Basic knowledge of valves
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Section 1: Overview Valves are control devices used in fluid pipelines. Their primary functions are to enable or stop the flow of the medium within the pipeline, to change the direction of the medium’s flow, to regulate the pressure and flow rate of the medium, and to ensure the proper operation of the pipelines and associated equipment. The widespread use of industrial valves came after Watt invented the steam engine. Over the past twenty to thirty years, demands from industries such as petroleum, chemicals, power generation, metallurgy, shipbuilding, nuclear energy, and aerospace have led to higher requirements for valves. This has spurred research and development of valves capable of operating under extreme conditions: working temperatures ranging from ultra-low temperatures of -269°C to high temperatures of 1200°C, or even up to 3430°C; working pressures ranging from ultra-high vacuum of 1.33x10^-8 Mpa (1x10^-1 mmHg) to ultra-high pressures of 1460 MPa. The diameter of these valves ranges from 1 mm to 600 mm, or even up to 9750 mm. The materials used for valves have evolved from cast iron and carbon steel to titanium and titanium alloys, as well as high-strength corrosion-resistant steels. The methods of actuating valves have also progressed from manual operation to electric, pneumatic, hydraulic, programmable, computer-controlled, and remote control systems. With the continuous development of modern industry, the demand for valves is on the rise; a modern petrochemical plant requires tens of thousands of various types of valves, meaning that they are used in large quantities. Valves are opened and closed frequently, but due to issues such as improper manufacturing, selection for use, or maintenance, problems such as leakage can occur. This can lead to incidents like fires, explosions, poisoning, and burns, or it can result in poor product quality, increased energy consumption, equipment corrosion, higher material costs, environmental pollution, and even shutdowns of operations. Such situations are all too common. As a result, there is a desire for high-quality valves, as well as an emphasis on improving the way they are used and maintained. This places new demands on those who operate, maintain, and engineer these valves; in addition to designing them carefully, selecting them appropriately, and operating them correctly, it is also necessary to carry out timely maintenance and repairs to minimize leakage and other related problems.
Valves have a wide range of uses, come in many types, and there are also various methods for classifying them. Generally, they can be divided into two main categories: The first category is automatic valves – valves that operate automatically relying on the properties of the medium itself (liquid or gas). Such as check valves, safety valves, control valves, steam traps, pressure relief valves, etc. Category 2 drive valves: Valves whose operation is controlled by manual, electric, hydraulic, or pneumatic means. Such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc.
1. Gate type: The closing element moves along the center of the valve seat, as shown in Figure 1-1. 2. Gate type: The closing element moves along the vertical center of the valve seat, as shown in Figure 1–2. 3. Plug and ball type: The closing element is a plunger or a ball that rotates around its own central axis, as shown in Figure 1–3. 4. Swing-type ； The closing element rotates around an axis outside the valve seat, as shown in Figure 1–4. 5. Disc type: The disc of the closing element rotates around an axis within the valve seat, as shown in Figure 1–5. 6. Slide valve type: The closing element slides in a direction perpendicular to the channel, as shown in Figure 1–6.
1. Vacuum valve: Absolute pressure
1. Ordinary valves: Valves suitable for media temperatures ranging from -40°C to 425°C. 2. High-temperature valves: Valves suitable for media temperatures ranging from 425°C to 600°C. 3. Heat-resistant valves: Valves suitable for media temperatures above 600°C. 4. Low-temperature valves: Valves suitable for media temperatures ranging from -40°C to -150°C. 5. Ultra-low temperature valves: Valves suitable for media temperatures below -150°C.
1. Small-diameter valves: Nominal diameter DN