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Know the valve performance parameters
Valve sealing performance refers to the ability of a valve to prevent leakage of the media it controls. This is one of the most critical technical characteristics of a valve, as it directly affects its functionality and safety. A valve typically has three main sealing areas: the contact between the closing element and the valve seat, the seal between the packing and the stem, and the connection between the body and the cover. Any leakage from these points can compromise the valve's effectiveness.
Leakage before closure, often called internal leakage, occurs when the medium passes through the valve even when it is supposed to be closed. For shut-off valves, internal leakage is not acceptable, as it may lead to improper control of the process. On the other hand, external leakage happens when the medium escapes from the valve into the environment. This can cause material loss, environmental contamination, and in severe cases, serious accidents. In particular, for flammable, toxic, or radioactive media, any form of leakage is completely unacceptable. Therefore, a reliable sealing performance is essential for all types of valves.
As the medium flows through the valve, pressure loss occurs due to the resistance created by the valve. This results in a pressure difference between the upstream and downstream sides. The energy required to overcome this resistance is a key consideration in valve design. To improve energy efficiency, engineers aim to minimize the flow resistance within the valve during its development and manufacturing.
The opening and closing force and torque are the forces or torques needed to operate the valve. When closing, the valve must create sufficient pressure between the sealing surfaces while also overcoming friction from the stem, packing, and bearings. These forces vary throughout the operation, with the highest values occurring at the moment of full closure or initial opening. Reducing these forces and torques is an important goal in valve design to make operation easier and more efficient.
The opening and closing speed refers to how quickly a valve can be opened or closed. While many applications do not require strict speed control, some situations demand rapid operation to prevent accidents, while others require slow closure to avoid issues like water hammer. The appropriate type of valve should be selected based on these specific requirements.
Valve sensitivity and reliability refer to how effectively the valve responds to changes in the media parameters. This is especially crucial for specialized valves such as pressure relief valves, control valves, safety valves, and steam traps, which are designed to regulate or protect against fluctuations in the system. High sensitivity and reliability ensure long-term performance and operational safety, making them vital factors in both technical and economic terms. Ensuring that the valve meets the required sealing standards over time is also an important measure of its overall performance.