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Last updated on 2024年5月8日

What are the best practices for sizing and selecting control valves?

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Control valves are essential components of any plant engineering system that involves fluid flow. They regulate the pressure, temperature, level, and flow rate of the process fluid according to the desired set point. However, selecting and sizing control valves is not a trivial task. It requires a careful analysis of the process conditions, the valve characteristics, and the control objectives. In this article, you will learn some of the best practices for sizing and selecting control valves that can help you optimize your system performance, reliability, and safety.

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Toni Lozano

Técnico comercial - Instrumentación y Control

1 Process Data

The first step in sizing and selecting control valves is to collect and verify the relevant process data. This includes the fluid properties, such as density, viscosity, vapor pressure, and compressibility, as well as the operating conditions, such as pressure, temperature, flow rate, and rangeability. These data are used to calculate the valve flow coefficient (Cv), which is a measure of the valve capacity under specific conditions. The Cv value determines the size of the valve that can handle the required flow rate with the minimum pressure drop.

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Toni Lozano

Técnico comercial - Instrumentación y Control
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Es importante saber qué queremos regular. Un caudal, un nivel, una temperatura, una presión , etc. En cuanto a las condiciones de proceso es importante conocer la presión de entrada y si esta es fija o variable. También es necesario conocer la pérdida de carga aproximada para que el cálculo sea lo más real posible.

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2 Valve Type

The second step in sizing and selecting control valves is to choose the appropriate valve type based on the process requirements and the control objectives. There are many types of control valves, such as globe, ball, butterfly, plug, and diaphragm valves, each with its own advantages and disadvantages. When selecting a valve type, you should consider the nature of the fluid (liquid, gas, or steam? Clean, corrosive, or abrasive?), the flow characteristics (laminar, turbulent, or critical? Steady or pulsating?), the control action (linear, equal percentage, or quick opening? On-off, throttling, or modulating?), and the installation and maintenance (how much space is available? How easy is it to access and service the valve?).

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Toni Lozano

Técnico comercial - Instrumentación y Control
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También es importante saber si se trata de válvulas auto-accionadas, válvulas neumáticas o eléctricas Dependiendo de la regulación deseada o del tipo de respuesta, estas serán todo/nada, de regulación lineal, isoporcentual o incluso con respuesta parametizable mediante el posicionamiento o mediante la configuración del obturador

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3 Valve Sizing

The third step in sizing and selecting control valves is to perform the valve sizing calculations based on the Cv value and the valve type. The valve sizing calculations involve finding the valve size that can deliver the required flow rate with the minimum pressure drop and the maximum valve authority. The valve authority is the ratio of the pressure drop across the valve to the total pressure drop in the system. A high valve authority means that the valve can control the flow more effectively and accurately. The valve sizing calculations also account for the effects of fluid compressibility, cavitation, flashing, and noise on the valve performance and selection.

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Toni Lozano

Técnico comercial - Instrumentación y Control
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Hay que tener en cuenta las condiciones de trabajo mínimas , normales y máximas a la hora de realizar los cálculos y poder seleccionar el CV más adecuado

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4 Valve Selection

In the fourth step of sizing and selecting control valves, you must select the specific valve model and configuration that meets the process and control specifications. This requires comparing different valve manufacturers and models based on their technical features, such as materials, trim design, actuator type, positioner type, accessories, and certifications. When selecting a valve model and configuration, factors such as compatibility with the process fluid and piping system, durability and reliability under operating conditions, ease of operation and adjustment, availability and cost of spare parts and service, as well as compliance with applicable standards and regulations should all be taken into account.

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5 Valve Testing

The fifth step in sizing and selecting control valves is to test the valve performance and functionality before installation and commissioning. This involves conducting various tests, such as hydrostatic, pneumatic, functional, and calibration tests, to verify that the valve meets the design and quality criteria. The valve testing also provides an opportunity to fine-tune the valve settings, such as the flow characteristic, the stroke, and the response time, to match the process and control requirements.

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6 Valve Monitoring

The sixth and final step in sizing and selecting control valves is to monitor the valve operation and condition during the service life. This involves collecting and analyzing data, such as the valve position, the flow rate, the pressure drop, the temperature, and the vibration, to assess the valve performance and health. The valve monitoring also helps to identify and diagnose any problems, such as leakage, wear, erosion, corrosion, or fouling, that may affect the valve functionality and safety. The valve monitoring also enables to plan and schedule preventive and corrective maintenance activities to ensure the valve reliability and longevity.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are the best practices for sizing and selecting control valves?

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1 Process Data

2 Valve Type

3 Valve Sizing

4 Valve Selection

5 Valve Testing

6 Valve Monitoring

7 Here’s what else to consider

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