What Is a Low-Load Butterfly Control Valve?
In modern industrial production, fluid control equipment plays a crucial role. As an efficient and reliable fluid control device, the low-load butterfly control valve is widely used in various complex working environments. This article will provide an in-depth discussion on the design features, working principle, installation considerations, and applications of low-load butterfly control valves, helping readers fully understand this important industrial equipment.
Low-load butterfly control valves are primarily used for medium regulation, and their sealing performance differs from that of metal-seated butterfly valves. When in the closed position, the butterfly valve still retains a certain gap, but this does not affect its ability to regulate pipeline opening, thereby achieving automatic furnace pressure control. This design enables low-load butterfly control valves to perform well in dust-containing flue gas control equipment, allowing effective flow regulation even when closed.
Low-load butterfly control valves are similar to metal-seated butterfly valves in terms of fluid characteristics. The opening of the valve is basically linearly proportional to the flow, meaning that precise control of the medium flow can be achieved by adjusting the valve opening. However, the flow characteristics are closely related to the flow resistance coefficient of the connected pipeline. Even if two valves installed in pipelines have the same diameter and type, if the loss coefficients of the pipelines differ, the valve flow will also vary significantly. Therefore, in practical applications, it is necessary to select the appropriate butterfly valve according to the specific pipeline system to ensure accurate flow control.
When the butterfly valve is in a large throttling range, during the process of closing from mid-opening, the disc will form completely different conditions on the two sides. One side of the disc moves in the direction of the medium flow, while the other side moves against the medium flow. This causes one side of the valve body and disc to form a nozzle-like opening, while the other side forms a throttle-like opening. The flow velocity on the nozzle side is much higher than that on the throttle side, and the throttle side often generates negative pressure. To prevent ash blockage at the pipeline-valve connection, when installing a low-load butterfly control valve horizontally, the nozzle side should be placed at the bottom of the pipeline.
The main functions of low-load butterfly control valves are flow cut-off and regulation. Especially in large-diameter butterfly valves, operating conditions significantly affect valve deformation, and deformation is difficult to control. Therefore, structural design must fully consider the influence of environmental factors.
The sealing form of low-load butterfly control valves is ideally planar and can be designed as a vertical plate or oblique plate structure. The valve body and disc use the side plane as the sealing surface, and the disc outer diameter can be smaller than the valve bore. This design allows easy valve operation even if the valve cavity walls have adhesion. Compared with radial sealing, pipeline deformation has less impact on the main sealing performance.
However, this structure requires high symmetry of the valve body sealing surface, especially for the oblique plate structure. The side sealing plane of the valve body is difficult to machine on ordinary mechanical equipment and must use a reasonable process to achieve ideal assembly accuracy and sealing effect.
Using a lever-type planar seal structure can solve problems in the machining of the sealing plane. Whether it is a vertical or oblique plate structure, the lever-structured valve has a side-plane seal that does not cause radial jamming. The sealing side planes of the valve body and disc are machined as a continuous whole, and the disc outer diameter is designed smaller than the valve bore. During closing, the disc first rotates and then translates, and the seal surface tightens progressively. During opening, the disc first translates and then rotates, also avoiding jamming. This structure is particularly suitable for low-load butterfly control valves because they generally operate under low pressure and high temperature, which does not affect valve opening and closing.
The structural design of low-load butterfly control valves should be optimized according to valve operating conditions. In high-temperature, high-dust smelting environments, a planar oblique plate structure can be used. A gap is maintained between the disc and valve body, with the gap value determined by the valve diameter and working conditions, generally controlled within 0.5% of the passage area. This design meets the installation requirements of low-load butterfly control valves while accommodating temperature changes and smelting process demands.
In high-temperature, low-dust acid production environments, a vertical plate structure can be used. The sealing surface is easy to machine, and the gap is controlled within 0.2% of the passage area. The sealing surface dimensions of the valve body and disc can be machined to meet design requirements.
For high-temperature, low-pressure, and strict sealing conditions, a lever-type planar structure can be used. This structure's sealing pair configuration and disc movement trajectory can meet the process requirements of high-sealing pipeline equipment.
The shaft-end structure of low-load butterfly control valves adopts an external support structure with excellent heat insulation and sealing effects. This design allows the two shaft ends to be sealed before supported, facilitating adjustment and preventing jamming. When directly connected with crank or link mechanisms and the transmission device, adding a heat-insulating sleeve effectively isolates the high-temperature environment, ensuring normal valve operation.
The installation position and pipeline layout of low-load butterfly control valves significantly affect their performance. In pipelines with high dust, a closed-type funnel should be designed at the valve opening end or valve connection corner and cleaned regularly to prevent excessive ash accumulation, facilitating disc rotation.
Other installation considerations include:
Use of metal gaskets: Ensure uniform load to avoid additional pressure from temperature, self-weight, or welding stress, which could deform the valve flange and pipeline.
Install support brackets: For valves on long pipelines, support brackets should be installed to ensure pipeline stability.
Medium flow direction: Align the valve disc opening with the flow direction to promote self-cleaning and reduce dust accumulation.
Enhance thermal insulation protection: Maintain pipe wall temperature above the dew point to reduce adhesion of low-temperature sticky dust. If the pipe wall temperature is higher than the flue gas acid dew point, it prevents condensation of acid vapors on heated pipe walls, controls SO₃ formation, and improves valve performance.
The installation position of low-load butterfly control valves varies with pipeline design, including horizontal, vertical, and corner installations. Generally, vertical installation achieves the best performance, horizontal second, and corners the worst. Turns on either side of the valve inlet and outlet are most prone to uneven flow and ash blockage, increasing operating torque.
Due to their unique structural design and excellent performance, low-load butterfly control valves demonstrate broad application value in various industrial conditions.
Under smelting conditions, flue gas temperatures are high and dust content is large, so oblique plate planar seals are recommended. This structure effectively handles high temperatures and high dust content, ensuring normal valve operation.
In refining and chemical acid production, temperatures and dust content are relatively low. A planar vertical plate seal with sealing rings can be chosen. This structure is easy to machine, meets working condition requirements, and ensures valve sealing performance.
For refining equipment, sealing requirements are strict and temperatures are high. A lever-type planar seal structure is recommended. This structure meets the high-sealing process requirements of pipeline equipment, ensuring reliable valve operation under harsh conditions.
As an efficient fluid control device, low-load butterfly control valves play an important role in industrial production. Their unique sealing performance, flexible structural design, and reliable installation and maintenance requirements enable them to adapt to various complex working conditions. Whether in high-temperature, high-dust smelting conditions or lower-temperature, low-dust acid production conditions, low-load butterfly control valves provide ideal solutions. Proper selection and installation can significantly improve industrial efficiency and reliability, providing strong support for modern industrial development.
