1. Core structure differences
Number of eccentric layers
Double eccentric butterfly valve: adopts a double-layer offset design with the valve stem axis deviating from the center of the butterfly plate (first eccentricity) and the valve stem deviating from the center of the valve body (second eccentricity).
Triple eccentric butterfly valve: on the basis of double eccentricity, the sealing surface cone angle eccentricity (third eccentricity) is added to form an inclination angle α between the valve seat sealing surface and the valve body axis.
Sealing surface shape
Double eccentricity: The sealing surface is a positive cone, the butterfly plate and the valve seat are in line contact, and the sealing is achieved by elastic deformation.
Triple eccentricity: The sealing surface is an oblique cone, and a metal hard seal is used, and a surface contact seal is formed by torque pressure.
2. Performance Comparison
| Dimensions | Double eccentric butterfly valve | Triple Eccentric Butterfly Valve |
|---|---|---|
| Sealing principle | Extrusion of elastic materials (such as rubber/PTFE) | Metal seal + torque pressurization |
| Pressure resistance | Up to PN40 (approximately ANSI CL 300) | Up to PN160 (ANSI CL 900) |
| Temperature range | -30~200℃(Rubber valve seat) | -196~650℃(Metal valve seat) |
| Opening and closing torque | Medium, needs regular lubrication | Low, the friction coefficient is only 1/3 of the double eccentric. |
| Leakage rate | ANSI/FCI 70-2 Class IV5 | Achieve Class VI zero leakage |
3. Applicable scenarios
Double eccentric butterfly valve
Suitable for medium and low pressure and normal temperature conditions, such as urban water supply and drainage, HVAC systems.
When the medium contains particulate matter, it is necessary to match the elastic valve seat to prevent blocking.
Triple eccentric butterfly valve
Used in high pressure, high temperature, and highly corrosive environments, such as high temperature steam pipelines in refineries and acid and alkali storage tank cut-offs.
It has bidirectional pressure bearing capacity and can replace some gate valves or stop valves.
4. Economic efficiency and maintenance
Manufacturing cost
Double eccentricity: The cost is lower, and the price of the same specification is about 40-60% of the triple eccentricity.
Triple eccentricity: The processing accuracy requirements are high, and the price is 2-3 times higher.
Maintenance difficulty
Double eccentricity: The elastic valve seat can be replaced on site, and the downtime is short.
Triple eccentricity: The metal sealing surface needs to be repaired in the factory, and the cycle is as long as 4-6 weeks.
Summary
Double eccentric butterfly valves meet conventional needs with low cost and easy maintenance, while triple eccentric butterfly valves break through the high pressure and high temperature limitations through multi-layer geometric optimization, but their high cost and complex maintenance characteristics need to be weighed. When selecting a model, the operating pressure, medium characteristics and full life cycle cost should be comprehensively evaluated.
