What is Internal Leakage?
Differences from External Leaks and Detection Methods

What is Internal Leakage: The Invisible Air Leak Inside Equipment

Internal leakage refers to compressed-air leakage that occurs inside equipment such as valves, cylinders, and fittings. Because the air does not escape to the atmosphere, it makes no audible hissing sound and cannot be spotted by visual inspection. Even spraying soapy water on the pipe surface produces no bubbles — in other words, internal leaks are a type of leak that conventional inspection methods simply cannot find.

Typical locations include the interiors of ball valves, solenoid valves, and check valves, the packing area of air cylinders, and degraded seal sections inside regulators. The U.S. Department of Energy (DOE) similarly lists "valves, flanges, packings, fittings, and pipe joints" among the most common problem areas for compressed-air leaks^[1]. Wear, age-related deterioration, or trapped debris can prevent the valve element or seal from closing fully, causing air to keep flowing past components that should be sealing it off.

Differences from External Leakage

"Air leak" is often used as a single term, but internal and external leaks differ completely in location, detection difficulty, and operational impact.

Aspect	External Leakage	Internal Leakage
Location	Pipe joints, hoses, flange surfaces — outside the equipment	Inside valves, cylinders, and regulators
Where the air goes	Into the atmosphere	To the downstream side (pipes, tanks)
Sound / signal	Audible hiss and slight vibration	Silent and motionless from the outside
Detection difficulty	Relatively easy: hearing, soap water, or ultrasonic detector	Impossible from external inspection — requires dedicated testing
Main impact	Higher compressed-air consumption and electricity costs	Pressure drops, quality defects, malfunctions, shortened equipment life

What Happens When Internal Leakage Goes Unnoticed

1. Product quality defects

When internal leakage progresses inside a cylinder, the actuation force drops, reducing positioning accuracy in assembly, conveying, and pressing processes. On precision machining lines, this surfaces as dimensional errors and assembly failures, driving up the defect rate.

2. Equipment malfunctions and near-miss incidents

If a valve fails to seal completely, an actuator may move at an unintended time, or a process meant to stop may keep running — creating real safety concerns.

3. Hidden, accumulating energy loss

Because air keeps being consumed downstream, the compressor stays under high load. According to the U.S. Department of Energy, compressed-air leaks "often waste as much as 20%–30% of the compressor's output" across an entire system^[1]. Unlike external leaks, there is no sound to alert anyone, and the cumulative cost can reach hundreds of thousands to several million yen per year before being noticed.

4. Inflated maintenance costs

When unexplained pressure drops recur, troubleshooting eats up labor and often results in unnecessary valve replacements or pipe rework. Identifying the one truly faulty unit could resolve the issue — but without proper detection, maintenance spend balloons several times over.

How to Detect Internal Leakage

Pressure-Drop Testing

The classic method: pressurize a section and infer the leak volume from the pressure drop over a set period. It requires stopping the equipment and cannot pinpoint the specific leak location (only the whole section), but it is a reliable approach when shutdown is acceptable.

Flow Measurement

Install a flow meter on a circuit, and if flow is observed during a stand-by period when there should be none, internal leakage is presumed. It is useful for trend monitoring but offers limited resolution at the individual-component level.

Ultrasonic and Vibration Detection

When internal leakage occurs, turbulent flow inside the equipment generates ultrasound (generally in the 20 kHz and higher range), beyond the human audible spectrum. The U.S. Department of Energy states that "the best way to detect leaks is to use an ultrasonic acoustic detector"^[1]. By applying an ultrasonic or vibration sensor to a valve or cylinder, the presence and approximate severity of a leak can be judged without stopping operation. Recent devices apply machine learning to grade the severity of the leak automatically, combining inspection efficiency with improved accuracy.

For Internal Leak Detection, Choose AirMore's "Algoleak"

AirMore offers Algoleak AL64, an acoustic camera that combines ultrasonic sensing with proprietary AI to detect internal leakage. Without stopping operation, it identifies internal leaks in valves and cylinders — not just as "present / absent" but with an estimated leak volume — so you can prioritize repairs and quantify loss costs in a single workflow.

For factories that find it difficult to staff and equip their own inspections, we also provide an on-site air leak diagnosis service. One client achieved approximately ¥5.6 million in annual energy savings through this approach. From "visualizing" internal leaks to implementing improvements, AirMore supports the entire workflow.

If you have noticed unexplained pressure drops lately, or wonder whether routine valve replacements are really needed, feel free to get in touch.