1. Differences in sealing mechanisms
Bellows sealed valve:
The valve stem is completely wrapped with a metal bellows assembly, and dynamic sealing is achieved through the elastic expansion and contraction of the bellows, forming a permanent isolation barrier between the medium and the atmosphere.
Double protection design: When the main seal fails, the auxiliary packing can still provide emergency sealing (mostly seen in stop valve structures).
The leakage rate is extremely low (≤10⁻⁶ mL/s), meeting the zero leakage requirements of highly toxic, radioactive and other media.
Piston valve:
Relying on piston rings or packing seals (such as graphite or flexible polymers), the flow of the medium is controlled by the vertical movement of the piston in the cylinder.
After long-term use, the seal is easily worn due to friction and needs to be replaced and maintained regularly.
2. Applicable media and environment
Bellows sealed valve:
High-risk media: corrosive fluids such as natural gas, liquid ammonia, strong acids/alkalis, and high-purity media in pharmaceutical aseptic production lines.
Extreme working conditions: vacuum systems (such as semiconductor manufacturing), ultra-low temperature (liquid oxygen/nitrogen storage and transportation) or high-temperature steam (≤425℃) scenarios.
Piston valve:
Conventional media: water, low-pressure steam, non-corrosive industrial fluids (such as cooling circulating water systems).
Typical scenarios: medium and low pressure flow regulation in chemical processes, conventional fluid control in the power industry.
3. Structural and maintenance features
Bellows sealed valve:
Integrated bellows: The manufacturing process is complex (precision welding is required), the initial cost is high, but the service life is more than 10 years, and it is basically maintenance-free.
Pressure limit: The axial pressure bearing capacity of the bellows is weak, usually suitable for pressure levels ≤Class 600, and severe vibration must be avoided.
Piston valve:
Modular design: Simple structure, easy to disassemble and maintain, but the frequency of shutdown and maintenance is high (seals need to be replaced every 1-2 years).
Pressure advantage: Some high-pressure models can support Class 1500 and above conditions (depending on the strength of the cylinder and piston materials).
4. Economic efficiency and selection recommendations
Bellows valve: High initial investment (special alloy bellows cost accounts for about 40%), but low long-term operating cost (reduces leakage accidents and production stoppage losses). Mandatory use for ISO 15848 certification scenarios or API 624 standard fugitive emission control.
Piston valve: Outstanding cost-effectiveness, suitable for conventional industrial systems with limited budgets and low media risks.
