MRO Magazine

15 Rules for Condensation

here are very few things that can cause more trouble than the condensation that accumulates in compressed air systems. Here are 15 important tips to help reduce the problem.

September 1, 2004 | By Dan Wise

here are very few things that can cause more trouble than the condensation that accumulates in compressed air systems. Here are 15 important tips to help reduce the problem.

Rule 1: Never under estimate the damage that can be caused by condensation.

An inconsistent supply of dry air will cause production problems. For example, the moisture will wash away the lubrication from air tools and cause erratic performance, downtime and the need for maintenance.

The presence of water will lead to the formation of rust and scale in the air piping system. This solid contamination will foul equipment.


Your air dryers and inline filtration products will not perform if they become overloaded with liquid contamination. Also, water can back up into the compressor and wreck machinery.

Rule 2: Remember that the volume of condensation in a system will vary with changes in weather conditions. This is because the amount of moisture in the air being compressed is determined by the temperature and relative humidity of the inlet air that enters the compressor.

A 200-hp compressor operating in a climate of 60F with 40% relative humidity will generate approximately 50 gallons of condensate a day. However, that same compressor operating in a climate of 90F with 70% relative humidity will generate approximately 260 gallons of condensate a day.

Rule 3: Always slope or pitch the pipe in the main air header and in the branch air lines downward at least 1 inch per 10 feet of pipe, in the direction of the air flow. This will allow condensation to collect at the low points, where it can be trapped and drained from the compressed air system.

Rule 4: Always install a valve in the line ahead of your condensation drains. This gives you a way to make sure the drain is working, and it makes it easier to do maintenance on the drain.

Rule 5: Avoid using a blind discharge, like a line made of solid pipe, on your drains. This will make it impossible to observe if your drains are working.

Rule 6: Always take the air from the top of an air pipe when running a line to the point of air usage (this line is called a drop leg). This makes it difficult for the condensation to migrate to the equipment that is using the compressed air.

Rule 7: Never take the air directly from the bottom of a drop leg. The air outlet should be positioned on the side of the drop leg, rather than the bottom. This is done so that any condensation that is carried from the main line or is formed in the drop leg will collect below the connection for the air usage.

Rule 8: Always install drip legs in the pipe distribution system. A drip leg is a pipe that extends downward from the bottom of an air line to collect the condensation flow in the air piping.

Drip legs should be at all low points in the air line, and at any point where the air line dips to go around an obstruction. Also, a drip line should be located at any place where the air piping is coming into a building from outdoors.

Rule 9: Stainless steel is the best choice for the air piping on a system that uses non-lubricated compressors as the exclusive supply of compressed air. Although oil carryover from compressors is not desired, it does lessen the corrosive impact on an air system that uses the traditional black iron pipe. The absence of oil carryover in a non-lubed system will make the condensation mixture too aggressive for the typical black iron pipe that is found in most air systems.

Rule 10: The disposal of the condensation you remove from the system will be an environmental issue if you have lubricated compressors. Oil carryover will be unavoidable if you have compressors that use oil in the compression chamber. The lubricant will mix with the condensation and create an oily water that must be properly handled to avoid violating environmental regulations.

You have two basic options. The first is to collect the oily water and pay a company to dispose of the waste. The second option is to buy a product to treat the oily water mixture. This is a sensitive subject and you would be well served to get advice from an expert on this topic.

Rules about drains

There are several types of drains that are being used to remove the condensation from compressed air systems. Some of these products have specific issues that demand attention.

The following gives you some background on the shortcomings of the main types of drains.

Manual drains: A manual drain is a ball or gate valve that is installed at a drain point in the air system. These valves have to be opened manually to dump the condensation. This leads to the next rule.

Rule 11: Avoid leaving manual valves partly open to constantly drain the condensation. This is tempting to do on drain points that have a high volume of condensation, such as the aftercooler separator and the air receiver tank.

Leaving the valve open will eliminate the need for continued attention, and it will be effective at getting the condensation out the system. However, this creates an obvious compressed air leak, and even a small continual leak will waste several hundred dollars in annual energy cost.

It should be noted that the compressor controls will respond to the loss of air by loading the compressor to fill what is really an artificial demand for compressed air when a continual leak is left in the system. This will waste energy, and shorten the service life of the compressors.

Rule 12: Map out the drain locations on your entire system to avoid forgetting about manual drains on remote or low-volume drain points. This might include inline filter drains that are located high in the air piping, and drip lines on the outer reaches of the pipe distribution system.

Float-operated drains: These drains use a float mechanism in a housing to control the valve that dumps the condensation. The float will rise as condensation accumulates in the housing. Then, at a preset point, the outlet valve will open to automatically drain the condensation. This accounts for the next rule.

Rule 13: Remember to clean the housing and the float mechanism on a regular basis. The moving parts of this drain are always in contact with the condensation. This liquid will be contaminated by dirt, rust, pipe scale and oil from the carryover on lubricated compressors. This mixture will cause the float mechanism to malfunction.

The float will jam, either in the open or closed position. You will be able to hear the air leak if the float becomes stuck in the open position. However, you may not realize that there is a problem if the float sticks in the closed position — until liquids begin to back up into the system.

Timer drains: These drains have an electronic timer that activates a valve to dump the condensation. These drains are inexpensive and popular because many vendors that make and package air equipment will include timer drains with their products.

You can adjust the drain cycles by setting the number of cycles per hour and the length of time the valve will stay open during each cycle. The theory is to set the timer for a long enough period to completely drain the condensation without setting it long enough to waste compressed air.

The problem is that the amount of condensation will vary according to changes in the temperatures and relative humidity of the ambient environment. This means that the settings will have to be adjusted to compensate for climate and seasonal changes. The next rule now applies.

Rule 14: Take the time to change the settings on your timer drains to match the changes in the temperature and humidity. Avoid the temptation of using settings that will keep the valve open longer than necessary. This approach may get the condensation out of the system, but it sets up an automatic leak point for compressed air.

As mentioned previously, the compressor controls will respond to the loss of air by loading the compressor to fill what is really an artificial demand for compressed air when a continual leak is left in the system. This will waste energy, and
shorten the service life of the compressors.

Electronic sensor drains: These drains are often called “zero air loss” drains. They have electronic sensors that monitor the level of condensation within a housing. Electronic drains are typically the most expensive type, with prices ranging from $800 to $1,000 for the brand names.

One sensor opens the outlet valve to dump the condensation when the housing registers as being full. Another sensor will close the outlet valve before completely draining the condensate to avoid wasting air. However, the next rule should be applied.

Rule 15: Clean the sensors and the housing of an electronic drain on a regular schedule. The sensing devices are in constant contact with the contaminants found in compressor condensation. This will foul the sensors and reduce the reliability of the drain.


Water in a compressed air system is a nuisance that causes downtime and maintenance. The rules in this article will help you effectively remove the condensation from your compressed air system.

However, your choice of drain will affect the reliability of the draining process. It pays to consider how technology can improve your system.

This article was provided by Dan Wise, the webmaster for If you would like to receive a report on electronic drains, send a note by e-mail to


Stories continue below

Print this page