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Cryogenic Valve Test Device Based on Computer Data Acquisition
A kind of low temperature valve performance testing device based on computer data acquisition is introduced. The device has the function of storing, displaying and printing test data, and can realize the automatic control of liquid nitrogen tank self-pressurization system, which can improve the working efficiency of the test, Operation timeliness, accuracy and safety. It is pointed out that the application of computer technology and optoelectronic technology to the experimental device is the future direction of development. 1, Overview With the development of cryogenic technology, cryogenic fluid is more and more widely used, such as liquid nitrogen is widely used in industrial production, scientific research, medical and health, liquid nitrogen and liquid oxygen as rocket propellant in the field of national defense Show significant advantages. In addition, LNG has also become one of the major energy sources in recent years due to the shortage of energy sources. In all aspects of the use of cryogenic liquid, the cryogenic valve is an indispensable plumbing accessory. However, due to the type of valves that operate at cryogenic temperatures below -100 ° C, special requirements are placed on their structural design, material selection, manufacturing processes, and inspection tests. Especially in the low-temperature valve product testing, in addition to meet the same at room temperature in the same general valve performance testing requirements, but also for low temperature performance test. The main task of low temperature test is to check the valve in the low temperature gas tightness and opening and closing performance. Therefore, the test device is very important, advanced performance of the device determines the accuracy and reliability of the test results. To this end, a new type of low temperature valve comprehensive testing device has been developed. Its functions include low temperature test and cryogenic treatment. The temperature signal, pressure signal and valve leakage are all automatically measured by using the computer data acquisition system. The device has a centralized test data storage, display and printing capabilities. This article focuses on the device in the valve seat sealing low temperature test content. 2, the status quo of low-temperature test device Domestic and foreign manufacturers and research institutes involved in the low-temperature valve cryogenic valve performance testing attaches great importance to actively carry out research and development work in this area. Due to the different cooling and low temperature methods used, there is a big difference in the layout of the test device. Are often used immersion method and cold method in two ways. Impregnation method (ie, external cooling method) is the valve directly into the cold liquid nitrogen tank cooling, when the valve temperature quenched to operating temperature and then use helium sealing performance test. Cold insulation method (ie, internal cooling method) is the valve installed in the cold box, the introduction of low temperature medium into the valve to cool down, when the temperature dropped to the required value, the low temperature medium let go, and then pass the prescribed pressure helium test . In addition there is a spray method, the valve is installed in the cold box, the use of sprinkler to spray cold liquid nitrogen tank, when the cold box temperature reaches the test temperature, stop spraying liquid nitrogen, and then press the required pressure Nitrogen test. However, spray method does not apply to ultra-low temperature valve. Domestic and international commonly used low temperature test device has the following. 2.1, Japanese valve industry with low-temperature valve test device Japan's valve industry with low-temperature valve test device (Figure 1) using the impregnation method and cold insulation two ways. Impregnation method low temperature test device for gate valve, globe valve and check valve. Cold method low temperature test device for all types of valves. Low temperature valve seat seal test pressure and duration shown in Table 1, low temperature test allows leakage rate in Table 2, the leakage detection method shown in the figure as a measuring vessel in the sink. (a) Immersion method Low-temperature test device (opposite to the check valve inlet / outlet pipe) (b) Low-temperature test device for cold insulation method (temperature difference between point A and point B should be within 20 ℃) ​​Fig.1 Low temperature test device for Japanese valve industry 2.2 , Europe and the United States valve industry with low-temperature valve test device Europe and the United States valve industry to use the valve standard developed by the United Kingdom 3.3, test methods (1) temperature test temperature measurement involves room temperature to liquid nitrogen temperature range, the use of thermocouple thermometer to measure the temperature signal through the digital Multimeter measurement, acquisition and input measurement and control computer, displayed on the computer interface, and the computer automatically record and save. At the same time, the computer sends the temperature measurement to the temperature display on the instrument panel for on-site display. (2) pressure test pressure measurement range of 0 ~ 10MPa. The use of pointer precision pressure gauge and digital pressure gauge on the instrument panel on-site display of system pressure at the same time, the use of pressure transmitters to measure system pressure and converted to voltage signals measured by the digital multimeter to collect and input measurement and control computer , Displayed on the computer interface and automatically recorded and saved by the computer. (3) Level In order to ensure the liquid nitrogen level to meet the valve test requirements, the use of differential pressure transmitter to measure the liquid level. Measurement of electrical signals through the digital multimeter measurement, acquisition and input to the computer for display, and reminded filling liquid nitrogen and stop liquid nitrogen filling operation. (4) flow rate According to the different forms of valve sealing, the valve allows the amount of leakage is different. Soft seal structure of the valve, the amount of leakage should be zero. For hard-sealed valve itself is allowed to have a certain amount of leakage. Based on the above, two devices for measuring the flow rate are provided, one of which is a low-flow meter for measuring the leakage of a hard-sealed valve or a soft-sealed valve that allows a certain amount of leakage in a relatively abnormal working state. For a small amount of leakage, as the general flowmeter has been unable to detect, you need to observe and count the number of open-ended bubbles in the water to measure the number of leaks. Using computer data acquisition system to record the number of electrical pulses to achieve automatic counting. 4 Conclusion Based on the computer data acquisition system of low-temperature valve performance testing device, the thermocouple, pressure sensor, liquid level sensor and flowmeter of the various signals, pre-input into the computer, through the data acquisition software for data Display, store and print. The self-pressurizing system of liquid nitrogen tank can also be controlled according to the setting of relevant parameters. Liquid nitrogen can be filled into the low-temperature test tank. The test system uses centralized data monitoring, which not only enables the computer to issue commands to operate automatically, improve work efficiency, timeliness, accuracy and security of operation, but also facilitate the unified data storage and management. [2] JB / T7749-1995, cryogenic valve technical conditions 〔S〕. 〔3〕 BS6364-1984 (R1998) , Low temperature valve [S] 〔4〕 SHELLMESCSPE77 / 306: 2002, low temperature valve product test 〔S〕 Keywords for the article: Valve