Minimizing And Fixing Compressed Air Leaks
Compressed air leaks are a considerable obstacle to successful system operations. Perhaps the most common issue in a compressed air system, leaks have many undesirable consequences. Compressed air leaks can damage your equipment, consume unnecessary energy, and reduce productivity. Leaks also translate to resources wasted on equipment repairs, excess compressor capacity, and a decreased output.
Leaks cause a drop in system pressure that lead to rapid compressor cycling and increased production and maintenance costs. To reach the same levels of performance as a sound compressor, operators must increase the capacity of a leaky compressor. This taxes the system and hikes energy costs, without improving efficiency or production. The U.S. Department of Energy estimates that half of all compressed air is wasted, due to leaks, artificial demand and inappropriate uses.
Fortunately, compressed air leak detection doesn’t have to be a difficult process. You can avoid the consequences of compressed air leaks by learning best practices within the industry to detect, fix and prevent future leakages.
In preparation for these procedures, it is also important to understand your system’s leakage rates and calculate the associated costs. All of these subject areas are discussed in the following chapters.
With the right tools and knowledge, plant operators and managers can easily locate and fix leaks in compressed air systems, and prevent new leaks in the future.
Types of Leaks
Leaks fall into one of two categories: intentional and unintentional. Intentional leaks are deliberate uses of a system, while unintentional leaks are unplanned.
The unintentional leaks are the type that commonly cause maintenance and repair issues, but intentional leaks can often be reduced to minimize associated costs.
Intentional leaks of compressed air are used to serve an alternate purpose. Examples of such functions include station cleaning, equipment cooling, staff cooling, and drying.
In contrast, unintentional leaks are wasted air. They can develop over time due to natural wear and tear in the pipe network, or because of corrosion and poor workmanship.
Incompatible materials in the compressed air system can also result in unintentional leaks. These types of leaks are detrimental to the health of your compressed air system, and can negatively affect its performance and energy efficiency.
Air Leakage Rates
The first step to minimizing compressed air leaks is to calculate your leakage rate. A leakage rate can be defined as the measurement, in cubic feet per minute, of wasted air from an air compressor.
According to the U.S. Department of Energy, leakage rates are “a function of the supply pressure in an uncontrolled system.” The higher the system pressure, the higher the leakage rate. As most leak orifices are shaped irregularly, leakage rate calculations are adjusted to account for both well-rounded and sharp-edged orifices. The size of the orifice will also directly affect your leakage rate.
The compressed air leakage rate will help you evaluate the severity of your compressed air leaks. It will also help you determine your need and plan for corrective action.
Estimating Amounts of Leakage
If you use a compressor with start/stop controls, another way to determine the degree of your leakage problem is through estimation. Unlike leakage rates, this method is expressed as the total leakage percentage.
First, turn off all air-operated end-use equipment. Then, start the compressor and measure the time it takes for it to load and unload. You may have to repeat this step several times and average your findings to get an accurate reading. You can then use the following formula to calculate your leakage percentage:
Leakage (%) = [(T x 100)/(T+t)]
In this calculation, T represents the on-load time and t represents the off-load time of the compressor, in minutes.
A well-maintained air compressor should lose no more than 10% of its capacity to leaks. If you arrive at a figure below this amount, you may not need to perform corrective action on your air compressor system. In an ideal world, your compressed air system should have no leaks at all. However, it is almost impossible to achieve leak-free status.
If you find that your leakage percentage is over 10%, repairs and maintenance are recommended. You may be able to address some leaks on your own with the proper tools. A service professional can handle any issues that you are unable to resolve.
Leakages between 20-30% throughout the system are considered a serious problem. In such situations, corrective action is strongly recommended. Without intervention, a system with high leakage percentages will wear down your entire system, rack up energy expenses, and reduce the efficiency of any air-operated end-use air leak detection equipment.
If your compressor does not have start/stop controls, you can still estimate your leakage percentage with the help of a pressure gauge downstream of the receiver. Like the previous method, you must turn off all end-use equipment and start the system to obtain certain measurements. The amounts of leakage are expressed in cubic feet per minute.
To perform this calculation, you will need to know the following:
- Estimate of total system volume in cubic feet (V)
- Normal operating pressure in psig (P1)
- Time in minutes it takes for the system to drop to a lower pressure after the system is started (T)
- Lower operating pressure (P2)
These measurements can be inserted into the following formula:
Leakage (cfm free air) = (V x (P1-P2)/T x 14.7) x 1.25
The Cost of Leaks
You may also want to determine how compressed air leaks impact your bottom line.
The costs assume that the compressor is consuming electricity at a rate of $0.10 per kWh. If you detect multiple leaks, you may combine multiple costs to arrive at the total cost per year of leakages.
Ultrasonic Air Leak Detection
Once you’ve determined that your compressor needs corrective action for leakages, you may begin leak detection methods. There are two reliable ways to detect leaks in your compressor. The first requires an ultrasonic acoustic detector. The second method simply calls for soapy water and a paintbrush.
An ultrasonic leak detector is a device that identifies the high-frequency hissing sound caused by escaping air. A highly effective tool, it uses sound waves to quickly detect and pinpoint the origin of the leak, then tag and map the leaks. Ultrasonic leak detectors are often included in leak detection kits that include accessories such as headsets and focusing probes. They are easy to use and a wise investment for any facility with a compressor.
In the absence of an ultrasonic leak detector, you may also use a paintbrush to go over suspect areas with soapy water. If there is a leak, a telltale soap bubble will form over the area. This method is time consuming and certainly not as accurate as a high-tech ultrasonic leak detector. However, it remains an effective way to detect most compressed air leaks.
There are a few approaches to fixing a leakage problem.
You may be able to stop a leak simply by tightening loose connections or replacing faulty parts. If you choose this approach, be sure to use genuine OEM parts to ensure reliability. Areas where leaks commonly occur include:
Another option is to lower the rate of air flow as much as possible, thus reducing system pressure. This will effectively minimize your leakage rate.
After you’ve fixed or reduced the leaks, you can recalculate the system’s leakage rates and leakage percentage using an air leak calculator to confirm that the issue is resolved.
Air Compressor Leak Repair & Prevention
A leak prevention program is the key to preventing future system leaks.
An effective leak prevention program establishes a target leak reduction goal of between 5-10%. Operators should know how to identify and repair common leaks, and be able to perform follow-up procedures consistently. Every prevention program should also incorporate a thorough, annual review of compressor parts that are susceptible to leaks.
Compressed air leaks can be a costly drain on equipment service life, energy, and efficiency.
Take the time to quantify system leakages by calculating your leakage rate. If your system’s compressed air leaks are serious, you can take steps to locate the origin of the leaks and repair them. Combined with an effective leak prevention program, you may be able to significantly minimize system leakages on your own.
If you have difficulty locating leaks in your system or need advice or guidance regarding leak repair or prevention, don’t hesitate to contact a professional. The experts at Compressed Air Systems have years of experience in the industry and are happy to provide assistance.