Control Valve Technology. How Do I Choose?

Control Valve Technology: How Do I Choose?

According to an article from Expert Valve Selection's website, "Selecting a control valve requires an understanding of the process conditions, including temperature, pressure, flow rate, and the physical and chemical properties of the fluid." So, how does one navigate the plethora of options and make an informed decision?

For instance, the first question to consider is, "How accurate does the control need to be?" While it might seem the accuracy should always be high, it really depends on the specific process needs. The required level of accuracy has a direct correlation with the cost, so it’s essential to find a balance.

As control packages become more precise and their response times increase, costs typically rise. There are cases where more expensive control packages are used than necessary, or conversely, where less expensive packages fail to meet the needed requirements. Therefore, understanding the process demands is crucial for making the best choice.

The Available Options

Globe Valves

Globe valves are known for their durability and variety in severe service options. They feature replaceable trim sizes, making them adaptable to changing capacity requirements. However, they can struggle with suspended solids, are heavy, and often the most expensive for a given size.

Quarter-Turn or Rotary Valves

Rotary valves, including butterfly, ball, segment, or eccentric plug valves, have become more common. Thanks to advancements in materials and design, these valves now fit into a broader range of applications. They are typically smaller and lighter, making them easier to accommodate within tight spaces.

Temperature, Pressure, and Steam

Temperature Considerations

If temperature requirements are moderate, soft-seated rotary valves will suffice. For temperatures exceeding 400°F, metal-seated valves become necessary, increasing costs. Temperatures around 800°F generally call for a globe control valve.

Pressure Considerations

Rotary valves can handle high-pressure conditions but tend to generate more noise and are prone to cavitation under high differential pressures. Proper sizing and noise calculations are essential. Conversely, globe valves are easier to find for high-pressure applications and offer better noise and cavitation control.

Steam Applications

Steam can cause significant erosion. Basic rotary valves perform well with air and water, but steam often requires specially designed severe-service rotary valves. High-performance butterfly valves can be effective and cost-efficient in low to medium pressure drop applications, while high differential applications may necessitate expensive globe valves.

Control Requirements

Precision Needed

Owners must determine how precise control needs to be. For example, a water temperature control system can utilize a ball valve if precision is not critical, saving costs over a more accurate three-way globe control valve.

Rangeability

Rangeability, the difference between the lowest and highest flow, varies among valve types. Globe valves can control flow from 5% to 90%, offering significant rangeability. Butterfly valves, on the other hand, should not operate below 10% or above 70% open. Segmented ball valves offer a broader rangeability similar to globe valves but at a lower cost.

Cost Considerations

Price plays a significant role in the decision process. Ball valves become pricier as size increases, but at small sizes, they may be comparable to high-performance butterfly valves. For larger sizes, butterfly valves are generally more cost-effective. Globe control valves can be three to four times more expensive than butterfly valves, impacting total cost of ownership (TCO).

Selecting the Right Valve

Ultimately, the choice should be application-driven. Globe control valves are indispensable for high-temperature and high-pressure-drop applications. However, if a rotary valve meets the conditions, it should be considered for its cost efficiency and adequate performance.

For more information, please visit our website.

Best Flow Control Valve for Your Needs

Flow control valves can serve multiple functions within a hydraulic system, such as regulating motor speed or cylinder pressure. They are crucial in sectors from material handling to food processing, thanks to their versatility and reliability.

Gate Valves

Primarily used for on/off service, gate valves are suitable for applications requiring minimal restrictions. They perform well under specific temperature and pressure conditions.

Globe Valves

Used for on/off and throttling applications, globe valves provide reliable flow control although they induce higher pressure drops compared to other valve types.

Butterfly Valves

Affordable and less precise, these valves suit applications that do not need high accuracy.

Plug Valves

Often used in flow control, plug valves come in various designs, the most common being the eccentric plug valve that offers excellent shut-off capabilities.

Ball Valves

Popular for their low cost and durability, ball valves are suitable for applications where fine-flow adjustments aren't critical.