Depending on inlet conditions, air compressors can produce lots of water. If this water is not removed, it can travel through your piping and overwhelm your air dryer (if you have one). The water will rust steel pipes, and act as a solvent for compressor lubricant. The water picks up the rust, oil, and dirt in your piping—and washes it downstream to clog your pneumatic components or even worse, get all over your product. This can be a major concern in industries producing food.

Where does this water come from? It is in your ambient air! A characteristic of compressed air is that it can’t contain the same amount of water vapor as the ambient air if it is compressed to a smaller volume and cooled. The water is squeezed out of the air just like squeezing a sponge. On a warm humid summer day, say 80° F, a fully loaded 75-hp compressor will produce about 23 gal of condensed water in an 8 hour shift. Another 4 gal will come out of the air dryer.

Compressors usually contain water separators that remove free water from the air stream, but the air coming out of a compressor is generally warmer than the ambient conditions. As the saturated warm discharge air cools in your pipes, it will release some of its water to condensate—and you will get water in your pipes.

This is why air dryers are used for compressed air system, the simplest ones being refrigerated dryers that cool the discharge air down to about 35°, then remove the condensed water. When this air exits the dryer, its dew point is much lower than the ambient temperature, so no water forms unless the pipes cool all the way down to 35° F. If you have special requirements, such as the need to run the air outside in freezing temperatures, you will need a desiccant dryer. These produce dew points of -40°.

If you have an air dryer but you are still getting water in your air, here are some common things you should check:

• A quick way to assess if a refrigerated dryer refrigeration system is working at all is to feel for a temperature difference between inlet and outlet, or shoot temperatures with an IR gun. No difference, then call for service.
• Check the dryer bypass valve, did some dummy forget to close it?
• Check the inlet temperatures, if the level is higher than the dryer rating, usually 100° F (it should be on the nameplate), then the dryer may be overloaded. Every 20° F rise in air temperature doubles the amount of water vapor in the air; some dryers simply can’t handle the extra water.
• Check to ensure the drains on the compressor water separator and dryer water separator are working. If they are not, then all that water must go through your dryer, and it is not designed to process free water.
• If you have a desiccant dryer, then check to ensure the purge exhaust mufflers are not plugged.

If you are still having problems, then it is time to call in an expert. Phone your service provider and have your system checked out.