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Compressed air system drain efficiency

May 11, 2022
For the best energy and cost savings, don’t overlook this simple and fairly inexpensive part of your system.

Your manufacturing operation is a complex ecosystem, and keeping that system not only running but efficient as well is a never-ending, always changing task. Each process, machine, and throughput calculation requires trained and experienced engineers and other specialists to design, run, and maintain. Millions of dollars are often injected into the facility and machinery, and process efficiency is tirelessly studied, measured, and re-designed—all in the name of profitability and efficiency.

Focus and investment in the rigors of design, maintenance, and high tech and trending machinery, and process improvements, however, can sometimes cause the process engineer to overlook a simple, but significant detail: the compressed air system drain. This seemingly small detail can provide some noteworthy energy savings—and in a world of tightening sustainability targets, every little bit helps.

Will the installation of the correct drain solve all your compressed air (and other) efficiency woes? Likely not, but it is one of the easiest and least expensive updates you can make that will have a measurable and consequential impact on your efficiency goals.

Compressed air—where does the water come from?

To understand how and why your compressed air system drain is so important, we need to first look at what is draining and from where and why. Air compressors ingest ambient air, which is mostly nitrogen, with oxygen and trace other gases along with particulate contaminants and water vapor. Compressed air cannot hold the same amount of water vapor as ambient air, so the moisture eventually condenses and must be removed.

Because of inefficiencies in the compression process, the temperature of the air being compressed increases during the compression process, causing the ingested water to remain in its vapor state. The temperature of compressed air at the exit of the compression chamber is typically too high for use in an industrial setting, so it is cooled before being discharged to the downstream air treatment components. As the compressed air is cooled, water vapor condenses into liquid and is removed by the moisture separator downstream of the compressor aftercooler. Once the liquid water, or condensate, is collected, it must be removed from the system.

Retained liquid, or bulk water, can result in the development of rust, scale, and corrosion in the compressed air piping system. The water can also be very damaging to pneumatic tools, often washing the lubricant from the internal moving parts. Because of these considerations, removal of water from the compressed air system is an important design, operation, and maintenance consideration.

However, removing the water from the system needs to be done in a manner that minimizes the discharge of compressed air from the system. Air unintentionally escaping the compressed air system—along with the water—constitutes an unproductive or inappropriate use of compressed air that costs money in the form of wasted electricity.

Drain types

Condensate management is likely the most overlooked aspect of compressed air system design. Installing the proper drains within a compressed air system is vital to avoid the needless discharge of compressed air and the associated demand increase. A properly designed compressed air system will have multiple drains. Locations requiring drains include the moisture separators, filters, receivers, piping dead legs, and any other place that condensate may collect.

It is important to recognize that the volume of condensate discharged from the different locations will vary significantly. A well-designed condensate management system not only includes drains at the appropriate locations, but also sizes the drains correctly. Condensate drains are not a “one-size-fits-all” proposition.

In practice, a variety of condensate drains are used throughout the system. Some users employ a cracked open valve or a V-notch valve. Others have adopted a manual drain that needs to be operated by maintenance personnel. These options likely either result in a waste of compressed air and/or ineffective removal of condensate from the compressed air system.

About the Author: Brian Mann

Still other systems use a timer drain to remove condensate—a seemingly more efficient option. An issue with timer drains is that they usually have a strainer upstream of the reduced port valve so that particulates do not clog the valve. The strainer will foul and plug instead, rendering the timer drain just as ineffective as if the valve itself were clogged. Despite the strainer being easy to clean, it is still another component to be maintained. Timer drains are typically set to discharge the largest anticipated condensate volume, with a factor of safety. The drain opens regardless of the presence of condensate.  If condensate is absent, the drain discharges compressed air—adding to the compressed air demand in the facility.

The simple solution

The best drain for both function and process efficiency, including eliminating wasted compressed air, is a no-loss drain. There are many styles, sizes, and designs for every application. They are called no-loss for a reason; no compressed air is exhausted when the drain opens to discharge condensate. Typically, a small amount of condensate is retained in the drain; much like the water that remains in the trap on your home sink drain piping, ensuring that no compressed air is discharged.

Many no-loss drains use capacitance to sense the presence of moisture. As an additional benefit, they often include self-clearing functions. If the drain senses that the reservoir remained full after a discharge cycle, the drain will repeat the discharge cycle. After multiple discharge cycles, a fault is indicated, usually with a visible fault indicator bringing the problem to the attention of plant maintenance personnel. If you have a limited maintenance staff, the dry contacts usually provided can be wired to a control panel to remotely indicate a drain failure.

Stop draining your profits

The drain is likely the least expensive component in the entire compressed air system—or even the entire manufacturing operation. Many capacitance-style no-loss drains can be purchased for less than $500. The high-tech Variable Speed Drive (VSD) controlled refrigerant dryer purchased for $50,000+ will not provide dry air if the $500 drain isn’t working correctly, which makes this inexpensive component suddenly very important.

And, in terms of energy and cost savings, the no-loss drain can have a significant impact on a company’s bottom line. Air leaks can be notoriously expensive and when the facility is losing air through a partially opened valve for “continuous draining operation,” literally throwing away money. Consider the opened valve as a 1/8” opening and the compressed air system is operating at 100 psig. If the blended power cost is $0.10/kWh, the operating cost of this drain exceeds $4,000 per year. The ROI on that $500 no-loss drain is therefore significant and worth more than a passing glance.


Now that a drain has removed the moisture, reduced the demand for compressed air and saved a few bucks, don’t forget that the expelled condensate must be managed. Be sure that the discharge of any drain goes to an approved location. Approved locations exclude the ground, the roof, the floor, and a stream. Be sure to consult your EH&S department, environmental permits and/or municipal sewer provider before discharging condensate anywhere.

Put the right drain in the right place for an inexpensive, often overlooked, but impactful upgrade to your plant’s ecosystem efficiency.

This story originally appeared in the May 2022 issue of Plant Services. Subscribe to Plant Services here.

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