How to Read Butterfly Valve Specifications (NPS, DN, Class Ratings) Like a Pro

Understanding butterfly valve specifications is essential for anyone working with pipelines. Here, we’ll look at the fundamentals, particularly NPS, DN, and Class Ratings, so you can read them quickly and confidently and make informed decisions.  

What are Butterfly Valves?

A butterfly valve is a quarter-turn valve featuring a rotating disc, widely used to regulate flow or completely shut it off. It’s a compact and lightweight valve. You’ll often see it in water treatment facilities, HVAC, and oil, gas, and chemical industries. 

The Right Getting Butterfly Valve Specifications

Getting butterfly valve specifications right directly affects its efficiency and safety as it functions in a system. Overlooking or misreading them may cause:

• Leaks or even complete failure if the pressure class is too low
• Flow restrictions and energy losses occur if the size of the valve doesn’t match the pipeline
• Downtime and cost overruns when materials don’t suit the fluid or temperature.  

Learning how to read them correctly is a good way to safeguard system performance and your project’s budget. 

Professional Lined Butterfly Valve Manufacturer

Available in wafer, lug, and flanged designs with manual or automated operation options. Compliant with API608, ASME B16.10, ASME B16.5, JIS B2220 and API 598 standards.

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Pipe Sizing Terms (NPS and DN)

Since valves are sized to fit pipes, you will encounter two main sizing systems for this purpose. These are the NPS (Nominal Pipe Size) and DN (Diameter Nominal). 

NPS and DN are close equivalents. However, to be safe, always check conversation charts when you need to match them. 

What are Class Ratings?

Class ratings refer to the amount of pressure the butterfly valve can handle. This directly affects their safety and reliability. 

• Class 150: Suitable for low-pressure systems like HVAC or municipal water. 
• Class 300: Commonly used in mid-pressure systems like industrial plants.
• Class 600+: Best for high-pressure conditions, particularly in industries like oil, gas, and chemical processing. 

It’s important to note that higher classes don’t necessarily mean they’re better for your systems. The butterfly valve’s class rating should still align with its actual operating conditions to be effective.   

Understanding Butterfly Valve Specifications

Here is how a specification might look:

Butterfly valve, NPS 10 (DN 250), Class 600, Ductile Iron Body, Nitrile Seat

What this means:

• Size: 10 inches (NPS) / 250 mm (DN)
• Pressure: High-pressure rating (since it states Class 600)
• Body Material: Ductile iron (for strength)
• Seat: Nitrile rubber (which is suited for oil-based fluids)

This is how engineers ensure the butterfly valves meet both system and safety needs. You can now use this to cross-check the size, pressure class, and materials of the valve against the specifications on the spec sheets.  

FAQs

1. Can butterfly valves be used for throttling flow?

Yes, as they can partially open to control flow. However, if you need to throttle with precision, other valve types, such as globe valves, may perform better.

2. How long do butterfly valves last?

Butterfly valves may last 10-20 years, though the exact length will depend on their material, operating conditions, and maintenance.   

3. Are butterfly valves bi-directional?

Most are, but it’s better to confirm in the manufacturer’s data. Some of them might handle flow better in one direction only. 

Get the Right Butterfly Valve for Your Needs

Correctly interpreting butterfly valve specifications is crucial for preventing costly mismatches that can damage your system. Our guide above can help make an informed decision from here on out.
Our company, YOUFUMI, produces lined butterfly valves designed for optimal durability and performance. Contact us today for a quote.