Control Valves
Control valves are a key component of the instrumentation field but they can also be the least understood part as well. A basic understanding of control valves is essential for an Instrumentation Apprentice. It is expected that you will be able to install valves as well as troubleshoot them as a Instrumentation Journeyman.
Why Do We Use Control Valves?
Control valves are used to regulate the flow of material through a process. As the process calls for more material the valve will open and if it calls for less then the valve will close.
The valve receives this information on when to open or close as a signal from a controller. The controller is in charge of keeping the process as close as possible to its setpoint and it does this by adjusting the valve.
Control valves don’t always have to control flow. They can be used to control many different things such as Level, Temperature, or Pressure.
Fail Open / Fail Close
Understanding a valve’s fail state—fail open or fail closed—is crucial. Imagine placing a valve on your workbench without any air supply. If it remains closed, it’s termed ‘fail closed.’ If it’s open, it’s ‘fail open.’ This state, often referred to as its ‘shelf state,’ determines its default position in the absence of control input.
There are two main types of control valves. There are Throttling valves and there are On/Off valves.
Throttling Valves
What sets throttling valves apart is their ability to modulate. They can be fully opened, fully closed, or anywhere in between, responding dynamically to the controller’s output for precise process control.
For example, let’s say you are controlling the temperature of a tank. This tank needs to stay above 125 degrees F but can’t go over 175 degrees F or else the process inside will go bad. You want a valve that is quick to react and adjust the steam that heats the tank so that the process never drops out of the temperature range.
Your article provides a solid introduction to control valves for Instrumentation Apprentices, covering their importance, operation, and types. Here’s a revised version of your article, aiming for enhanced clarity and readability:
Understanding Control Valves: A Guide for Instrumentation Apprentices
Control valves play a pivotal role in the field of instrumentation, often being a complex element to grasp for many. For those embarking on an Instrumentation Apprenticeship, acquiring a foundational knowledge of control valves is not just beneficial—it’s essential. As you progress to become an Instrumentation Journeyman, the expectation is that you’ll not only install but also troubleshoot these critical components efficiently.
The Purpose of Control Valves
At their core, control valves regulate the flow of materials through a process. When a process demands more material, the valve opens to accommodate this need. Conversely, it closes when less material is required. This adjustment is directed by a signal from a controller, tasked with maintaining the process as close to its setpoint as possible by manipulating the valve.
Interestingly, control valves’ application isn’t limited to flow control. They’re versatile, regulating aspects like Level, Temperature, or Pressure, adapting to the needs of various processes.
Fail Open vs. Fail Closed
Understanding a valve’s fail state—fail open or fail closed—is crucial. Imagine placing a valve on your workbench without any air supply. If it remains closed, it’s termed ‘fail closed.’ If it’s open, it’s ‘fail open.’ This state, often referred to as its ‘shelf state,’ determines its default position in the absence of control input.
Types of Control Valves
Throttling Valves
What sets throttling valves apart is their ability to modulate. They can be fully opened, fully closed, or anywhere in between, responding dynamically to the controller’s output for precise process control.
Consider the scenario of maintaining a tank’s temperature between 125 degrees F and 175 degrees F. A throttling valve can adjust the steam input swiftly to ensure the temperature remains within this critical range, preventing process spoilage.
Common throttling valves include:
- Globe Valve
- Pinch Valve
- Butterfly Valve
- Ball Valve
On/Off Valves
As you may be able to guess from the name of them, On/Off valves are either open or closed. There is no in-between like the Throttling valve. Think of them like a switch. The valve is either on or it is off. They too can be fail open or fail close.
I have seen these kinds of valves work typically with timers. It may be that the valve needs to open every 10 minutes to blow out the moisture build-up in an air dryer. It can also be triggered through a PLC as well. An analyser may need to open up a valve to flush it’s lines to prepare for a new sample.
Types of On/Off Valves
Solenoid Valves
Plug Valves
In our next article we will delve more into the specifics of each kind of valve as well as their components and uses.
