Main technical properties of valves

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Main technical properties of valves 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 time. 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 of a valve. 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 media. 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. 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 presents 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 operating element 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. Sensitivity and reliability of operation: This refers to the degree to 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 opening and closing cycles required to ensure the sealing requirements, or it can also be expressed in terms of the time of use.