Choosing a control valve style that is perfect for your specific project can be as daunting as settling on the right valve sizing, design, and functionality. The choice -- that is, whether to use ball, globe, butterfly, gate, or check valves, among others -- is commonly based on tradition or the preferences of a specific plant/system.
A good example of this fact is that in most pulp and paper mills, the control valves used are ball or segmented ball valves. On the other hand, petroleum refineries traditionally have relied on globe valves for the majority of their processes, but concerns about emissions have necessitated a shift to rotary valves by some refineries.
In terms of functionality, globe valves are highly acclaimed for offering the widest range of options for pressure, flow, temperature, cavitation, and noise reduction. However, they are more expensive than other valve styles.
Segmented ball valves with a comparable size to their globe valve companions tend to have a higher range-ability and almost double the flow capacity at that same size. They are also cheaper compared to globe valves. However, they have a limited range of options and are hardly available for extreme pressures and temperatures. They are also more likely to have cavitation and noise troubles than globe valves.
An even cheaper option for control valves is butterfly valves, which are less expensive than ball valves, particularly in larger sizes (8 inches and above). However, they offer a lower range-ability than ball valves and are even more prone to noise and cavitation than the latter.
Another control valve style, the eccentric rotary plug valves, takes the key features in rotary valves such as compact construction and high life cycle stem seals and combines them with the jagged construction of a globe valve to create a better product. Eccentric rotary plug valves have a flow capacity equal to that of globe valves, making them different from rotary valves, whose flow capacity is almost double that of globe valves.
Selecting a control valve style is quite subjective. However, if it is not clear what specific valve is required or there is no plant preference, you can use the following approach to choose a control valve style for your application:
• If your valve will be 6 inches or smaller, take note of factors such as temperature, pressure differential, flow characteristic, noise, and cavitation. With these, determine if a segment ball valve will work. If it’s not suitable, use a globe valve.
• If your application requires a valve that is 8 inches or larger, first determine if high-performance butterfly valves will work to save on costs and weight.