Industrial process control valves & piping components

Automated Control Valves: Selecting The Right One

When it comes to automated control valves, the most important thing to know is that they play a very important role in the regulation of fluid pressure or liquid flow. They act in response to independent signals generated by flow meters and other such devices.

Of course, there are different types of control valves.

The three main types of automation are

  • Electric
  • Hydraulic
  • Pneumatic

Electrical control valves operate on electricity. Hydraulic respond to mechanical signals caused by the pressure of fluid upon their parts. And pneumatic valves convert energy and into mechanical pressure.

Types Of Automated Control Valve Bodies

Control valve bodies are generally angled or globe-style. However, there are other types of bodies. They can also consist of pistons, diaphragms, rotaries, sliding cylinders, and air operated parts. The main parts of most automated control valves are the actuator and positioner. Control valves may include:

  • Pressure-reducing valves
  • Flow control valves
  • Back-pressure sustaining valves
  • Altitude valves
  • Relief valves

How To Select The Right Automated Control Valve

To pick the right automated control valve you have to start with the type of valve you need. After that, you should determine the size of the valve necessary to fit your components. You should also take note of the individual characteristics of your particular valve system so that you understand the relationship between your control valve and how flow is processed in your machine.

In determining the characteristics of your control valve, check the percentage of change in your control signal versus the change in the flow of liquid through the valve. The ratio of these two measurements determine your valve's gain, which is expressed as either linear, quick opening, or equal percentage.

Next, you'll need to measure the distortion of your valve characteristics.

You'll also want to measure the rangeability of your valve, which is the ratio between the maximum and the minimum controllable flow. It's important that you realize this does not mean when the valve is closed. We're talking about minimum controllable flow.

The most important characteristics of automated control valves are gain and stability. The gain is figured by dividing output by input. A linear valve has a constant gain. You'll want to note whether you have a quick opening, linear, or equal percentage valve.

What Is A Slurry Valve?

There is no perfect slurry valve. Ideally, you want a valve that is open and provides full pipeline opening. It should provide a streamlined flow path when throttling and have high pressure and temperature ratings. You'll also want to ensure it is self-draining and is available with corrosion-resistant materials. Finally, you'll want to make sure the actuator stem is sealed from the flow process.

Slurry valves can come as pinch valves or weir-type diaphragm valves. They have similar features, but for corrosion-resistance, you should use diaphragm valves. Pinch valves are recommended for low pressure.

If the process pressure is high and the valve drop low, then you should use lined butterfly valves.

For any type of slurry valve, and there are more types, you'll want to pay close attention to the size of the orifice, size of the particle, and rangeability. Small and constant valves are best for optimal rangeability. For the best particle and orifice size fit, ensure you shape the valve to the minimum opening where plugging will occur.

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