Simplified Guide to Industrial Valves

Analysis of Various Valve Characteristics

In the chemical industry, we need different valves for different requirements. It is important to know the pros and cons of each valve type before choosing one for a specific process. Process fluids can be liquids, mixtures, or gas-liquid combinations at various temperatures and pressures. The rules for selecting valves remain consistent. Focus on the valve's operating principles rather than specific design variations.

Types of Valves

Butterfly Valves

Butterfly valves cause minimal pressure drop when fully open. They are good for large pipes (up to 3000 mm). Partial opening can cause flow issues like cavitation and noise. Quick closing in liquid applications may cause water hammer. Butterfly valves are sensitive to slurries or thick substances. If these substances exceed 20% concentration, they can accumulate and cause problems. Extra force (torque) is needed to clear these accumulations. Butterfly valves are best for simple on/off tasks with clean liquids or gases and infrequent use.

Ball Valves

Ball valves also have minimal pressure drop when fully open. They are good for applications needing full bore flow, especially with smaller diameters. Ball valves can handle flow in both directions and prevent sediment buildup by allowing flow direction reversal. They are not ideal for scaling or coagulating media, especially if the valve stays closed for long periods. The performance of ball valves is less smooth than butterfly valves, but they are effective connectors for full flow volume transmission in clean liquid or gas applications.

Plug Valves

Plug valves have a 90° rotating closure element, either cylindrical or conical. They are lightweight with good sealing performance but have a higher pressure drop. Plug valves are used for throttling and flow control due to their versatility. Non-lubricated plug valves, particularly sleeved types, are effective in preventing leakage, making them suitable for handling suspensions with solids.

Globe Valves

Globe valves are ideal for high-pressure systems with a tendency to close due to differential pressure across the valve. These valves need a specific force to stay closed, which changes with flow direction. They are good for applications needing precise control of flow rates and can handle high temperatures and pressures. Globe valves provide excellent sealing with materials ranging from plastic to metal, depending on the application needs.

Conclusion

Each valve type has its practical uses and limits. This guide helps with initial valve selection. Consider the materials and sealing mechanisms, with options like PVC, ABS, polypropylene, PTFE, PVDF, and various metals and alloys. Understanding how fluid properties affect valve materials is key. The selection process should also consider manual, pneumatic, or electric actuation methods, ensuring safety and environmental compatibility. Consult with valve manufacturers and experts for the best valve choice.

FAQs

1. What factors should be considered when selecting a valve for a chemical process?
   • Consider the type of fluid, pressure and temperature conditions, flow characteristics, and specific process needs.
2. How does a butterfly valve function?
   • A butterfly valve has a disc that rotates around an axis perpendicular to the flow, providing quick and efficient shutoff.
3. What are the advantages of using a ball valve?
   • Ball valves offer minimal pressure drop, full bore flow, and effective sealing, making them good for clean fluid applications.
4. In what applications are plug valves most effective?
   • Plug valves are effective in handling suspensions with solids due to their good sealing performance and versatility.
5. Why are globe valves preferred for high-pressure systems?
   • Globe valves are preferred for their ability to handle high-pressure differences and provide precise control over flow rates.