To correctly understand water problems in compressed air systems, it is important to understand why moisture in the air turns into liquid water. Once you understand condensation, it becomes easier to see why water can still appear even after an air dryer.
Key Points
- Air naturally contains water vapor.
- Compression and cooling make water vapor more likely to become liquid water.
- Even after a dryer, re-condensation can occur due to temperature differences and piping conditions.
- Condensation countermeasures should be considered based on where condensation actually occurs.
The basic mechanism of condensation in compressed air
The air around us always contains invisible water vapor. A compressor takes in this air, compresses it, and sends it to equipment in the factory.
In other words, compressed air contains the source of moisture from the very beginning.
When air is compressed, the density of moisture contained in a given volume increases. After that, when the compressed air cools down, the moisture that can no longer remain as water vapor appears as liquid water. This is condensation.
In the field, it may look as if water suddenly appeared. In many cases, however, it is the result of compressed air cooling down.
Point: Condensation is not necessarily an abnormal event. It is a phenomenon that can structurally occur when air is compressed and used.
Why condensation can occur even after installing a dryer
A very common question is: “Why does water still appear even though we have installed a dryer?” The important point is that a dryer is not an all-in-one solution. It is a device that conditions the air on the upstream side.
Even once air has been dried, it can condense again if the temperature drops later in the piping or just before the equipment.
Re-condensation is especially likely under the following conditions.
Long piping
The longer the piping distance, the more easily the air is affected by ambient temperature.
Large temperature differences
Sites with large day-night, seasonal, or indoor-outdoor temperature differences are more likely to experience re-condensation.
Many branches or stagnant sections
In areas where air flow is unstable, water droplets may remain more easily.
Cooling just before equipment
Even in the final short section before equipment, droplets may form depending on the conditions.
For this reason, it is not enough to judge water trouble only by whether a dryer exists. It is necessary to look at the air condition just before it is used.
It is important to see where condensation occurs
A common mistake in condensation countermeasures is thinking, “We installed equipment on the compressor side, so everything should be fine.” In reality, the location where trouble occurs and the location where treatment is installed are often different.
| Location | What tends to happen |
|---|---|
| Immediately after the compressor | The moisture load increases due to compression. |
| After the dryer or upstream treatment | Even if the air is once conditioned, it can change again depending on the downstream piping conditions. |
| In long piping | Re-condensation can occur due to ambient temperature and surrounding conditions. |
| Just before equipment | Liquid droplets may flow directly into equipment and cause trouble. |
Many field problems occur because droplets have formed just before the equipment.
In other words, it is important not only to understand the phenomenon of condensation itself, but also to identify where it becomes a liquid droplet problem.
Common countermeasures and how to think about them
There are various countermeasures for condensation, such as refrigerated dryers, desiccant dryers, drain traps, and line filters. Each has its own role, but no single method can solve every problem by itself.
Dryers
Dryers are important for conditioning upstream air quality, but they may not prevent re-condensation that occurs later.
Drain traps
Drain traps are effective for discharging generated water, but they cannot always handle every location reliably.
Line filters
Line filters are effective for downstream protection, but replacement and clogging management are required.
Point-of-use countermeasures
By treating droplets near the point of use, countermeasures can be applied closer to where actual trouble occurs.
Basic concept: Condition the air as much as possible upstream, then also check the condition near the point of use. This viewpoint is important for preventing condensation trouble from recurring.
Checkpoints when considering condensation problems
If water problems are occurring in the field, it is useful to organize the situation before immediately selecting equipment.
1. Where is water found?
Separate whether it is found immediately after the compressor, in the piping, or just before equipment.
2. Condition of existing equipment
Check whether the dryer, drain traps, and filters are functioning properly.
3. Temperature differences
Check conditions with large temperature changes, such as outdoor piping, nighttime shutdowns, and morning startup.
4. Equipment to protect
Clarify the purpose, such as preventing defects, protecting solenoid valves, or protecting cylinders.
Related articles
If you want to understand this from a field-trouble viewpoint
If you understand the theory but want to know why water still does not stop in actual facilities, this article may also be helpful.
If you want to review the basic concept
We provide materials that summarize the causes of compressed air trouble, countermeasure concepts, and the mechanism of WELL AIR.
Because condensation is difficult to avoid completely, where you apply countermeasures is important
Condensation in compressed air cannot be judged only by whether a dryer is installed. It is important to consider role-sharing between upstream treatment and point-of-use protection according to actual site conditions.
- You want to identify where condensation is occurring
- You want to review your existing dryer and filter configuration
- You want to consider moisture countermeasures just before equipment
This article provides general information about condensation and moisture problems in compressed air systems used in manufacturing sites. When selecting or installing equipment, please confirm air flow, piping conditions, temperature environment, and existing system configuration.