Butterfly valves are different according to their structural design and application scenarios.
1. Concentric Butterfly Valve
Structural features
The valve stem axis is completely coincident with the center of the valve plate and the center of the valve body channel (no offset).
The valve plate keeps in contact with the valve seat when rotating, and seals by squeezing when closed.
Advantages and disadvantages
Advantages: simple structure, low cost, and easy installation.
Disadvantages: The sealing surface has large friction and is easy to wear, suitable for low-pressure and normal temperature conditions.
Application scenarios
Ventilation system, water supply and drainage pipelines, low-pressure gas transmission, etc.
2. Single Offset Butterfly Valve
Structural features
There is an axial offset between the valve stem axis and the center of the valve plate (that is, the valve stem deviates from the center line of the valve plate).
When opening, the valve plate first leaves the valve seat to reduce initial friction.
Advantages and disadvantages
Advantages: reduced friction, reduced operating torque, and extended life.
Disadvantages: There is still a certain amount of friction on the sealing surface, and the sealing performance is limited.
Application scenarios
Medium and low pressure water treatment, air conditioning system, light industrial pipeline, etc.
3. Double Offset Butterfly Valve
Structural Features
Axial offset + radial offset:
The valve stem axis deviates from the center line of the valve plate (axial offset).
The valve stem axis deviates from the center line of the valve body channel (radial offset).
When closed, the valve plate contacts the valve seat in a wedge-shaped extrusion manner to form a self-tightening effect.
Advantages and Disadvantages
Advantages:
The friction force is extremely small, and the operating torque is reduced by 30%-50%.
Excellent sealing performance, suitable for high pressure and high temperature conditions.
Disadvantages: Complex structure and high cost.
Application scenarios
Steam, gas, and oil transportation in industries such as petroleum, chemical, electric power, and metallurgy.
4. Extension: Triple Offset Butterfly Valve
Structural Features
Adding sealing surface angle offset on the basis of double eccentricity:
The valve seat sealing surface and the valve plate sealing surface are in conical contact.
When closed, zero friction opening and closing is achieved, and the sealing surface is only in contact at the last 1°.
Advantages and Disadvantages
Advantages:
Excellent sealing performance, suitable for high temperature, high pressure, and highly corrosive media.
Lifespan of more than 50 years, almost maintenance-free.
Disadvantages: Extremely high cost, demanding machining accuracy.
Application scenarios
Extreme working conditions such as nuclear power plants, LNG receiving stations, and supercritical boilers.
V. Summary and comparison
Type Offset design Sealing principle Applicable working conditions Typical applications
Centerline butterfly valve No offset Extrusion seal Low pressure, normal temperature, low frequency opening and closing Ventilation system, water supply and drainage
Single eccentric butterfly valve Axial offset Extrusion after disengagement Medium and low pressure, medium frequency opening and closing Water treatment, air conditioning system
Double eccentric butterfly valve Axial + radial offset Wedge extrusion self-tightening High pressure, high temperature, high frequency opening and closing Petrochemical, electric power
Triple eccentric butterfly valve Axial + radial + angle offset Conical zero friction seal Ultra-high temperature, ultra-high pressure, strong corrosion Nuclear power plant, LNG receiving station
