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I’ve seen rumblings across a few valve forums about the ability of a butterfly valve to be used as a control valve. Some people say it’s fine to use, others say it’s just a way of cheaping out on the process, that there’s no way a butterfly valve can deliver the control one would need. Who’s right?
To get the answer, I called up one of our Senior Application Engineers for valves, Ralph Lechner.
I explained to him the things I had read, and asked “So when is it appropriate to use a butterfly valve in a control application?” He responded with “It’s always appropriate! A butterfly valve can be used in control applications, BUT… you must first weigh your expectations against the valve’s capabilities in the process conditions set forth.”
Butterfly valves are a great (and less expensive) alternative to globe and other control valves in applications where 1-2% accuracy is acceptable. Process conditions will dictate whether a resilient seated or high performance butterfly valve should be selected.
A resilient seated butterfly valve is the most economical choice. If pressures and temperatures are not extreme, this type of valve should work just fine. If pressure and temperature exceed the limits of a resilient seat, a high performance butterfly valve is necessary.
Other control valves have linear flowing characteristics. A butterfly valve’s design does not allow it to have linear flow characteristics (due to the shape of the disc and its relationship to the pipe), thus making it more difficult to control.
Consider adding instrumentation and a positioner to the valve to help gain more precise control of the valve. Also, make sure operating process conditions are ideal for proper control. Excessive temperatures and high velocities always need to be considered.
Though the butterfly valve isn’t the right choice for processes that require precise control, like mixing paints or food flavors, don’t throw it out of contention. It still has a place in the control valve category. Ralph recommends looking to the butterfly valve first for control applications. It could mean the difference between $100 and $1,000.
Not sure what to select for a control valve? Ask us about it! We gladly provide technical assistance for valve selection to businesses and municipalities in the United States.
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