1. Overview With the rapid development of modern petrochemical industry, some media used in special working conditions are extremely corrosive. Even stainless steel valves and valves lined with rubber and porcelain enamel cannot meet the needs. If Hastelloy, Monel, or No. 20 alloy is used as the valve material, because it contains a large amount of rare metals such as Ni, Cr, Ti, Mo, Nb, and Pt, its resources are limited and expensive. According to the results of modern science and technology, fluorocarbons have fluorine carbon bonds and their shielding effect in the molecular structure, and they have excellent corrosion resistance, high (low) temperature resistance, non-adhesion, and electrical insulation, and can almost resist all chemical media. (including hydrofluoric acid, concentrated sulfuric acid, and aqua regia). Using the principle of plastic processing of fluorine plastic, the fluorine plastic is lining in the ordinary steel outer shell to isolate the direct contact between the steel metal and the strong corrosive medium, which not only solves the problem that the fluorine plastic has low strength and can not withstand high pressure, but also solves Iron and steel materials are not resistant to corrosion. Fluorine plastic lining valves have excellent heat resistance and cold resistance, excellent electrical insulation and excellent chemical stability, can resist corrosion of various strong acids, strong alkalis and strong oxidants, and have very low friction and self-lubricating properties. , It can be used in the range of -195～200°C for a long time.

2, the structure and design 2.1, structure and main parts name shown in Figure 1 and Figure 2.

1 Drive 2 Dust seal 3 O-ring 4 Disc 5 Disc liner 6 Valve seat lining 7 Body
Figure 1 Double flanged butterfly valve 2.2. Application Fluorine plastic lining butterfly valve nominal pressure is PN116 (fluorine plastic can withstand pressure up to 215MPa). DN50 ~ 1 200. The applicable temperature of the valve is based on the comprehensive assessment of the temperature to which the different materials (metal materials and non-metal materials) selected can withstand. Such as steel lined fluoroplastic (WCB + F46) material, the use of temperature - 29 ~ 150 °C. The maximum limit value does not exceed 150°C. Suitable media are low-viscosity acids and alkalis and other corrosive media, mainly referring to acidic, alkaline, organic and inorganic solvents and other corrosive media. Low viscosity is a relatively high concentration of granular media, fluorine plastic lining valves should try to avoid the use of solid particles of media.

3.3 Test methods (1) Temperature test Temperature measurement involves the range of room temperature to liquid nitrogen temperature. It is measured with a thermocouple thermometer. The temperature signal is measured by a digital multimeter, collected and entered into the measurement and control computer, displayed on the computer interface, and displayed by the computer. Record and save automatically. At the same time, the computer sends temperature measurements to the temperature display on the instrument panel for on-site display.

2) Pressure test pressure measurement range is 0 ~ 10M Pa. Using the pointer-type precision pressure gauge and digital pressure gauge to display the system pressure on the instrument panel. At the same time, the pressure transmitter is used to measure the system pressure and convert it into a voltage signal. The digital multimeter measures, collects and inputs the measurement and control computer. , Displayed on the computer interface, and the computer automatically completes the recording and saving.

(3) Level To ensure that the liquid nitrogen level meets the valve test requirements, a differential pressure transmitter is used to measure the level height. The measured electrical signal is measured by a digital multimeter, collected and input to a computer for display, and reminded to add liquid nitrogen and stop the liquid nitrogen filling operation.

(4) Flow According to the type of valve seal, the allowable leakage of the valve is different. Valves with a soft seal structure should have zero leakage. For hard-sealed valves, it is permissible to have a certain amount of leakage. Based on the above situation, two kinds of devices for measuring flow rate are provided, one of which is a small-flow rate flowmeter for measuring leaks when a hard-seal valve or a soft-seal valve having a certain leak amount is allowed to operate under a relatively abnormal operating condition.

For a small amount of leakage, the measurement must be performed by observing and counting the number of air bubbles leaking at the open end in the water because the general flow meter cannot detect it. The use of computer data acquisition system to record the number of electrical pulses to achieve automatic counting.

4. Conclusion Based on the low-temperature valve performance testing device of computer data acquisition system, each signal of thermocouple, pressure sensor, liquid level sensor and flow meter can be input into the computer after pre-processing, and the data can be obtained through data acquisition software. Display, storage and printing, also can control the self-pressurization system of liquid nitrogen tank to add liquid nitrogen to the low temperature test tank according to the setting of relevant parameters. The test system adopts centralized data monitoring, which not only achieves automatic operation through instructions issued by computers, but also improves work efficiency, timeliness, accuracy, and security of operations, and facilitates the unified preservation and management of data.