Manual butterfly valves have certain limitations in terms of pressure and temperature that should be considered when selecting and operating these valves in industrial applications.

Here are some of the key limitations:

1. Pressure Rating: Manual butterfly valves typically have lower pressure ratings compared to other types of valves, such as gate valves or ball valves. While they can handle moderate to high pressures depending on their design and construction, they may not be suitable for extremely high-pressure applications. The pressure rating of a manual butterfly valve is usually specified by the manufacturer and should be selected based on the maximum pressure expected in the system.
2. Temperature Range: Manual butterfly valves are limited in their ability to handle extreme temperatures, particularly at the extremes of the temperature range. The materials used in the construction of the valve, including the body, disc, seat, and seals, may have temperature limitations that restrict their use in very high or very low temperature environments. Extreme temperatures can affect the integrity of the materials, leading to deformation, degradation, or failure of the valve components.
3. Material Compatibility: The materials used in manual butterfly valves may not be compatible with certain process fluids or environments. For example, certain chemicals, acids, or abrasive substances may corrode or erode the valve materials over time, compromising their performance and integrity. It’s essential to select materials that are compatible with the specific application conditions to ensure the longevity and reliability of the valve.
4. Sealing Integrity: Manual butterfly valves rely on resilient seals, such as elastomers or PTFE, to provide a tight seal against leakage when the valve is closed. However, these seals may be susceptible to degradation or damage under high temperatures or pressures, leading to leakage or loss of sealing integrity. Regular inspection and maintenance of the seals are necessary to ensure proper functioning of the valve.
5. Flow Characteristics: Manual butterfly valves may have limitations in terms of flow characteristics, particularly in applications requiring precise control of flow rates or throttling. While butterfly valves offer good flow capacity and low pressure drop, they may not provide the same level of flow control as other types of valves, such as globe valves or control valves.
6. Torque Requirements: Operating manual butterfly valves may require significant torque, especially for larger valve sizes or valves installed in high-pressure systems. This can make manual operation challenging, particularly in applications where frequent operation or precise control is required. Using gear operators or lever extensions can help reduce the manual effort required to operate the valve.

Overall, while manual butterfly valves offer advantages such as simplicity, reliability, and cost-effectiveness, they also have limitations in terms of pressure and temperature capabilities that should be carefully considered when selecting and using these valves in industrial applications. It’s essential to consult with valve manufacturers or engineers to ensure that the selected valve meets the specific requirements and operating conditions of the application.