I had an interesting meeting recently with Tyco Flow Control’s Jac Rompa. He is one of the Product Managers for Industrial Valves and we got to talking about their various designs and applications.
Now, by simple dint of keeping my ears pinned back over the years, I have learnt how butterfly valves have developed from simple, rubber-lined models suited for say on/of duties in low pressure water lines, through to double-offset and even triple-offset, metal-seated designs suited for much more arduous duties, such as isolation service in tank farms where zero leakage can be permitted.
In short, you can do a lot with a butterfly valve, and Mr Rompa generally finds a receptive audience when he discusses butterfly valve applications with end users.
However, there is one potential use, he says, which for some reason engineers have yet to embrace: using butterfly valves in control applications.
“Oh, don’t get me wrong,” he notes. “I am not for a minute stating that we can throw away all the globe valves and replace them with butterfly models. But there are many instances in which a butterfly valve will deliver the degree of control you need at a very attractive cost.”
The main issue, he explained, is to properly consider the required rangeability.
Now, not having had the benefit of an engineering course I had to look that one up. In fact, I consulted a very nice technical paper, written by one of Mr Rompa’s colleagues, Hans van Lier. In his article The potential of butterfly valves in control applications Mr van Lier states: “Rangeability is the ratio between the minimum and maximum controllable Cv figures. For example, if the Cv(min) is 12 and Cv(max) is 100, the rangeability can be determined as 1:8.”
To put that into some kind of perspective, globe valves might have a rangeability of 1:50, whereas centre-disk butterfly valves typically have a rangeability of 1:15. Triple offset butterfly valves might have a rangeability of say 1:35.
Obviously, rangeability is just one of the factors to be taken into account when looking at control valves, but I did see the point in what Mr Rompa was saying.
He concluded our talk by stating: “my real message is this: there is no such thing as a ‘one size fits all’ solution to flow control. Therefore, I would suggest you take a moment to consider what kind of rangeability you really need. You might well discover that a butterfly valve is an economical solution well worth considering for your control application.”
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