I. Introduction Automatic temperature control valve is a new type of valve to control the fluid temperature, also known as self-temperature thermostatic valve or automatic thermostatic valve, referred to as the thermostatic valve. It relies on the expansion of the temperature sensor temperature sensing material to drive the valve opening and closing, so as to regulate the flow of cold and hot fluid into the valve to control the fluid outlet temperature purposes. It is a kind of automatic temperature controller that does not need external energy, but absorbs the heat of the fluid by the heat sensitive element and transforms into the mechanical energy, causes the implementing agency to work according to the certain regulation law. Second, the automatic thermostatic valve working principle, performance characteristics and classification 1. Working principle Automatic thermostatic valve its basic structure by the temperature sensor self-acting actuator and the valve body. Temperature sensing element structure shown in Figure 1, the fluid flow through the valve, located inside the body temperature sensing element is heated (or cold) → heat through the rigid copper seal the outer wall of the cup so that the temperature of the melting wax within the heat melting (or condensation) volume Expansion (or contraction) → promote diaphragms, tapered rubber body → push the piston → adjust the opening and closing pieces, thereby regulating the valve opening. The actual structure, the general design are: (1) amplification mechanism will pass the piston to the tiny axial displacement amplification to the ring, making the valve opening degree adjustment ability greatly increased. (2) Reset spring mechanism makes the temperature of the wax volume when the piston shrinks when cold back. (3) Temperature control setting mechanism makes the valve in use according to the actual situation of the control temperature settings and adjustments [1], [2]. Figure 2 is a single actuator three-way valve structure, Figure 3 is a two-way automatic thermostatic valve structure, Figure 4 is suitable for large flow when using a multi-actuator three-way valve structure. 2. Automatic thermostatic valve features [1], [2] relative to the electric, pneumatic, electromagnetic temperature control valve, automatic thermostatic valve has the following advantages: ①no external power supply or compressed air, simple structure, high safety. ⒅ high temperature control accuracy, stable work. ③ over-temperature protection device is sensitive and reliable, a wide range of protection, to ensure the safe operation of equipment under special circumstances. ④ proportional control, will not cause water hammer damage. ⑤ wide range of applications, can be used for a variety of medium temperature control applications. ⑥ small size, not afraid of cold, light weight, easy to install. Third, the application of automatic temperature control valve Widely used in heating, hot water supply, aerospace, power, energy and power, metallurgy, marine and other industrial heat exchange equipment, automatic temperature control, such as compressors, steam turbines, internal combustion engines, gearbox , Large vacuum pumps and other mechanical cooling systems that require constant temperature lubrication and dyeing and printing, textiles, food, leather and other industries need to be heated fluid discharge occasions. Industrial applications of automatic temperature control valve has the following aspects. 1. In the lubrication system of power machinery lubrication Compressors, steam turbines, internal combustion engines and other high-speed rotary power of its bearing parts require good lubrication and cooling. And for the lubricating oil temperature is very strict, the oil temperature is too high or too low will affect the normal operation of the machine. The actual project commonly used cooler heat transfer method to cool, but difficult to control the temperature after cooling. Install automatic temperature control valve in the lubricating oil circulation pipeline, the cooled lubricating oil and uncooled lubricating oil flow into the automatic temperature control valve, the outlet oil temperature will automatically ensure the best oil temperature. For example, in the screw compressor lubrication circuit cooling system constant temperature, when the lubricant temperature is maintained at 42 ℃ ± 5 ℃ to ensure good activity and lubrication performance. Automatic temperature control valve and heat exchanger in the cooling circuit in the installation shown in Figure 5. This configuration well maintained the stability of the oil temperature, both to ensure that the oil temperature is not too high and will result in decreased viscosity of lubricating oil, lower lubrication performance, but also to avoid the oil temperature is too low caused by excessive viscosity of lubricating oil, and even moisture in System precipitation. According to reports, high-precision automatic temperature control valve oil temperature can be controlled to 42 ℃ ± 5 ℃. The same applies to steam turbines, internal combustion engines and transmission gearboxes. At present, the generator sets above 300MW in our country mainly adopt the imported equipment or technology, among them the automatic temperature control valve is adopted in the lubricating oil cooling system of steam turbine to control the lubricating oil temperature. Locomotive internal combustion engine, marine diesel engine, V8 car engine also uses the front of the cooler plus tees automatic temperature control valve configuration to control the temperature of the lubricating oil [3]. Aircraft engine gearbox gear box in high speed operation is also similar with the power machinery working conditions, it also uses three-way automatic temperature control valve to maintain the form of the oil cooling circuit. 2. In the hydraulic system cooling circuit thermostat system Hydraulic system requires its oil temperature control, especially for the operation of the temperature control accuracy of the hydraulic system, such as servo system, proportional system, hydraulic components test stand And continuous operation of large-scale hydraulic equipment, the current use of electrical control and mechanical combination of matching cooling control that solenoid valve way, the biggest drawback of this control method is a control form of digital control, can not be achieved with the system The amount of cooling water and adjust the amount of heat, and often due to water rust and mixed particles, causing electromagnetic valve action heart valve failure, electromagnet burned and other failures and waste of water. The other is the use of proportional cooling water control means that the electric control valve way, compared with the previous method, it has the ability to adjust the amount of cooling water with the system heat and the advantages of high control accuracy, but because of its components More, the failure rate is high, and the current composition of electric actuators with the smallest diameter of the water delivery valve are more than 50mm, while the hydraulic system are commonly used in 50mm below, it is limited in use. The application of automatic temperature control valve in the hydraulic system cooling circuit has the advantages of simple structure, reliable operation, stable performance, no external power and high precision. It forms a closed-loop cooling water regulating system with the cooler and is an ideal hydraulic system cooling Water regulation method. A large number of new foreign countries have adopted a self-regulating valve hydraulic system as a cooling water conditioning components, the operation is very satisfactory [4], [5]. 3 in the production process fluid temperature control applications Automatic temperature control valve is widely used in a variety of production process fluid temperature control, such as printing and dyeing, textiles, food, leather and other industries need to be heated fluid discharge occasions. For example, in the continuous ingot production line mold cooling water temperature control application: Baotou Iron and Steel Company Vertical bending continuous casting line mold cooling water is closed circuit water softener circulation system, red hot liquid (temperature greater than 1600 ℃) initial setting is in Mold completed, the formation of 3-8mm blank shell (the center is still red hot molten steel), under the action of the dummy bar into the sector, further spray curing until straightening machine to form the final slab. If the cooling in the mold uneven or poor shape, there is leakage, dip the serious consequences of steel. The system by the German company SMS basic design, is the use of DN500 tee automatic temperature control valve, through the bypass backwater and plate heat exchanger backwater mixing, thermal equilibrium to achieve the casting process temperature 40-45 ℃ [ 6]. In order to increase efficiency, reduce energy consumption and reduce pollution, the German L & E Company is the most energy-consuming part of the new paper machine, especially the dry part of the paper machine. Its vacuum station condenser cooling water outlet temperature control adopts three-way automatic temperature control valve , Used to automatically change the amount of cooling water discharge to control its discharge temperature, prevent thermal pollution, and to make full use of cooling water. Not only reduces the consumption of cooling water, but also to a certain temperature water into other processes, such as the preparation of pulp, which in turn uses the heat [7]. IV. Conclusion With the development of science and technology and the expansion of industrial scale, the industrial production shows the trend of high capacity, high parameters, high efficiency and low consumption, low pollution and high automation, and the requirements on accuracy and safety and reliability of temperature control are getting higher and higher. Automatic temperature control valve with its superior performance and has a vast space for development. At present, there are already some enterprises and universities in China that are engaged in research and development in this area, which undoubtedly will benefit the localization of major technological equipment in China.
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