Eccentric Structure Butterfly Valve In Industrial Piping Systems

In industrial piping systems, butterfly valves are frequently used in water supply and drainage, HVAC, chemical, and power industries due to their compact structure, strong flow capacity, and ease of operation. However, traditional center-line butterfly valves often face problems such as seal wear, high opening and closing torque, and short service life under high pressure, high temperature, or wear-resistant conditions. The emergence of the "eccentric structure" represents a key breakthrough in butterfly valve design, fundamentally solving these pain points.

This article will delve into the core function, common types, and industrial application logic of the eccentric structure in butterfly valves, helping practitioners fully grasp this core technical point.

I. Pain Points of Traditional Center-Line Butterfly Valves: Why Has the Eccentric Structure Become Inevitable?

To understand the value of the eccentric structure, it is essential to first clarify the design limitations of traditional center-line butterfly valves. In a center-line butterfly valve, the valve stem axis coincides with the valve body centerline and the butterfly plate centerline. When closed, the butterfly plate is in full circumferential contact with the valve seat, forming a "surface seal." While this structure appears symmetrical and stable, it presents several problems in actual operation:

Severe Seal Wear: During the opening and closing of the center-line butterfly valve, sliding friction occurs between the butterfly plate and the valve seat. Especially under conditions containing particulate impurities or high pressure, the sealing surface is prone to scratches and deformation, increasing the risk of internal leakage. After prolonged use, the sealing performance deteriorates sharply, requiring frequent valve seat replacements.

High Opening and Closing Torque: Because the butterfly plate and valve seat are completely fitted together, closing requires overcoming medium pressure and contact surface friction, increasing operational difficulty and potentially leading to valve stem deformation, actuator overload, and other malfunctions.

Limited Applicable Conditions: The friction problem of the center-line butterfly valve makes it unsuitable for high-temperature (>200℃), high-pressure (>1.6MPa), or highly corrosive conditions. It can only be used in low-pressure, normal-temperature, clean media scenarios, limiting its application range.

The eccentric structure, by altering the relative positions of the valve stem, disc, and valve body, allows the disc to achieve "incomplete contact" or "rolling contact" with the valve seat during opening and closing, fundamentally solving the aforementioned pain points and greatly expanding the application scenarios of butterfly valves.

II. Core Functions of the Eccentric Structure: 3 Key Advantages Solving Industry Challenges

The eccentric design of a butterfly valve is not a simple structural offset, but an optimized solution based on precise mechanical calculations. Its core functions can be summarized in three points:

Reduced sealing surface friction and extended service life: This is the most crucial value of the eccentric structure. By rationally setting the eccentricity, the disc quickly disengages from the valve seat upon opening and only contacts the seat in the final stage upon closing, avoiding sliding friction throughout the entire opening and closing process.

Especially in media containing particles, this "disengagement-contact" movement reduces scratches on the sealing surface caused by impurities, lowering the wear rate of the sealing surface by more than 60% and extending the service life by 3-5 times.

Reduced opening and closing torque, improved operational convenience: The eccentric structure utilizes the principle of mechanical levers, allowing the medium pressure on the butterfly plate to create a "helping torque" when opening, rather than the "resisting torque" of a centerline butterfly valve.

Data shows that, for the same diameter and pressure rating, the opening and closing torque of an eccentric butterfly valve is only 1/3 to 1/2 that of a centerline butterfly valve. This not only reduces manual operation intensity but also allows for the use of smaller power actuators, saving equipment costs.

Improved sealing reliability, adaptable to complex operating conditions: The eccentric design ensures more uniform contact pressure between the butterfly plate and the valve seat, avoiding localized sealing failures caused by uneven force in centerline butterfly valves.

Simultaneously, reduced friction-induced damage to the sealing surface allows the butterfly valve to adapt to complex operating conditions such as high pressure, high temperature, and media containing particles. The sealing rating can easily reach PN10 or higher in GB/T 13927, meeting the stringent sealing requirements of industrial pipelines.

III. Common Eccentric Butterfly Valve Types and Characteristics: 2 Mainstream Structures + 1 Special Design

Based on the number and direction of the eccentricity, butterfly valve eccentric structures are mainly divided into two mainstream types, and one derivative design for special working conditions, each with a clear applicable scenario:

Single Eccentric Butterfly Valve

The single eccentric butterfly valve is the most basic eccentric structure. Its design feature is that the valve stem axis is parallel to and offset from the center line of the butterfly plate, with only one eccentricity (usually offset to one side of the valve seat sealing surface).

Working Principle: When opening, the butterfly plate rotates around the offset valve stem, disengaging from the valve seat sealing surface in the initial stage of rotation, avoiding sliding friction; when closing, the butterfly plate tightly fits against the valve seat under the pressure of the medium, forming a reliable seal.

Core Advantages: Simple structure, mature manufacturing process, and low cost; it is the most widely used type of eccentric butterfly valve. Compared to centerline butterfly valves, the sealing wear and opening/closing torque issues are significantly improved, making it suitable for most low-to-medium pressure applications (PN≤2.5MPa) and media at normal or medium temperatures (≤300℃), such as water supply and drainage, HVAC, and general chemical pipelines.

Note: A small amount of localized friction still exists on the sealing surface of a single eccentric butterfly valve. In high-pressure media or media containing a large amount of hard particles, the sealing life will be affected, requiring careful selection.

Double Eccentric Butterfly Valve

The double eccentric butterfly valve is a further optimization of the single eccentric design, adding a second eccentricity: the valve stem axis is offset not only from the butterfly plate centerline but also perpendicular to the valve body centerline (sealing surface centerline), forming a "two-way eccentric" structure.

Working Principle: This double eccentric design makes the butterfly plate's movement trajectory an "elliptical arc." When opening, the butterfly plate can disengage from the valve seat more quickly and completely; when closing, the "wedge effect" caused by the eccentricity allows the butterfly plate to form a line contact seal with the valve seat, resulting in greater and more uniform contact pressure.

Core Advantages: Superior sealing performance, achieving bidirectional sealing; further reduced opening and closing torque, suitable for large-diameter butterfly valves (DN≥500mm); minimal friction loss, suitable for high-pressure (PN≤4.0MPa), medium-high temperature (≤400℃) conditions, and media containing small amounts of particles, such as industrial steam pipelines, chemical raw material transportation pipelines, and cooling water systems in thermal power plants.

Typical Application: A chemical plant's caustic soda transportation pipeline (DN300, PN2.5MPa, temperature 80℃). Previously, when using a center-line butterfly valve, the sealing surface needed to be replaced every 3 months; after replacing it with a double eccentric butterfly valve, the sealing life was extended to 2 years, saving approximately 10,000 RMB in maintenance costs annually.

Triple Eccentric Offset Butterfly Valve

The triple eccentric butterfly valve is a special structure designed for extreme conditions such as high temperature, high pressure, and strong corrosion. Based on double eccentricity, a third eccentricity is added: the butterfly plate sealing surface adopts a conical design, forming a certain conical eccentricity with the valve seat sealing surface.

Working Principle: After the triple eccentricity is superimposed, the butterfly plate's movement trajectory is a "spiral line." When opening, the butterfly plate completely disengages from the valve seat without friction. When closing, the "self-tightening effect" of the conical sealing surface achieves a zero-leakage seal under media pressure. Simultaneously, the conical sealing surface reduces impurity adhesion, improving wear resistance and corrosion resistance.

Core Advantages: Highest sealing level, achieving ANSI Class VI zero-leakage standard; adaptable to extreme conditions such as high temperature (≤600℃), high pressure (PN≤10.0MPa), and strong corrosion (e.g., strong acids, strong alkalis, high-temperature flue gas); long service life and extremely low maintenance frequency, making it the first choice for high-end industrial fields.

Precautions: Triple eccentric butterfly valves have a complex structure, require high manufacturing precision, and are relatively expensive. They are suitable for applications with strict requirements on sealing performance and service life, such as petrochemical cracking units, high-temperature flue gas desulfurization systems, and nuclear power plant cooling pipelines.

IV. Key Points for Eccentric Butterfly Valve Selection: Choose the Right Structure Type Based on Operating Conditions

In industrial applications, the selection of eccentric butterfly valves must follow the principle of "matching operating conditions" to avoid blindly pursuing high eccentricity levels, which could lead to cost waste, or inadequate selection that could cause malfunctions. Here are the key selection considerations:

For low to medium pressure, normal temperature, and clean media (such as tap water and compressed air): prioritize single eccentric butterfly valves, balancing cost-effectiveness and practicality;

For medium to high pressure, medium to high temperature, and media containing a small amount of particulate matter (such as steam and chemical raw materials): select double eccentric butterfly valves to balance sealing performance and cost;

For high temperature and high pressure, extreme corrosion, and zero leakage requirements (such as high-temperature flue gas and strong acids and alkalis): triple eccentric butterfly valves are essential to ensure long-term stable operation;

For large-diameter pipelines (DN≥500mm): prioritize double or triple eccentric butterfly valves to reduce opening and closing torque and operational difficulty.

ZZJG Valve provides the above information on eccentric structure butterfly valve. If you want to know more about eccentric structure butterfly valve, please contact us via WhatsApp or email.