1. Structural design differences
Center axis layout:
Concentric butterfly valve: The valve stem axis, the butterfly plate center, and the valve body center completely overlap, and the butterfly plate rotates symmetrically around the center axis;
Eccentric butterfly valve: The axis position is changed through at least one offset design (such as single eccentric, double eccentric or triple eccentric). For example, the valve stem axis of the double eccentric butterfly valve deviates from the center of the butterfly plate and the valve body, forming an asymmetric rotation trajectory.
Sealing surface contact mode:
The butterfly plate of the concentric butterfly valve is always in contact with the valve seat, and continuous friction during the opening and closing process can easily cause wear on the sealing surface;
Eccentric butterfly valves (such as double eccentric or triple eccentric) quickly separate the butterfly plate from the valve seat when opening, and achieve progressive sealing through the eccentric trajectory when closing, which significantly reduces friction.
2. Sealing performance and applicable scenarios
Sealing mechanism:
Concentric butterfly valves mostly use soft seals (such as rubber and polytetrafluoroethylene), relying on elastic deformation to compensate for processing errors, but the temperature resistance is limited (usually ≤120℃);
Eccentric butterfly valves (especially three-eccentric ones) use metal hard seals, and the sealing surface is an oblique cone structure, which is resistant to high temperatures (up to 425℃) and has a lower leakage rate (≤0.01%).
Applicable working conditions:
Concentric butterfly valves are suitable for low-pressure, normal temperature, non-corrosive media (such as water supply and drainage, air conditioning systems);
Eccentric butterfly valves are suitable for high-pressure, high-temperature, highly corrosive or particle-containing media (such as petrochemicals, high-temperature steam pipelines).
3. Operating characteristics and maintenance requirements
Operating torque:
Concentric butterfly valves have large opening and closing resistance (due to continuous friction), high operating torque, and require a larger drive device;
Eccentric butterfly valves reduce friction by axial offset, and the operating torque is reduced by 40%~60%, which is more suitable for large-diameter high-pressure valves. Service life:
Concentric butterfly valves have a short service life due to rapid friction loss (soft seal type is about 30,000 to 50,000 opening and closing times);
The metal seal design of double eccentric or triple eccentric butterfly valves can extend the service life to more than 100,000 times.
4. Installation and maintenance differences
Installation requirements:
Concentric butterfly valves have low requirements for pipeline coaxiality and are suitable for quick installation scenarios;
Eccentric butterfly valves (such as double eccentric) require precise calibration of pipeline coaxiality to avoid eccentric wear of butterfly plates.
Maintenance focus:
Concentric butterfly valves require regular replacement of elastic sealing rings to prevent aging and leakage;
Eccentric butterfly valves require monitoring of the wear depth of the sealing surface (recommended ≤0.1mm) and the lubrication status of the actuator.
Summary
Concentric butterfly valves have the core advantages of simple structure and low cost, and are suitable for low-pressure conventional working conditions; eccentric butterfly valves optimize sealing performance and durability through the axis offset design, making them the first choice for high pressure, high temperature and harsh working conditions. The selection needs to comprehensively consider the medium characteristics, pressure temperature and long-term maintenance costs. For example, three-eccentric butterfly valves are preferred for steam pipelines, while concentric butterfly valves can be used for low-pressure water treatment.