A multi-stage pump frequency conversion constant pressure water supply system suitable for low flow rates in drilling rig groups

Abstract

This invention provides a multi-stage pump frequency conversion constant pressure water supply system suitable for low-flow drilling rig groups. A centralized controller (1) is connected to three parallel centralized water supply branches (4) via a frequency converter (2). The outlets of the centralized water supply branches (4) are connected to two secondary distribution water supply units (9). A booster device (11) is located between the two secondary distribution water supply units (9). A fourth electric gate valve (12) and a fifth electric gate valve (13) are connected in series on a second connecting pipe (17), and a sixth electric gate valve (14) and a seventh electric gate valve (15) are connected in parallel on a first connecting pipe (16). The outlet of the booster device (11) is connected to the second connecting pipe (17) between the fourth electric gate valve (12) and the fifth electric gate valve (13). This device meets the usage requirements of low-flow drilling rig groups and solves the problem of pump overheating.

Description

Technical Field

[0001] This utility model relates to the field of coalbed methane depressurization and outburst suppression technology, specifically to a multi-stage pump frequency conversion constant pressure water supply system suitable for low-flow drilling rig groups. Background Technology

[0002] Hydraulic perforation technology is a key technology for coal seam decompression, permeability enhancement, and outburst prevention. Within the influence range of hydraulic perforation, the coal body surrounding the perforation channel is continuously eroded by high-pressure water, further releasing the stress in the coal body and causing expansion and deformation. At the same time, the coal seam is decompressed, the ground stress decreases, the porosity and fractures increase, the permeability of the coal seam increases, the gas desorption rate in the coal reservoir increases, and gas extraction is promoted. Currently, drilling rigs that integrate drilling and perforation are widely used in the field of coalbed methane decompression and outburst prevention technology. Multistage pumps or self-balancing multistage pumps are used as the high constant pressure water supply equipment for drilling rigs, thus replacing emulsion pumps. This greatly stabilizes the water supply pressure for perforation drilling through layers in bottom rock roadways, not only ensuring the quality of drilling and perforation but also reducing labor intensity and improving the automation level and operational efficiency of water supply for perforation drilling through layers in bottom rock roadways.

[0003] Multistage pumps or self-balancing multistage pumps are used as the supply equipment for high-pressure water for drilling and punching of drilling rig groups. In order to achieve coordinated operation of drilling rig groups, several multistage pumps or self-balancing multistage pumps are usually operated in parallel. When drilling rig groups are working together, the number or speed of the multistage pumps or self-balancing multistage pumps operating in parallel is adjusted in real time by frequency converter according to the number of drilling rigs and the pressure of the water storage tank, so as to achieve a constant high-pressure water supply for drilling and punching of drilling rig groups. However, if, for some reason, the number of drilling rigs in the drilling rig group is small, and the high-pressure water supplied by the frequency converter adjusting the number or speed of the multistage pumps or self-balancing multistage pumps is much greater than the high-pressure water consumption of the drilling rigs in operation, the multistage pumps or self-balancing multistage pumps installed in parallel will still be in operation. At this time, the water medium in the multistage pumps or self-balancing multistage pumps is circulating in the pump body, and the kinetic energy of the water medium in the pump body will be converted into heat, which will cause the pump body of the multistage pumps or self-balancing multistage pumps to heat up. In severe cases, the pump shaft may seize up, which will also affect the service life of the multistage pumps or self-balancing multistage pumps.

[0004] Therefore, in order to meet the usage requirements of drilling rig groups under low flow conditions, and at the same time prevent the pump body of multi-stage pumps or self-balancing multi-stage pumps from overheating, there is an urgent need for a multi-stage pump variable frequency constant pressure water supply system that is suitable for low flow conditions of drilling rig groups without affecting their normal operation. Summary of the Invention

[0005] This invention proposes a multi-stage pump frequency conversion constant pressure water supply system suitable for drilling rig groups with low flow rates. By connecting two water storage tanks and using a booster device, along with a control unit mainly composed of a programmable logic controller and a frequency converter, it can not only provide stable high constant pressure water for the normal operation of drilling rig groups, but also solve the technical problem of pump body overheating under low flow rate conditions of drilling rig groups.

[0006] To achieve the above objectives, the technical solution of this utility model is as follows: A multi-stage pump frequency conversion constant pressure water supply system suitable for small flow rates in drilling rig groups, comprising a centralized controller, a frequency converter, a pressure stabilizing tank, centralized water supply branches, a safety valve, an outlet pressure sensor, a flow sensor, a second electric gate valve, a third electric gate valve, a secondary distribution water supply unit, a booster device, a fourth electric gate valve, a fifth electric gate valve, a sixth electric gate valve, a seventh electric gate valve, and a switch. The centralized controller is connected to three centralized water supply branches installed in parallel via the frequency converter. The bottom outlet of the pressure stabilizing tank is connected to the three centralized water supply branches via pipelines. The outlets of the three centralized water supply branches are connected to two secondary distribution water supply units via centralized water supply pipelines. A safety valve, an outlet pressure sensor, and a flow sensor are installed sequentially in the direction of internal medium flow. The second and third electric gate valves are installed between the two secondary water distribution units and the centralized water supply pipeline, respectively. A booster device is located between the two secondary water distribution units. The two ends of the first and second connecting pipes are connected to the two secondary water distribution units, respectively. The fourth and fifth electric gate valves are installed in series on the second connecting pipe, and the sixth and seventh electric gate valves are installed in parallel on the first connecting pipe. The outlet of the booster device is connected to the second connecting pipe between the fourth and fifth electric gate valves via a manual shut-off valve. The signal control lines of the two secondary water distribution units are connected to the centralized controller via a switch, respectively.

[0007] Furthermore, the secondary distribution water supply unit includes a water storage tank, a drilling rig connecting pipe, a pressure gauge, a water storage tank pressure sensor, and a secondary distribution controller. Several drilling rig connecting pipes are connected to the water storage tank via outlet flanges on the side of the water storage tank. The other end of each drilling rig connecting pipe is connected to the drilling rig. The pressure gauge and the water storage tank pressure sensor are respectively installed on the top of the water storage tank. The pressure gauge can directly display the pressure inside the water storage tank. The water storage tank pressure sensor transmits the collected water storage tank pressure signal to the input terminal of the secondary distribution controller via a signal line. One port at the bottom of the water storage tank is connected to the centralized water supply pipeline via a third electric gate valve. Another port at the bottom of the water storage tank is connected to one end of a first connecting pipe. The other end of the first connecting pipe is connected to the corresponding port at the bottom of another water storage tank. The side port of the water storage tank is connected to the corresponding port on the side of another water storage tank via a second connecting pipe. The secondary distribution water supply unit is connected to a switch via a signal control line.

[0008] Furthermore, the signal control lines of the fourth and sixth electric gate valves are connected to the secondary distribution controller of a secondary distribution water supply unit, and the signal control lines of the fifth and seventh electric gate valves are connected to the secondary distribution controller of another secondary distribution water supply unit. When a secondary distribution water supply unit is in a low flow condition, the electric gate valves controlled by the two secondary distribution controllers respectively form an interlock function.

[0009] Furthermore, the outlet pressure sensor, flow sensor, second electric gate valve, and third electric gate valve are connected to the centralized controller via signal control lines. The outlet pressure sensor and flow sensor monitor the pressure and flow data of the fluid medium in the centralized water supply pipeline in real time, and compare them with the monitoring data of the pressure sensor in the water storage tank of the secondary distribution water supply unit and the volume data of the fluid medium in the water storage tank to further determine the number of multi-stage pumps to start and stop and the speed. The second electric gate valve and the third electric gate valve are connected to the secondary distribution water supply unit, and the opening and closing of the second electric gate valve and the third electric gate valve are determined by the working status of the secondary distribution water supply unit.

[0010] Furthermore, the centralized water supply branch includes a first shut-off valve, an inlet pressure sensor, a multistage pump, a first manual ball valve, a check valve, and a first electric gate valve. The first shut-off valve and the inlet pressure sensor are respectively installed on the inlet pipe of the multistage pump, and the first manual ball valve, the check valve, and the first electric gate valve are respectively installed on the outlet pipe of the multistage pump. The three-phase asynchronous motor of the multistage pump in each centralized water supply branch is respectively connected to the output terminal of the frequency converter, and the inlet pressure sensor and the first electric gate valve are respectively connected to the centralized controller through signal control lines.

[0011] Furthermore, the centralized controller, frequency converter, pressure stabilizing tank, and centralized water supply branch are installed in the roadway, the two secondary distribution water supply units are installed near the coal seam mining face, and the switch is set between the two secondary distribution water supply units, or the switch is set at the booster device, which realizes the spatial separation of centralized water supply and secondary distribution water supply, and also solves the problem of long-distance water transportation for drilling rig groups.

[0012] Furthermore, there are two pressure stabilizing tanks, which are installed in series at the inlet of the centralized water supply branch. The pressure stabilizing tanks can stabilize the pressure of the fluid medium entering the centralized water supply branch, avoid pressure fluctuations in the fluid entering the centralized water supply branch, and thus ensure the pressure stability of the fluid medium in the water storage tank.

[0013] Compared with the prior art, the multi-stage pump frequency conversion constant pressure water supply system for drilling rig groups with low flow rates described in this utility model has the following beneficial effects: (1) By setting the minimum speed parameter of the multi-stage pump in the centralized water supply branch, when the water consumption of drilling and punching in a certain secondary distribution water supply unit is less than the flow rate at the minimum speed of the multi-stage pump, the centralized controller sends a multi-stage pump shutdown command to avoid the pump body of the multi-stage pump from overheating.

[0014] (2) By cooperating with the booster device and the fourth, fifth, sixth and seventh electric gate valves, the technical problem of a single secondary distribution water supply unit operating at low flow rate or two secondary distribution water supply units operating at low flow rate simultaneously after the multi-stage pump stops is solved. This not only ensures the stability of the drilling and punching water pressure of the drilling rig, but also ensures sufficient water flow.

[0015] (3) Through the secondary distribution controller of each secondary distribution water supply unit, the individual control of the secondary distribution water supply unit is realized. At the same time, the secondary distribution controller realizes the linkage and coordination between the secondary distribution water supply unit and the centralized water supply branch through the information transmission between the switch and the centralized controller, which greatly improves the intelligence level of coalbed methane depressurization and outburst elimination. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structural system of this utility model; Figure 2 This is a schematic diagram of the secondary water supply system of this utility model; Figure 3 This is a schematic diagram of the centralized water supply system of this utility model; Figure 4 This is a schematic diagram of the centralized water supply branch system of this utility model.

[0017] The diagram is labeled as follows: 1: Central controller; 2: Frequency converter; 3: Pressure stabilizing tank; 4: Central water supply branch; 41: First shut-off valve; 42: Inlet pressure sensor; 43: Multistage pump; 44: First manual ball valve; 45: Check valve; 46: First electric gate valve; 5: Safety valve; 6: Outlet pressure sensor; 61: Flow sensor; 7: Second electric gate valve; 8: Third electric gate valve; 9: Secondary distribution water supply unit; 91: Water storage tank; 92: Drilling rig connecting pipe; 93: Pressure gauge; 94: Water storage tank pressure sensor; 95: Secondary distribution controller; 10: Switch; 11: Booster device; 12: Fourth electric gate valve; 13: Fifth electric gate valve; 14: Sixth electric gate valve; 15: Seventh electric gate valve; 16: First connecting pipe; 17: Second connecting pipe. Detailed Implementation

[0018] In the description of this utility model, it should be noted that the terms "left", "right", "front", "rear", "inner", "outer", "both ends", "one end", "the other end", etc., indicate the orientation or positional relationship based on the fluid medium flow direction shown in the accompanying drawings. They are only for the convenience of describing this utility model and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0019] To make the technical problem to be solved, the technical solution and the implementation effect of this utility model clearer, the following is in conjunction with the appendix. Figure 1-4 The following is a further description of one embodiment of the present invention, with appended details. Figure 1-4 Thin solid lines represent devices or pipes, while dashed lines represent control signal lines.

[0020] See appendix Figure 1-4 As a preferred embodiment, the present invention provides a multi-stage pump frequency conversion constant pressure water supply system suitable for small flow rates in drilling rig groups, comprising a centralized controller 1, a frequency converter 2, a pressure stabilizing tank 3, centralized water supply branches 4, a safety valve 5, an outlet pressure sensor 6, a flow sensor 61, a second electric gate valve 7, a third electric gate valve 8, a secondary distribution water supply unit 9, a booster device 11, a fourth electric gate valve 12, a fifth electric gate valve 13, a sixth electric gate valve 14, a seventh electric gate valve 15, and a switch 10. The centralized controller 1 is connected to three centralized water supply branches 4 installed in parallel via the frequency converter 2. The bottom outlet of the pressure stabilizing tank 3 is connected to the three centralized water supply branches 4 via pipes. The outlets of the three centralized water supply branches 4 are connected to two secondary distribution water supply units 9 via centralized water supply pipes. The flow path of the medium within the centralized water supply pipes... Safety valve 5, outlet pressure sensor 6, and flow sensor 61 are installed sequentially. Second electric gate valve 7 and third electric gate valve 8 are respectively installed between two secondary water distribution units 9 and the centralized water supply pipeline. Booster device 11 is set between two secondary water distribution units 9. The two ends of the first connecting pipe 16 and the second connecting pipe 17 are respectively connected to the two secondary water distribution units 9. Fourth electric gate valve 12 and fifth electric gate valve 13 are installed in series on the second connecting pipe 17. Sixth electric gate valve 14 and seventh electric gate valve 15 are installed in parallel on the first connecting pipe 16. The outlet of booster device 11 is connected to the second connecting pipe 17 between the fourth electric gate valve 12 and the fifth electric gate valve 13 through a manual shut-off valve. The signal control lines of the two secondary water distribution units 9 are respectively connected to the centralized controller 1 through switch 10.

[0021] As a preferred embodiment, see Appendix Figure 1 and 2The secondary water distribution unit 9 includes a water storage tank 91, a drilling rig connection pipe 92, a pressure gauge 93, a water storage tank pressure sensor 94, and a secondary distribution controller 95. Several drilling rig connection pipes 92 are connected to the water storage tank 91 via outlet flanges on the side of the water storage tank 91. The other end of each drilling rig connection pipe 92 is connected to the drilling rig. The pressure gauge 93 and the water storage tank pressure sensor 94 are respectively installed on the top of the water storage tank 91. The pressure gauge 93 can directly display the pressure inside the water storage tank 91, and the water storage tank pressure sensor 94 collects the pressure from the water storage tank 91. 1. The pressure signal is transmitted to the input terminal of the secondary distribution controller 95 through the signal line. One port at the bottom of the water storage tank 91 is connected to the centralized water supply pipeline through the third electric gate valve 8. The other port at the bottom of the water storage tank 91 is connected to one end of the first connecting pipe 16. The other end of the first connecting pipe 16 is connected to the corresponding port at the bottom of another water storage tank 91. The side port of the water storage tank 91 is connected to the corresponding port on the side of another water storage tank 91 through the second connecting pipe 17. The secondary distribution water supply unit 9 is connected to the switch 10 through the signal control line.

[0022] As a preferred embodiment, see Appendix Figure 1 and 2 The secondary distribution controller 95 of the secondary distribution water supply unit 9 controls the switching between drilling and punching operation modes of the drilling rig in the secondary distribution water supply unit 9. The secondary distribution controller 95 in the secondary distribution water supply unit 9 collects the signal from the pressure sensor 94 of the water storage tank and transmits the signal to the central controller 1 through the switch 10. At the same time, a minimum liquid level sensor is installed inside the water storage tank 91 of the secondary distribution water supply unit 9. The information from the minimum liquid level sensor is also transmitted to the secondary distribution controller 95 and then to the central controller 1 through the switch 10, thereby serving as the basis for adjusting the flow and pressure in the central water supply branch 4.

[0023] As a preferred embodiment, see Appendix Figure 1 and 2The signal control lines of the fourth electric gate valve 12 and the sixth electric gate valve 14 are connected to the secondary distribution controller 95 of a secondary distribution water supply unit 9. The signal control lines of the fifth electric gate valve 13 and the seventh electric gate valve 15 are connected to the secondary distribution controller 95 of another secondary distribution water supply unit 9. The electric gate valves controlled by the two secondary distribution controllers 95 form an interlock function. Under normal operating conditions, the fourth electric gate valve 12, the fifth electric gate valve 13, the sixth electric gate valve 14, and the seventh electric gate valve 15 are normally closed. When a secondary distribution water supply unit 9 is in a low flow condition, only the electric gate valves connected to the secondary distribution controller 95 in that secondary distribution water supply unit 9 are open. Or, when both secondary distribution water supply units 9 are in a low flow condition, the fourth electric gate valve 12, the fifth electric gate valve 13, the sixth electric gate valve 14, and the seventh electric gate valve 15 are all in an open state.

[0024] As a preferred embodiment, see Appendix Figure 1 and 3 The outlet pressure sensor 6, flow sensor 61, second electric gate valve 7, and third electric gate valve 8 are connected to the centralized controller 1 via signal control lines. The outlet pressure sensor 6 and flow sensor 61 monitor the pressure and flow data of the fluid medium in the centralized water supply pipeline in real time, and compare them with the monitoring data of the water storage tank pressure sensor 94 in the secondary distribution water supply unit 9 and the volume data of the fluid medium in the water storage tank 91 to further determine the number of multi-stage pumps 43 to start and stop and the speed. The second electric gate valve 7 and the third electric gate valve 8 are connected to the secondary distribution water supply unit 9, and the opening and closing of the second electric gate valve 7 and the third electric gate valve 8 are determined by the working status of the secondary distribution water supply unit 9.

[0025] As a preferred embodiment, see Appendix Figure 1 , 3 4. The centralized water supply branch 4 includes a first shut-off valve 41, an inlet pressure sensor 42, a multistage pump 43, a first manual ball valve 44, a check valve 45, and a first electric gate valve 46. The first shut-off valve 41 and the inlet pressure sensor 42 are respectively installed on the inlet pipe of the multistage pump 43. The first manual ball valve 44, the check valve 45, and the first electric gate valve 46 are respectively installed on the outlet pipe of the multistage pump 43. The three-phase asynchronous motor of the multistage pump 43 in each centralized water supply branch 4 is respectively connected to the output terminal of the frequency converter 2. The inlet pressure sensor 42 and the first electric gate valve 46 are respectively connected to the centralized controller 1 through signal control lines.

[0026] In a preferred embodiment, the inlet pressure sensor 42 in the centralized water supply branch 4 and the outlet pressure sensor 6 in the water supply manifold monitor the inlet and outlet pressures of the multistage pump 43 in the centralized water supply branch 4 in real time, respectively. Combined with the power frequency of the multistage pump 43 and the monitoring data of the flow sensor 61, the real-time head and flow rate of the multistage pump 43 are calculated, providing accurate data support for the secondary distribution water supply unit 9 to supply fluid media that meet the design requirements.

[0027] In a preferred embodiment, the first shut-off valve 41 is normally open. The water flow rate of each centralized water supply branch 4 can also be controlled by adjusting the opening degree of the first shut-off valve 41. The other end of the first manual ball valve 44 is connected to the outside. Before starting the pump, the air in the multistage pump 43 can be vented through the first manual ball valve 44 to avoid cavitation in the multistage pump 43. The check valve 45 can prevent the high-pressure medium in the water storage tank 91 from flowing back to the multistage pump 43 under the circumstances of pump stoppage or other reasons, thereby damaging the multistage pump 43.

[0028] In a preferred embodiment, the centralized controller 1, frequency converter 2, pressure stabilizing tank 3, and centralized water supply branch 4 are installed in the roadway, the two secondary distribution water supply units 9 are installed near the coal seam mining face, and the switch 10 is set between the two secondary distribution water supply units 9, or the switch 10 is set at the booster device 11, which realizes the spatial separation of centralized water supply and secondary distribution water supply, and also solves the problem of long-distance water transportation of drilling rig groups.

[0029] In a preferred embodiment, there are two pressure stabilizing tanks 3. The two pressure stabilizing tanks 3 are installed in series at the inlet of the centralized water supply branch 4. The pressure stabilizing tanks 3 can stabilize the pressure of the fluid medium entering the centralized water supply branch 4, avoid pressure fluctuations of the fluid entering the centralized water supply branch 4, and thus ensure the pressure stability of the fluid medium in the water storage tank 91.

[0030] As a preferred embodiment, the present invention provides a multi-stage pump frequency conversion constant pressure water supply system suitable for low-flow drilling rig groups. By setting the minimum speed parameter of the multi-stage pump 43 in the centralized water supply branch 4, when the water consumption for drilling and perforation in the secondary distribution water supply unit 9 is less than the flow rate at the minimum speed of the multi-stage pump 43, in order to avoid overheating of the pump body, the centralized controller 1 sends a shutdown command to the multi-stage pump 43. At the same time, the second electric gate valve 7 and the third electric gate valve 8 change from the open state to the closed state. If only some drilling rigs in a certain secondary distribution water supply unit 9 are in working state at this time, the secondary water supply unit 9... The distribution controller 95 sends a start command to the booster device 11. Simultaneously, the electric gate valve connected to the secondary distribution controller 95 opens, while the electric gate valve connected to the secondary distribution controller 95 in the other secondary distribution water supply unit 9 closes. The booster device 11 increases the pressure in the water storage tank 91 of the other secondary distribution water supply unit 9, and the fluid medium inside enters the secondary distribution water supply unit 9 in its working state along the first connecting pipe 16. This not only ensures the pressure stability of the secondary distribution water supply unit 9 in its working state but also provides it with sufficient fluid medium. When the secondary distribution water supply unit 9 in its working state... When the volume of the fluid medium decreases to the set value, the secondary distribution controller 95 of the secondary distribution water supply unit 9 transmits the signal to the central controller 1 through the switch 10. At this time, the central controller 1 starts the centralized water supply branch 4 and opens the corresponding inlet electric gate valve of the secondary distribution water supply unit 9 to continue to provide the secondary distribution water supply unit 9 with a stable pressure. If some drilling rigs are in operation in both secondary distribution water supply units 9 at this time, under the combined action of the secondary distribution controllers 95 of the two secondary distribution water supply units 9, the booster device 11 is started, and the fourth electric gate valve 12 and the fifth electric gate valve 13 are activated. Both the sixth electric gate valve 14 and the seventh electric gate valve 15 are in the open state. The booster device 11 provides pressure to the water storage tanks 91 of the two secondary water distribution units 9. Due to the connection effect of the first connecting pipe 16, the water storage tanks 91 in the two secondary water distribution units 9 are at the same pressure. When the volume of the fluid medium in the two secondary water distribution units 9 decreases to the set value, the secondary distribution controller 95 of the two secondary water distribution units 9 transmits the signal to the central controller 1 through the switch 10, and starts the central water supply branch 4 to continue to provide the two secondary water distribution units 9 with a stable pressure water medium.

[0031] The above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A multi-stage pump frequency conversion constant pressure water supply system suitable for small flow rates in drilling rig groups, comprising a centralized controller (1), a frequency converter (2), a pressure stabilizing tank (3), a centralized water supply branch (4), a safety valve (5), an outlet pressure sensor (6), a flow sensor (61), a second electric gate valve (7), a third electric gate valve (8), a secondary distribution water supply unit (9), a booster device (11), a fourth electric gate valve (12), a fifth electric gate valve (13), a sixth electric gate valve (14), a seventh electric gate valve (15), and a switch (10), characterized in that: The central controller (1) is connected to three central water supply branches (4) installed in parallel via a frequency converter (2). The bottom outlet of the pressure stabilizing tank (3) is connected to the three central water supply branches (4) via pipelines. The outlets of the three central water supply branches (4) are connected to two secondary distribution water supply units (9) via central water supply pipelines. Safety valves (5), outlet pressure sensors (6), and flow sensors (61) are installed sequentially along the flow direction of the medium in the central water supply pipeline. The second electric gate valve (7) and the third electric gate valve (8) are installed between the two secondary distribution water supply units (9) and the central water supply pipeline, respectively. The booster device (11) is installed in the two secondary distribution water supply units. Between (9), the two ends of the first connecting pipe (16) and the second connecting pipe (17) are respectively connected to the two secondary distribution water supply units (9). The fourth electric gate valve (12) and the fifth electric gate valve (13) are installed on the second connecting pipe (17) in series. The sixth electric gate valve (14) and the seventh electric gate valve (15) are installed on the first connecting pipe (16) in parallel. The outlet of the booster device (11) is connected to the second connecting pipe (17) between the fourth electric gate valve (12) and the fifth electric gate valve (13) through a manual shut-off valve. The signal control lines of the two secondary distribution water supply units (9) are respectively connected to the central controller (1) through the switch (10).

2. The multi-stage pump frequency conversion constant pressure water supply system suitable for low flow rates in drilling rig groups according to claim 1, characterized in that: The secondary distribution water supply unit (9) includes a water storage tank (91), a drilling rig connection pipe (92), a pressure gauge (93), a water storage tank pressure sensor (94), and a secondary distribution controller (95). Several drilling rig connection pipes (92) are connected to the water storage tank (91) through outlet flanges on the side of the water storage tank (91). The other end of the drilling rig connection pipe (92) is connected to the drilling rig. The pressure gauge (93) and the water storage tank pressure sensor (94) are respectively installed on the top of the water storage tank (91). The water storage tank pressure sensor (94) is connected to the secondary distribution controller through a signal line. (95) is connected to the input end. One port at the bottom of the water tank (91) is connected to the centralized water supply pipeline through the third electric gate valve (8). Another port at the bottom of the water tank (91) is connected to one end of the first connecting pipe (16). The other end of the first connecting pipe (16) is connected to the corresponding port at the bottom of another water tank (91). The side port of the water tank (91) is connected to the corresponding port on the side of another water tank (91) through the second connecting pipe (17). The secondary distribution water supply unit (9) is connected to the switch (10) through the signal control line.

3. The multi-stage pump variable frequency constant pressure water supply system suitable for small flow of rig group according to claim 1, characterized in that: The signal control lines of the fourth electric gate valve (12) and the sixth electric gate valve (14) are connected to the secondary distribution controller (95) of a secondary distribution water supply unit (9), and the signal control lines of the fifth electric gate valve (13) and the seventh electric gate valve (15) are connected to the secondary distribution controller (95) of another secondary distribution water supply unit (9).

4. The multi-stage pump variable frequency constant pressure water supply system suitable for small flow of rig group according to claim 1, characterized in that: The outlet pressure sensor (6), flow sensor (61), second electric gate valve (7) and third electric gate valve (8) are connected to the central controller (1) via signal control lines.

5. The multi-stage pump variable frequency constant pressure water supply system suitable for small flow of rig group according to claim 1, characterized in that: The centralized water supply branch (4) includes a first shut-off valve (41), an inlet pressure sensor (42), a multistage pump (43), a first manual ball valve (44), a check valve (45), and a first electric gate valve (46). The first shut-off valve (41) and the inlet pressure sensor (42) are respectively installed on the inlet pipe of the multistage pump (43). The first manual ball valve (44), the check valve (45), and the first electric gate valve (46) are respectively installed on the outlet pipe of the multistage pump (43). The three-phase asynchronous motor of the multistage pump (43) in each centralized water supply branch (4) is connected to the output end of the frequency converter (2). The inlet pressure sensor (42) and the first electric gate valve (46) are respectively connected to the centralized controller (1) through signal control lines.

6. The multi-stage pump variable frequency constant pressure water supply system suitable for small flow of rig group according to claim 1, characterized in that: The central controller (1), frequency converter (2), pressure stabilizing tank (3), and central water supply branch (4) are installed in the roadway. Two secondary distribution water supply units (9) are installed near the coal seam mining face. The switch (10) is set between the two secondary distribution water supply units (9), or the switch (10) is set at the booster device (11).

7. The multi-stage pump variable frequency constant pressure water supply system suitable for small flow of rig groups according to claim 1, characterized in that: There are two pressure stabilizing tanks (3), and the two pressure stabilizing tanks (3) are installed in series at the inlet of the centralized water supply branch (4).

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