Schematic diagram of central butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve

Centered butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve are three main structural types of butterfly valves. The core difference lies in the relative position design of valve shaft and sealing surface (eccentric structure), which directly affects sealing performance, operating torque and working conditions. The following is a detailed comparison and application scenarios of them:

Centre butterfly valve (concentric butterfly valve)

Design feature ：

The center of the valve shaft and butterfly plate is concentric with the center of the valve body (no eccentricity).

The sealing surface is a soft seal (such as rubber, PTFE), which relies on the butterfly plate to squeeze the valve seat to achieve the seal.

Merit ：Simple structure, low cost.

Good sealing performance (zero leakage at low pressure and room temperature).

Small operating torque, light opening and closing.

Shortcoming ：Valve seat is easy to wear, not high temperature and high pressure.

Not suitable for containing particles or corrosive media.

Applicable occasions:Low pressure (below PN10), normal temperature (≤120℃) water, air, gas and other clean media.

Common in municipal water supply, air conditioning system, food industry and so on.

Central butterfly valve application case:

• Scenario:The water supply pipeline system of a waterworks in Shanghai.Operates under low pressure and normal temperature, meeting clean water needs efficiently.
• Choice: Use central butterfly valve (EPDM rubber seal, cast iron valve body), brand is Newway Valve (Neway).
• Reason: The central butterfly valve has low cost, good sealing performance, suitable for clean water medium, simple operation and low maintenance cost.The system ran stably with no leakage for five years; only routine seat replacement needed.
• Source: Reference Newway Valve website (https://www.newayvalve.com/) and “Water Supply and Drainage Engineering Design Manual”.

Double eccentric butterfly valve (single eccentric + radial eccentric)

Design feature ：First eccentricity: The valve shaft deviates from the center of the butterfly plate (single eccentricity), reducing the friction between the butterfly plate and the valve seat during opening and closing.

Secondary eccentricity: Valve shaft is radially offset from the body’s sealing surface center, allowing the disc to disengage rapidly from the seat during opening/closing.

Seal surface is mostly soft seal or metal hard seal.

Merit ：The opening and closing torque is smaller than the central butterfly valve, and the service life is longer.

Can adapt to slightly higher pressure and temperature.

Shortcoming ：The sealing performance under high pressure is not as good as the three eccentric butterfly valve.

Applicable occasions:Medium low pressure (PN16~PN25), medium temperature (≤200℃) of liquid or gas.

General medium for sewage treatment, chemical industry, electric power and other industries.

Double eccentric butterfly valve example: Used in a Jiangsu chemical plant’s sewage system (2023) for treating industrial wastewater with trace particles at PN16 and 50-80℃.

Handles industrial waste, balancing performance and durability under relevant temperature and pressure.

Choice: Double eccentric butterfly valve (PTFE seal, carbon steel body), brand: Emerson (Emerson Fisher series).

Reason: The double eccentric design reduces valve seat wear and is suitable for medium and low pressure and mildly corrosive media, balancing cost and performance.

Effect: The service life of the valve is extended to more than 3 years, the opening and closing is smooth, and the maintenance cycle is longer than that of the central butterfly valve.

Source: Refer to Emerson’s website (emerson.com) and Chemical Equipment Design Code.

Three eccentric butterfly valves

Design feature ：First two eccentricities: The same as double eccentricity (valve shaft deviates from the center of the butterfly plate + radial eccentricity).

Third eccentricity: The sealing surface of the valve seat is inclined at a certain angle (conical eccentricity), so that the contact between the butterfly plate and the valve seat is linear sealing.

The sealing surface is a metal hard seal (such as stainless steel, alloy steel).

Merit ：Zero friction opening and closing, minimal torque, long life.

High temperature (≤600℃), high pressure (PN100 above) and corrosive media.

Excellent bidirectional sealing performance (can replace gate valve, stop valve).

Shortcoming ：Complex structure, high cost.

The processing accuracy is strict.

Applicable occasions:High temperature and high pressure, harsh medium (steam, oil and gas, acid and alkali, etc.).

Petrochemical, nuclear power, shipbuilding, metallurgy and other key systems.

Tri-eccentric butterfly valve application case:

Scenario:High pressure steam pipeline of CNOOC offshore oil and gas platform (2024).

Background:The pipeline conveys high temperature and high pressure steam (PN64,350℃), which needs to be corrosion-resistant and leak-free.

Choice:Three eccentric butterfly valve (stainless steel sealing surface, alloy steel valve body), brand is Velan.

Reason:The three eccentric designs realize zero-friction opening and closing, the metal hard seal is resistant to high temperature and high pressure, and the two-way seal meets the harsh working conditions.

Effect:The valve operates reliably, meets the API 609 standard, and reduces the maintenance costs of traditional gate valves.

Source: Refer to Velan’s website (velan.com) and API 609 standard (Butterfly Valves: Double-offset, Triple-offset, and Concentric-disc).

Comparative summary

Recommendations for selectionPriority center butterfly valve:Limited budget, low pressure, normal temperature clean medium.

Select double eccentric butterfly valve: Medium and low pressure conditions that require balance between cost and performance.

Must choose three eccentric butterfly valve: High temperature and high pressure, corrosive medium or long life requirements of harsh working conditions.

By reasonable selection of eccentric structure, sealing performance, operation efficiency and service life can be optimized.

Selection of sealing materials:

• Center butterfly valve: Commonly used EPDM (water resistant, weak acid and alkali resistant) or PTFE (corrosion resistant), but not suitable for high temperature (> 120℃) or oil containing medium.
• Double eccentric butterfly valve: NBR (oil resistant), Viton (chemical corrosion resistant) or partial metal seal (such as stainless steel) can be selected to suit a wider range of media.
• Tri-ear butterfly valve: Multi-layer metal seal (such as SS316+ graphite) is often used, which can withstand high temperature and pressure, suitable for harsh working conditions, but requires high precision machining.
• Operating torque and life:
• Center butterfly valve: Small torque, but the valve seat wears fast, life about 5000 times open and close.
• Double eccentric butterfly valve:Torque reduced by about 20-30%, life can reach more than 10,000 times.
• Tri-eccentric butterfly valve: Near zero friction, life up to 50,000 times (refer to API 609 test data).
• Installation and maintenance:
• Center butterfly valve: Simple to install, but the wear of the valve seat needs to be checked regularly. It is recommended to replace the sealing ring every 1-2 years.
• Doubleeccentric butterfly valve: Attention should be paid to valve shaft alignment during installation, and maintenance cycle is long (about 2-3 years).
• Tri-eccentric butterfly valve: High installation requirements (flange parallel must be ensured), complex maintenance but low frequency (more than 5 years).