotors
14. Such making of the cones 29 provides for a linear contact
between the rollers 34 and the lines of intersection of the
truncated cones 29 with the part-cylindrical slots 30 of the heads
26.
The gap between the part-cylindrical slots 30 and 31 and the
rollers 34 placed between these slots limits the angle of deviation
of the member 27 from the axis of the rotor 14 and is selected so
that, with free rotation of the double universal joint 13 beyond
its one cover, the other free end of the joint 13 will not touch
housing 68 (FIG. 1) of the pump.
The axial load arising in the delivery chamber 20 is transmitted
from the rotors 14 to the part-spherical surfaces 28 (FIGS. 7,
9-12) of the caps 33 and the heads 26 of the double universal
joints 13 and is taken by the rigid member 27 which expands. If the
intake chamber 19 is disposed between the rotors 14 (FIG. 1), then
the rigid member 27 (FIGS. 7-12) will be compressed. To provide for
making of the part-spherical surfaces 28 of the caps 33 and the
heads 26 of hard wear-resistant material, they are in the form of
interchangeable inserts 36 and 37.
The safety valve 21 (FIG. 13) protects the oblong elastic bushings
16 against dry friction, excess pressure and eliminates their
untimely destruction. After sinking the pump into a well, the gate
48 and the pilot valve 49 of the valve 21 are in the bottom
position. Through the open ports 53 and the channels 52, the liquid
from the well is admitted into the bushing 50 of the pilot valve 49
and fills the empty tubing 67 which is used for sinking the pump
into the well. The gate 48 (FIG. 13) resting on the seating 46 does
not allow the liquid to enter the space between the rotors 14 (FIG.
1) and the shaped screw surface of the elastic bushings 16 of the
stators 15. Therefore, if the liquid contains mechanical
impurities, such cannot accumulate below the gate 48 and thus
impede the start of the pump during the operation.
After the pump has been started, the flow of liquid lifts the gate
48 (FIG. 13) in the guide bushing 45 up to the slots 47. The pilot
valve 49 raises, together with the gate 48, and closes the passage
of the liquid through the channels 52 to the delivery chamber 20
(FIGS. 1 and 2) of the tube 67 and back. The total amount of liquid
transferred by the pump is delivered to the daylight surface
through the tubes 67.
The pilot valve 49 (FIG. 13) and the gate 48 continue to move by
inertia and under the action of the liquid pumped. The pilot valve
49 enters the sleeve 54 of the hydraulic buffer 22 wherein it is
smoothly decelerated due to the presence of the calibrated hole
55.
The diameter of the hole 55 is determined depending on the
characteristics of the pump and the liquid being pumped. A portion
of the liquid is discharged from the space of the sleeve 54 of the
buffer through the channels 57 and the gap between the pilot valve
49 and the sleeve 54. The gentle transition along the oblique
surface 56 to the hole 55 is necessary for eliminating the
possibility of deposition of paraffin and sand in the inner space
of the sleeve 54 in advance of the hole 55.
Thus, the pilot valve 49 moves, together with the gate 48, under
the action of the difference of the forces of the flows of liquid
in the guide bushing 45 and in the bushing 54 of the buffer 22.
The hydraulic buffer 22 provides for a shock-free and reliable
operation of the entire valve and the pump as a whole. The gate 48
is located within the guide bushing 45 with a gap, the magnitude of
which depends on the output of the pump and the viscosity of the
liquid.
The pilot valve 49 moves downwards under the action of the pressure
of the liquid in the tubing 67 because the pilot valve 49 (FIG. 13)
is stepped and its cross section is different along its axis.
If the pump output exceeds the yield of the well or, for any
reason, the yield decreases during prolonged (several months)
operation of the pump, the dynamic level is reduced and the oil
column, which always contains gas, particularly in its upper
portion, descends to the delivery chambers 19 (FIG. 1) of the screw
rotors 14. The output of the pump is reduced due to an entrapping
of the gas by the rotors 14 together with the liquid and
compression of this gas within the closed spaces 18.
Simultaneously with the drop in the output capacity of the pump,
the velocity of the liquid in the gap between the gate 48 (FIG. 13)
and the walls of the guide bushing 45 is decreased. The remaining
constant force acting on the pilot valve 49 from above due to the
liquid pressure becomes greater than the force acting on the pilot
valve 48 from below. Thus, the pilot valve 49 moves downwards and
allows the liquid to pass from the delivery chamber 20 (FIG. 1)
into the well to the intake chambers 19 of the screw rotors 14,
thereby preventing the appearance of dry friction of the threads of
the elastic bushings 16 of the stators 15.
The liquid circulates through the safety valve 21 until it is
accumulated in the well and until the dynamic level is restored
necessary for reestablishing the rated output of the ump. In pump.
case the gate 48 (FIG. 13) emerges and overcomes the force of
pressure of the liquid acting on the pilot valve 49.
The pilot valve breaks the flow of liquid from the chamber 20
through the channels 52 and the ports 53, and the pump begins
pumping the liquid through the tubes 67 (FIG. 1) to the daylight
surface again.
Similarly, the safety valve 21 drops the liquid into the well at a
pressure exceeding the rated value and protects the elastic
bushings 16 and the double universal joints 13 against damage. The
pressure in the delivery chamber 20 can overpass the permissible
limit in the case of clogging the tubing 67 with sand and paraffin
or in the event of the gate on the surface being inadvertently left
closed.
When the pressure in the delivery chamber 20 rises at a constant
yield of the pump, the pilot valve 49 (FIG. 13) drops down and
opens the discharge ports 53 for a short period of time. After
reducing the pressure in the delivery chamber 20, the gate 48
raises the pilot valve 49 again, and the latter closes the
discharge channels 52 and the ports 53. When the tubing 67 is
closed, the pressure rises over again and the "up-down" movement of
the pilot valve 49 with the gate 48 is repeated.
When the pump stops to operate, the gate 48 (FIG. 1) is no more
affected by the effort on its bottom, and the pilot valve 49 lowers
under the action of the pressure of the liquid in the tubing 67.
The gate 48 will rest on its seating 46, thereby closing the way
for the liquid into the pump and its clogging. The liquid will flow
from the tubing 67 into the well, therefore the pump can be lifted
up from the well with the empty tubes should the need for its
repair arise.
The presence of the safety valve 21 provides for making a number of
technological operations during exploitation of oil wells: washing
of the tubing 67 for removing paraffin deposits if the pumped oil
contains paraffin, suppressing the wild flowing by means of thick
liquid prior to the raising of the pump if its output is
insufficient.
* * * * *