Protection and control method for fertilizer pump of integrated water and fertilizer machine

Abstract

The present invention discloses a protection and control method for a fertilizer pump of a water-fertilizer integrated machine, comprising a main irrigation pipe, a main irrigation pump, a venturi tube and a fertilizer pump, wherein the main irrigation pump is connected to a constant pressure control device, a main flow meter and a main pressure sensor are provided at a water outlet end of the main irrigation pipe, an input bypass pipe is provided at the water outlet end of the main irrigation pipe, the input bypass pipe is connected to the inlet end of the venturi tube, an output bypass pipe is provided at the outlet end of the venturi tube, the output bypass pipe is connected to the inlet of the fertilizer pump, the outlet of the fertilizer pump is connected to the water inlet end of the main irrigation pipe, a bypass pressure sensor is provided on the output bypass pipe, a fertilizer suction port of each venturi tube is connected to different fertilizer containers through a fertilizer flow meter and a fertilizer suction pipe; before irrigation work, an upper limit operating frequency of the fertilizer pump corresponding to different operating pressures of the main pipe is first obtained by test, and during normal work, an upper limit operating frequency is provided for the fertilizer pump according to an interval parameter table, so as to ensure that the pressure at the inlet end of the fertilizer pump is not too low and cavitation does not occur during work, thereby effectively protecting the fertilizer pump.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated water and fertilizer machines, and in particular to a protection and control method for a fertilizer pump of an integrated water and fertilizer machine. Background Art

[0002] Bypass-type integrated fertigation systems are widely used in fertigation. They can independently or collectively draw fertilizer from multiple feeds, then mix it with irrigation water to irrigate crops. To operate, the fertigation system first turns on the irrigation pump connected to the main pipeline, providing pressure and flow. Once the flow stabilizes, fertigation begins. When the fertilization pump in the bypass pipe is turned on, water is drawn from the end of the main pipe's mixing section into the bypass pipe. Water then flows through a Venturi tube, the fertilization pump, and the bypass pipe back to the beginning of the main pipe's mixing section. The bypass pipe's flow rate is much lower than the main pipe's. As the flow rate into the Venturi tube increases, the pressure at the throat of the Venturi tube (connected to the fertilizer intake port) decreases according to the Venturi principle. When the pressure drops below the liquid level in the fertilizer tank, the liquid in the tank enters the Venturi tube through the fertilizer intake port for primary mixing. The water then flows through the fertilization pump and the bypass pipe to the beginning of the main pipe's mixing section for secondary mixing. Most of the mixed fertilizer and water are then discharged through the main pipe outlet to irrigate crops.

[0003] Since the fertilizer barrel is usually placed open on the ground, as the liquid level in the barrel drops during the fertilizer absorption process, the liquid level may be lower than the height of the Venturi tube throat. Therefore, the fertilizer absorption process generally requires the Venturi tube throat to be in a negative pressure state in order to continuously absorb fertilizer.

[0004] The structure of the Venturi tube is shown in the attached figure. Figure 1 As shown, the relationship between flow and pressure is shown in formula (1-1). The flow rate Q is directly proportional to the pressure difference between the inlet and throat. At the same time, the operation of the Venturi tube will generate pressure loss (the pressure difference between the inlet and outlet of the Venturi tube). The relationship between the pressure difference between the inlet and outlet and the flow rate (volume) is directly proportional, as shown in formula (1-2). The fertilizer pump in the bypass pipe is the power source for the Venturi tube, providing it with flow and compensating for pressure loss.

[0005] Formula (1-1):

[0006] Formula (1-2): ΔP = KρV2 / 2;

[0007] Where K is the Venturi tube resistance coefficient; ρ is the fluid density; S1 is the inlet section pipe cross-sectional area, V1 is the inlet section fluid velocity, P1 is the inlet section fluid pressure; S2 is the throat section pipe cross-sectional area, V2 is the throat section fluid velocity; P2 is the throat section fluid pressure;

[0008] Because orchards and woodlands often have varying elevations, the fertigation system must adjust the main pipe pressure to meet irrigation head requirements and achieve optimal fertilization results. This avoids excessive irrigation pressure in low areas and insufficient pressure in high areas. In practice, the main irrigation pipe pressure is generally adjusted within a range of 0.10 to 0.3 MPa.

[0009] It can be seen from formula (1-1) that when the pressure at the inlet of the Venturi tube (the pressure of the irrigation main pipeline) increases, in order to keep the pressure at the throat of the Venturi tube unchanged (to keep the fertilizer suction volume unchanged), the pressure difference root between the inlet and throat of the Venturi tube will also increase, that is, the corresponding Venturi tube flow rate (speed) will also increase. According to formula (1-2), the pressure loss will also increase (the flow rate increases), so the flow rate and compensation pressure loss of the fertilizer pump will also increase at this time. Therefore, the parameter selection of the fertilizer pump is based on the design when all Venturi tubes are opened and the fertilizer suction volume can reach the maximum requirement at the maximum working pressure of the irrigation main pipeline.

[0010] When the integrated water and fertilizer machine reduces the pressure in the main irrigation pipe during operation, the pressure at the venturi throat also decreases. This increases the amount of fertilizer absorbed by the venturi tube and the flow rate through the fertilizer pump. According to the characteristics of the water pump (flow rate and head are inversely proportional), the head of the fertilizer pump will decrease at this time, which will reduce the flow from the main pipe into the bypass pipe (the inlet of the venturi tube). In other words, after adaptive adjustment, the flow rate and head flowing through the fertilizer pump will remain almost unchanged, that is, the operating point of the fertilizer pump will remain almost unchanged. However, as the main pipe pressure continues to decrease, the pressure value at the throat of the venturi tube will become lower and lower, and eventually the throat may reach a state close to absolute vacuum (-0.1MPa). Refer to the document "High-speed Video Analysis of Cavitation Process in Venturi Fertilizer Applicator" (written by Yan Haijun, Wang Zijun, Chen Yan, etc.) in the 10th issue of "Journal of Irrigation and Drainage Machinery Engineering" in 2014. When the negative pressure at the throat of the Venturi tube reaches a certain value, cavitation is likely to occur. In severe cases, it will wear the surface of the internal flow channel, and ultimately affect the fertilizer suction flow rate. What is more serious is that the inlet of the fertilizer pump is connected to the second half of the diffusion section of the Venturi tube. The inlet of the fertilizer pump is also susceptible to cavitation due to the influence of the Venturi tube. In the process of cavitation, the bubbles destroy the normal flow pattern of the water flow, causing the performance of the fertilizer pump to deteriorate. When the bubbles collapse, a strong local water hammer will be generated in the flow channel. The instantaneous local impact pressure can reach tens or even hundreds of MPa. Under the continuous action of the huge impact pressure, the metal surfaces of the impeller and the pump casing will suffer fatigue damage and surface cavitation.

[0011] If cavitation is not properly controlled, the fertilizer pump will operate abnormally and unstable, posing safety and operational risks. The pump will often operate within an abnormal operating characteristic curve, causing rapid declines in flow rate, head, and efficiency, and increased energy consumption. Operation is prone to vibration, noise, and cavitation, which not only affects the pump's service life and reliability but also creates noise pollution in the surrounding area. In severe cases, the pump will lose its liquid flow, malfunctioning, and, consequently, the fertilizer pump will lose its fertilizer absorption function.

[0012] Therefore, it is necessary to monitor and control the working process of the fertilizer pump to avoid cavitation and effectively protect the fertilizer pump. Summary of the Invention

[0013] In order to solve the above problems, the purpose of the present invention is to provide a protection and control method for the fertilizer pump of a water-fertilizer integrated machine. By configuring corresponding detection instruments and control systems in the water-fertilizer integrated machine, a parameter table of the upper limit operating frequency values ​​of the fertilizer pump corresponding to different working pressures of the main pipeline is obtained by experiment before formal irrigation work. During normal operation, the upper limit operating frequency is provided for the fertilizer pump according to the parameter table, and the operating frequency of the fertilizer pump is controlled not to be higher than the upper limit operating frequency in the parameter table to ensure that the pressure at the inlet end of the fertilizer pump is not too low and cavitation does not occur during operation, thereby effectively protecting the fertilizer pump.

[0014] To achieve the above object, the present invention adopts the following technical solutions:

[0015] A protection and control method for a fertilizer pump of a water and fertilizer integrated machine includes a main irrigation pipe, a main irrigation pump, a venturi tube, and a fertilizer pump, wherein the main irrigation pump is connected to a constant pressure control device, a main flow meter and a main pressure sensor are provided at the water outlet end of the main irrigation pipe, an input bypass pipe is provided at the water outlet end of the main irrigation pipe, the input bypass pipe is connected to the inlet end of the venturi tube, the output bypass pipe is provided at the outlet end of the venturi tube, the output bypass pipe is connected to the inlet of the fertilizer pump, the fertilizer pump outlet is further connected to the water inlet end of the main irrigation pipe, a bypass pressure sensor is provided on the output bypass pipe, a fertilizer flow meter is connected to the fertilizer suction port of the venturi tube, the fertilizer flow meter is connected to a fertilizer container via a fertilizer suction pipe, the main flow meter, the main pressure sensor, and the bypass pressure sensor are connected to a controller, and the fertilizer pump is connected to the controller via a frequency converter. The protection and control method for the fertilizer pump includes the following steps:

[0016] 1. Parameter table test:

[0017] S1. Start the equipment, control the main irrigation pump via the constant pressure control device, and detect whether the measured values ​​of the main pressure sensor and the main flow meter in the main irrigation pipe reach the maximum pressure value and normal irrigation volume required for irrigation and fertilization. When the pressure reaches and stabilizes, open the Venturi tube and start the fertilizer pump. Then, gradually increase the operating frequency of the fertilizer pump via the controller and the frequency converter. When the flow rate measured by the fertilizer flow meter reaches the maximum flow rate required for operation, record the measured pressure value of the main pressure sensor and the corresponding operating frequency value (upper limit) of the fertilizer pump at this time.

[0018] S2. The constant pressure control device controls the main irrigation pump to begin reducing the pressure at the outlet of the main irrigation pipe according to a set pressure drop. The amount of fertilizer suctioned by the fertilizer suction port of the Venturi tube gradually increases, and the pressure at the inlet of the fertilizer pump gradually decreases. When the pressure measured by the bypass pressure sensor drops to a pressure safety value, the controller and the frequency converter gradually reduce the operating frequency of the fertilizer pump to reduce the flow through the Venturi tube. When the flow of the fertilizer flow meter drops back to the maximum flow required for operation, the measured pressure value of the main pressure sensor and the corresponding operating frequency value (upper limit) of the fertilizer pump are recorded.

[0019] S3. Repeat step S2, continue to reduce the pressure at the outlet of the main irrigation pipe according to the set pressure drop, and stop the test when the pressure detected by the main pressure sensor at the outlet of the main irrigation pipe drops to the minimum pressure value required for fertigation. A series of data corresponding to the measured pressure values ​​of the main pressure sensor and the operating frequency value (upper limit) of the fertilization pump are formed into an interval parameter table and stored in the controller;

[0020] 2. Work Protection:

[0021] The integrated water and fertilizer machine enters normal working state, and the controller collects the measurement value of the main pressure sensor in real time and compares it with the data in the above interval parameter table. In different measurement pressure value intervals, the controller and the frequency converter control the operating frequency of the fertilizer pump to be no higher than the corresponding operating frequency value (upper limit) in the above interval parameter table.

[0022] Furthermore, the pressure safety value at the inlet end of the fertilizer pump is the cavitation parameter of the fertilizer pump multiplied by the safety factor.

[0023] Furthermore, the output bypass pipe is a transparent pipe, which is used to observe the working conditions of the fluid in the pipe.

[0024] Furthermore, the output bypass pipe is connected to an observation lens, which is connected to a monitoring screen.

[0025] Furthermore, the maximum pressure value and the minimum pressure value at the outlet end of the main irrigation pipe during fertigation operation are determined according to the maximum head and the minimum head during fertigation operation of the irrigation site.

[0026] Furthermore, the venturi tube includes one, two or more venturi tubes, and the two or more venturi tubes are arranged in parallel. The fertilizer suction port of each venturi tube is connected to a fertilizer flow meter, and each fertilizer flow meter is connected to a different fertilizer container through a fertilizer suction pipe.

[0027] Furthermore, when there are two or more Venturi tubes, one of the Venturi tubes is first opened in step S1, and then two more Venturi tubes are opened after step S3 is completed, and steps S1 to S3 are repeated, and the operation is performed in sequence until all the Venturi tubes are opened to complete the test; a series of data corresponding to the number of the Venturi tubes opened, the measured pressure value of the main pressure sensor, and the operating frequency value (upper limit) of the fertilizer pump are formed into an interval parameter table and stored in the controller.

[0028] Furthermore, the parameter test adopts manual test, and the fertilizer flow meter adopts float flow meter during manual test.

[0029] Furthermore, the parameter test adopts automatic testing; during the automatic test, the fertilizer flow meter adopts a flow transmitter, and the fertilizer flow meter and the constant pressure control device are connected to the controller together. The maximum pressure value, minimum pressure value and pressure drop required by the main irrigation pipe during irrigation and fertilization, the pressure safety value at the inlet end of the fertilizer pump and the maximum flow value of the fertilizer flow meter are input into the controller, and an automatic testing program is set in the controller to perform automatic testing. The corresponding series of data of the pressure value measured by the main pressure sensor and the working frequency value (upper limit) of the fertilizer pump when different numbers of venturi tubes are opened are automatically measured to form an interval parameter table and stored in the controller.

[0030] The present invention has the following beneficial effects:

[0031] 1. The present invention configures corresponding detection instruments and control systems in the integrated water and fertilizer system. Before the formal irrigation work, the upper limit operating frequency value of the fertilizer pump corresponding to different working pressures of the main pipeline is obtained through experiments to form an interval parameter table. During normal operation, the upper limit operating frequency is provided for the fertilizer pump according to the pressure interval in the interval parameter table, and the operating frequency of the fertilizer pump is controlled not to be higher than the upper limit operating frequency in the interval parameter table, so as to ensure that the pressure at the inlet end of the fertilizer pump is not too low during operation and cavitation does not occur, thereby effectively protecting the fertilizer pump.

[0032] 2. The parameter test of the present invention is matched according to the maximum head and minimum head required for fertilization work in the irrigation field. Manual testing or automatic testing can be adopted as needed. By gradually reducing the pressure at the outlet end of the main irrigation pipe according to the pressure drop set by the program, the operating frequency value of the fertilizer pump and the measured pressure value of the main pressure sensor at different working pressures are gradually measured to form a corresponding interval parameter table. During the test process, the inlet pressure sensor value of the fertilizer pump or the inlet transparent tube is observed to ensure that cavitation and erosion do not occur in the fertilizer pump, thereby achieving reliable protection of the fertilizer pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of the Venturi tube.

[0034] Figure 2 This is a schematic diagram of the system structure of the fertilizer pump of the water-fertilizer integrated machine of the present invention.

[0035] Description of reference numerals:

[0036] 1. Main irrigation pipe; 11. Main flow meter; 12. Main pressure sensor; 2. Main irrigation pump; 3. Venturi tube; 4. Fertilizer pump; 5. Input bypass pipe; 6. Output bypass pipe; 7. Bypass pressure sensor; 8. Fertilizer flow meter; 9. Fertilizer container. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0038] See also Figure 2 As shown, the protection control method for the fertilizer pump of the water-fertilizer integrated machine includes a main irrigation pipe 1, a main irrigation pump 2, a venturi tube 3 and a fertilizer pump 4. The main irrigation pump 2 is connected to a constant pressure control device. The outlet end of the main irrigation pipe 1 is provided with a main flow meter 11 and a main pressure sensor 12. Usually, a fertilizer liquid mixing parameter monitor can also be provided in the system to control the water-fertilizer ratio. The outlet end of the main irrigation pipe 1 is provided with an input bypass pipe 5 connected to the inlet end of the venturi tube 3. The outlet end of the venturi tube 3 is provided with an output bypass pipe 6 connected to the inlet of the fertilizer pump 4. The outlet of the fertilizer pump 4 is then connected to the water inlet of the main irrigation pipe 1. The outlet end is connected, a bypass pressure sensor 7 is provided on the output bypass pipe 6, the venturi tube 3 includes one, two or more, two or more venturi tubes 3 are arranged in parallel, an on-off valve is provided between the venturi tube 3 and the fertilizer pump 4, the fertilizer suction port of each venturi tube 3 is connected to a fertilizer flow meter 8, each fertilizer flow meter 8 is connected to a different fertilizer container 9 through a fertilizer suction pipe, the main flow meter 11, the main pressure sensor 12 and the bypass pressure sensor 7 are connected to the controller, and the fertilizer pump 4 is connected to the controller through a frequency converter; the fertilizer pump protection control method comprises the following steps:

[0039] 1. Parameter table test:

[0040] S1. Start the equipment, control the main irrigation pump 2 to work via the constant pressure control device, and detect whether the measured values ​​of the main pressure sensor 12 and the main flow meter 11 in the main irrigation pipe 1 reach the maximum pressure value and normal irrigation volume required for irrigation and fertilization. After reaching and stabilizing, open the Venturi tube 3, start the fertilizer pump 4, and then gradually increase the operating frequency of the fertilizer pump 4 through the controller and the frequency converter (the increase range is based on control experience in this field and can be adjusted as needed). When the flow rate of the fertilizer flow meter 8 reaches the maximum flow rate required for operation (the maximum flow rate set according to the requirements of fertilization operation in the irrigation field, such as 800 L / h), record the measured pressure value of the main pressure sensor 12 and the corresponding operating frequency value (upper limit) of the fertilizer pump 4 at this time;

[0041] S2. The main irrigation pump 2 is controlled by the constant pressure control device to start reducing the pressure at the outlet of the main irrigation pipe 1 according to a set pressure drop (for example, a set pressure drop of 0.01 MPa, which can be adjusted according to different irrigation needs). The fertilizer intake of the fertilizer intake port of the venturi tube 3 will gradually increase, and the pressure at the inlet of the fertilization pump 4 will gradually decrease. When the pressure measured by the bypass pressure sensor 7 drops to a pressure safety value, the operating frequency of the fertilization pump 4 is gradually reduced (the reduction range can be adjusted as needed) by the controller and the frequency converter to reduce the flow rate through the venturi tube 3. When the flow rate of the fertilizer flowmeter 8 drops back to the maximum flow rate required for operation, the measured pressure value of the main pressure sensor 12 and the corresponding operating frequency value (upper limit) of the fertilization pump 4 are recorded.

[0042] S3. Repeat step S2, continue to reduce the pressure at the outlet of the main irrigation pipe 1 according to the set pressure drop, and stop the test when the pressure detected by the main pressure sensor 12 at the outlet of the main irrigation pipe 1 drops to the minimum pressure value required for fertigation. The series of data corresponding to the measured pressure values ​​of the main pressure sensor 12 and the operating frequency value (upper limit) of the fertilization pump 4 are formed into an interval parameter table and stored in the controller;

[0043] When there are two or more Venturi tubes 3, in step S1, one of the Venturi tubes 3 is first opened, and then after step S3, two more Venturi tubes 3 are opened and steps S1 to S3 are repeated, and the operation is performed in sequence until all the Venturi tubes 3 are opened and the test is completed; a series of data corresponding to the number of the opened Venturi tubes 3, the measured pressure value of the main pressure sensor 12, and the operating frequency value (upper limit) of the fertilizer pump 4 are formed into an interval parameter table and stored in the controller;

[0044] The parameter test is performed manually, and during manual testing, the fertilizer flowmeter 8 uses a float flowmeter. The parameter test is also performed automatically; during automatic testing, the fertilizer flowmeter 8 uses a flow transmitter. The fertilizer flowmeter 8 and the constant pressure control device are connected to a controller. The controller inputs the maximum and minimum pressure values ​​and pressure drop required by the main irrigation pipe 1 during fertigation operation, the pressure safety value at the inlet of the fertilizer pump 4, and the maximum flow rate of the fertilizer flowmeter 8. An automatic test program is set in the controller to perform automatic testing. The controller automatically measures the corresponding pressure values ​​measured by the main pressure sensor 12 and the operating frequency values ​​of the fertilizer pump 4 when different numbers of venturi tubes are opened, and forms an interval parameter table with the data stored in the controller. The interval parameter table is stored in the controller with a save type that does not lose data in the event of a power failure, so that normal operation can continue after the parameter test is completed.

[0045] Example 1: Three parallel venturi tubes 3 are provided in the irrigation system. The maximum and minimum pressures at the outlet of the main irrigation pipe 1 required for fertigation are 0.3 MPa and 0.1 MPa, respectively. The set pressure drop is 0.01 MPa. The following table shows the interval parameter table formed by the pressure values ​​measured by the four main pressure sensors 12 and the operating frequency of the fertilization pump 4 when different numbers of venturi tubes 3 are opened.

[0046]

[0047]

[0048] 2. Work Protection:

[0049] The integrated water and fertilizer machine enters normal working state, and the controller collects the measurement value of the main pressure sensor 12 in real time and compares it with the data in the above interval parameter table. In different measurement pressure value intervals, the controller and the frequency converter control the operating frequency of the fertilizer pump 4 to be no higher than the corresponding operating frequency value in the above interval parameter table.

[0050] According to the parameter table obtained by measurement in Example 1, when one venturi tube 3 is opened, when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.2 MPa to 0.3 MPa, the maximum operating frequency of the fertilization pump 4 shall not exceed 35 Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.15 MPa to 0.2 MPa, the maximum operating frequency of the fertilization pump 4 shall not exceed 30 Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.10 MPa to 0.15 MPa, the maximum operating frequency of the fertilization pump 4 shall not exceed 25 Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is less than or equal to 0.1 MPa, the maximum operating frequency of the fertilization pump 4 shall not exceed 20 Hz.

[0051] When the two Venturi tubes 3 are opened, when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.2MPa~0.3Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 40Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.15MPa~0.2Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 36Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.10MPa~0.15Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 32Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is less than or equal to 0.1Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 28Hz.

[0052] When the three Venturi tubes 3 are opened, when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.2MPa~0.3Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 48Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.15MPa~0.2Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 42Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is 0.10MPa~0.15Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 35Hz; when the working pressure at the water outlet end of the main irrigation pipe 1 is less than or equal to 0.1Mpa, the maximum operating frequency of the fertilizer pump 4 shall not be higher than 30Hz.

[0053] The pressure safety value at the inlet end of the fertilizer pump 4 is the fertilizer pump cavitation parameter multiplied by the safety factor. The fertilizer pump cavitation parameter is provided by the fertilizer pump manufacturer according to the pump specifications, and the safety factor is selected according to system requirements.

[0054] The output bypass pipe 6 is a transparent pipe used to observe the working conditions of the fluid in the pipe. Alternatively, to facilitate automatic observation, an observation lens is connected to the output bypass pipe 6, and the observation lens is connected to a monitoring screen, facilitating remote or automatic monitoring using the observation lens.

[0055] During fertigation, the maximum and minimum pressure values ​​at the outlet of the main irrigation pipe 1 are set according to the maximum and minimum head of fertilization work at the irrigation site. For example, in Example 1, the maximum and minimum pressure values ​​at the outlet of the main irrigation pipe 1 are 0.3 MPa and 0.1 MPa, respectively.

[0056] The working principle of this invention is that, provided that the fertilization operating conditions (maximum head, minimum head, main flow rate, maximum fertilizer suction flow rate, etc.) remain unchanged in the irrigation field, parameter testing only needs to be done once, after the integrated water and fertilizer machine is installed. After the parameter test is completed and the machine is operating normally, it only needs to be started to enter the working protection state. Of course, parameters can also be modified and corrected through the human-machine interface of the controller when necessary.

[0057] Since the lift of the fertilizer pump 4 is in a quadratic relationship with the speed, and the flow rate is in a linear relationship with the speed, when the speed of the fertilizer pump 4 changes, the flow rate and lift of the fertilizer pump 4 will change; when the speed of the fertilizer pump 4 is reduced, the flow rate and lift of the fertilizer pump 4 will decrease, and changing the speed of the fertilizer pump 4 can be achieved by changing the working frequency of the fertilizer pump 4; when the water-fertilizer integrated machine is working, assuming that the pressure at the throat of the Venturi tube 3 is A value, it can meet the fertilizer absorption requirement. When the pressure at the outlet end of the main irrigation pipe 1 (i.e., the inlet of the Venturi tube 3) decreases, the pressure at the throat of the Venturi tube 3 will also be lower than A. value, the corresponding inlet pressure of the fertilizer pump 4 will also decrease. At this time, by appropriately reducing the flow rate (speed) of the output bypass pipe 6 (i.e., the outlet of the Venturi tube 3), the pressure at the throat of the Venturi tube 3 is restored to value A, and the corresponding inlet pressure of the fertilizer pump 4 will also increase. When the flow rate (speed) is reduced, the pressure loss of the Venturi tube 3 will also be reduced accordingly. Therefore, when the pressure of the main irrigation pipe 1 drops to a certain value, the flow rate and head of the fertilizer pump 4 can be reduced by reducing the operating frequency of the fertilizer pump 4. In this way, cavitation at the inlet end of the fertilizer pump 4 caused by too low pressure at the throat of the Venturi tube 3 can be avoided.

[0058] The above description is only a specific embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A protection and control method for a fertilizer pump of a water and fertilizer integrated machine, characterized in that: The invention comprises a main irrigation pipe (1), a main irrigation pump (2), a venturi tube (3) and a fertilizer pump (4), wherein the main irrigation pump (2) is connected to a constant pressure control device, a main flow meter (11) and a main pressure sensor (12) are provided at the outlet end of the main irrigation pipe (1), an input bypass pipe (5) is provided at the outlet end of the main irrigation pipe (1) and is connected to the inlet end of the venturi tube (3), an output bypass pipe (6) is provided at the outlet end of the venturi tube (3) and is connected to the inlet end of the fertilizer pump (4), and the fertilizer pump (4) is connected to the inlet end of the fertilization pump (4). ) outlet is connected to the water inlet end of the main irrigation pipe (1), a bypass pressure sensor (7) is provided on the output bypass pipe (6), a fertilizer flow meter (8) is connected to the fertilizer suction port of the venturi tube (3), and the fertilizer flow meter (8) is connected to the fertilizer container (9) through the fertilizer suction pipe, the main flow meter (11), the main pressure sensor (12) and the bypass pressure sensor (7) are connected to the controller, and the fertilizer pump (4) is connected to the controller through the frequency converter; the fertilizer pump protection control method includes the following steps:

1. Parameter table test: S1, start the equipment, control the main irrigation pump (2) to work through the constant pressure control device, detect whether the measured values ​​of the main pressure sensor (12) and the main flow meter (11) in the main irrigation pipe (1) reach the maximum pressure value and normal irrigation volume required for irrigation and fertilization, and after reaching and stabilizing, open the Venturi tube (3), start the fertilizer pump (4), and then gradually increase the working frequency of the fertilizer pump (4) through the controller and the frequency converter, measure the flow of the fertilizer flow meter (8) and record the measured pressure value of the main pressure sensor (12) and the corresponding working frequency value of the fertilizer pump (4) when the flow reaches the maximum flow value required for work; S2, controlling the main irrigation pump (2) through the constant pressure control device to start reducing the pressure at the outlet end of the main irrigation pipe (1) according to the set pressure drop, the amount of fertilizer sucked by the fertilizer suction port of the Venturi tube (3) will gradually increase, and the pressure at the inlet end of the fertilizer pump (4) will gradually decrease. When the pressure measured by the bypass pressure sensor (7) drops to the pressure safety value, the operating frequency of the fertilizer pump (4) is gradually reduced through the controller and the frequency converter to reduce the flow through the Venturi tube (3). When the flow of the fertilizer flow meter (8) drops back to the maximum flow value required for operation, the measured pressure value of the main pressure sensor (12) and the corresponding operating frequency value of the fertilizer pump (4) are recorded at this time; S3, repeating step S2, continuing to reduce the pressure at the outlet end of the main irrigation pipe (1) according to the set pressure drop, until the pressure detected by the main pressure sensor (12) at the outlet end of the main irrigation pipe (1) drops to the minimum pressure value required for fertilization and irrigation, then stopping the test, and forming an interval parameter table with the series of data corresponding to the measured pressure value of the main pressure sensor (12) and the working frequency value of the fertilization pump (4) and storing it in the controller; 2. Work Protection: The integrated water and fertilizer machine enters a normal working state, and the controller collects the measured value of the main pressure sensor (12) in real time and compares it with the data in the above interval parameter table; in different measured pressure value intervals, the controller and the frequency converter control the operating frequency of the fertilizer pump (4) to be no higher than the corresponding operating frequency value in the above interval parameter table.

2. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 is characterized in that: The pressure safety value at the inlet end of the fertilizer pump (4) is the cavitation parameter of the fertilizer pump multiplied by the safety factor.

3. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 is characterized in that: The output bypass pipe (6) is a transparent pipe, which is used to observe the working conditions of the fluid in the pipe.

4. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 or 3, characterized in that: The output bypass pipe (6) is connected to an observation lens, which is connected to a monitoring screen.

5. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 is characterized in that: The maximum pressure value and the minimum pressure value at the outlet end of the main irrigation pipe (1) during fertigation operation are determined according to the maximum head and the minimum head during fertigation operation of the irrigation site.

6. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 is characterized in that: The venturi tube (3) includes one, two or more venturi tubes (3); two or more venturi tubes (3) are arranged in parallel, the fertilizer suction port of each venturi tube (3) is connected to a fertilizer flow meter (8), and each fertilizer flow meter (8) is connected to a different fertilizer container (9) through a fertilizer suction pipe.

7. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 6 is characterized in that: When there are two or more Venturi tubes (3), one of the Venturi tubes (3) is first opened in step S1, and then two of the Venturi tubes (3) are opened after step S3 is completed, and steps S1 to S3 are repeated, and the operation is performed in sequence until all the Venturi tubes (3) are opened to complete the test; a series of data corresponding to the number of the opened Venturi tubes (3), the measured pressure value of the main pressure sensor (12), and the operating frequency value of the fertilizer pump (4) is formed into an interval parameter table and stored in the controller.

8. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 or 7, characterized in that: The parameter table test adopts manual test, and during the manual test, the fertilizer flow meter (8) adopts a float flow meter.

9. The protection control method for the fertilizer pump of the water-fertilizer integrated machine according to claim 1 or 7, characterized in that: The parameter table test adopts automatic testing; during the automatic testing, the fertilizer flow meter (8) adopts a flow transmitter, and the fertilizer flow meter (8) and the constant pressure control device are connected to the controller together. The maximum pressure value, the minimum pressure value and the pressure drop required by the main irrigation pipe (1) during the irrigation and fertilization operation, the pressure safety value at the inlet end of the fertilizer pump (4) and the maximum flow value of the fertilizer flow meter (8) are input into the controller. The automatic testing program is set in the controller to perform automatic testing, and the series of data of the pressure value measured by the main pressure sensor (12) and the working frequency value of the fertilizer pump (4) corresponding to the opening of different numbers of venturi tubes (3) are automatically measured to form an interval parameter table and stored in the controller.

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