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Basic technical terms 1. Strength performance: The strength performance of a valve refers to its ability to withstand the pressure of the medium. Valves are mechanical components that are subjected to internal pressure; therefore, they must possess sufficient strength and stiffness to ensure they do not crack or deform over long-term use. 2. Sealing performance: The sealing performance of a valve refers to the ability of its various sealing elements to prevent the leakage of the medium, and it is the most important technical parameter for valves. There are three sealing areas in a valve: the contact point between the moving part and the two sealing surfaces of the valve seat ； The interface between the packing and the valve stem as well as the packing box ； The connection between the valve body and the valve cover. The leakage in the former case is called internal leakage, which is what is commonly referred to as poor sealing; it affects the valve’s ability to stop the flow of the medium. For cut-off valves, internal leakage is not allowed. The leaks in the latter two locations are called external leaks, that is, the medium leaks from inside the valve to outside it. Leaks can result in material loss, environmental pollution, and in severe cases, accidents. For flammable, explosive, toxic, or radioactive media, leaks are absolutely unacceptable; therefore, valves must have reliable sealing properties. 3. Flowing medium: As the medium flows through the valve, pressure loss occurs (that is, a pressure difference before and after the valve). In other words, the valve exerts a certain resistance to the flow of the medium, and the medium must expend energy to overcome this resistance. From the perspective of energy conservation, when designing and manufacturing valves, it is necessary to minimize the resistance exerted by the valves on the flowing medium as much as possible. 4. Opening force and opening torque: The opening force and opening torque refer to the force or torque that must be applied to open or close a valve. When closing the valve, it is necessary to create a certain sealing pressure between the sealing surfaces of the moving part and the seat. At the same time, it is also required to overcome the friction forces between the valve stem and the packing, between the threads of the valve stem and the nut, at the support points at the end of the valve stem, and in other friction-prone areas. Therefore, a certain closing force and closing torque must be applied. During the opening and closing process of the valve, the required opening and closing forces and torques change, with their maximum values occurring at the final moment of closure or the initial moment of opening. When designing and manufacturing valves, efforts should be made to reduce their closing force and closing torque. 5. Opening and closing speed: The opening and closing speed is expressed as the time required for a valve to complete one cycle of opening or closing. Generally, there are no strict requirements regarding the opening and closing speed of valves, but certain operating conditions impose specific demands on this speed. For example, in some cases rapid opening or closing is required to prevent accidents, while in other cases slow closing is necessary to avoid water hammer effects. These factors should be taken into consideration when selecting the type of valve. 6. Response sensitivity and reliability: This refers to the degree of sensitivity with which the valve responds to changes in medium parameters. For valves such as throttle valves, pressure relief valves, and control valves that are used to regulate the parameters of a medium, as well as valves with specific functions like safety valves and steam traps, their functional sensitivity and reliability are very important technical performance indicators. 7. Service life: It indicates the durability of the valve, is an important performance indicator for valves, and holds great economic significance. It is usually expressed in terms of the number of openings and closings required to ensure the sealing requirements, or it can also be expressed in terms of the time of use. 8. Type: The classification of valves based on their purpose or main structural characteristics. 9. Model: The designation of valves based on their type, actuation method, connection style, structural features, material of the valve seat sealing surface, and nominal pressure. 10. Connection dimensions: The dimensions of the areas where the valve is connected to the pipes. 11. General dimensions: The height required for opening and closing the valve, the diameter of the handwheel, as well as the connection dimensions, etc. 12. Type of connection: The various methods used to connect valves to pipes or machinery and equipment (such as flange connection, threaded connection, welding connection, etc.). 13. Seal test: A test to evaluate the performance of the sealing surfaces between the operating parts and the valve body. 14. Back seal test: A test to evaluate the sealing performance of the seal between the valve stem and the valve cover. 15. Seal test pressure: The pressure specified for conducting a seal test on the valve. 16. Suitable medium: The medium for which the valve can be used. 17. Suitable temperature: The temperature range of the medium for which the valve is suitable. 18. Sealing face: The two contact surfaces between the closing element and the valve seat (valve body) that come into close contact to provide sealing. 19. Closing elements (disks) are a general term for components used to stop or regulate the flow of a medium, such as the gate plate in gate valves and the valve disc in throttle valves. 20. Packing: A filler that is placed in the packing box to prevent the medium from leaking at the valve stem. 21. Packing seat: A component that supports the packing and maintains its sealing function. 22. The gland is a component used to compress the packing in order to achieve sealing. 23. The yoke is a component located on the valve cover or valve body, used to support the valve stem nut and the transmission mechanism. 24. Dimension of connecting channel: The structural dimension of the assembly connection area between the closing element and the valve stem. 25. Flow area refers to the minimum cross-sectional area between the inlet end of the valve and the valve seat sealing surface (not the “curtain” area), and is used to calculate the theoretical discharge rate in the absence of any resistance effects. 26. The flow diameter corresponds to the diameter of the flow area. 27. Flow characteristics: In a steady-flow state, it is the functional relationship between the outlet pressure of a pressure reducing valve and the flow rate, when parameters such as inlet pressure remain constant. 28. Flow characteristics deviation: In a steady-flow state, it refers to the change in outlet pressure resulting from changes in the flow rate of the pressure regulator, when parameters such as inlet pressure remain constant. 29. General valves: These are valves that are widely used in pipelines across various industrial enterprises. 30. Self-acting valve: A valve that operates automatically thanks to the inherent properties of the medium (liquid, air, steam, etc.). 31. Actuated valve: A valve that is operated by manual force, electricity, hydraulics, or pneumatics. 32. Hammer blow handwheel: A handwheel design that utilizes impact force to reduce the effort required to operate the valve. 33. Wormgear actuator: A device that uses a wormgear mechanism to open, close, or adjust valves. 34. A pneumatic actuator is a driving device that uses air pressure to open, close, or regulate valves. 35. Hydraulic actuator: A driving device that uses hydraulic pressure to open, close, or regulate valves. 36. Hot condensate capacity: The maximum amount of condensate that can be discharged by a steam trap under given pressure differences and temperatures