In our last article, we discussed why more and more plants are adopting digital valve positioners.
Here, we'll focus on something more practical: once these positioners are in place, what data actually ends up being useful in day-to-day maintenance work.
Years ago, when many of our customers purchased positioners, their main concerns were control accuracy, installation method, and compatibility. But in recent years, we've noticed more and more customers proactively asking a different question:
"What kind of operating data can this positioner provide?"
Rather than waiting to deal with a valve after it fails, more plants now want to spot problems early.
Today's digital valve positioners can deliver a wealth of operating information - valve travel, cycle counts, position deviation, air consumption, and various diagnostic data.
In practice, however, few people sit down and analyze every parameter on a daily basis. What most maintenance personnel really care about comes down to a single question:
Has the operating condition of this valve changed compared to six months ago?
And that is precisely where diagnostic data delivers the most value.
Why do many engineers look at valve travel first?
Valve travel is often one of the first parameters engineers check. What most engineers care about is not the travel number itself, but whether the way the valve moves is still the same as before.
We have come across situations where a valve was still controlling the process properly, with no abnormalities reported by operations, yet maintenance personnel noticed from the data that the valve was no longer moving as smoothly as it once did. Response had slowed slightly, and occasional hesitations appeared during travel.
Individually, these changes are not serious - nowhere near the point of affecting production. But for an experienced maintenance team, they are enough to get attention.
Operators in the control room usually cannot detect such subtle changes because the process parameters remain within normal limits. The diagnostic data, however, may already be telling a different story.
That is why diagnostics are valued - they can often reveal these subtle changes long before an actual failure occurs. For maintenance teams, that kind of early warning is where the real value lies.
Two valves of the same model may not have worked equally hard
Cycle count is another data point that maintenance personnel frequently look at. It may not stand out in the diagnostic interface, but it is highly useful in practice.
Imagine two valves in the same plant. They might be the same model, and might even have been installed during the same turnaround. Judging by their appearance and nameplate information, there is almost no visible difference.
Yet their actual operating conditions could be completely different. One may actuate only a few times a day, while the other may be modulating continuously around the clock. Over a few years, the total amount of work done by these two valves could differ by a factor of dozens.
That is why more maintenance teams now factor cycle counts into their inspection planning. A valve's installed service life is certainly an important reference, but in many cases, the actual workload better reflects the true condition of the equipment.
A valve with a high number of operations does not mean it will definitely fail. But compared with devices with lower action frequencies, it obviously requires focus.
When deviation grows, it matters more than the deviation itself
Position deviation is another indicator that often draws attention.
Small deviations during operation are normal and do not automatically mean something is wrong. What experienced engineers really watch for is whether the deviation is gradually increasing.
Suppose a valve has been able to accurately follow the set position for a long time, but after a few months, the gap between the set value and the actual position begins to slowly increase. The valves still work, the process remains stable, but something has changed.
The cause may be increased internal friction, component wear, or it may be related to the actuator or connecting mechanism.Diagnostic data won't always tell you exactly what's wrong, but it can still flag that this valve needs a closer look.
In many cases, having that kind of alert is already enough.
Air consumption: exposing problems that are not easy to spot
Compared with valve travel and position data, air consumption tends to receive a bit less attention. But experienced technicians usually keep a particularly close eye on it.
The reason is that problems in pneumatic systems rarely appear suddenly.Small leaks, aging seals, and slowly degrading actuator performance usually develop over time. During routine walkdowns, these issues are not easy to catch just by visual inspection. On the surface, everything still looks normal and production keeps running as usual.Yet the air consumption data may be creeping up.
When maintenance personnel notice this trend, they usually conduct further investigation: Is there something abnormal in the actuator? Are there any leaks in the gas system? Does the valve require more actuation than before?
These issues may not be immediately identifiable.But the air consumption data at least helps the team narrow down where to look. For maintenance work, that kind of direction has real practical value. An increase in air consumption does not necessarily mean the valve is about to fail, but most maintenance teams will not ignore such a change.
Trends matter more than individual data points
In our discussions with the industry, we have found that there is sometimes a misunderstanding about diagnostics.
Some people hope that a digital positioner will work like a car's diagnostic system - spitting out a clear fault code that pinpoints exactly what is wrong.
But the reality is that experienced technicians can rarely make accurate judgments based on just one data point.What they pay attention to are trends.
A single instance of slightly higher air consumption may not mean much on its own. A slightly larger position deviation may not warrant immediate action. A subtle change in how a valve moves does not necessarily mean failure is around the corner.
But if these signs start appearing together and show a developing trend over time, the situation becomes different.
That is why historical data is often far more valuable than individual measurements. The more complete the operating records, the easier it is to identify abnormal trends. In a sense, the true role of diagnostics is not to tell you what problem occurred today, but to help you spot what may occur tomorrow.
Customers also often ask us:
"Which data point matters most?"
Honestly, there's no universal answer to that.
A control valve in a critical loop and an on-off valve that only moves a few times a day obviously won't be looked at in the same way.
Some plants put greater emphasis on valve travel and position performance, while others pay more attention to cycle counts and changes in air consumption.
But one thing is becoming increasingly clear: if we go back five or six years, many customers did not even bring up diagnostics during product selection. The situation today is entirely different.
More and more projects are incorporating operating data into maintenance decisions. More and more maintenance teams want to detect abnormalities before a failure occurs, rather than waiting until equipment problems start affecting production.
From the projects we have been involved with, this is one of the key reasons why digital valve positioners continue to draw attention.
For many plants, the value of a digital valve positioner is no longer just about controlling the valve more precisely. What really matters is that it keeps giving useful information during day-to-day operation, helping maintenance teams catch problems earlier.
And that's basically why predictive maintenance is becoming more and more important.
