An open-type gas injection four-stage vacuum reduction test system and method for a vane pump

Abstract

The present invention discloses an open-type gas injection four-stage vacuum reduction test system and method for a vane pump. The test system is mainly composed of a gas injection system, a liquid circulation system, a test section and a data acquisition system; the gas injection method is mainly to adjust the corresponding gas flow rate according to the inlet pressure conversion, and the gas enters the pipeline after mixing through the gas injection device; the four-stage vacuum reduction method is mainly achieved by adjusting the return gate valve, the vacuum pump, the inlet gate valve 1 and the inlet gate valve 2. The present invention provides a method for gas injection during the pressure reduction process, which reduces the influence of valve cavitation through the four-stage vacuum reduction method and improves the accuracy of the gas injection cavitation test in the open system.

Description

Technical Field

[0001] The invention belongs to the field of vane pump testing, and in particular relates to an open gas injection four-stage vacuum reduction testing system and method for a vane pump. Background Art

[0002] Gas-liquid two-phase flow and cavitation are not uncommon in fluid machinery. Pumps, as core equipment for fluid transmission, are widely used in aerospace, marine engineering, petrochemical, nuclear industry and other fields. In recent years, the cavitation problem under gas-liquid two-phase conditions in pumps has gradually become the focus of research. When the pump transports gas-liquid two-phase media, if the inlet gas content is too high, gas lock is likely to occur, resulting in a sudden drop in pump performance; if the inlet pressure is low, cavitation is likely to occur, causing damage to the flow-through components. In severe cases, the pump unit may even fail to operate normally.

[0003] After searching, the invention patent "A new intelligent open-loop centrifugal pump cavitation test system" (application number: 202210533856.X) adds a gas-liquid separation tank in front of the test pump as a degassing device to reduce the impact of valve cavitation on the test results, but this will change the flow state in the inlet pipeline to a certain extent, and the stability of the pressure reduction in the inlet pipeline is poor. The invention does not involve cavitation testing under gas injection conditions; the invention patent "A centrifugal pump injection cavitation performance test system and test method for uniform aeration" (application number: 202210615109.0) is aimed at cavitation testing under gas-liquid two-phase conditions, but the invention does not take into account the expansibility of the injected gas during the pressure reduction process, the gas injection method is not perfect, and for pumps with too low cavitation margin, the possibility of valve cavitation when the valve needs to be adjusted is not considered.

[0004] It can be seen that the test methods for gas-liquid two-phase and cavitation are still immature, and there are few experimental studies involving both flows at the same time. Therefore, it is necessary to establish a cavitation test system for the gas-containing conditions at the inlet of the vane pump and a four-stage vacuum reduction test method for gas injection. Summary of the invention

[0005] In view of the problems existing in the above-mentioned existing gas-liquid two-phase and cavitation testing systems and methods, the present invention aims to provide an open gas injection four-stage vacuum reduction testing system and method for a vane pump.

[0006] The technical solution provided by the present invention is as follows:

[0007] 1. An open gas injection four-stage vacuum reduction test system for a vane pump, which consists of a gas injection system (gas compressor, pressure-stabilizing tank, gas outlet regulating ball valve, gas volume flowmeter and gas injection device), a liquid circulation system (cavitation tank, inlet pipeline, outlet pipeline, open exhaust water tank and return pipeline), a test section (visualized organic glass tube and vane pump) and a data acquisition system (high-speed camera and computer), wherein the inlet pipeline includes inlet gate valve 1, inlet gate valve 2, inlet electromagnetic flowmeter, inlet hydrophone, inlet pressure pulsation sensor, inlet pressure sensor and inlet vibration acceleration sensor, the outlet pipeline includes outlet vibration acceleration sensor, outlet pressure sensor, outlet pressure pulsation sensor, outlet hydrophone, outlet electromagnetic flowmeter and outlet gate valve, and the main component of the return pipeline is the return gate valve;

[0008] The gas compressor is connected to the bottom inlet of the pressure stabilizing tank, the upper outlet of the pressure stabilizing tank is connected to the gas injection device through the gas outlet regulating ball valve and the gas volume flow meter in turn, the bottom outlet of the cavitation tank is connected to the inlet end of the vane pump through the inlet pipeline, the gas injection device and the visual organic glass tube, the outlet end of the vane pump is connected to the outlet pipeline, the outlet pipeline extends from the top into the open exhaust water tank, the bottom outlet of the open exhaust water tank is connected to the upper part of the cavitation tank through the reflux gate valve, and the top of the cavitation tank is connected to the exhaust ball valve and the vacuum pump;

[0009] Furthermore, the gas injection device adopts a bilateral middle horizontal 30° to 60° gas injection structure, the length of which is twice the diameter of the inlet pipeline, and includes an inlet flange, an outlet flange, an air inlet pipe, and an air inlet hole, wherein the diameter of the air inlet hole is 1 to 2 mm, and the air inlet pipeline between the gas volume flow meter and the gas injection device is connected by a rubber hose, the purpose of which is to prevent the injected bubbles from floating up and gathering at the top of the pipeline, and to give the bubbles a horizontal speed so that the bubbles are fully mixed with the liquid and flow evenly.

[0010] Furthermore, the open exhaust water tank is an open cylindrical water tank, the purpose of which is to allow the gas mixed in the liquid flowing out of the outlet pipeline to be discharged from the open top of the water tank, ensuring that the liquid in the return pipeline is free of gas impurities;

[0011] Furthermore, the cavitation tank is a closed stainless steel cylindrical water tank, the bottom diameter of which is 1 / 3 to 1 times that of the open exhaust water tank, and the height is 1 to 3 times that of the open exhaust water tank, in order to ensure that the liquid in the system can circulate and the liquid in the open exhaust water tank will not overflow during the test;

[0012] 2. A method for testing the open-type gas injection four-stage vacuum reduction of a vane pump, the specific steps are as follows:

[0013] Step 1: Fully open the exhaust ball valve, inlet gate valve 1, inlet gate valve 2, outlet gate valve and reflux gate valve, close the gas outlet regulating ball valve, add liquid medium to the open exhaust water tank, and stop adding liquid medium when the water level in the open exhaust water tank is stably higher than the bottom outlet pipe, that is, the water level is at 1 / 10 to 3 / 10 of the overall height of the open exhaust water tank. At this time, the water level of the cavitation tank is consistent with the water level of the open exhaust water tank;

[0014] Step 2: Close the exhaust ball valve, start the vane pump, and control the liquid volume flow Q of the test system through the outlet gate valve l ;

[0015] Step 3: Set the loading pressure value P through the control panel of the gas compressor set And start, wait until the pressure in the pressure regulating tank reaches the set pressure value P set After it remains stable, according to the vane pump inlet pressure value P in The gas volume flow Q of the gas volume flow meter is controlled by the gas outlet regulating ball valve g′ ;

[0016] Step 4: After the system has been running stably for a period of time, gradually close the return valve until the water level in the open exhaust water tank begins to rise (first-stage vacuum reduction). At this time, the pressure value measured by the inlet pressure sensor gradually decreases. According to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter g′ ;

[0017] Step 5: Adjust the outlet gate valve to control the liquid volume flow rate Q of the test system l Keep it stable. After the vane pump runs stably, collect and record relevant parameters such as head H and NPSH. Use a high-speed camera to synchronously shoot and visualize the gas-liquid-gas flow phenomenon in the organic glass tube and the vane pump.

[0018] Step 6: When the inlet pressure drops to about -40 kPa, start the vacuum pump, draw the vacuum in the cavitation tank and gradually reduce the inlet pressure (secondary vacuum reduction). in Adjust the gas volume flow rate Q of the gas volume flow meter g′ , repeat step 5;

[0019] Step 7: When the inlet pressure reaches the ultimate vacuum degree of the vacuum pump (the inlet pressure is about -80kPa) and cannot be further reduced, first gradually close the inlet gate valve 1 to reduce the pressure (three-stage vacuum reduction). To ensure that the valve does not cavitate, when the inlet pressure is about -86kPa, gradually close the inlet gate valve 2 to reduce the pressure (four-stage vacuum reduction). During the pressure reduction process, according to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter g′, repeat step 5;

[0020] Step 8: After each test, close the gas outlet regulating ball valve and vane pump in turn, fully open the inlet gate valve 2, inlet gate valve 1, return gate valve and exhaust ball valve in turn, and after the water level in the open exhaust water tank drops to the initial water level, completely close the exhaust ball valve, inlet gate valve 1 and return gate valve, start the vacuum pump to extract the gas in the cavitation tank, and then continue to let the test system stand for a while to ensure that the gas in the system is completely removed before starting the next test;

[0021] Furthermore, the gas injection method mainly comprises:

[0022] 1) According to the liquid volume flow Q l and the inlet volume fraction IGVF to determine the gas volume flow rate Q g . Vane pump inlet gas volume flow rate Where IGVF is the gas volume fraction at the inlet of the vane pump; Q l is the liquid volume flow rate, in m 3 / h;

[0023] 2) Conversion of different inlet pressures P of vane pump in The corresponding gas volume flow rate Q of the regulated gas volume flow meter g′ Taking into account the expansion of gas during the decompression process, according to the ideal gas state equation Among them, the outlet temperature of the surge tank T is ignored. 1 and vane pump inlet temperature T 2 The small temperature difference, T 1 =T 2 ; Therefore, the gas volume flow rate of the gas flow meter is Among them, P in is the vane pump inlet pressure value measured by the inlet pressure sensor, in kPa; P set It is the pressure value set in the pressure regulating tank, in kPa;

[0024] Furthermore, the four-stage vacuum reduction method is mainly as follows:

[0025] 1) First-stage vacuum reduction: gradually close the return valve to reduce the inlet pressure until the water level in the open exhaust water tank begins to rise;

[0026] 2) Secondary vacuum reduction: When the inlet pressure drops to about -40kPa, start the vacuum pump to extract the vacuum in the cavitation tank to gradually reduce the inlet pressure until the vacuum pump has reached the limit vacuum (the inlet pressure is about -80kPa) and can no longer reduce the pressure;

[0027] 3) Three-stage vacuum reduction: gradually close the inlet gate valve 1 to reduce the pressure, while ensuring that the valve does not cavitate;

[0028] 4) Fourth-stage vacuum reduction: When the inlet pressure is about -86 kPa, gradually close the inlet gate valve 2 to reduce the pressure, while ensuring that the valve does not cavitate.

[0029] The advantages of the present invention are as follows:

[0030] In the present invention, the expansibility of the gas during the depressurization process is taken into consideration, and the gas volume flow rate is adjusted according to the inlet pressure during the test process, thereby ensuring the accuracy of the inlet gas volume fraction;

[0031] In the present invention, a cavitation test is performed in an open test system mainly by using a vacuum pumping method (second stage vacuum reduction), and a two-stage valve adjustment method (third and fourth stage vacuum reduction) is used to reduce the possibility of valve cavitation and improve the stability of the pressure reduction process and the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of an open gas injection four-stage vacuum reduction test system for a vane pump according to the present invention;

[0033] Figure 2 Schematic diagram of the gas injection device of the present invention; (a) front view; (b) side view; (c) top view (gas-liquid flow direction); (d) gas injection device;

[0034] Figure 3 Q in the embodiment l =19m 3 / h at different inlet gas volume fractions IGVF pump inlet pressure P in and the gas volume flow rate Q of the gas flow meter g′ Conversion relationship diagram between ;

[0035] Figure 4 Q in the embodiment l =19m 3 NPSH-H diagram under different inlet gas volume fractions IGVF at / h;

[0036] Description of reference numerals:

[0037] 1- Vacuum pump 2- Exhaust ball valve 3- Cavitation tank 4- Import gate valve 1 5- Import gate valve 2 6- Import electromagnetic flowmeter 7- Import hydrophone 8- Import pressure pulsation sensor 9- Import pressure sensor 10- Gas injection device 11- Visualized organic glass tube 12- Import vibration acceleration sensor 13- Vane pump 14- Motor 15- Export vibration acceleration sensor 16- Export pressure sensor 17- Export pressure pulsation sensor 18- Export hydrophone 19- Export electromagnetic flowmeter 20- Export gate valve 21- Open exhaust water tank 22- Backflow gate valve 23- Gas compressor 24- Pressure stabilizing tank 25- Gas outlet regulating ball valve 26- Gas volume flowmeter 27- High-speed camera 28- Computer DETAILED DESCRIPTION

[0038] To further illustrate the purpose, content and advantages of the present invention, specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings and examples.

[0039] A centrifugal pump with an inducer was selected as the test object, and the design flow rate was Q d =19m 3 / h, design head H d =55m, rated speed n=5000r / min.

[0040] The test system is composed of a gas injection system, a liquid circulation system, a test section and a data acquisition system, wherein the gas injection system includes a gas compressor (23), a pressure regulating tank (24), a gas outlet regulating ball valve (25), a gas volume flow meter (26) and a gas injection device (10), the liquid circulation system includes a cavitation tank (3), an inlet pipeline, an outlet pipeline, an open exhaust water tank (21) and a return pipeline, the test section includes a visual organic glass tube (11) and a vane pump (13), and the data acquisition system includes a high-speed camera (27) and a computer (28);

[0041] The inlet pipeline includes an inlet gate valve 1 (4), an inlet gate valve 2 (5), an inlet electromagnetic flowmeter (6), an inlet hydrophone (7), an inlet pressure pulsation sensor (8), an inlet pressure sensor (9) and an inlet vibration acceleration sensor (12);

[0042] The outlet pipeline comprises an outlet vibration acceleration sensor (15), an outlet pressure sensor (16), an outlet pressure pulsation sensor (17), an outlet hydrophone (18), an outlet electromagnetic flowmeter (19) and an outlet gate valve (20);

[0043] The main component of the return pipeline is the return gate valve (22);

[0044] The gas injection device (10) adopts a double-sided middle horizontal 45° gas injection structure, the length of which is twice the diameter of the inlet pipeline, and comprises an inlet flange (101), an outlet flange (102), an inlet pipe (103), and an inlet hole (104), wherein the diameter of the inlet hole is 1 mm, and the inlet pipeline between the gas volume flow meter (26) and the gas injection device (10) is connected by a rubber hose;

[0045] The open exhaust water tank (21) is an open cylindrical water tank, and the cavitation tank (3) is a closed stainless steel cylindrical water tank, the bottom diameter of which is 1 / 2 times that of the open exhaust water tank (21), and the height of which is twice that of the open exhaust water tank (21);

[0046] The gas compressor (23) is connected to the bottom inlet of the pressure regulating tank (24), the upper outlet of the pressure regulating tank (24) is connected to the gas injection device (10) through the gas outlet regulating ball valve (25) and the gas volume flow meter (26) in sequence, the bottom outlet of the cavitation tank (3) is connected to the inlet end of the vane pump (13) through the inlet pipeline, the gas injection device (10) and the visual organic glass tube (11), the outlet end of the vane pump (13) is connected to the outlet pipeline, the outlet pipeline extends from the top into the open exhaust water tank (21), the bottom outlet of the open exhaust water tank (21) is connected to the upper part of the cavitation tank (3) through the return gate valve (22), and the top of the cavitation tank (3) is connected to the exhaust ball valve (2) and the vacuum pump (1);

[0047] The test steps are as follows:

[0048] Step 1: Fully open the exhaust valve (2), the inlet gate valve 1 (4), the inlet gate valve 2 (5), the outlet gate valve (20) and the return gate valve (22), close the gas outlet regulating ball valve (25), add liquid medium to the open exhaust water tank (21), and stop adding liquid medium when the water level in the open exhaust water tank (21) is stably higher than the bottom outlet pipeline, that is, the water level is at 1 / 5 of the overall height of the open exhaust water tank (21). At this time, the water level in the cavitation tank (3) is consistent with the water level in the open exhaust water tank (21);

[0049] Step 2: Close the exhaust ball valve (2), start the vane pump (13), and control the liquid volume flow rate Q of the test system by adjusting the outlet gate valve (20). l =19m 3 / h;

[0050] Step 3: Set the loading pressure value P through the control panel of the gas compressor (23) set =130kPa and start, wait until the pressure in the pressure regulating tank (24) reaches the set pressure value P set =130kPa and remain stable, according to the vane pump inlet pressure value P in The gas volume flow Q of the gas volume flow meter (26) is controlled by the gas outlet regulating ball valve (25)g′ ;

[0051] Step 4: After the system runs stably for a period of time, gradually close the return valve (22) until the water level in the open exhaust water tank (21) begins to rise (first-stage vacuum reduction). At this time, the pressure value measured by the inlet pressure sensor (9) gradually decreases. According to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter (26) g′ ;

[0052] Step 5: Adjust the outlet gate valve (20) to control the liquid volume flow rate Q of the test system l =19m 3 / h remains stable, and after the vane pump (13) runs stably, relevant parameters such as head H and NPSH are collected and recorded, and a high-speed camera (27) is used to synchronously shoot and visualize the gas-liquid-gas flow phenomenon in the organic glass tube (11) and the vane pump (13);

[0053] Step 6: When the inlet pressure drops to about -38 kPa, start the vacuum pump (1) to draw the vacuum in the cavitation tank (3) to gradually reduce the inlet pressure (secondary vacuum reduction). in Adjust the gas volume flow rate Q of the gas volume flow meter (26) g′ , repeat step 5;

[0054] Step 7: When the inlet pressure reaches the ultimate vacuum degree of the vacuum pump (the inlet pressure is about -78 kPa) and cannot be further reduced, first gradually close the inlet gate valve 1 (4) to reduce the pressure (three-stage vacuum reduction). To ensure that the valve does not cavitate, when the inlet pressure is about -84 kPa, gradually close the inlet gate valve 2 (5) to reduce the pressure (four-stage vacuum reduction). During the pressure reduction process, according to the pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter (26) g ', repeat step 5;

[0055] Step 8: After each test, close the gas outlet regulating ball valve (25) and the vane pump (13) in turn, fully open the inlet gate valve 2 (5), the inlet gate valve 1 (4), the return gate valve (22) and the exhaust ball valve (2) in turn, and after the water level in the open exhaust water tank (21) drops to the initial water level, completely close the exhaust ball valve (2), the inlet gate valve 1 (4) and the return gate valve (22), start the vacuum pump (1) to extract the gas in the cavitation tank (3), and then continue to let the system stand for a period of time to ensure that the gas in the system is completely removed before starting the next test;

[0056] The gas volume flow rate Q of the gas volume flow meter (26) is adjusted. g The specific method of gas injection is:

[0057] 1) According to the liquid volume flow Q l and the inlet volume fraction IGVF to determine the gas volume flow rate Q g . Pump inlet gas volume flow rate Where IGVF is the gas volume fraction at the pump inlet; Q l is the liquid volume flow rate, in m 3 / h;

[0058] 2) Conversion of different pump inlet pressures P in The corresponding gas volume flow rate Q of the regulated gas volume flow meter g′ Taking into account the expansion of gas during the decompression process, according to the ideal gas state equation Among them, the outlet temperature of the surge tank T is ignored. 1 and pump inlet temperature T 2 The small temperature difference, T 1 =T 2 ; Therefore, the gas volume flow rate of the gas flow meter is Among them, P in is the pump inlet pressure value measured by the inlet pressure sensor, in kPa; P set is the pressure value set in the pressure regulating tank, in kPa. The test results are as follows Figure 3 As shown;

[0059] The head H is the inlet pressure P measured by the inlet pressure sensor (9). in and the outlet pressure P measured by the outlet pressure sensor (16) out , and then through the formula Calculated; NPSH is calculated by the formula Calculated, where P v is the saturated vapor pressure, in kPa, and ρ is the density of the gas-liquid two-phase mixed medium, in kg / m 3 , g is the acceleration due to gravity, take 9.8m / s 2 , Q l Measured by imported electromagnetic flowmeter, unit is m 3 / h,D in is the pump inlet pipe diameter, in m. The test results are as follows: Figure 4 shown.

[0060] The test object of the above embodiment is a centrifugal pump with an inducer, and the test condition is Q l =19m 3 / h, IGVF=0.5%, 1%, 2%, but the present invention is not limited thereto, and can also be applied to the testing of other types of vane pumps such as axial flow pumps and mixed flow pumps under various flow conditions and various inlet gas volume fraction conditions.

Claims

1. An open-type gas injection four-stage vacuum reduction test system for a vane pump, characterized in that: It is mainly composed of a gas injection system, a liquid circulation system, a test section and a data acquisition system, wherein the gas injection system includes a gas compressor, a pressure-stabilizing tank, a gas outlet regulating ball valve, a gas volume flow meter and a gas injection device connected in sequence; the liquid circulation system includes a cavitation tank, an inlet pipeline, an outlet pipeline, an open exhaust water tank and a reflux pipeline; the test section includes a connected visual organic glass tube and a vane pump; the data acquisition system includes a connected high-speed camera and a computer; the gas compressor is connected to the bottom inlet of the pressure-stabilizing tank, the upper outlet of the pressure-stabilizing tank is connected to the gas injection device through the gas outlet regulating ball valve and the gas volume flow meter in sequence, the bottom outlet of the cavitation tank is connected to the inlet end of the vane pump through the inlet pipeline, the gas injection device and the visual organic glass tube in sequence, the outlet end of the vane pump is connected to the outlet pipeline, the outlet pipeline extends into the open exhaust water tank from the top, the bottom outlet of the open exhaust water tank is connected to the upper part of the cavitation tank through the reflux pipeline, and the top of the cavitation tank is connected to the exhaust ball valve and the vacuum pump; The gas injection device is a 30° to 60° gas injection structure in the middle of both sides, with a length twice the diameter of the inlet pipeline, including an inlet flange, an outlet flange, an air inlet pipe, and an air inlet hole; The inlet pipeline includes an inlet gate valve 1, an inlet gate valve 2, an inlet electromagnetic flowmeter, an inlet hydrophone, an inlet pressure pulsation sensor, an inlet pressure sensor and an inlet vibration acceleration sensor which are arranged in sequence, and the inlet vibration acceleration sensor is installed on the inlet end flange of the vane pump; The outlet pipeline includes an outlet vibration acceleration sensor, an outlet pressure sensor, an outlet pressure pulsation sensor, an outlet hydrophone, an outlet electromagnetic flowmeter and an outlet gate valve which are arranged in sequence. The outlet vibration acceleration sensor is installed on the outlet end flange of the vane pump, and the outlet end of the vane pump extends from the top into the open exhaust water tank through the outlet pipeline.

2. The open-type gas injection four-stage vacuum reduction test system for a vane pump according to claim 1, characterized in that: The diameter of the air inlet hole is 1 to 2 mm, and the air inlet pipeline between the gas volume flow meter and the gas injection device is connected by a rubber hose.

3. The open-type gas injection four-stage vacuum reduction test system for a vane pump according to claim 2, characterized in that: The reflux pipeline is a reflux gate valve, the bottom outlet of the open exhaust water tank is connected to the upper part of the cavitation tank through the reflux gate valve, the open exhaust water tank is an open cylindrical water tank, the cavitation tank is a closed stainless steel cylindrical water tank, the bottom diameter is 1 / 3 to 1 times that of the open exhaust water tank, and the height is 1 to 3 times that of the open exhaust water tank.

4. The test method of the open-type gas injection four-stage vacuum reduction test system for a vane pump according to claim 3 is characterized in that: The specific steps are as follows: Step 1: Fully open the exhaust ball valve, inlet gate valve 1, inlet gate valve 2, outlet gate valve and reflux gate valve, close the gas outlet regulating ball valve, add liquid medium to the open exhaust water tank, and stop adding liquid medium when the water level in the open exhaust water tank is stably higher than the bottom outlet pipe, that is, the water level is at 1 / 10 to 3 / 10 of the overall height of the open exhaust water tank. At this time, the water level of the cavitation tank is consistent with the water level of the open exhaust water tank; Step 2: Close the exhaust ball valve, start the vane pump, and control the liquid volume flow Q of the test system by adjusting the outlet gate valve l ; Step 3: Set the loading pressure value P through the control panel of the gas compressor set And start, wait until the pressure in the pressure regulating tank reaches the set pressure value P set After it remains stable, according to the vane pump inlet pressure value P in The gas volume flow Q of the gas volume flow meter is controlled by the gas outlet regulating ball valve g′ ; Step 4: After the system has been running stably for a period of time, gradually close the return valve until the water level in the open exhaust water tank begins to rise and reaches the first-level vacuum level. At this time, the pressure value measured by the inlet pressure sensor gradually decreases. According to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter g′ ; Step 5: Adjust the outlet gate valve to control the liquid volume flow rate Q of the test system l Keep it stable. After the vane pump runs stably, collect and record relevant parameters such as head H and NPSH. Use a high-speed camera to synchronously shoot and visualize the gas-liquid-gas flow phenomenon in the organic glass tube and the vane pump. Step 6: When the inlet pressure drops to about -40kPa, start the vacuum pump, draw the vacuum in the cavitation tank and gradually reduce the inlet pressure to reach the second-level vacuum reduction. According to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter g′ , repeat step 5; Step 7: When the inlet pressure reaches the limit vacuum degree of the vacuum pump and cannot be further reduced, first gradually close the inlet gate valve 1 to reduce the pressure to achieve the third level of vacuum reduction. To ensure that the valve does not cavitate, when the inlet pressure is about -86kPa, gradually close the inlet gate valve 2 to reduce the pressure to achieve the fourth level of vacuum reduction. During the pressure reduction process, according to the vane pump inlet pressure value P in Adjust the gas volume flow rate Q of the gas volume flow meter g′ , repeat step 5; Step 8: After each set of tests, close the gas outlet regulating ball valve and vane pump in turn, fully open inlet gate valve 2, inlet gate valve 1, return gate valve and exhaust ball valve in turn, and after the water level in the open exhaust water tank drops to the initial water level, completely close the exhaust ball valve, inlet gate valve 1 and return gate valve, start the vacuum pump to extract the gas in the cavitation tank, and then continue to let the test system stand for a while to ensure that the gas in the system is completely removed before starting the next set of tests.

5. The method according to claim 4, characterized in that Adjust the gas volume flow rate Q of the gas volume flow meter g′ The specific method of gas injection is: 1) According to the liquid volume flow Q l and the inlet volume fraction IGVF to determine the gas volume flow rate Q g , gas volume flow rate at the vane pump inlet Where IGVF is the gas volume fraction at the inlet of the vane pump; Q l is the liquid volume flow rate, in m 3 / h; 2) Conversion of different inlet pressures P of vane pump in The corresponding gas volume flow rate Q of the regulated gas volume flow meter g′ , considering the expansibility of gas during decompression, according to the ideal gas state equation Among them, the small temperature difference between the outlet temperature T1 of the pressure regulating tank and the inlet temperature T2 of the vane pump is ignored, that is, T1 = T2; therefore, the gas volume flow rate of the gas flow meter Among them, P in is the vane pump inlet pressure value measured by the inlet pressure sensor, in kPa; P set It is the pressure value set in the pressure regulating tank, in kPa.

6. The method according to claim 4, characterized in that The specific method to achieve the four-stage vacuum reduction is: 1) First-stage vacuum reduction: gradually close the return valve to reduce the inlet pressure until the water level in the open exhaust water tank begins to rise; 2) Secondary vacuum reduction: When the inlet pressure drops to about -40kPa, start the vacuum pump to extract the vacuum in the cavitation tank to gradually reduce the inlet pressure until the vacuum pump has reached the limit vacuum and can no longer reduce the pressure; 3) Three-stage vacuum reduction: gradually close the inlet gate valve 1 to reduce the pressure, while ensuring that the valve does not cavitate; 4) Fourth-stage vacuum reduction: When the inlet pressure is about -86 kPa, gradually close the inlet gate valve 2 to reduce the pressure, while ensuring that the valve does not cavitate.

7. The open-type gas injection four-stage vacuum reduction test method for a vane pump according to claim 4, characterized in that: The NPSH is calculated by the formula Calculated, where P v is the saturated vapor pressure, in kPa, and ρ is the density of the gas-liquid two-phase mixed medium, in kg / m 3 , g is the acceleration due to gravity, take 9.8m / s 2 , Q l Measured by imported electromagnetic flowmeter, unit is m 3 / h,D in It is the inlet pipe diameter of the vane pump, in m.

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