Moisture in Instrument Air

The cause is higher humidity in the atmosphere during summer.

Do you have a dryer on the outlet just after the compressor?

Do you have a dryer on the inlet of the instrument?

I have encountered this on occasion. Some instruments in the plant were dry while others (due to air pipe routing) were damp therefore we would add a small dryer at the instrument itself.

Free water condenses any time you compress atmospheric air. That free water is normally removed using a coalescing filter with a liquid dump. If you cool the compressed (saturated) air, it will again condense more water. Sometimes a point-of-use coalescing filter is enough. Don't forget that just a tiny amount of free water will freeze hard at -.5 deg C. and shut down your process until you thaw it out.

In industrial plants, one normally will "dry" the air by refrigeration or a variety of desiccant drying techniques, depending upon your volume and adversity to water. Desiccant adsorbs water vapor from air, preventing condensation and freezing at much lower temperatures (such as -40 deg. C, and industry standard). These can be designed by a professional to meet your needs.

If you have a dryer and still see water downstream, either the dryer is malfunctioning, or the coalesing filter has flooded or failed, or your flow rate has greatly exceeded the filter/dryer design flow rate at some time.

These guys can help: www.instrumentair.com

It usually indicates the air dryer isn't working. Beware of water in instrument air lines. It is a portent of doom for anything in pneumatically-operated equipment that water can corrode and an early indicator of impending mechanical failure, leading to process problems.

In high-end manufacturing facilities, typically -40degC dewpoint instrument air can be found, indicating its high dryness.

This sounds very worrying - summer increases the water load in two ways.

Higher temperatures mean the Max Absolute Humidity (water carrying potential) increases

Depending on your location relative humidity increases.

These two effects increase the water load in atmospheric air significantly

I assume you compress and cool the air to a standard temperature irrespective of season which will have a constant humidity. This means that more water needs tbe removed in summer.

The fact that water is found in the system screams a warning your instrument air system is not working properly. I work in the oil/gas/chemical industry and air is dried as mentioned above to -40°C and the vendor has to guarantee performance under the worst humidity conditions to guarantee that there can never be water in the system.

Water in instrument air lines is a problem with corrosion; two phase flow potentially fast moving slugs that act like projectiles; just the weight of water on impulse lines and probably a whole load of other issues.

Do you have a drier on the system or is the air just compressed and cooled and any water knocked out in water trap or KO Vessel. It is worrying that the attitude seems to be oh that happens. Water while essential for life is dangerous in the wrong hands or situation

The explanations of why the moisture is there were spot-on. One thing I would like to add is that any instrument that relies on a throttling action to control a pressure will also be damaged by the corrosion that accompanies the moisture. Also, the small pieces of corroded material will not allow units such as pressure regulators to properly seat and this will result in the 'regulated' pressure slowly creeping towards the value of the supply pressure.

The atmospheric moisture content tends to be higher during summer months. All pneumatic control and instrumentation systems should have a refrigerated drier device in the main air piping from the receiver. It's needed winter and summer. Lou Bindner