The working principle and application of temperature control valve
**Abstract:**
Thermostatic valves play a crucial role in regulating the flow of heating systems, making them essential components for accurate heat metering and billing. Without thermostatic valves, a system cannot be considered as a fully functional hot metering and charging system. This paper provides an in-depth overview of the structure and working principle of thermostatic valves. By analyzing their flow characteristics and integrating them with the thermal performance of radiators, the concept of valve authority is introduced to explain how these elements work together to ensure efficient temperature control. The paper also discusses the installation strategy of thermostatic valves and highlights their energy-saving potential.
**Keywords:** Thermostatic valve, flow characteristics, valve authority, heat measurement, radiator, temperature control
**1. Structure and Working Principle of Radiator Thermostatic Valve**
User temperature control in heating systems is primarily achieved through the use of radiator thermostatic control valves. These valves consist of three main parts: a thermostat controller, a flow control valve, and connecting components. The thermostat, often referred to as a temperature capsule, acts as the core sensing element. It detects changes in ambient temperature and undergoes volume expansion or contraction accordingly. This movement drives the valve stem to shift, thereby adjusting the water flow through the radiator and controlling its heat output.
The set temperature of the thermostatic valve can be manually adjusted by the user. Based on the desired indoor temperature, the valve automatically regulates the flow of water to maintain a stable and comfortable environment. This mechanism ensures that the system operates efficiently while minimizing energy waste.
**2. Flow Characteristics and Valve Authority**
The adjustment performance of a radiator is influenced by three key factors: the thermal characteristics of the radiator, the flow characteristics of the thermostatic valve, and the valve authority. The relative flow of a thermostatic valve at a certain opening is defined as the ratio of actual flow (G) to the maximum flow (Gmax), i.e., G/Gmax. Similarly, the relative travel (l) is the ratio of the actual valve position to the full stroke. The relationship between relative travel and relative flow is known as the flow characteristic curve, expressed as G/Gmax = f(l). Common types include linear, quick-opening, equal percentage, and parabolic characteristics.
From a hydraulic stability and heat regulation perspective, the relationship between heat output (Q) and flow rate (G) for a radiator follows a saturation curve. As the flow increases, the heat dissipation gradually reaches a plateau. To improve system regulation, it is common to use valves with equal percentage flow characteristics, which help compensate for the non-linear behavior of radiators.
Valve authority refers to the ability of the thermostatic valve to control the flow within a specific range. The adjustable ratio (R) is calculated as R = Gmax / Gmin, where Gmax is the flow when the valve is fully open, and Gmin is the minimum controllable flow. In a series-connected system consisting of a radiator and a thermostatic valve, the effective adjustable ratio depends on the valve's authority. For example, if a radiator has a flow capacity of 5 m³/h and the thermostatic valve has an authority of 88%, the actual adjustable ratio may be around 28, covering a flow range from 100% to 4%. The actual adjustable range also varies depending on the temperature difference between the inlet and outlet of the radiator.
By properly selecting and installing thermostatic valves, users can significantly enhance the efficiency and comfort of their heating systems while achieving substantial energy savings.
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