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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 devices 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 fit 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 block the flow of medium. For shut-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. Leakage 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 process of opening and closing 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. Sensitivity and reliability of operation: This refers to the degree of sensitivity with which the valve responds to changes in the parameters of the medium. For valves such as throttle valves, pressure relief valves, and control valves that are used to adjust 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 usage time. 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, among other factors. 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 in a gate valve or the valve disc in a throttle valve. 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. Yoke: A component 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 it is used to calculate the theoretical displacement 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 trap under given pressure differences and temperatures. Valve definition term 1. Valve: A mechanical device with a movable mechanism used to control the flow of fluid in pipes. 2. Gate valve (slide valve): A valve in which the closing element (gate) is driven by a valve stem to move up and down along the valve seat (sealing surface). 3. Globe valve (stop valve): A valve in which the opening and closing element is driven by the valve stem to move up and down along the axis of the valve seat (sealing surface). 4. A throttle valve is a valve that regulates flow and pressure by changing the cross-sectional area of the passage through its opening and closing element (valve disc). 5. Ball valve: A valve that opens and closes by rotating a sphere around an axis perpendicular to the flow path. 6. Butterfly valve: A valve in which the closing element (butterfly plate) rotates around a fixed axis. 7. Diaphragm valve: A valve that operates by means of a diaphragm driven by a valve stem, moving up and down along the axis of the stem; it separates the actuation mechanism from the medium. 8. Globe valve: A valve that opens and closes by rotating a plug around its axis. 9. Check valve (non-return valve): A valve whose opening and closing mechanism – the valve disc – automatically prevents the flow of the medium from reversing itself, thanks to the force exerted by the medium. 10. Safety valve (relief valve): It is of the opening/closing type (with a valve disc) and opens automatically to release pressure when the pressure of the fluid inside the pipeline or machinery exceeds the specified value ； A valve that shuts off automatically when the value falls below the specified level, serving to protect pipes or machinery. 11. A pressure reducing valve is a valve that reduces the pressure of a fluid by throttling through a moving part (valve disc), and maintains the pressure downstream of the valve within a certain range thanks to the direct effect of that pressure. 12. Steam trap: A valve that automatically drains condensate and prevents steam leakage. 13. Draining Valves: Valves used for draining waste from equipment such as boilers and pressure vessels. 14. Low-pressure valve: Various valves with a nominal pressure of PN ≤ 1.6 MPa. 15. Medium-pressure valves: various valves with a nominal pressure of PN≥2.0～PN＜10.0 MPa. 16. High-pressure valve: Various valves with a nominal pressure PN ≥ 10.0 MPa. 17. Super high pressure valves: various valves with a nominal pressure PN ≥ 100.0 MPa. 18. High-temperature valve: Valves used for media with temperatures greater than 450°C. 19. Sub-zero valves are used for various types of valves in applications where the medium temperature ranges from -40°C to -100°C. 20. Cryogenic valves are used for various valves in applications where the medium temperature is below -100°C. Valve structure terms 1. Structural length (face-to-face dimension, face-to-centre dimension) The distance between the inlet and outlet end faces of the valve ； Or the distance from the inlet end face to the outlet axis. 2. Face to face dimensions of through-way type valves: The distance between the two planes perpendicular to the valve axis at the ends of the valve body passage. 3. Structural length of angle type valves (dimensions for face-to-face, end-to-end, center-to-face, and center-to-end configurations): The distance between the plane perpendicular to the axis at one end of the valve body’s passage and the axis at the other end of the valve body. 4. Type of construction: The main structural and geometric characteristics of various valves. 5. Through-way type: A valve body design in which the inlet and outlet axes coincide or are parallel to each other. 6. Angle type: A valve body design in which the inlet and outlet axes are perpendicular to each other. 7. DC type (y-globe type, y-type, diaphragm type): A valve body design in which the flow path is in a straight line, and the position of the valve stem forms an acute angle with the axis of the valve body’s flow path. 8. Three-way type: A valve body format with three flow directions. 9. T-pattern three way: A three-way configuration in which the passages of the plug (or ball) form a “T” shape. 10. L-pattern three way: A three-way type in which the passage of the plug (or ball) is in an “L” shape. 11. Balance type: A structural design that utilizes medium pressure to balance the axial force on the valve stem. 12. Lever type: It adopts a structure in which a lever is used to operate the opening and closing mechanism. 13. Normally open type: A structural design in which the opening and closing element is automatically in the open position when no external force is applied. 14. Normally closed type: A structural design in which the closing element is automatically in the closed position when no external force is applied. 15. Insulated type (steam jacket type): Various valves equipped with a steam heating jacket structure. 16. Bellows seal type: Various valves equipped with a bellows structure. 17. Full-opening valve: A valve in which the inner diameter of the flow channels in all parts of the valve is identical to the nominal inner diameter of the pipeline. 18. Reduced-opening valve: A valve whose internal flow passage diameter is reduced. 19. Reduced-bore valve: A valve in which the diameter of the flow passage inside the valve is reduced, and the flow passage opening of the valve’s closing element is non-circular. 20. A un-directional valve is a valve designed to be sealed in only one direction of fluid flow. 21. A bi-directional valve is a valve designed to be sealed in both directions of fluid flow. 22. Twin-seat, both seats bi-directional valve: A valve that has two sealing seats, allowing for sealing in both flow directions for each seat. 23. A twin-seat valve with one un-directional seat and one bi-directional seat is a valve that has two sealing pairs; in the closed position, both sealing pairs can maintain a sealed state simultaneously. The valve body within the intermediate chamber (between the two sealing pairs) possesses an interface for releasing the pressure of the medium. Denotes the symbol DBB. 24. Back seal (back seat, back face): A sealing mechanism that prevents the medium from leaking through the packing gland when the valve is fully open. 25. Pressure seal: A mechanism that utilizes the pressure of the medium to achieve automatic sealing at the junction between the valve body and the valve cover. 26. Dimension of valve stem head: The structural dimension at the connection point where the valve stem is fitted to the handwheel, handle, or other operating mechanisms. 27. Dimension of valve stem end: The structural dimension at the connection point between the valve stem and the operating element. 28. Dimension of connecting channel: The structural dimension of the assembly connection area between the closing element and the valve stem. 29. 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.). Terminology for valve components 1. Valve body: The component that is directly connected to the pipeline (or machinery) and forms the flow channel for the medium. 2. The bonnet, cover, cap, or lid is a component that is connected to the valve body and, together with the valve body (or through other components such as diaphragms), forms the pressure chamber. 3. Closing elements (discs) are a general term for components used to stop or regulate the flow of a medium, such as the gate in a gate valve or the valve disc in a throttle valve. 4. Disc: The moving part in valves such as gate valves, throttle valves, and check valves. 5. Valve seat (body seat ring, shoulder seated, bottom seat) – a component mounted on the valve body that forms a sealing pair with the moving part of the valve. 6. Sealing face: The two contact surfaces between the closing element and the valve seat (valve body) that ensure sealing. 7. Stem: The main component that transmits the opening and closing force to the valve element. 8. The valve stem nut (yoke bushing, yoke nut) is the component that forms a moving pair with the valve stem thread. 9. Packing box: A structure on the valve cover (or valve body) that contains packing to prevent the medium from leaking at the valve stem. 10. Stuffing box: A component that fills with packing to prevent the medium from leaking from the valve stem. 11. Gland (gland flange, pne-piece gland) – A component used to compress the packing in order to achieve sealing. 12. Packing (packing rings) are fillers placed in the packing box to prevent leakage of the medium at the double stem area. 13. Packing seat (packing washer): A component that supports the packing and maintains its sealing function. 14. Yoke: A component on the valve cover or valve body, used to support the valve stem nut and the actuation mechanism. 15. Impact handwheel: A handwheel design that utilizes impact force to reduce the effort required to operate the valve.