Sometimes you have to go with the flow. When it comes to fluids, it’s the job of a valve to make things go or stop. But, valves do more than that. They also control flow by regulating pressure, and, importantly for some applications, they prevent backflow. So, how do you go about selecting the right valve for the job?
First, consider the operating conditions. Then take a look at the valve materials and the valve type. Examine all that and you’ll end up with the right valve for a given situation.
As for conditions, you’ll need to start by answering some basics:
- Are you handling a liquid or gas?
- Does it change state? That is, is it a liquid that becomes a gas and vice versa?
- If a liquid, is it only a liquid or does it contain some solids?
- Is it corrosive or explosive?
- What are the operating temperatures and pressures?
- What’s the valve going to do: simple on-off, throttling, or prevent backflow?
- How frequently will the valve be operated?
Valve materials can range from the familiar, like steel or plastic, to the exotic, like refractory metals and ceramics. Unless you have some unusual requirements, such as handling white hot gases or liquids, the materials will be the well-known plastic, bronze, iron or steel.
Since many of these will work for typical operating temperatures and pressures, which of these to pick may come down to corrosion resistance. For instance, if a valve is supposed to last for years in a steamy environment, it’s best if it’s not iron.
OK, what about valve types? (Figure 1 provides examples of Schneider Electric’s current valve offering.)
Well, ball valves, as their name implies, look like balls. Internally, they have a smooth and unobstructed flow path,
so they can handle viscous fluids and slurries. Ball valves are well suited to shut-off applications, cases where flow is either completely on or totally off.
Globe valves, on the other hand, are good for throttling applications. The internal zigs-and-zags of the fluid flow lead to a considerable pressure drop, though. That should be kept in mind if that’s important to your application.
Butterfly valves are useful in throttling applications where a larger valve is needed. A disc sits inside the valve, with this rotated to be either completely blocking flow, minimally impacting it, or somewhere in-between. It’s important when considering a butterfly valve that you look at all materials used in it. The liners, for instance, are important for sealing and so must be able to handle the temperature and pressure.
For most heating, ventilating and air conditioning (HVAC) systems or heating/domestic water applications, either a ball or globe valve will be suitable. Beyond the valve itself, look for such factors as simplicity, efficiency and cost effectiveness of operation. Also, it’s best if the designs are interchangeable. That’s because when a system’s being designed and deployed, it may seem that a simple on-off operation is all that’s needed. But at some point, it may be best to instead have the ability to throttle flow from a maximum to a minimum, adjusting it as desired. If valves are interchangeable, then the switch is as simple as swapping out, say, a gate valve for a ball valve.
So, start with the operating conditions, consider the material and finally take a look at the valve type. Do that, and when you have to go with the flow, you’ll have the right valve for the job.