Understand Bidirectional Butterfly Valve from this Guide

In industrial fluid control systems, valves play a crucial role. They not only control the flow rate and direction of fluids but also ensure the safety and efficient operation of the system. Today, we will delve into a special type of butterfly valve: the bidirectional butterfly valve. This valve, with its unique bidirectional sealing function and outstanding performance, is widely used in various complex industrial scenarios.

Butterfly valves are common industrial valves that can generally be divided into two major categories based on their structural characteristics: centerline butterfly valves and eccentric butterfly valves. Centerline butterfly valves inherently possess bidirectional sealing capabilities, while eccentric butterfly valves are typically designed for unidirectional sealing. However, through special design, eccentric butterfly valves can also achieve bidirectional sealing. Most butterfly valves available on the market are unidirectional, meaning they have a distinct inlet and outlet direction, usually indicated by an arrow on the valve body to show the direction of fluid flow.

A bidirectional butterfly valve, as the name suggests, is a type of butterfly valve that can achieve bidirectional sealing. It is an improvement on the conventional hard-sealed butterfly valve, capable of withstanding pressure from both directions. Regardless of the direction from which the fluid flows, it ensures excellent sealing performance. The structural design of this valve excels in bidirectional pressure resistance and metal-to-metal sealing. Its special structure also allows for adjustable sealing contact pressure, thereby enhancing the valve's service life and reliability.

The structure of a bidirectional butterfly valve is relatively complex. It mainly consists of components such as the valve body, disc, stem, packing, bonnet, packing gland, guide block, upper wedge block shaft, and lower wedge block shaft. These components work together to ensure bidirectional sealing under complex operating conditions.

Bidirectional Pressure Resistance and Metal Sealing: The bidirectional butterfly valve employs a bidirectional metal sealing design. This means that the sealing surfaces of the valve are made of metal materials, capable of withstanding high pressure and temperature while maintaining sealing performance. This design ensures good sealing effects under bidirectional pressure.

Special Structural Form: The special structure of the valve allows for adjustable sealing contact pressure. By adjusting the position and angle of the upper and lower wedge block shafts, the contact pressure between the disc and the valve body's sealing surface can be changed to meet different operating conditions.

Eccentric S-shaped Conical Seat Sealing Surface: This unique sealing surface design makes the sealing surface more durable and further extends the valve's service life. The eccentric S-shaped conical seat sealing surface better accommodates the movement of the disc, reducing wear while ensuring sealing performance.

The working principle of a bidirectional butterfly valve is relatively complex but can be summarized in the following steps:

When the stem rotates clockwise, the guide block directs the stem to move upward, pushing the lower wedge block upward. The wedge-shaped surface of the lower wedge block contacts the disc, causing the disc to translate and separate its sealing surface from the valve body's sealing surface. As the stem continues to rotate clockwise, the guide block directs the stem to turn, driving the disc to rotate 90° to the left, opening the valve.

When the stem rotates counterclockwise, the guide block directs the stem to move downward, pushing the lower wedge block downward. The wedge-shaped surface of the lower wedge block contacts the disc, causing the disc to translate and bring its sealing surface into contact with the valve body's sealing surface to achieve sealing. As the stem continues to rotate counterclockwise, the guide block directs the stem to turn, driving the disc to rotate 90° to the right, closing the valve.

This design ensures good sealing performance during both the opening and closing processes of the bidirectional butterfly valve, while also reducing the operating torque, making the valve operation more convenient and rapid.

The sealing principle of the bidirectional butterfly valve mainly relies on the cooperation between the upper and lower wedge block shafts and the disc. When the fluid flows in the forward direction, the required sealing force (FMF) applied by the stem torque on the disc's sealing surface is increased by the fluid force (FMJ), resulting in an actual sealing force (FMZZ) that is the sum of these two forces, i.e., FMZZ = FMF + FMJ. During reverse sealing, the force applied by the stem on the disc's sealing surface is the sum of the required sealing force and the fluid force, meaning the force applied by the stem during reverse sealing is greater than that during forward sealing.

To ensure the reliability of reverse sealing, the bidirectional butterfly valve employs a special structural design. The upper and lower wedge block shafts are positioned at the top and bottom of the valve chamber, respectively. By appropriately increasing the cross-sectional area of the upper and lower wedge block shafts, i.e., increasing the moment of inertia (I), the stiffness of the stem is enhanced, reducing the deformation (δ2). Thus, even when the fluid flows in the reverse direction, the stem will not bend and deform to the extent that it affects the sealing performance.

High Reliability: The bidirectional sealing design of the bidirectional butterfly valve ensures good sealing performance in both forward and reverse fluid flow directions, significantly enhancing the valve's reliability.

Compact Structure: The valve's compact design makes it lightweight, facilitating easy installation and maintenance.

Convenient Operation: The bidirectional butterfly valve requires a relatively low operating torque. A 90° rotation is sufficient to complete the opening and closing operations, making the valve easy to operate and quick in action.

Good Hydraulic Characteristics: The bidirectional butterfly valve has low flow resistance, with a flow characteristic that is approximately a sloping straight line. This design is energy-efficient and does not require a specific direction of fluid flow.

Long Service Life: The special structural form and material selection make the sealing surface of the bidirectional butterfly valve more durable, thereby extending the valve's service life.

Due to its outstanding performance and reliability, the bidirectional butterfly valve is widely used in various industries, including coal chemical, petrochemical, power, water supply and drainage, and environmental protection. In these industries, the bidirectional butterfly valve can meet the demands of complex operating conditions, ensuring the safety and efficient operation of the systems.

In the coal chemical production process, a large amount of high-temperature, high-pressure, and corrosive fluids need to be handled. The bidirectional sealing and metal hard sealing design of the bidirectional butterfly valve enable it to withstand these harsh conditions, ensuring reliable fluid control.

The petrochemical industry has extremely high requirements for valve sealing performance and corrosion resistance. The bidirectional metal sealing and special structural design of the bidirectional butterfly valve meet these requirements, making it widely used in various piping systems.

In the power industry, bidirectional butterfly valves are commonly used in cooling water systems and steam systems. Their good hydraulic characteristics and energy-saving effects can effectively reduce the operating costs of the system while ensuring its safe operation.

In water supply and drainage systems, the bidirectional sealing function of the bidirectional butterfly valve allows it to adapt to different water flow directions, ensuring the stable operation of the system. Its convenient operation and simple maintenance make it an ideal choice for the water supply and drainage industry.

In the environmental protection field, bidirectional butterfly valves are often used in sewage treatment and exhaust gas treatment systems. Their reliable sealing performance and corrosion resistance effectively prevent the leakage of pollutants, protecting the environment.

The main differences between bidirectional and unidirectional butterfly valves lie in the sealing direction and structural design.

Unidirectional Butterfly Valve: The disc of a unidirectional butterfly valve must face the direction of fluid flow when closed. The fluid flows in one direction only, and the valve body has an arrow indicating the direction of fluid flow. Attention must be paid to the direction of fluid flow during installation.

Bidirectional Butterfly Valve: The disc of a bidirectional butterfly valve can face or be opposite to the direction of fluid flow, and there is no need to consider the direction of fluid flow during installation. The valve body typically does not have an arrow indicating the direction of fluid flow.

Unidirectional Butterfly Valve: The design of a unidirectional butterfly valve is relatively simple, with less force applied to the stem. Under the same diameter and pressure conditions, the stem diameter of a unidirectional butterfly valve is usually smaller.

Bidirectional Butterfly Valve: The design of a bidirectional butterfly valve is more complex, with greater force applied to the stem. Under the same diameter and pressure conditions, the stem diameter of a bidirectional butterfly valve is usually larger than that of a unidirectional butterfly valve. This design enables the bidirectional butterfly valve to maintain good sealing performance under bidirectional pressure.

Unidirectional Butterfly Valve: Unidirectional butterfly valves are typically used in scenarios where the fluid flows in one direction, such as in simple water supply and drainage systems and low-pressure fluid systems.

Bidirectional Butterfly Valve: Bidirectional butterfly valves are suitable for complex operating conditions where the fluid flows in both directions, such as in the petrochemical, power, and coal chemical industries. These industries have extremely high requirements for valve sealing performance and reliability, which bidirectional butterfly valves can meet.

As a high-performance industrial valve, the bidirectional butterfly valve is widely used in various complex industrial scenarios due to its bidirectional sealing, convenient operation, compact structure, and long service life. By gaining a deep understanding of its structure, working principle, and performance advantages, we can better select and use this type of valve to meet the demands of different operating conditions. Proper installation and maintenance are also key to ensuring the performance and service life of the bidirectional butterfly valve. It is hoped that this article will provide you with valuable information to help you better understand and apply bidirectional butterfly valves.