Air leaks

Air leaks are a concern for anyone operating a compressed air system.

by Dan Wise

The average plant with no formal leak management program will have air leaks that waste 25 percent to 30 percent of total air capacity. The extreme cases can be as high as 50 percent. 

Air leaks can cost you money. Leaks are a direct waste of the energy it takes to produce the compressed air when using compressors powered by electrical motors. 

For example, a 100 horsepower air compressor operates 6,000 hours a year with a power rate of 7 cents per KW and a motor efficiency of .90. This one compressor will have an annual power cost of $34,800.

You can determine the approximate annual electric power cost of your compressors with this formula. The first step is to multiply the horsepower of the compressor times .746 times the hours of operation times your power rate (HP x .746 x hours x power rate). Then, divide that number by the motor efficiency. 

Everyone involved with the compressed air system in your plant should be made aware of the total energy cost for operating the compressors. 

Leaks will cause compressors to run at full load for longer periods of time. The compressors will not only use more energy but, may also need additional maintenance due to the increased loads.

Leaks can also give the false impression that additional compressors are required to meet the demand for compressed air. This misconception can lead to money being spent on a rental compressor or on the addition of a compressor to the plant.

Common leak points
The majority of leaks are between the header and the point of air usage. The following leak points are found in most plants. 

Quick connections fittings have o-rings to seal the hose connections. A damaged or missing o-ring will cause the quick connection to leak. 

Most systems have FRLs (Filter, Regulator, Lubricator) immediately before air tools and other air use equipment. Low-priced models and installation errors will lead to leaks. 

The welds found on pipe joints and pipe flanges can leak due to vibrations, age or improper welding.

Timer controlled condensation drains wastes air when they remain open longer than it is required to drain. They also can close too soon and leave condensation in the system.

The timer settings for how often to open the drain and how long to keep the drain open must be adjusted for changes to the inlet air temperature and humidity. This is seldom done because few people have the time to monitor these factors.

Send an email to for details on a condensation drain that will automatically remove condensate when it appears at the drain without wasting air.

Float or mechanical type condensation drains are another common source of air leaks. These devices can malfunction because they have parts that are in constant contact with the condensation. 

The contamination will cause the drains to stick in the open position or prevent the drains from closing completely after draining. The above mentioned automatic drain will eliminate this problem.

Manual condensation valves are often left cracked open to keep water out of the system and save time from periodically opening the valve. This is an obvious waste of air and the above mentioned automatic drain will eliminate this problem.

Air piping valves will leak if the stem packing is worn and needs replacing.

Reciprocating compressors are often operated with little regard to monitoring the performance of the packing that seals around the piston rod. The seals leak when they are left in the compressor too long.

Pipe thread connections will leak when the threads are not sealed with the appropriate pipe dope for the application. It is common for people to use tape products to seal pipe thread connections but, these products are not an effective way to seal pipe threads. 

Air tools will leak internally when they are worn and need service.

Air powered production equipment will leak air when the machines are not in use unless air flow to the equipment is shut off.

Ultrasonic leak detection
An ultrasonic leak detection tool is a necessary part of any leak prevention program. This opinion is a result of research of air leak surveys conducted by outside vendors.

The majority of the leaks will be too small to detect without an ultrasonic tool. Eighty percent of the leaks found in professional leak surveys could not be found without an ultrasonic tool. This is because of background noise and because the leaks were so small (usually less than 5 CFM). These smaller leaks will make up one-half of the air leak total found in the average leak survey. 

It is unusual to find leaks larger than 20 CFM. This does not count obvious open drain type leaks that are fixed soon because the leak is audible and usually causing some aggravation.

Seeing is believing. The tools are easy to use and very helpful at finding air leaks. This was demonstrated during the process of the leak surveys.

Most of the customers did not own an ultrasonic tool prior to the leak survey. However, many of them purchased one after seeing the tool in action. 

There are many ultrasonic tools on the market. Compare these and any others you find to determine which would be best for your situation.

The prices will range from a little less than $3,000 to almost $5,000. This makes it important to consider all the options that are available with each tool when making a comparison. Also, ask for a demonstration of any ultrasonic tool that you seriously consider buying.

Companies that sell ultrasonic leak detectors include Superior Signal Company in Spotswood, N.J.; CTRL Systems in Westminster, Md.; and UE Systems in Elmsford, N.Y.

Other tips
Conduct your own leak survey as opposed to having this work done by an outside vendor. You will save considerable money, learn more and will be more committed to the long-term success of the leak program.

Avoid using an orifice flow chart to quantify air leaks. These charts are based on perfectly round orifices and a known back pressure. This is not an accurate description of the leaks that are found in compressed air systems.

It is important to remember the interdependent relationship between air system components. Eliminating air leaks will not translate into reduced energy cost unless the compressor controls, air piping and air receiver system will allow you to recover energy.

Hire an outside vendor to conduct an air audit (not leak survey) of your air system. This will identify the cost of air per CFM and find ways to make the system capable of translating less air used into lower energy use.

An air audit should be done by qualified experts.  Send an email to for a copy of our research on the best company for an air audit. 

Free advice
A leak prevention program can produce energy savings.  However, we would suggest that you speak with an expert before committing the time, money and manpower required for a successful program.

CompressorWise has a special offer for anyone involved with a compressed air system in the U.S. or Canada. Send an email to for free advice on improving or starting a leak prevention program in your plant. Remember to include a phone number with the best time to call so that CompressorWise can call back to answer any questions.

Dan Wise is the Webmaster for CompressorWise.com, a Web site dedicated to helping industry with information about how to get the most from compressors and compressed air systems. For more information, visit www.CompressorWise.com.

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