6. Desuperheating and pressure reducing valve (high and low pressure bypass valve): control requirements: adjust high-temperature and high-pressure steam to steam with a certain temperature and pressure; Provide a bypass channel for the steam turbine, and the boiler can work independently of the steam turbine. Working condition: high-temperature and high-pressure steam temperature and pressure reduction. Valve requirements: thermal shock resistance, noise reduction, rapid response.

Fluoroplastic lined valves have excellent heat resistance and cold resistance, excellent electrical insulation and excellent chemical stability, and can resist the corrosion of various strong acids, alkalis and strong oxidants. They have very good low friction and self-lubricating properties, and can be used in the range of - 195~200 ℃ for a long time. Scope of application The nominal pressure of fluoroplastic lined butterfly valve is PN116 (the maximum bearing pressure of fluoroplastic can reach 215 MPa). DN50～1 200。 The applicable temperature of valves shall be comprehensively evaluated according to the temperature that different materials (metal materials and non-metallic materials) can withstand. For example, the use temperature of steel fluoroplastic lining (WCB+F46) material is - 29~150 ℃. The maximum limit shall not exceed 150 ℃. The applicable medium is corrosive medium such as low viscosity acid and alkali, which mainly refers to strong corrosive medium such as acid, alkali, organic and inorganic solvents. Low viscosity refers to granular medium with relatively high concentration. The medium test method of solid particles should be avoided for fluoroplastic lined valves
(1) The temperature measurement of temperature test involves the range from room temperature to liquid nitrogen temperature. Thermocouple thermometer is used for measurement. The temperature electrical signal is measured, collected and input into the measurement and control computer through the digital multimeter, displayed on the computer interface, and automatically recorded and saved by the computer. At the same time, the computer transmits the temperature measurement value to the temperature display on the instrument panel for on-site display.
(2) The pressure measurement range of pressure test is 0 ～ 10MPa. Pointer type precision pressure gauge and digital pressure gauge are used to display the system pressure on the instrument panel on site. At the same time, pressure transmitter is used to measure the system pressure and convert it into voltage signal, which is measured by digital multimeter, collected and input into the measurement and control computer, displayed on the computer interface, and automatically recorded and saved by the computer.
(3) Liquid level In order to ensure that the liquid nitrogen level height meets the requirements of valve test, differential pressure pressure transmitter is used to measure the liquid level height. The measured electrical signal is measured, collected and input into the computer through the digital multimeter for display, and reminds the liquid nitrogen filling operation and stops the liquid nitrogen filling operation.
(4) The allowable leakage amount of the valve varies according to the sealing form of the valve. For valves with soft sealing structure, the leakage shall be zero. For hard sealed valves, a certain amount of leakage is allowed. Based on the above conditions, two kinds of flow measurement devices are equipped. One is a small flow meter, which is used to measure the leakage of hard sealed valves or soft sealed valves that allow a certain amount of leakage under relatively abnormal operating conditions. For small leakage, since ordinary flow meters can no longer detect it, it is necessary to measure it by observing and counting the number of leaking bubbles in the water at the open end. The computer data acquisition system is used to record the number of electric pulses and realize automatic counting.