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Imported bellows-type back-pressure balanced safety valve

Imported bellows-type back-pressure balanced safety valve

The imported bellows‑type back‑pressure‑balanced safety valve is a pressure‑resistant device designed for use on pipelines and vessels handling toxic, hazardous, flammable, or explosive media as an overpressure protection system. It employs a formed stainless‑steel bellows to ensure zero external leakage of the process medium while simultaneously balancing the back pressure at the safety valve outlet, thereby maintaining the accuracy of the set pressure.

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Design and Selection of Metal Bellows

Design and Selection of Metal Bellows

In bellows applications, the specified operating conditions of the system (the complete machine) or subsystem (component) serve as the primary basis for bellows design and selection. Typically, the following design parameters are provided: 1. Maximum spatial dimensions or nominal diameter 2. Nature and magnitude of the working load 3. Required working displacement 4. Operating temperature range 5. Properties of the working medium 6. Precision requirements 7. Service life Content and Principles of Metal Bellows Design and Selection The main tasks in bellows design and selection involve choosing the appropriate material, structural configuration, geometric dimensions, and performance characteristics based on the known system specifications. During the selection process, it is essential to meet the system’s functional requirements while striving for an advanced and rational structural design, with optimization pursued whenever feasible. Practical experience demonstrates that proper design and selection are critical; even if the manufactured bellows exhibit high quality, inadequate design and selection will still fail to satisfy operational demands. 1. Material Selection Based on the bellows’ intended application, types and magnitudes of loads, precision requirements, working medium, operating temperature, service life, and other relevant factors—while also considering the material’s formability and weldability—a suitable material should be selected. Additionally, market availability should be taken into account. 2. Determination of Structural Configuration (1) Selection of Corrugation Shape Choose a corrugation shape that best suits the bellows’ application, performance needs, and operating requirements, taking into consideration the performance characteristics and manufacturing features of various waveforms. In most cases, U‑shaped corrugations are preferred. (2) Determination of Number of Layers The number of layers depends on the bellows’ application, operating pressure, stiffness, and working medium. For higher operating pressures, multi‑layer bellows are generally chosen, with careful selection of both the number of layers and the wall thickness of each layer. (3) Preliminary Assessment of Coupling with Other Elastic Elements In certain situations, bellows are used in parallel with helical springs—for example, to enhance measurement accuracy, under relatively high operating pressures, or when subjected to impact loads. (4) Selection of End‑Connection Configurations When determining the end‑connection type, consider the forming and welding processes involved, as well as any structural constraints imposed by the overall system. (5) Consideration of Guiding Devices For bellows with significant effective lengths, guiding devices should be incorporated to prevent column buckling during operation. For instance, valve‑type bellows typically include such guiding mechanisms. (6) Evaluation of Reinforcement Rings To accommodate higher operating pressures, reinforcement rings may be employed, or a multi‑layer structure can be adopted; alternatively, a combination of both approaches may be utilized. Reinforcement rings provide localized strengthening, whereas multi‑layer structures offer comprehensive reinforcement. 3. Design Calculations and Selection of Structural Parameters The performance of a bellows is largely determined by its structural configuration. Key structural parameters include inner diameter, outer diameter, wall thickness, pitch, amplitude, number of corrugations, number of layers, dimensions of the end‑fitting sections, effective length, and overall length. Generally, users should select standard bellows from applicable industry standards or product catalogs provided by manufacturers rather than designing entirely new products. This approach minimizes development challenges, reduces manufacturing costs, and shortens production lead times. 4. Design Calculations for Performance Parameters Once the principal geometric dimensions have been determined through design calculations or preliminary selection, further computations are performed to establish the bellows’ performance characteristics. If the resulting performance parameters fail to meet technical requirements, appropriate adjustments to the geometric dimensions should be made. Since different applications impose distinct technical requirements, tailored design methodologies must be developed accordingly. For measurement purposes, the primary considerations are stiffness, strength, and elastic properties. Although various bellows with differing geometries and dimensional parameters may all satisfy the same stiffness criteria, the stress levels they generate can vary significantly. Solutions that not only meet stiffness requirements but also minimize operational stresses are preferable. Reducing stress not only enhances safety margins but also diminishes the adverse effects of material elasticity—such as hysteresis, creep, and fatigue—thereby improving both the precision and reliability of the bellows.

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