Engeering Horizon

VALVE-SELECTION BEST PRACTICES

VALVE-SELECTION BEST PRACTICES

January 11
17:19 2017

By: Ray Herrera, Valin Corp

 

Precise combinations of valves and other equipment lead to process success. A biopolymer fermentation process provides an example of proper valve selection

In chemical processes requiring automated control, a properly selected valve can make the difference between a mediocre outcome and a top-quality product. Mistakes are often made when selecting the proper equipment for each job function. The decision process of selecting these components requires extensive knowledge and expertise. There are many factors to consider when engineering an automated chemical process, including motion requirements, cost effectiveness and chemical compatibility. In most cases, a precise combination of valves, sensors and other equipment is required to ensure an efficient and successful operation.

Using a biopolymer fermentation process as an illustrative example, this article discusses how specific pairings between valves and surrounding equipment, such as sensors, can increase safety and product quality. Each individual step in the process of fermenting the liquid to create this biopolymer requires a different valve/sensor pairing to ensure the success of the overall process. The article analyzes the process from beginning to end and explains how and why the decisions were made for selecting each individual valve involved.

The benefits of selecting the correct components for a chemical processing application are numerous. The most obvious is the overall quality of the operation. Another important benefit of proper valve selection is the prevention of system damage and process malfunctions. When a valve is required to fulfill an essential process function, but is not properly designed to do so, the results can be catastrophic to the individual valve, as well as the overall process.

Finally, correctly selected valves will enhance the safety, efficiency and reliability of a chemical processing application. Choosing the correct valve will result in the system performing at the peak of its ability for the longest period of time and with the least maintenance requirements (Figure 1). An example process is used to illustrate valve-selection considerations.

 

FIGURE 1. Properly selected valves enhance the safety, efficiency and reliability of a chemical processing application. Correctly selected valves reduce maintenance and promote optimal system function

 

VALVE-SELECTION PROCESS

Before turning to the details of the fermentation process, it is useful to review the general steps to take when selecting a valve for a chemical processing application.

The first step in every situation is to consider the type of application for which the valve will be used and select the most cost-effective option that fulfills the requirements of that particular application. Common application types for chemical-processing valves include the following: frequent versus infrequent operation, process versus drain, firesafe, normally open (N/O), normally closed (N/C), critical service, safety and environment. All other valve selection decisions will be based on the category and specific requirements of the application.

Once the application data are gathered, engineers can move on to examine the details of the application and determine which valve will work best for the particular requirements at the lowest price.

The most common types of valves used in chemical processing operations include the following: ball, butterfly, check, control, diaphragm, float, gate, globe, needle, plug, relief, solenoid, segmented or V-port, Y-pattern and three-way. Each of these valve types has unique characteristics that make it more suitable for some applications than for others. The details of all the valves will be discussed in further depth when we look at their involvement in the fermentation operation.

The valve-selection process involves a series of questions designed to systematically narrow down the possible valve solutions until one particular valve stands out as the ideal choice. First, consider the size required by the application. Ask the following questions:

What is the pipe size at the inlet and outlet of the valve? What is the flow capacity ( Cv)?

The answers to these questions will immediately limit the options of valves depending on the sizes available from the manufacturer.

TEMPERATURE AND PRESSURE

Moving forward with the process, critical consideration are the temperates and pressures to which the valve will be exposed. A few important questions to ask at this point include the following:

  • What is the maximum pressure of the process?
  • Where does the fluid go between the source and the valve (upstream)?
  • Where does the process media go after it leaves the valve (downstream)?
  • What is the maximum fluid temperature?

 

The process fluid’s combined pressure and temperature must be within the manufacturer’s published rating for a given valve. The rating will be unique to a given body shell, valve body and trim-material combination, as well as seal material and end connections. Select a rating that ensures these combinations are sufficient to handle the maximum possible process conditions for temperature and pressure.

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Engineering Horizons

Engineering Horizons

“Engineering Horizons” is the first & leading technical magazine of Pakistan covering Process, Mechanical, Metallurgical, Mining, Electrical & Electronics field under a single cover. We also feel pleasure in saying that this is the only magazine of its own kind & style, which is widely circulated in all Engineering Sectors of Pakistan.

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