Each industrial process control application and project has its own special set of requirements and circumstances. Selecting valves to control fluid flow presents the specifier with a huge array of choices for valve type, actuation, construction materials, seals, and more. One method of reducing the number of selection options is to focus on whatever basic type of valve would be best suited for the application at hand. An initial choice of valve type will get you the basic functionality, robustness, and performance you need for the project and allow you to focus on selecting from a substantially reduce field of candidates of the chosen type. Let’s take a look at
butterfly valves.
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Butterfly Valve, Manual Operator
Courtesy Linuo USA |
For fluid flow control, valve type generally refers to the method or structure used to restrict media flow through the valve body. Common types include ball, plug, gate, and butterfly. Butterfly valves have a disc positioned in the fluid flow path within the valve body. The disc rotates on the stem which defines the central axis of the disc. Operation of the stem will rotate the disc through a 90 degree arc, from a position perpendicular to the flow path in the closed position to one that is parallel to the flow direction in the fully open position. The stem extends to the exterior of the valve body, where hand driven or powered actuators control the rotational position of the stem and disc. This valve type, with its simple operating procedure, has attributes that may be evaluated as positives for an application.
Here are a few potential positives:
- Butterfly valves generally are of comparatively small size and weight, due to the closure mechanism arrangement. This can provide cost benefits, along with reduced space and support requirements.
- Low pressure drop in the fully open position is a characteristic of butterfly valves. The disc in the flow path is relatively thin, presenting minimal obstruction to the flow when positioned parallel to the flow direction.
- This valve type has low torque requirements for valve position changes.
- With a 90 degree transit from fully open to closed, rapid operation is possible.
- Butterfly valves can provide limited throttling capability for applications with low pressure drop.
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Butterfly Valve, Electric Actuator
Courtesy Linuo USA |
- Low maintenance requirements, small parts count.
Some other attributes to consider for butterfly valves:
- Cavitation is a possibility under some conditions, especially when throttling.
- Instances of choked flow are possible under certain conditions.
- Throttling capability is generally limited to low pressure drop applications.
- Rapid closing may be disadvantageous, producing physical shock to the piping system.
Applying knowledge and understanding of your process conditions and requirements, in concert with the product and application expertise of a
valve expert, will insure that the valve configuration you specify with provide superior service.
