A liquid level control system with two pumps operating in turn

Abstract

The application discloses a liquid level control system with double pumps running in turns, which comprises a total control circuit connected with a main power supply, wherein the total control circuit comprises a main pump control circuit, a standby pump control circuit, a first floating ball liquid level controller and a second floating ball liquid level controller; the main pump control circuit and the standby pump control circuit are connected with the main power supply through a three-grade knob switching switch; the main pump automatic control circuit and the standby pump automatic control circuit form an automatic control total circuit with the normally open contact of a first relay; the automatic control total circuit is connected with a main standby turn control circuit in parallel at both ends; the normally closed contact of a second contactor, the normally open contact of a first contactor and the coil of a third relay are sequentially and in series connected on the main standby turn control circuit; and the normally open contact of the third relay is connected in parallel at both ends of the normally open contact of the first contactor; and the double pumps run in turns through the main standby turn control circuit. The application adopts commonly used electrical components to form the control circuit, and has the advantages of simple circuit structure, high control efficiency and cost saving.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid level control, in particular to a liquid level control system with double pumps running alternately. BACKGROUND

[0002] At present, for the automatic control of liquid level of water pool, tank and the like, a common relay control circuit is used to realize the alternate running of main pump and standby pump, effectively utilize the service life of water pump, and prevent the standby pump from being stopped for a long time and the components from deteriorating, but the common relay has the problem of being unable to start in an emergency. In addition, the prior art discloses that: first, a main circuit is used to control the starting of water pump by a floating ball liquid level meter, and a manual button is used to select the running of main pump or standby pump, so that the selected pump runs each time the liquid level is raised, and the double pumps cannot run alternately and need to be manually switched, thereby increasing the management cost; second, a PLC is used for control, and a counter is added in the PLC program, the counter is triggered by the rising of liquid level, the main pump is started when the counter is odd, and the standby pump is started when the counter is even, but the PLC system has high cost and high design and maintenance technical requirements. Therefore, the existing liquid level control system needs to be further improved. SUMMARY

[0003] The purpose of the present application is to provide a liquid level control system with double pumps running alternately, which uses common electrical components to form a control circuit, has simple circuit structure, can realize automatic and manual control switching, can realize the alternate running of double pumps, has high automation control efficiency, and does not need PLC control, thereby saving cost.

[0004] To achieve the above purpose, the present application provides the following solutions:

[0005] A liquid level control system with double pumps running alternately, comprising: a main power supply and a total control circuit connected with the main power supply, the total control circuit comprising a main pump control circuit, a standby pump control circuit, a first floating ball liquid level controller and a second floating ball liquid level controller, the main pump control circuit being used to control the start and stop of a main drainage pump, the standby pump control circuit being used to control the start and stop of a standby drainage pump, the main drainage pump and the standby drainage pump being arranged in the same water pool, a floating ball switch of the first floating ball liquid level controller being arranged at a middle liquid level of the water pool, and a floating ball switch of the second floating ball liquid level controller being arranged at a high liquid level of the water pool.

[0006] The main pump control circuit and the standby pump control circuit are connected with the main power supply through a three-gear knob switching switch SB1, and the three-gear knob switching switch SB1 comprises an automatic gear, a manual gear and an empty cutting gear.

[0007] The main pump control circuit includes a main pump manual control circuit and a main pump automatic control circuit, and the standby pump control circuit includes a standby pump manual control circuit and a standby pump automatic control circuit; the main pump manual control circuit and the standby pump manual control circuit are connected with the manual gear, and the main pump automatic control circuit and the standby pump automatic control circuit are connected with the automatic gear through the normally open contact of the first relay KA1; the main pump automatic control circuit and the standby pump automatic control circuit and the normally open contact of the first relay KA1 form an automatic control total circuit, and the automatic control total circuit is connected with a main-standby rotation control circuit in parallel at both ends, and the main-standby rotation control circuit is sequentially connected with the normally closed contact of the second contactor KM2, the normally open contact of the first contactor KM1 and the coil of the third relay KA3 in series, and the normally open contact of the first contactor KM1 is connected with the normally open contact of the third relay KA3 in parallel at both ends;

[0008] The float switch of the first float ball liquid level controller is connected with the coil of the first relay KA1 in series to form a loop, and the float switch of the second float ball liquid level controller is connected with the coil of the second relay KA2 in series to form a loop;

[0009] The main pump manual control circuit and the main pump automatic control circuit are connected with the normally closed contact of the first thermal relay FR1, the normally closed contact of the first thermal relay FR1 is connected with the coil of the first contactor KM1, and the normally open main contact of the first contactor KM1 and the first thermal relay FR1 are connected in series on the power supply main circuit of the main drainage pump; the stop button SB2 and the start button SB3 are connected in series on the main pump manual control circuit, the start button SB3 is connected with the normally open auxiliary contact of the first contactor KM1 in parallel at both ends, the normally closed contact of the second contactor KM2 and the normally closed contact of the third relay KA3 are connected in series on the main pump automatic control circuit, and the normally open contact of the first contactor KM1 and the normally open contact of the second thermal relay FR2 are connected in parallel at both ends of the normally closed contact of the third relay KA3;

[0010] The standby pump manual control circuit and the standby pump automatic control circuit are connected with the normally closed contact of the second thermal relay FR2, the normally closed contact of the second thermal relay FR2 is connected with the coil of the second contactor KM2, and the normally open main contact of the second contactor KM2 and the second thermal relay FR2 are connected in series on the power supply main circuit of the standby drainage pump; the stop button SB4 and the start button SB5 are connected in series on the standby pump manual control circuit, the start button SB5 is connected with the normally open auxiliary contact of the second contactor KM2 in parallel at both ends, the normally open contact of the third relay KA3 and the normally closed contact of the first contactor KM1 are connected in series on the standby pump automatic control circuit, and the normally open contact of the second contactor KM2 and the normally open contact of the first thermal relay FR1 are connected in parallel at both ends of the normally open contact of the third relay KA3;

[0011] Further, the two ends of the main pump automatic control circuit are also connected in parallel with the normally open contact of the second relay KA2.

[0012] Further, the two ends of the main pump automatic control circuit are also connected in parallel with the normally open contact of the second relay KA2.

[0013] Further, the main control circuit further comprises an alarm circuit connected with the main power supply, the alarm circuit is provided with the normally open contact of the second relay KA2 and the sound and light alarm lamp ED3 in series, and the two ends of the normally open contact of the second relay KA2 are connected in parallel with the normally open contact of the first thermal relay FR1 and the normally open contact of the second thermal relay FR2.

[0014] Further, the two ends of the coil of the first contactor KM1 are connected in parallel with the main pump operation indicator lamp ED1.

[0015] Further, the two ends of the coil of the second contactor KM2 are connected in parallel with the standby pump operation indicator lamp ED2.

[0016] Further, the main control circuit further comprises a power supply indicator lamp ED4 connected with the main power supply.

[0017] Further, the fourth air switch QF4 is arranged between the main control circuit and the main power supply.

[0018] Further, the second air switch QF2 is arranged on the power supply main circuit of the main drainage pump, the third air switch QF3 is arranged on the power supply main circuit of the standby drainage pump, and the first air switch QF1 is arranged between the main power supply and the power supply main circuit of the main drainage pump and the power supply main circuit of the standby drainage pump.

[0019] According to the specific embodiments provided by the application, the following technical effects are achieved: the liquid level control system with double pumps operating in turns provided by the application, (1) the automatic control mode and the manual control mode are switched by the three-grade knob switching switch SB1, the diversification of the control mode is realized; (2) in the circuit of the double pumps, the automatic working condition realizes the double pump rotation start-stop control through the KA3 auxiliary relay, wherein the KA3 normally closed contact is arranged in the main pump automatic control circuit, the KA3 normally open contact is arranged in the standby pump automatic control circuit, the two pumps are alternately operated, the circuit structure is simple, and the control efficiency is high; (3) through the cooperation of multiple relays and contactors, the automation control is realized by using common electrical components, without setting PLC, the operation cost is low, the circuit principle is simple, and the maintenance is convenient; (4) the independent double pump control circuit is arranged, when the elements of one control circuit fail, the other set can continue to work independently, so that the drainage is not affected, the manual intervention of the operation personnel is reduced, and the requirement of improving the automation degree is met. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0021] Figure 1 Circuit diagram of main power supply circuit of liquid level control system with double pumps running alternately according to the present application;

[0022] Figure 2a Circuit diagram of total control circuit of liquid level control system with double pumps running alternately according to the present application;

[0023] Figure 2b Circuit diagram of main pump control circuit and standby pump control circuit according to the present application;

[0024] Figure 3 Structural schematic diagram of control panel of distribution box according to the present application;

[0025] Figure 4 Circuit diagram of state when first alarm of liquid level control system with double pumps running alternately according to the present application;

[0026] Figure 5 Circuit diagram of state when low liquid level after first alarm of liquid level control system with double pumps running alternately according to the present application;

[0027] Figure 6 Circuit diagram of state when second alarm of liquid level control system with double pumps running alternately according to the present application;

[0028] Figure 7 Circuit diagram of state when high liquid level and double pumps running of liquid level control system with double pumps running alternately according to the present application;

[0029] Figure 8 Circuit diagram of scheme A of conventional liquid level control system with double pumps running alternately;

[0030] Explanation of reference numerals: QF1: first air switch, total air switch; QF2: second air switch, main pump power supply; QF3: third air switch, standby pump power supply; KM1: first contactor; KM2: second contactor; FR1: first thermal relay; FR2: second thermal relay; QF4: fourth air switch, secondary circuit power supply; SB1: three-grade knob switch, used for manual and automatic control switching of pump; KA1, KA2, KA3: relays; SB1, SB2, SB3: buttons; ED1, ED2: indicator lamps; ED3: sound and light alarm lamp; DC24V: 24V power supply module; UK221: first floating ball water level controller; UK222: second floating ball water level controller. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0032] The purpose of the present application is to provide a liquid level control system with double pump rotation, which adopts common electrical components to form a control circuit, has simple circuit structure, can realize automatic and manual control switching, and can realize double pump rotation, has high automatic control efficiency, and does not need PLC control, thereby saving cost.

[0033] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0034] As shown in Figure 1 and Figures 2a-2b The liquid level control system with double pump rotation provided by the present application comprises a main power supply and a total control circuit connected with the main power supply, the total control circuit comprises a main pump control circuit, a standby pump control circuit, a first floating ball liquid level controller UK221 and a second floating ball liquid level controller UK222, the main pump control circuit is used for controlling start and stop of a main drainage pump, the standby pump control circuit is used for controlling start and stop of a standby drainage pump, the main drainage pump and the standby drainage pump are arranged in the same pool, a floating ball switch of the first floating ball liquid level controller is arranged at a middle liquid level of the pool, and a floating ball switch of the second floating ball liquid level controller is arranged at a high liquid level of the pool.

[0035] The main pump control circuit and the standby pump control circuit are connected with the main power supply through a three-gear knob switching switch SB1, the three-gear knob switching switch SB1 comprises an automatic gear, a manual gear and an empty cutting gear.

[0036] The main pump control circuit includes a main pump manual control circuit and a main pump automatic control circuit, and the standby pump control circuit includes a standby pump manual control circuit and a standby pump automatic control circuit; the main pump manual control circuit and the standby pump manual control circuit are connected with the manual gear, and the main pump automatic control circuit and the standby pump automatic control circuit are connected with the automatic gear through the normally open contact of the first relay KA1; the main pump automatic control circuit and the standby pump automatic control circuit and the normally open contact of the first relay KA1 form an automatic control total circuit, and the both ends of the automatic control total circuit are connected in parallel with a main-standby rotation control circuit, and the normally closed contact of the second contactor KM2, the normally open contact of the first contactor KM1 and the coil of the third relay KA3 are sequentially and serially arranged on the main-standby rotation control circuit, and the both ends of the normally open contact of the first contactor KM1 are connected in parallel with the normally open contact of the third relay KA3;

[0037] The float switch of the first float ball liquid level controller UK221 is connected in series with the coil of the first relay KA1, and the float switch of the second float ball liquid level controller UK222 is connected in series with the coil of the second relay KA2.

[0038] The main pump manual control circuit and the main pump automatic control circuit are connected with the normally closed contact of the first thermal relay FR1, the normally closed contact of the first thermal relay FR1 is connected with the coil of the first contactor KM1, and the both ends of the coil of the first contactor KM1 are connected in parallel with the main pump operation indicator ED1.

[0039] The normally open main contact of the first contactor KM1 and the first thermal relay FR1 are serially arranged on the power supply main circuit of the main drainage pump; the stop button SB2 and the start button SB3 are serially arranged on the main pump manual control circuit, the both ends of the start button SB3 are connected in parallel with the normally open auxiliary contact of the first contactor KM1; the normally closed contact of the third relay KA3 and the normally closed contact of the second contactor KM2 are serially arranged on the main pump automatic control circuit, the both ends of the normally closed contact of the third relay KA3 are connected in parallel with the normally open contact of the first contactor KM1 and the normally open contact of the second thermal relay FR2; and the both ends of the main pump automatic control circuit are also connected in parallel with the normally open contact of the second relay KA2.

[0040] The standby pump manual control circuit and the standby pump automatic control circuit are connected with the normally closed contact of the second thermal relay FR2, the normally closed contact of the second thermal relay FR2 is connected with the coil of the second contactor KM2, and the both ends of the coil of the second contactor KM2 are connected in parallel with the standby pump operation indicator ED2.

[0041] The main power supply circuit of the backup drainage pump is connected in series with the normally open main contact of the second contactor KM2 and the second thermal relay FR2; the manual control circuit of the backup pump is connected in series with the stop button SB4 and the start button SB5, and the two ends of the start button SB5 are connected in parallel with the normally open auxiliary contact of the second contactor KM2; the automatic control circuit of the backup pump is connected in series with the normally open contact of the third relay KA3 and the normally closed contact of the first contactor KM1, and the two ends of the normally open contact of the third relay KA3 are connected in parallel with the normally open contact of the second contactor KM2 and the normally open contact of the first thermal relay FR1; the two ends of the automatic control circuit of the backup pump are also connected in parallel with the normally open contact of the second relay KA2.

[0042] Specifically, the main control circuit also includes an alarm circuit connected to the main power supply. The alarm circuit is connected in series with the normally open contact of the second relay KA2 and the audible and visual alarm light ED3. The normally open contacts of the first thermal relay FR1 and the second thermal relay FR2 are connected in parallel across the two ends of the normally open contact of the second relay KA2.

[0043] In addition, the main control circuit also includes a power indicator light ED4 connected to the main power supply.

[0044] A fourth air switch QF4 is installed between the main control circuit and the main power supply.

[0045] A second air switch QF2 is installed on the main power supply circuit of the main drainage pump, a third air switch QF3 is installed on the main power supply circuit of the standby drainage pump, and a first air switch QF1 is installed between the main power supply and the main power supply circuits of the main drainage pump and the standby drainage pump.

[0046] For example, the power of the main drainage pump is 5.5 kW, and the power of the standby drainage pump is 5.5 kW.

[0047] like Figure 3 As shown, the present invention also includes a power distribution box, wherein the three-position rotary switch SB1, stop button SB2, start button SB3, stop button SB4, start button SB5, main pump running indicator ED1, standby pump running indicator ED2, audible and visual alarm light ED3, and power indicator ED4 are all located on the control panel of the power distribution box.

[0048] In the dual-pump alternating operation liquid level control system provided by this invention, the two pumps share a main power input switch QF1, and the two pumps serve as backups for each other. There is a first float level controller UK221 and a second float level controller UK222. At the middle liquid level, one pump starts and stops when the liquid level is reached; at the high liquid level, both pumps start operating. If one pump fails, a thermal relay activates, automatically starting the other pump.

[0049] In the main pump control circuit, the main pump manual control circuit and the main pump automatic control circuit are connected in parallel. When the three-position rotary switch is rotated to the manual position, the main pump manual control circuit is active; when rotated to the automatic position, the main pump automatic control circuit is active. The standby pump control circuit has the same control principle.

[0050] The key structure in the main control circuit is the KA3 relay. The main and standby alternating control circuit, which consists of the normally open auxiliary contact of the KA3 relay, the normally open contact of KM1, and the normally closed contact of KM2, enables the main and standby drainage pumps to be energized and start running in turn after each liquid level alarm.

[0051] The working principle of the liquid level control system with dual pumps operating alternately provided by this invention is as follows:

[0052] Initial state:

[0053] SB1 is in the automatic position, low level, UK221 is open, KA1 is not energized, and all electrical components are in the same position. Figure 1 and Figures 2a-2b As shown, both pumps are not powered and have not started;

[0054] like Figure 4 As shown, the first liquid level alarm occurred:

[0055] When UK221 is turned on, the KA1 coil is energized, the KA1 normally open auxiliary contact closes, the main pump control circuit is energized, the KM1 coil is energized, the KM1 contactor in the main pump power supply circuit closes, and the main drainage pump starts running. When the KM1 coil is energized, the KM1 normally open auxiliary contact in the main / standby alternating control circuit closes, the KA3 coil is energized, and the KA3 normally open auxiliary contact in the main / standby alternating control circuit closes and latches. When the KA3 normally closed auxiliary contact in the main pump control circuit opens, the KM1 normally open contact closes and latches, and the main drainage pump runs continuously.

[0056] In the standby pump automatic control circuit, the normally open contact of KA3 is closed, the normally open contact of KM2 is open, and the normally closed contact of KM1 is open, so the standby drainage pump does not start.

[0057] like Figure 5 As shown, after the first medium-level alarm pump starts and pumps the water in the tank to a low level:

[0058] When UK221 disconnects, the KA1 coil loses power, the KA1 normally open auxiliary contact opens, the main pump control circuit loses power, the KM1 coil loses power, the KM1 contactor in the main pump power supply circuit opens, and the main drainage pump stops. When the KM1 coil loses power, the KM1 normally open auxiliary contact in the main / standby alternating control circuit opens, while the KA3 normally open contact remains energized and self-locking. The KA3 normally closed auxiliary contact in the main pump control circuit opens, and the main drainage pump stops.

[0059] like Figure 6 As shown, the second liquid level alarm occurred:

[0060] When UK221 is turned on, coil KA1 is energized, its normally open contact closes, and its normally closed contact opens; coil KM1 is de-energized, its normally open contact opens, and its normally closed contact closes; coil KM2 is energized, its normally open contact closes, and its normally closed contact opens; coil KA3 is de-energized, its normally open contact in the main / standby alternating control circuit opens, its normally closed contact in the main pump automatic control circuit closes, and its normally open contact in the standby pump automatic control circuit opens; the standby drainage pump is energized and starts, while the main drainage pump is de-energized and stops.

[0061] Third liquid level alarm:

[0062] When UK221 is turned on, the normally open contact KA3 of the main and standby alternating control circuit is in the open state, the normally closed contact KA3 in the main pump automatic control circuit is closed, the normally open contact KA3 in the standby pump automatic control circuit is open, the main drainage pump is energized and starts, and the standby drainage pump is de-energized and stops.

[0063] In turn, the main drainage pump is energized and operates during odd-numbered cycles, and the standby drainage pump is energized and operates during even-numbered cycles.

[0064] like Figure 7 As shown, at high liquid level:

[0065] Both UK221 and UK222 are conducting, energizing the KA2 relay coil. This closes the normally open contact of KA2 in the parallel automatic control circuit of the main and standby drainage pumps, energizing the main pump KM1 coil and initiating operation. The standby pump KM2 coil is also energized and starts operating, resulting in simultaneous operation of both pumps and increased drainage volume. When the liquid level drops to the low level, UK221 disconnects, de-energizing the KA1 coil. This causes the normally open contact of KA1 in the dual-pump automatic control circuit to open, stopping both pumps.

[0066] like Figure 8 As shown, in conventional technologies such as Scheme A, when the main drainage pump is automatically controlled, after the liquid level alarm, the normally open contact KA1 in the main pump control circuit closes, the KM1 coil is energized, the contact is self-locked, and the main drainage pump runs continuously.

[0067] When the standby pump is in automatic position, after the liquid level alarm, the normally open contact KA2 in the standby pump control circuit closes, the KM2 coil is energized, the contact is self-locked, and the standby drainage pump runs continuously.

[0068] This invention is a further improvement on scheme A, realizing the alternating operation of the two pumps.

[0069] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the general technical personnel in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present specification should not be understood as the limitation of the present application.

Claims

1. A liquid level control system with dual pumps operating alternately, characterized in that, include: The system includes a main power supply and a main control circuit connected to the main power supply. The main control circuit includes a main pump control circuit, a standby pump control circuit, a first float level controller, and a second float level controller. The main pump control circuit is used to control the start and stop of the main drainage pump, and the standby pump control circuit is used to control the start and stop of the standby drainage pump. The main drainage pump and the standby drainage pump are installed in the same water tank. The float switch of the first float level controller is set at the middle level of the water tank, and the float switch of the second float level controller is set at the high level of the water tank. The main pump control circuit and the standby pump control circuit are connected to the main power supply through a three-position rotary switch SB1. The three-position rotary switch SB1 includes an automatic position, a manual position, and an off position. The main pump control circuit includes a main pump manual control circuit and a main pump automatic control circuit. The standby pump control circuit includes a standby pump manual control circuit and a standby pump automatic control circuit. The main pump manual control circuit and the standby pump manual control circuit are connected to the manual gear position. The main pump automatic control circuit and the standby pump automatic control circuit are both connected to the automatic gear position through the normally open contact of the first relay KA1. The main pump automatic control circuit, the standby pump automatic control circuit, and the normally open contact of the first relay KA1 constitute an automatic control main circuit. The two ends of the automatic control main circuit are connected in parallel with a main and standby alternating control circuit. The normally closed contact of the second contactor KM2, the normally open contact of the first contactor KM1, and the coil of the third relay KA3 are connected in series in the main and standby alternating control circuit. The two ends of the normally open contact of the first contactor KM1 are connected in parallel with the normally open contact of the third relay KA3. The float switch of the first float level controller is connected in series with the coil of the first relay KA1 to form a circuit; the float switch of the second float level controller is connected in series with the coil of the second relay KA2 to form a circuit. Both the main pump manual control circuit and the main pump automatic control circuit are connected to the normally closed contact of the first thermal relay FR1. The normally closed contact of the first thermal relay FR1 is connected to the coil of the first contactor KM1. The normally open main contact of the first contactor KM1 and the first thermal relay FR1 are connected in series in the main power supply circuit of the main drainage pump. The main pump manual control circuit is connected in series with a stop button SB2 and a start button SB3. The two ends of the start button SB3 are connected in parallel with the normally open auxiliary contact of the first contactor KM1. The main pump automatic control circuit is connected in series with the normally closed contact of the third relay KA3 and the normally closed contact of the second contactor KM2. The two ends of the normally closed contact of the third relay KA3 are connected in parallel with the normally open contact of the first contactor KM1 and the normally open contact of the second thermal relay FR2. Both the standby pump manual control circuit and the standby pump automatic control circuit are connected to the normally closed contact of the second thermal relay FR2. The normally closed contact of the second thermal relay FR2 is connected to the coil of the second contactor KM2. The normally open main contact of the second contactor KM2 and the second thermal relay FR2 are connected in series on the main power supply circuit of the standby drainage pump. The standby pump manual control circuit is connected in series with a stop button SB4 and a start button SB5. The two ends of the start button SB5 are connected in parallel with the normally open auxiliary contact of the second contactor KM2. The standby pump automatic control circuit is connected in series with the normally open contact of the third relay KA3 and the normally closed contact of the first contactor KM1. The two ends of the normally open contact of the third relay KA3 are connected in parallel with the normally open contact of the second contactor KM2 and the normally open contact of the first thermal relay FR1.

2. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The two ends of the main pump automatic control circuit are also connected in parallel with the normally open contacts of the second relay KA2.

3. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The standby pump automatic control circuit is also connected in parallel with the normally open contacts of the second relay KA2.

4. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The main control circuit also includes an alarm circuit connected to the main power supply. The alarm circuit is connected in series with the normally open contact of the second relay KA2 and the audible and visual alarm light ED3. The normally open contacts of the first thermal relay FR1 and the second thermal relay FR2 are connected in parallel across the two ends of the normally open contact of the second relay KA2.

5. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The main pump running indicator light ED1 is connected in parallel across the two ends of the coil of the first contactor KM1.

6. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The two ends of the coil of the second contactor KM2 are connected in parallel with the standby pump operation indicator light ED2.

7. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, The main control circuit also includes a power indicator light ED4 connected to the main power supply.

8. The liquid level control system with dual pumps operating alternately according to claim 1, characterized in that, A fourth air switch QF4 is installed between the main control circuit and the main power supply.

9. The liquid level control system with dual pumps operating alternately according to any one of claims 1-8, characterized in that, A second air switch QF2 is installed on the main power supply circuit of the main drainage pump, a third air switch QF3 is installed on the main power supply circuit of the standby drainage pump, and a first air switch QF1 is installed between the main power supply and the main power supply circuits of the main drainage pump and the standby drainage pump.

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