When dealing with compressed air systems, you’ve likely heard the term “dew point. When working with compressed air systems, you’ve probably heard the word “dew point” in maintenance meetings, equipment manuals, or with your instrumentation supplier. If you’re like many plant managers and maintenance engineers, however, you may be asking yourself: Why is one number so important?
The short answer is that dew point monitoring is among the most underutilized and most important components of a compressed air system, helping ensure efficient operation, prevent damage to expensive equipment, and avoid costly downtime. Get it wrong, and you’ve got corrosion, contamination, product quality problems, and rework that could have been avoided with the right sensor and proper maintenance practices.
Let’s now look into the meaning of dew point, the importance of proper dew point control in compressed air systems, and how to monitor it properly to ensure long-term reliability of your system.
What Is Dew Point, Exactly?
First, let’s get a bit more specific about what we’re discussing before we go on and explain why it matters.
Dew point is the temperature at which the air can no longer hold the water vapor, and the water vapor starts to condense into liquid water. Simply put, it is the temperature at which water vapor in the air condenses into liquid water.
This is important in a compressed air system because moisture is always present. As this air is compressed, the moisture is condensed. The dew point temperature of the compressed air will also influence whether condensation occurs within the system if it travels through pipework, tanks, or downstream equipment whose temperature is lower than the compressed air’s dew point.
You’ll encounter two types of dew point measurement:
- Pressure Dew Point (PDP): Dew point temperature at the system pressure; the standard pressure for compressed air applications.
- Atmospheric Dew Point (ADP): Dew point of air at atmospheric pressure, used as a reference.
The first step to getting dew point monitoring right is knowing which dew point your equipment reports and which your process requires.
Why Dew Point Monitoring Matters So Much
It is easy to consider compressed air as “just air”. However, in most industrial applications, compressed air is a utility, akin to electricity or water, and moisture is its enemy.
There’s a reason why it’s no longer adequate to ignore dew point if you want a system that will last.
1. Corrosion Protection
Over time, moisture in pipework, valves, and tanks causes internal rusting and corrosion. Corrosion can be a cosmetic problem, but it can also lead to loss of strength in parts, particulates entering the air stream, and ultimately to a total failure of equipment. When properly maintained, a dew point sensor will alert you to the onset of moisture accumulation in the structure long before it becomes a structural issue.
2. Protecting Sensitive Equipment
Compressed air is used in a number of industries for producing a wide range of “moisture-sensitive” pneumatic tools, control systems, and instrumentation. Any condensation can cause pneumatic valves to stick, sensors to malfunction, or actuators to fail prematurely. When you are using compressed air for precision equipment, dew point control is not an option; it’s a necessity.
3. Product Quality and Contamination Control
Compressed air can come into direct or indirect contact with products in various manufacturing processes, including those in the food and beverage, pharmaceutical, and electronics industries. Too much moisture may lead to microbial growth, powder clumping, and damage to moisture-sensitive parts during assembly. In these industries, regulatory standards frequently are based on the maximum allowable dew point.
4. Energy Efficiency
Many facilities don’t know this: dew point monitoring can save you money. Many compressed air dryers are fixed-cycle, wasting energy by operating cycles that are unnecessary for the moisture load. Real-time dew point monitoring systems can control the dryer’s performance based on conditions, thus reducing unnecessary energy consumption and ensuring air quality meets specified requirements.
5. Avoiding Costly Downtime
Downtime from moisture-induced failures is costly, not only for repairs but also for lost production time. Consistent monitoring also means you identify issues early, plan maintenance in advance, and avoid emergencies that can disrupt your entire production process.
Common Signs Your Compressed Air System Has a Moisture Problem
If you don’t have a complete monitoring system, there are some indicators that your dew point may be excessive:
- Pooling in air lines, filters, or drain traps.
- Rust inside pipework, or on fittings, is a sign of this.
- Pneumatic tools or valves are sticking and/or operating irregularly.
- More often, filter changes
- In moisture-sensitive processes, product defects are not explained.
- A lack of fresh air or a “musty, damp odor” near air outlets.
If you hear any of these, it is best to examine your existing dew point readings or get the right monitoring if you do not have it.
How to Measure Dew Point Correctly
Accurate dew point measurements are not simply a matter of attaching a sensor to the system and calling it a day. The type of sensor, its location, and the accuracy of the calibration determine the accuracy of the measurement; if any of these are incorrect, you’ll have false confidence in the air quality that isn’t there.
Types of Dew Point Sensors
In industrial compressed air applications, there are a few common sensor technologies used in the measurement of dew point:
- Chilled Mirror Hygrometers
These are the most accurate available. They operate by cooling a mirrored surface just until condensation starts, then measuring the exact temperature at which this occurs. They’re very accurate, but can be costly and more difficult to maintain than other options.
- Capacitive Polymer Sensors
In these sensors, the polymer film’s capacitance varies with the amount of moisture absorbed. They are very useful in industrial applications because of their durability, relatively low maintenance requirements, and ability to provide reliable, continuous measurements over a wide range of dew points.
These work in the same way as capacitive sensors, but with an oxide layer rather than a polymer. They typically perform well in very dry conditions and are frequently employed in applications with very low dew points.
Depending on your application, budget, and desired accuracy, each sensor type offers advantages, making it crucial to work with an instrumentation partner with the expertise to help you select the right sensor for your needs.
Where to Install Dew Point Sensors
The type of sensor is as important as the placement. Typical installation locations are:
- Before the receiver tank, after the dryer, to ensure that the dryer is operating properly.
- In areas at critical points of use, particularly where moisture-sensitive equipment or processes are located
- For facilities that have long pipe runs or multiple branch lines, at multiple points across a distributed system
You can tell how well your dryer is working by reading a single sensor at the dryer outlet, but you can’t tell what is going on by the time it reaches a sensitive tool three hundred feet away. If the system is larger or more complex, multiple monitoring points will provide you with a much better understanding of what is really going on in your compressed air network.
Calibration and Maintenance
Even the best sensor will drift over time if it isn’t properly maintained. Calibrating regularly against a traceable reference standard will help keep your readings accurate. Most manufacturers recommend calibration checks every 6 months to annually, depending on the type of sensor and operating conditions.
Monitoring sensor housings and filters is also important, as dust, oil vapors, or particulate buildup may compromise sensor response time and accuracy.
Best Practices for Effective Dew Point Monitoring
Realize that to derive real and lasting value from your monitoring, you should follow the following best practices:
- Pair sensors with the application. If you need tighter tolerances, you should not go for the lowest price. Use a sensor range and accuracy that is appropriate for your equipment and/or industry requirements.
- Check regularly, rather than at regular intervals. Transient issues may go undetected during spot checks. Rather than waiting for issues to become problems, continuous monitoring detects them before they do.
- Determine alarm limits. Set up your system to notify maintenance staff when the dew point approaches the limits, and prevent problems before they start.
- Make time series observations. By monitoring dew point data over time, you can identify gradual degradation of the dryer before a complete failure.
- Connect to the rest of your control system. Incorporate dew point data into your building management or SCADA system where possible so you have a single source of information and can respond more quickly.
- Work with a trusted instrumentation supplier. The right partner will not only sell you a sensor but also help you choose the right technology, placement, and maintenance schedule for your system.
Choosing the Right Partner for Dew Point Instrumentation
When it comes to how much is at stake when it comes to accurate dew point measurement, equipment longevity, product quality, energy costs, and system uptime, the instrumentation you choose, and who you choose to source it from, make all the difference.
That’s why a knowledgeable distributor is beneficial. A knowledgeable partner can guide you through the trade-offs, explain calibration needs, and be there to assist you after installation, rather than trying to guess what sensor technologies might be suitable for your application.
Conclusion
Dew point may appear trivial in a spec sheet, but it is one of the most significant indicators of the true health of your compressed air system. Dew point monitoring can have an impact on almost any aspect of your operation that uses compressed air, from corrosion and damage to equipment to product quality and the elimination of unnecessary energy costs.
Thankfully, it’s not hard to get right. If you have the right sensor technology, sensor placement, regular sensor calibration, and a partner well-versed in your specific application, you will be able to maintain your compressed air system clean, dry, and reliable for years to come.
Ready to get your compressed air system’s moisture levels under control? With decades of technical experience, JLC International offers a suite of precision dew-point measurement and compressed-air monitoring solutions. Contact JLC International today to find the ideal sensor solution for your facility and ensure your compressed air system operates from the inside out.