Automatic condensate drains are essential components in every compressed air treatment system, purging liquid from receiver tanks, water separators, coalescing filters, and air dryers. Auto drains are small and relatively inexpensive, making them easy to overlook, and too often plant operators underestimate the consequences of a drain failure.

A simple drain mishap can easily cause thousands of dollars in equipment damage and product spoilage. I’ve seen it happen too many times to count.

Plumbing multiple liquid reservoirs into a single auto drain is a leading cause of failure, as illustrated below.

The illustration shows two coalescing filters installed in series. On the left, the system operator has tried to save both time and money by using a single drain for both filters. This is a tempting practice that will cause big headaches.

The leftmost filter in each illustration always has slightly higher pressure than the one on the right. This pressure differential is due to friction in the piping and flow restrictions through the filter elements. As plumbed in the illustration marked incorrect, the pressure differential will likely cause liquid to gather—not in the drain housing, but in the reservoir of the second filter. Eventually, the second filter might fill with liquid, which could spill into the air distribution system. Moreover, air is flowing through the drain couplings and by-passing the filtration elements of the second housing.

The fix is simple. Every liquid accumulation point in the air system must have a dedicated auto drain. Do not try to outsmart this advice by putting check valves in the drain lines. Extra drains and piping should only cost you several hundred dollars each. It is a wise investment.

Tyler Currie began working in the compressed air industry in 1993. He is the owner of Moisture Boss, LLC and can be reached at tyler@moistureboss.com.