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How Come Control Valves Are Smaller Than Line Size

valve size and line size

Control valves are an essential part of any piping system, yet they are often smaller than the line size they are connected to. This is because smaller valves can better regulate flow rate, take up less space, and have lower pressure drops when open. By using control valves that are smaller than the line size, it makes it possible to achieve exact flow control, save on space, and reduce turbulence. All these advantages make using control valves smaller than pipelines an ideal solution for many industrial applications.

In the industrial process, you may have noticed that the size of flow control valves is often smaller than the size of the pipe they are connected to. This is in contrast to on/off valves, which are typically the same size as the pipe. The purpose of this article is to explain why this is often the case. We will discuss how the size of the control valve affects the flow rate, how it affects the overall pressure of the system, and why it is often beneficial to use a smaller control valve than the size of the pipe.

Why Flow Control Valves Smaller Than Line Size?

  • Controlling Pressure Drop

Control valves are crucial components in many industrial systems, as they control the pressure drop across the system. To ensure efficient operation, selecting the right size of a control valve concerning the pipe diameter is vital, as this will determine the amount of pressure drop generated. By setting smaller control valves than the pipe diameter, more significant pressure drops can be developed to fulfill system requirements.

  • Market Competition

To ensure optimal control performance of a control valve, selection, and calculation must consider factors beyond just pressure drop or the control of flow rate, temperature, and other essential parameters. In this regard, market competition and pricing must be considered as they directly influence the quality of the product and its professionalism. We must always remember this when selecting the suitable valve for the job.

However, by taking advantage of the pressure reduction needs and selecting a control valve size one or two sizes smaller than the pipe size, the overall cost can be reduced without regard for cavitation, noise, or cavitation phenomenon. This will increase the probability of obtaining the order and lessen the bidding process time.

  • Steam or Gas Service

When it comes to steam or gas service, proper sizing of control valves is essential to ensure that excessive release of gas into low-pressure downstream systems is avoided in the event of a valve failure. This, in turn, helps avoid unnecessarily large relief valves, tank vents, and flare system sizes. To ensure the proper sizing, drawings, and systems or connection systems should be consulted, often located some distance from the valve.

  • Control Valve Sizing

In the past, engineering designs that attempted to reduce manufacturing costs often employed crude and dangerous methods, such as reducing the size of control valves. This can lead to a higher pressure drop across the control valve, making its control action more sensitive and perpetuating a low-cost design. Such approaches are no longer acceptable, and modern engineering designs should always prioritize safety and quality above cost.

 By making the control valve one or two sizes smaller than the pipe, you can achieve improved accuracy in the control flow due to the smaller diameter and narrower control range while allocating around 30% of the system pressure drop to the control valve. This allows for better control of the flow rate and improved overall system efficiency.

Simply put, a smaller flow area provides greater control accuracy, especially for applications requiring precise micro-flow regulation. On the other hand, control valves that are too large can be overly sensitive; even small changes in valve position can cause significant variations in flow, making control difficult.

  • Smaller Valves Take Up Less Space

Smaller valves can save you space! Control valves with smaller pipe sizes will naturally take up less installation space than those with the same pipe size, especially for large pipelines with diameters over DN100. The larger the bore, the larger the actuator, which directly affects the space reserved for installation in the piping system. Installing a control valve with a smaller pipe size can help you save valuable space.

  • Lifespan

The service life of control valves is critical for ensuring reliable and efficient process control loops. If you select an oversized control valve, not only will you experience poor control performance, but the valve will also suffer from a shorter service life due to its limited operation at or below 30% of its maximum opening. By selecting the correct size valve for your applications, you can ensure that it operates between 30-80% of its travel, maximizing its service life and performance.

BCST Control Valves

At BCST, we understand that an unfit control valve can significantly impact your budget, both in terms of capital expenditure and operating cost. Worse yet, it can lead to unscheduled shutdowns, which cost you even more. That’s why we provide control valve calculation and sizing services explicitly tailored to your project’s needs. With our expertise and customization options, you can ensure that your valves are optimized for maximum efficiency and the lowest cost. Contact us today to learn more about our control valve services!

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