Flanged Butterfly Valve

Water Supply Systems
Pressure Range: Typically low to medium pressure, ranging from 0.5 to 10 MPa (5 to 100 bar) depending on the system.

Valve Design: For most water supply systems, a centerline (single eccentric) butterfly valve is ideal because it’s simple and cost-effective. It provides a good seal for low to medium-pressure applications, making it suitable for most municipal water pipelines.

Materials:

●Body: Ductile Iron (also known as nodular cast iron) is a good choice because it has good mechanical properties, is strong, and resists corrosion in water systems.
●Stem: Stainless Steel (e.g., SS304 or SS316) is commonly used for the valve stem because it resists corrosion, especially when it’s in contact with water and other liquids.
●Seal: EPDM (Ethylene Propylene Diene Monomer) is a good choice for water systems because it seals well, resists aging, and works well in both cold and warm water.
●Valve Size: For standard water supply systems, centerline butterfly valves are fine. However, for larger systems with higher flow rates, you might consider a double-eccentric design (see below).

Large Diameter Pipes or High Flow Systems

Pressure Range: Similar to water systems, the pressure might still be low to medium (up to 10 MPa), but the flow rate will be higher because the pipe is bigger.

Valve Design: For large diameter valves or high flow systems, a double-eccentric butterfly valve is a good choice. The double-eccentric design reduces the friction between the seat and the disc, making the valve easier to operate and reducing the torque needed to open or close the valve. This is especially important for larger valves where high torque can make the valve hard to operate.

Materials:

●Body: Ductile Iron is still a good choice for large-sized valves because it balances strength and weight, although in some cases, you might consider carbon steel or stainless steel for more durability and corrosion resistance.
●Stem: Stainless Steel (typically SS304 or SS316) is still the preferred material for the stem because it resists corrosion and is reliable over the long term.
●Seal: EPDM for water or NBR for oil-based applications. For larger systems or special environments, you might use metallic sealing (e.g., Stainless Steel seats) for high temperature or high-pressure situations.

Seawater or Coastal Environments

Pressure Range: Generally low to medium pressure (around 0.5 to 6 MPa depending on the location and application).

Valve Design: A triple-eccentric butterfly valve (also known as a concentric triple-offset valve) is a great choice for harsh environments like seawater applications. The triple-eccentric design ensures that the valve is less affected by temperature changes and provides superior performance when opening or closing the valve.
Materials:
●Body: Ductile Iron with marine-grade coatings or Stainless Steel (especially SS316 or SS316L) for maximum corrosion resistance in salty environments.
●Stem: Stainless Steel (preferably SS316) to resist corrosion from the salty seawater environment.
●Seal: EPDM for cold water or NBR for oil-based fluids. In highly corrosive environments, you might use a rubber-lined valve with ceramic or PTFE lining.

Oil and Gas Systems

Pressure Range: Can be medium to high pressure (typically 5 MPa to 20 MPa or more).

Valve Design: In oil and gas systems, double-eccentric butterfly valves or triple-eccentric butterfly valves are preferred. These valves can handle higher pressures and make it easier to operate the valve because they require less torque.

Materials:

●Body: Carbon Steel or Stainless Steel (often SS316 or SS304) for better strength and durability in oil and gas applications.

●Stem: Stainless Steel (again, SS316 is a popular choice) because it resists corrosion and the high mechanical stresses found in the industry.

●Seal: NBR (Nitrile Rubber) seals are commonly used in oil-based systems because they resist oils and petroleum products.

Chemical Processing

Pressure Range: Varies, but can often be high-pressure systems (up to 20 MPa or more depending on the application).

Valve Design: Double-eccentric or triple-eccentric butterfly valves are ideal for chemical processes because they minimize seat wear and provide excellent sealing properties even at high pressures or with corrosive media.
Materials:
●Body: Stainless Steel (SS304 or SS316) for most chemical processes, although you might need specialized alloys (like Hastelloy or Inconel) for very aggressive chemicals.
●Stem: Stainless Steel (typically SS316 or SS316L).
●Seal: For aggressive chemicals, you might need PTFE (Polytetrafluoroethylene) or Viton seals because they resist chemical attack.