Application of automatic thermostatic valve in industry

**I. Introduction** An automatic temperature control valve is a modern device designed to regulate the temperature of fluids without the need for external power sources. It is also known as a self-acting thermostatic valve or an automatic thermostatic valve, commonly referred to as a thermostatic valve. This type of valve operates by using the thermal expansion or contraction of a temperature-sensitive material within the sensor to adjust the valve’s opening and closing, thereby controlling the flow of hot and cold fluids to maintain the desired outlet temperature. Unlike traditional valves, it does not require electricity or compressed air; instead, it uses the heat absorbed by the sensing element to generate mechanical movement, allowing the actuator to function according to a set regulation. **II. Working Principle, Performance Characteristics, and Classification** **1. Working Principle** The basic structure of an automatic thermostatic valve includes a temperature-sensing element, a self-acting actuator, and a valve body. The temperature-sensing element, as shown in Figure 1, is placed inside the valve body where fluid flows through. When the fluid heats up (or cools down), the heat is transferred through a copper seal to the outer cup, causing the wax inside to melt (or condense), which results in expansion (or contraction). This movement pushes the diaphragm and the tapered rubber body, which in turn moves the piston to adjust the valve's opening. In addition to this basic mechanism, the actual design often includes: (1) A magnifying mechanism that amplifies small axial displacements into radial movements, improving the valve’s ability to regulate flow. (2) A reset spring that allows the wax volume to contract when the piston retracts. (3) A temperature control setting mechanism that enables users to adjust the target temperature during operation [1], [2]. Figure 2 shows a single-actuator three-way valve structure, while Figure 3 presents a two-way automatic thermostatic valve. For larger flow applications, a multi-actuator three-way valve, as shown in Figure 4, is used. **2. Features of Automatic Thermostatic Valves [1], [2]** Compared to electric, pneumatic, or electromagnetic temperature control valves, automatic thermostatic valves offer several advantages: ① No need for external power or compressed air, making them simple, safe, and cost-effective. ② High temperature control accuracy and stable performance. ③ Sensitive and reliable over-temperature protection, ensuring equipment safety under abnormal conditions. ④ Proportional control that prevents water hammer damage. ⑤ Wide range of applications suitable for various media and environments. ⑥ Compact size, lightweight, and easy to install, even in cold conditions. **III. Applications of Automatic Temperature Control Valves** Automatic temperature control valves are widely used in heating systems, hot water supply, aerospace, power generation, metallurgy, marine engineering, and other industrial processes. They are particularly useful in systems requiring constant temperature control, such as compressors, steam turbines, internal combustion engines, gearboxes, large vacuum pumps, and in industries like printing, textiles, food processing, and leather manufacturing. **1. In Lubrication Systems of Power Machinery** High-speed rotating machines like compressors, steam turbines, and internal combustion engines require precise lubrication and cooling. The oil temperature must be carefully controlled, as both high and low temperatures can affect machine performance. Installing an automatic temperature control valve in the lubricating oil circuit allows for the mixing of cooled and uncooled oil, maintaining the optimal oil temperature. For example, in screw compressor systems, the oil temperature is maintained at 42°C ± 5°C to ensure good lubrication and activity. This configuration helps prevent issues like reduced viscosity or excessive viscosity due to temperature fluctuations. Similarly, steam turbines, locomotive engines, and marine diesel engines use these valves to regulate oil temperature effectively. Aircraft engine gearboxes also use three-way automatic valves to manage oil cooling. **2. In Hydraulic System Cooling Circuits** Hydraulic systems require precise temperature control, especially in servo and proportional systems, hydraulic testing stands, and large-scale hydraulic equipment. Traditional methods using solenoid valves have limitations, including poor control over cooling water flow and potential failures from debris or corrosion. Proportional control valves improve accuracy but are complex and costly. Automatic temperature control valves provide a simpler, more reliable solution. They form a closed-loop system with coolers, offering stable performance, no external power requirements, and high precision. Many foreign countries now use these valves in hydraulic systems, achieving excellent results [4], [5]. **3. In Industrial Fluid Temperature Control** These valves are extensively used in production processes involving fluid heating, such as in textile, food, and leather industries. For instance, in continuous casting lines, automatic valves help maintain mold cooling water at 40–45°C, ensuring proper solidification of molten steel. In paper mills, they control the temperature of condenser cooling water, reducing waste and enabling reuse in other processes like pulp preparation. **IV. Conclusion** With the advancement of technology and the expansion of industrial scale, modern production trends emphasize high efficiency, low energy consumption, and automation. As a result, the demand for accurate and reliable temperature control systems has increased significantly. Automatic temperature control valves, with their robust performance and adaptability, are well-suited for future industrial needs. Several Chinese companies and universities are already conducting research in this field, which will contribute to the localization of advanced technologies in China.

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