Hydraulically-driven differential type drainage and mining pump

Abstract

The utility model provides a hydraulic drive differential type drainage pump. The hydraulic drive differential type drainage pump comprises an oil drainage assembly, a hollow pipe plug assembly, a plunger assembly, an outer pipe assembly, an upper thick-wall pump cylinder, a lower thick-wall pump cylinder and a standing valve assembly. The plunger assembly slides in the upper thick-wall pump cylinder and the lower thick-wall pump cylinder; the upper portion of the hollow pipe plug assembly is connected with a hollow sucker rod, the upper portion of the oil drainage assembly is connected with an oil pipe, and the lower portion of the oil drainage assembly is connected with the outer pipe assembly, so that an inner pressure channel and an outer pressure channel are formed in the pump. According to the working principle of hydraulic differential driving, an inner hydraulic channel and an outer hydraulic channel are designed, and the plunger assembly reciprocates up and down through reversing of ground hydraulic driving. The whole pump has the advantages of long service life, convenience in operation, simplicity in maintenance and the like, and can be widely applied to sand-containing, ultra-deep, ultra-large tail pipe load, high inclination and horizontal coal-bed gas wells.

Description

Technical Field

[0001] The utility model relates to the field of drainage pumps, in particular to a hydraulic-driven differential drainage pump. Background Technique

[0002] As an important unconventional natural gas resource, the efficient development of coalbed methane is of great significance for ensuring national energy security and promoting the utilization of clean energy. However, the mining environment of coalbed methane wells is often very complex, especially for deep coalbed methane wells, whose well types are mostly large-inclination wells or horizontal wells, which puts higher requirements on drainage equipment.

[0003] At present, domestic coalbed methane drainage mainly relies on traditional drainage equipment such as beam pumping unit screw pumps, jet pumps, and rodless hydraulic pumps. Although these equipment ensure the normal production of coalbed methane to a certain extent, they each have some inherent limitations:

[0004] Rod and pipe eccentric wear problem: During the drainage process of large-inclination wells and horizontal wells, rod pumps and surface screw pumps are prone to rod and pipe eccentric wear, resulting in frequent equipment damage, high maintenance costs, and limited operation efficiency.

[0005] Insufficient pump setting depth: In deep coalbed methane wells, due to the limitation of pump setting depth, electric ordinary screw pumps are difficult to achieve efficient drainage, affecting production and economy.

[0006] Low efficiency of jet pumps: Jet pumps are prone to encounter surging flow and friction problems during use, resulting in low pump efficiency, and their operation requires a large amount of power fluid and high pressure, which not only increases energy consumption but also puts higher power requirements on the ground power fluid supply system.

[0007] In view of the above problems, dewatering and pressure reduction, and establishing a stable and reliable gas-water production channel have become the key to ensuring the production continuity of coalbed methane wells. Therefore, there is an urgent need for a new drainage technology that can work efficiently under complex well conditions, overcome the limitations of existing technologies, and improve the mining efficiency and economic benefits of coalbed methane wells. Content of the Utility Model

[0008] The main purpose of the utility model is to provide a hydraulic-driven differential drainage pump to solve the problems in the above background technique.

[0009] To solve the above technical problems, the technical solution adopted by the utility model is: including an oil drainage assembly, a hollow pipe plug assembly, a plunger assembly, an outer pipe assembly, an upper thick-walled pump barrel, a lower thick-walled pump barrel, and a fixed valve assembly;

[0010] The plunger assembly slides within the upper thick-walled pump barrel and the lower thick-walled pump barrel;

[0011] The upper part of the hollow pipe plug assembly is connected to the hollow sucker rod, the upper part of the oil drainage assembly is connected to the tubing, and the lower part is connected to the outer pipe assembly, thereby forming an internal pressure channel and an external pressure channel in the pump;

[0012] The upper part of the upper thick-walled pump barrel is connected to the upper coupling buffer body in the outer pipe assembly, and the lower part is connected to the lower coupling buffer body in the outer pipe assembly;

[0013] The upper part of the lower thick-walled pump barrel is connected to the lower coupling buffer body in the outer pipe assembly, and the lower part is connected to the fixed valve assembly;

[0014] The upper part of the outer pipe assembly is connected to the oil drainage assembly, and the lower part is connected to the downhole tubing.

[0015] Preferably, the oil drainage assembly includes an oil drainage coupling, an oil drainage pin, an oil drainage sliding sleeve and a spring;

[0016] The oil drainage sliding sleeve and the spring are arranged inside the oil drainage coupling, the oil drainage pin is arranged on both sides of the oil drainage coupling and passes through the oil drainage coupling and the oil drainage sliding sleeve to connect the two;

[0017] The upper part of the oil drainage sliding sleeve abuts against the oil drainage coupling, one end of the spring abuts against the oil drainage sliding sleeve, and the other end abuts against the reducer tubing coupling in the outer pipe assembly. The lower part of the oil drainage coupling is connected to the reducer tubing coupling.

[0018] Preferably, the outer pipe assembly includes a reducer tubing coupling, a crossover pipe, an upper coupling buffer body, an upper outer pipe, a lower coupling buffer body, a lower outer pipe and a reducer joint connected in sequence;

[0019] Hydraulic buffer cavities are provided at opposite ends of the upper coupling buffer body and the lower coupling buffer body. The upper thick-walled pump barrel is arranged inside the upper outer pipe. The upper part of the upper thick-walled pump barrel is threadedly connected to the upper coupling buffer body, and the lower part is in clearance fit with the lower coupling buffer body through a sealing ring.

[0020] Preferably, a pressure cavity is formed between the upper outer pipe and the upper thick-walled pump barrel. The bottom of the pressure cavity is a sand settling ring cavity. The top of the pressure cavity passes through the upper coupling buffer body and is communicated with the tubing through the external pressure channel;

[0021] The upper thick-walled pump barrel is provided with oil inlets on both sides above the lower coupling buffer body.

[0022] Preferably, the plunger assembly includes an upper buffer joint body, a spray-welded upper plunger, an intermediate floating valve cover, a central tube, a spray-welded lower plunger, a lower floating valve cover and a valve seat plug connected in sequence;

[0023] A lower buffer joint body is fixedly arranged outside the intermediate floating valve cover. The upper buffer joint body and the lower buffer joint body are arranged between the upper coupling buffer body and the lower coupling buffer body in the outer pipe assembly. The end parts of the upper buffer joint body and the lower buffer joint body respectively abut against the hydraulic buffer cavities on the upper coupling buffer body and the lower coupling buffer body and slide therein;

[0024] The outer seal of the spray-welded upper plunger abuts against the inner wall of the upper thick-walled pump barrel and slides therein.

[0025] Preferably, a return spring and a floating valve ball are provided in both the middle floating valve cover and the lower floating valve cover. One end of the return spring abuts against the middle floating valve cover and the lower floating valve cover, and the other end abuts against the floating valve ball.

[0026] Preferably, a plurality of centering ribs are provided on the inner walls of the middle floating valve cover, the lower floating valve cover and the fixed valve cover, and the periphery of the floating valve ball abuts against the centering ribs and slides thereon.

[0027] Preferably, through holes are provided on both sides of the ends of the upper buffer joint body and the lower buffer joint body, and the through holes are higher than the hydraulic buffer cavity.

[0028] Preferably, the fixed valve assembly includes a fixed valve cover, a fixed valve joint and a liquid inlet screen pipe connected in sequence;

[0029] A return spring and a fixed valve ball are provided in the fixed valve cover. One end of the return spring abuts against the fixed valve cover, and the other end abuts against the fixed valve ball;

[0030] Both ends of the lower thick-walled pump barrel are respectively connected to the fixed valve cover and the lower collar buffer body.

[0031] The utility model provides a hydraulic-driven differential drainage pump. The plunger assembly adopts a structure of upper and lower double plungers, an upper large-diameter plunger and a lower small-diameter plunger, achieving the displacement of a large-diameter pump and the effect of a hydraulic feedback pump. Both the valve ball and the valve seat are made of cemented carbide to improve the adaptability to the well conditions of the ball seat. The guide rib structure is adopted in the valve cover, enabling the valve ball to only reciprocate up and down, greatly reducing the phenomena such as the valve ball being deflected, the closing being delayed, or even not closing under the influence of gravity in highly deviated wells or horizontal wells; an outer pipe structure is designed outside the pump barrel, greatly increasing the load-bearing capacity of the whole pump and the load of the tail pipe. At the same time, an annular cavity is formed between the outer pipe and the pump barrel, which can play the role of sediment settling. This pump breaks through the problem of eccentric wear of the sucker rod and pipe during the conventional coalbed methane extraction process. Through the working principle of hydraulic differential drive, two internal and external hydraulic channels are designed, and by reversing the ground hydraulic drive, the plunger assembly reciprocates up and down. The whole pump has the advantages of long service life, being widely applicable to sand-containing, ultra-deep, extra-large tail pipe load, highly deviated and horizontal coalbed methane wells, convenient operation and simple maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further describes the present utility model in conjunction with the drawings and embodiments:

[0033] Figure 1 is the front sectional view of the overall structure of the pump body of the present utility model;

[0034] Figure 2 is the front sectional view of the plunger assembly of the present utility model;

[0035] Figure 3 It is a sectional view of the centralizing rib inside the valve cover of the present utility model;

[0036] In the figure: oil drain coupling 1; oil drain pin 2; reducer tubing coupling 3; upper coupling buffer body 4; upper outer tube 5; upper thick-walled pump barrel 6; lower coupling buffer body 7; lower thick-walled pump barrel 8; fixed valve cover 9; reducer joint 10; oil drain sliding sleeve 11; spring 12; hollow tube plug assembly 13; cross-over pipe 14; upper buffer joint body 15; spray-welded upper plunger 16; intermediate floating valve cover 17; return spring 18; floating valve ball 19; lower buffer joint body 20; central tube 21; spray-welded lower plunger 22; lower floating valve cover 23; valve seat pipe plug 24; lower outer tube 25; fixed valve ball 26; fixed valve joint 27; liquid inlet screen pipe 28; hydraulic buffer cavity 29; sand grains 30; centralizing rib 31; internal pressure channel 32; external pressure channel 33. Detailed implementation mode

[0037] Embodiment 1

[0038] As Figures 1 to 3 shown, a hydraulically driven differential pumping unit includes an oil drain assembly, a hollow tube plug assembly 13, a plunger assembly, an outer tube assembly, an upper thick-walled pump barrel 6, a lower thick-walled pump barrel 8 and a fixed valve assembly;

[0039] The plunger assembly slides inside the upper thick-walled pump barrel 6 and the lower thick-walled pump barrel 8;

[0040] The upper part of the hollow tube plug assembly 13 is connected to a hollow sucker rod, the upper part of the oil drain assembly is connected to a tubing, and the lower part is connected to the outer tube assembly, thereby forming an internal pressure channel 32 and an external pressure channel 33 inside the pump;

[0041] The upper part of the upper thick-walled pump barrel 6 is connected to the upper coupling buffer body 4 in the outer tube assembly, and the lower part is connected to the lower coupling buffer body 7 in the outer tube assembly;

[0042] The upper part of the lower thick-walled pump barrel 8 is connected to the lower coupling buffer body 7 in the outer tube assembly, and the lower part is connected to the fixed valve assembly;

[0043] The upper part of the outer tube assembly is connected to the oil drain assembly, and the lower part is connected to the tubing downhole.

[0044] The hollow tube plug assembly 13 is connected to the hollow sucker rod, used to transmit power to the plunger assembly, and at the same time ensure the pressure seal inside the pump. The plunger assembly slides inside the upper thick-walled pump barrel 6 and the lower thick-walled pump barrel 8, and through its movement, a pressure change is generated to promote the liquid to be pumped from the bottom of the well to the surface.

[0045] The outer pipe assembly connects various parts of the pump to form a whole and is connected to the downhole tubing to transfer the pumped liquid. The upper thick-walled pump barrel 6 and the lower thick-walled pump barrel 8 provide a sliding space for the plunger and bear high pressure at the same time, and are key pressure-bearing components in the pump structure.

[0046] The fixed valve assembly is located at the bottom of the pump, controls the one-way flow of the liquid, and ensures that the liquid can only flow upward and will not flow back.

[0047] The whole pump uses hydraulic drive, without the reciprocating motion of the rod and tubing string, effectively avoiding the eccentric wear problem caused by the reciprocating motion of the rod and tubing, and is suitable for horizontal wells and highly deviated wells, greatly improving the life and reliability of the whole pump.

[0048] The plunger assembly of this pump adopts a double plunger structure, with a large plunger in the upper part and a small plunger in the lower part, enabling the whole pump to have the displacement of a large pump, achieving the effect of a hydraulic feedback pump and improving the pump efficiency.

[0049] Preferably, the oil drain assembly includes an oil drain collar 1, an oil drain pin 2, an oil drain sliding sleeve 11 and a spring 12;

[0050] The oil drain sliding sleeve 11 and the spring 12 are arranged inside the oil drain collar 1, the oil drain pin 2 is arranged on both sides of the oil drain collar 1 and passes through the oil drain collar 1 and the oil drain sliding sleeve 11 to connect the two;

[0051] The upper part of the oil drain sliding sleeve 11 abuts against the oil drain collar 1, one end of the spring 12 abuts against the oil drain sliding sleeve 11, and the other end abuts against the reducer tubing collar 3 in the outer pipe assembly. The lower part of the oil drain collar 1 is connected to the reducer tubing collar 3.

[0052] An oil drainer is designed at the upper part of the pump. When the whole pump is lifted out of the well, a striking head is dropped at the wellhead to strike the oil drainer, causing the oil drain pin 2 to open and completing automatic oil drainage, thus ensuring the oil pollution at the wellhead.

[0053] Preferably, the outer pipe assembly includes a reducer tubing collar 3, a crossover pipe 14, an upper collar buffer body 4, an upper outer pipe 5, a lower collar buffer body 7, a lower outer pipe 25 and a reducer joint 10 connected in sequence;

[0054] Hydraulic buffer cavities 29 are provided at the opposite ends of the upper collar buffer body 4 and the lower collar buffer body 7. The upper thick-walled pump barrel 6 is arranged inside the upper outer pipe 5. The upper part of the upper thick-walled pump barrel 6 is threadedly connected to the upper collar buffer body 4, and the lower part is in clearance fit with the lower collar buffer body 7 through a sealing ring.

[0055] The outer pipe assembly can completely transfer the force of the whole pump to the outer pipe. At the same time, the outer pipe uses high-strength tubing with high mechanical properties, thus greatly increasing the load-bearing capacity of the whole pump.

[0056] Preferably, a pressure chamber is formed between the upper outer tube 5 and the upper thick-walled pump barrel 6, the bottom of the pressure chamber is a sand settling annular chamber, and the top of the pressure chamber passes through the upper coupling buffer body 4 and communicates with the oil pipe through the external pressure channel 33;

[0057] The upper thick-walled pump barrel 6 is provided with oil inlets on both sides above the lower coupling buffer body 7. The sand settling annular cavity can effectively deposit sand particles 30 in the coalbed methane well, can effectively prevent sand jamming, and play a role in sand prevention.

[0058] Preferably, the plunger assembly includes an upper buffer joint body 15, a spray-welded upper plunger 16, an intermediate floating valve cover 17, a center pipe 21, a spray-welded lower plunger 22, a lower floating valve cover 23 and a valve seat pipe plug 24 which are connected in sequence;

[0059] A lower buffer joint body 20 is fixedly arranged on the outer side of the intermediate floating valve cover 17, and the upper buffer joint body 15 and the lower buffer joint body 20 are arranged between the upper coupling buffer body 4 and the lower coupling buffer body 7 in the outer pipe assembly, and the ends of the upper buffer joint body 15 and the lower buffer joint body 20 respectively slide against the hydraulic buffer cavity 29 on the upper coupling buffer body 4 and the lower coupling buffer body 7;

[0060] The outer side of the spray-welded upper plunger 16 is sealed against and slides in the upper thick-walled pump barrel 6 .

[0061] A hydraulic buffer chamber 29 is provided on the upper coupling buffer body 4 and the lower coupling buffer body 7 at the limit positions of the upper and lower strokes of the plunger assembly, and a guide structure is provided at the ends of the upper buffer joint body 15 and the lower buffer joint body 20. The guide structure is inserted into the hydraulic buffer chamber 29, which can effectively prevent the mechanical impact of the plunger assembly at the upper and lower limit positions, causing damage to parts and thus causing failure of the entire pump.

[0062] The threaded connections of the various parts of the plunger assembly are designed with clamping surfaces, which can effectively ensure the coaxiality of all parts on the plunger assembly and avoid misalignment that causes eccentric wear of the plunger assembly.

[0063] The intermediate floating valve cover 17 and the valve seat are located on the upper part of the center tube 21, which can effectively reduce the tension of the liquid column in the pipe column on the center tube 21 during the upward stroke of the plunger assembly, so that the load of the liquid column is fully loaded on the floating valve cover 17 and the valve seat, which can effectively improve the life of the entire pump.

[0064] The whole pump is designed with double floating valves and double fixed valves, which can ensure the reliability of the pump, reduce the pump inspection cycle, extend the life of the whole pump, reduce operating costs and improve economic benefits.

[0065] Preferably, a return spring 18 and a travel valve ball 19 are provided in both the intermediate travel valve cover 17 and the downstream travel valve cover 23 , and one end of the return spring 18 abuts against the intermediate travel valve cover 17 and the downstream travel valve cover 23 , and the other end abuts against the travel valve ball 19 .

[0066] Preferably, the inner walls of the intermediate movable valve cover 17 , the lower movable valve cover 23 and the fixed valve cover 9 are all provided with a plurality of centralizing ribs 31 , and the peripheral side of the movable valve ball 19 abuts against the centralizing ribs 31 and slides.

[0067] The movable valve ball 19 can only move up and down, and at the same time, a strong closing structure of a reset spring 18 is added inside the fixed valve cover 9. The upper part of the fixed valve is designed to be acted upon by the elastic force of the spring. The spring is always in contact with the surface of the valve ball, and the preload force of the spring is greater than the weight of the valve ball, so that the valve ball can be reset at any well inclination angle. When the ball valve is closed, the valve ball can be seated on the valve seat in time under the action of the spring force, thereby reducing the phenomenon of the valve ball falling off, delayed closing, or even not closing due to the influence of gravity in highly inclined wells or horizontal wells.

[0068] Preferably, both sides of the ends of the upper buffer joint body 15 and the lower buffer joint body 20 are provided with through holes, and the through holes are higher than the hydraulic buffer chamber 29 .

[0069] Preferably, the fixed valve assembly includes a fixed valve cover 9, a fixed valve connector 27 and a liquid inlet screen pipe 28 connected in sequence;

[0070] A return spring 18 and a fixed valve ball 26 are arranged in the fixed valve cover 9, one end of the return spring 18 abuts against the fixed valve cover 9, and the other end abuts against the fixed valve ball 26;

[0071] The two ends of the lower thick-walled pump barrel 8 are respectively connected to the fixed valve cover 9 and the lower coupling buffer body 7.

[0072] Key components such as plunger, pump barrel, valve cover, ball valve, etc. are made of materials with strong corrosion resistance and excellent mechanical properties. They have excellent wear resistance and corrosion resistance and are suitable for use in H-containing 2 S, CO 2 All parts are treated with mature heat treatment and surface treatment technology to enhance the wear and corrosion resistance and improve the reliability and service life of the pump.

[0073] Example 2

[0074] like Figures 1 to 3 As shown, in combination with Example 1, a method for using a hydraulically driven differential drainage pump is further described, and the steps of the method are as follows:

[0075] S1, the oil pipe is connected to the oil drain assembly, and after the drainage pump is lowered to the predetermined position underground along with the oil pipe, the hollow sucker rod is docked with the hollow pipe plug assembly 13, thereby forming two channels, the external pressure channel 33 and the internal pressure channel 32, in the pump;

[0076] S2. During operation, when the pressure in the external pressure passage 33 is greater than that in the internal pressure passage 32, the plunger assembly moves upward under the drive of the external pressure, the floating valve ball 19 closes, and the liquid column above the plunger is discharged from the hollow pipe driven by the plunger assembly. At the same time, the volume of the pump chamber below the plunger assembly increases and the pressure drops, and the fixed valve ball 26 opens under the action of the submerged pressure, and the confined water in the coalbed methane enters the pump chamber from the fixed valve assembly.

[0077] S3. During the downward stroke, the pressure in the internal pressure passage 32 is greater than that in the external pressure passage 33. The plunger assembly moves downward under the drive of the internal pressure, the floating valve ball 19 opens, the volume of the pump chamber below the plunger assembly decreases and the pressure increases, and the fixed valve ball 26 closes under the action of the chamber pressure. The liquid in the pump chamber below the plunger assembly enters the hollow pipe above the plunger assembly through the floating valve.

[0078] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A hydraulically driven differential drainage pump, characterized in that: It includes an oil drain assembly, a hollow tube plug assembly (13), a plunger assembly, an outer tube assembly, an upper thick-walled pump barrel (6), a lower thick-walled pump barrel (8) and a fixed valve assembly; The plunger assembly is located and slides inside the upper thick-walled pump barrel (6) and the lower thick-walled pump barrel (8); The upper portion of the hollow pipe plug assembly (13) is connected to the hollow sucker rod, the upper portion of the oil drain assembly is connected to the oil pipe, and the lower portion is connected to the outer pipe assembly, thereby forming an internal pressure channel (32) and an external pressure channel (33) in the pump; The upper portion of the upper thick-walled pump barrel (6) is connected to an upper coupling buffer body (4) in the outer tube assembly, and the lower portion is connected to a lower coupling buffer body (7) in the outer tube assembly; The upper part of the lower thick-walled pump barrel (8) is connected to the lower coupling buffer body (7) in the outer tube assembly, and the lower part is connected to the fixed valve assembly; The upper part of the outer pipe assembly is connected to the oil drain assembly, and the lower part is connected to the oil pipe downhole.

2. A hydraulically driven differential drainage pump according to claim 1, characterized in that: The oil drain assembly comprises an oil drain coupling (1), an oil drain pin (2), an oil drain sliding sleeve (11) and a spring (12); The oil drain sleeve (11) and the spring (12) are arranged inside the oil drain coupling (1), and the oil drain pin (2) is arranged on both sides of the oil drain coupling (1) and passes through the oil drain coupling (1) and the oil drain sleeve (11) to connect the two. The upper part of the oil drain sleeve (11) abuts against the oil drain coupling (1), one end of the spring (12) abuts against the oil drain sleeve (11), and the other end abuts against the variable buckle oil pipe coupling (3) in the outer pipe assembly, and the lower part of the oil drain coupling (1) is connected to the variable buckle oil pipe coupling (3).

3. A hydraulically driven differential drainage pump according to claim 1, characterized in that: The outer tube assembly comprises a variable buckle oil pipe coupling (3), a bridge pipe (14), an upper coupling buffer body (4), an upper outer tube (5), a lower coupling buffer body (7), a lower outer tube (25) and a variable buckle joint (10) which are connected in sequence; A hydraulic buffer chamber (29) is provided at opposite ends of the upper coupling buffer body (4) and the lower coupling buffer body (7). The upper thick-walled pump barrel (6) is provided inside the upper outer tube (5). The upper portion of the upper thick-walled pump barrel (6) is threadedly connected to the upper coupling buffer body (4), and the lower portion is gap-fitted with the lower coupling buffer body (7) via a sealing ring.

4. A hydraulically driven differential drainage pump according to claim 3, characterized in that: A pressure chamber is formed between the upper outer tube (5) and the upper thick-walled pump barrel (6), the bottom of the pressure chamber is a sand settling annular chamber, and the top of the pressure chamber passes through the upper coupling buffer body (4) and is connected to the oil pipe through the external pressure channel (33); The upper thick-walled pump barrel (6) is provided with oil inlets on both sides above the lower coupling buffer body (7).

5. The hydraulically driven differential drainage pump according to claim 1, characterized in that: The plunger assembly comprises an upper buffer joint body (15), a spray-welded upper plunger (16), an intermediate movable valve cover (17), a center pipe (21), a spray-welded lower plunger (22), a lower movable valve cover (23) and a valve seat pipe plug (24) which are connected in sequence; A lower buffer joint body (20) is fixedly provided on the outer side of the intermediate floating valve cover (17); the upper buffer joint body (15) and the lower buffer joint body (20) are arranged between the upper coupling buffer body (4) and the lower coupling buffer body (7) in the outer pipe assembly; the ends of the upper buffer joint body (15) and the lower buffer joint body (20) respectively abut against and slide in hydraulic buffer cavities (29) on the upper coupling buffer body (4) and the lower coupling buffer body (7); The outer side of the spray-welded upper plunger (16) is sealed against and slides inside the upper thick-walled pump barrel (6).

6. A hydraulically driven differential drainage pump according to claim 5, characterized in that: A return spring (18) and a travel valve ball (19) are provided in the middle travel valve cover (17) and the lower travel valve cover (23). One end of the return spring (18) abuts against the middle travel valve cover (17) and the lower travel valve cover (23), and the other end abuts against the travel valve ball (19).

7. The hydraulically driven differential drainage pump according to claim 1, characterized in that: The inner walls of the intermediate movable valve cover (17) and the lower movable valve cover (23) in the plunger assembly and the fixed valve cover (9) in the fixed valve assembly are all provided with a plurality of centering ribs (31), and the peripheral side of the movable valve ball (19) abuts against the centering ribs (31) to slide.

8. The hydraulically driven differential drainage pump according to claim 5, characterized in that: Through holes are provided on both sides of the ends of the upper buffer joint body (15) and the lower buffer joint body (20), and the through holes are higher than the hydraulic buffer chamber (29).

9. The hydraulically driven differential drainage pump according to claim 1, characterized in that: The fixed valve assembly comprises a fixed valve cover (9), a fixed valve connector (27) and a liquid inlet screen pipe (28) which are connected in sequence; A return spring (18) and a fixed valve ball (26) are arranged in the fixed valve cover (9), one end of the return spring (18) abuts against the fixed valve cover (9), and the other end abuts against the fixed valve ball (26); Both ends of the lower thick-walled pump barrel (8) are respectively connected to the fixed valve cover (9) and the lower coupling buffer body (7).

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