Compressed air systems are best designed to be resilient to system upsets. It is not uncommon for a slug of water and oil to make its way down a line. If that slug makes it to your equipment you’re in for downtime and unscheduled maintenance. Depending on the equipment, you’ll want to install coalescing filtration and in some cases a membrane air dryer to guarantee that your equipment sees dry air. However, if and when that unexpected system upset occurs, you don’t want to overwhelm your filters or dryer. No matter how good the coalescer is, a drip leg before it will assure the filter’s proper operation.
To install a drip leg, come off the top of your feeder supply line from the top of the pipe as I explained earlier. Then drop the line 2 – 3 feet (1 meter) below the inlet filters. At the bottom of this pipe install an automatic drain to remove built up water and oil. At the height of the filters, install a tee to direct the air to the filters and your equipment. A drip leg like this is an added layer of protection from oil and water that is very inexpensive to install.
Here is an example of a drip leg configuration: