HeMaTech Prüftechnik GmbH & Co. KG
Leak Testing Procedures
Everything You Need to Know About Leak Testing
Fundamentals, Methods, and Applications of Leak Testing
In the metal and plastics processing industries, leak testing is one of the most important quality assurance measures. Numerous components must reliably prevent media such as air, water, or oil from escaping uncontrollably or mixing with one another. Even the smallest leaks can impair a component’s function and later lead to customer complaints or failures.
To reliably test the leak tightness of manufactured workpieces, various leak testing methods and corresponding leak testing devices are used. Which method is used depends, among other things, on the workpiece’s design, the permissible leakage rate, the required measurement accuracy, and the economic requirements of the testing process.
To reliably test the leak tightness of manufactured workpieces, various leak testing methods and corresponding leak testing devices are used. Which method is used depends, among other things, on the workpiece’s design, the permissible leakage rate, the required measurement accuracy, and the economic requirements of the testing process.
The following section provides an overview of the basics of leak testing as well as the various methods used in industrial manufacturing today.
Over the years, various leak testing methods have been developed for different applications. These range from simple tests in water-filled immersion tanks to high-precision mass spectrometry, which can detect leaks on the order of 10⁻⁶ cm³ of gas per minute .
The choice of an appropriate leak testing method depends in particular on:
The choice of an appropriate leak testing method depends in particular on:
Detect Leaks Reliably
What is a leak test procedure?
A leak testing procedure is used for quality control of components to verify their leak-tightness.
Particularly in the metal and plastics processing industries, numerous hollow components must reliably fulfill their function of separating media.
These include, among others:
Particularly in the metal and plastics processing industries, numerous hollow components must reliably fulfill their function of separating media.
These include, among others:
These components must prevent media such as air, water, or oil from escaping uncontrollably or being transferred between different areas. Even the smallest leaks can impair the component’s function and significantly affect product quality.
Any other questions about this?Ensuring Quality Over the Long Term
Why is the leak test so important?
Leak testing is an essential component of industrial quality assurance. It ensures that manufactured components continue to perform their intended function over the long term and meet the required quality standards.
In mass production in particular, testing methods must not only be precise but also integrate cost-effectively into existing production processes. The goal is to detect defective components early on while avoiding unnecessary rework on flawless workpieces.
Requirements for leak testing vary significantly depending on the industry and application. For this reason, different testing methods are used, each tailored to the specific application.
In mass production in particular, testing methods must not only be precise but also integrate cost-effectively into existing production processes. The goal is to detect defective components early on while avoiding unnecessary rework on flawless workpieces.
Requirements for leak testing vary significantly depending on the industry and application. For this reason, different testing methods are used, each tailored to the specific application.
Important Technical Concepts
Fundamentals of Leak Testing
For the automatic leak testing of mass-produced parts—particularly in the automotive industry—compressed-air testing has proven itself due to its high cost-effectiveness. The differential pressure method is primarily used here.
This method meets key requirements for modern production testing equipment:
This method meets key requirements for modern production testing equipment:
high accuracy and reliability
objective quality statements
cost-effective operation
short testing times
Easy integration into linked production processes
Gentle handling of workpieces
Under certain operating conditions, however, the use of differential pressure testers can be challenging.
These include, for example:
Discuss Your Needs NowThese include, for example:
If the temperature of the test air inside the workpiece changes during the measurement phase, the pressure changes accordingly. In this case, the measurement result does not reflect solely the actual leakage of the test specimen.
This can have two different consequences:
This can have two different consequences:
For this reason, leak testing procedures must always be tailored to the specific operating conditions.
Understanding Threshold Values Correctly
What does "tightness" mean?
The concept of leak tightness is fundamentally a relative measure. It always depends on the requirements placed on the specific test specimen.
Strictly speaking, there is no such thing as an absolutely leak-tight connection, since, for example, diffusion processes can occur through the material. For this reason, a workpiece-specific threshold value is used to assess the leak tightness of a component.
This threshold value is referred to as the leakage limit.
In practice, determining a limit leakage is often challenging, as there is no universally applicable calculation formula for this purpose. Instead, one relies primarily on empirical values from comparable applications.
Depending on the leak test method, application area, or industry, different units of measurement are used. The following unit has become standard in vacuum technology today:
1 mbar · l · s⁻¹
It describes the volume of gas that causes a pressure change of one millibar in a volume of one liter within one second.
Strictly speaking, there is no such thing as an absolutely leak-tight connection, since, for example, diffusion processes can occur through the material. For this reason, a workpiece-specific threshold value is used to assess the leak tightness of a component.
This threshold value is referred to as the leakage limit.
In practice, determining a limit leakage is often challenging, as there is no universally applicable calculation formula for this purpose. Instead, one relies primarily on empirical values from comparable applications.
Depending on the leak test method, application area, or industry, different units of measurement are used. The following unit has become standard in vacuum technology today:
1 mbar · l · s⁻¹
It describes the volume of gas that causes a pressure change of one millibar in a volume of one liter within one second.
Detecting Small Leaks
Why is air used as a test medium?
Leak testing with gases—particularly with air—is based on the low viscosity of the test medium used.
Media with higher viscosity cannot penetrate microporosities in a test specimen at all, or can do so only to a practically negligible extent. For this reason, air is particularly well-suited for the reliable detection of even the smallest leaks.
Interpreting Blood Pressure Readings Correctly
Conversion of Key Units of Pressure
Various units of pressure are used in leak testing.
The corresponding conversion factors can be found in the respective pressure conversion table.
Submit a Request Now| Unit | Abbreviation |
|---|---|
| Pascal | Pa |
| Bar | cash |
| millibar | mbar |
| millimeters of water column | mmWS |
| Physical Atmosphere | atm |
Overview of Methods
The Various Leak Testing Methods
Generally speaking, leak testing methods can be divided into two groups:
The distinguishing factor is the pressure inside the test specimen. Depending on whether this pressure is higher or lower than atmospheric pressure, the appropriate test method is applied.
The following section explains the individual methods in more detail.
Testing at pressures above atmospheric pressure
Leak Test Method Using Overpressure
In a pressure test, the test specimen is subjected to a test pressure that exceeds atmospheric pressure. Depending on the measurement principle, various methods are available, which differ in terms of accuracy, test speed, and area of application.
Testing at Atmospheric Pressure
Leak Test Method Using Negative Pressure (Vacuum Test)
In a negative pressure or vacuum test, the pressure inside the test specimen is lower than atmospheric pressure. Here, too, there are various test methods available, which are used depending on the application.
Detecting Leaks
Bubble Method (Bubble Test)
The bubble method is one of the oldest and simplest leak testing procedures for mass-produced parts.
The test setup consists of an immersion tank, a testing fixture, and a pressure regulator. The test specimen is pressurized and then immersed in a water-filled tank. If air bubbles escape, this indicates a leak.
The bubble method is particularly suitable for simple testing tasks and provides a quick visual inspection for leaks.
The test setup consists of an immersion tank, a testing fixture, and a pressure regulator. The test specimen is pressurized and then immersed in a water-filled tank. If air bubbles escape, this indicates a leak.
The bubble method is particularly suitable for simple testing tasks and provides a quick visual inspection for leaks.
Pressure Increase in a Vacuum
Pressure-Rise Method
In this procedure, the test specimen is first evacuated using a vacuum pump or a vacuum pump set.
A valve then isolates the test specimen from the pump.
If there is a leak in the workpiece, ambient air can enter. This causes the pressure inside the test specimen to rise. This pressure increase serves as the basis for assessing the tightness.
A valve then isolates the test specimen from the pump.
If there is a leak in the workpiece, ambient air can enter. This causes the pressure inside the test specimen to rise. This pressure increase serves as the basis for assessing the tightness.
Measuring Pressure Changes Precisely
Absolute Pressure Method
In the absolute pressure test method, the leak test is generally conducted in three consecutive phases:
During the measurement phase, the pressure behavior within the test specimen is monitored. The method can be used as either a pressure-drop method or a pressure-rise method.
Depending on the application, the absolute pressure method provides reliable information about the leak tightness of a workpiece.
Depending on the application, the absolute pressure method provides reliable information about the leak tightness of a workpiece.
Leaks in a vacuum
Vacuum Leak Detection Using Leak Detectors
When it comes to vacuum leak detection, a distinction is made between two methods:
When it comes to vacuum leak detection, a distinction is made between two methods:
Detect even the smallest differences in pressure
Differential Pressure Method
The differential pressure method bears a strong resemblance to the absolute pressure method.
The main difference lies in the measurement principle. A system consisting of two chambers separated by a diaphragm serves as the sensor. Movements of this diaphragm are detected and used to determine the differential pressure.
Due to its high cost-effectiveness, the differential pressure method has proven particularly effective for the automatic leak testing of mass-produced parts in the automotive industry.
The main difference lies in the measurement principle. A system consisting of two chambers separated by a diaphragm serves as the sensor. Movements of this diaphragm are detected and used to determine the differential pressure.
Due to its high cost-effectiveness, the differential pressure method has proven particularly effective for the automatic leak testing of mass-produced parts in the automotive industry.
Reliably Measuring Airflow
Pneumatic Flow Systems
In a leak test using the flow method, the workpiece is first securely sealed in a fixture and then pressurized to the required test pressure.
The compressed air supply is then shut off by a valve. An integrated flow sensor monitors the air flow within the system.
If air escapes through a leak in the test specimen, a measurable air flow is generated, which is detected by the flow sensor. In this way, any existing leak can be reliably detected.
The compressed air supply is then shut off by a valve. An integrated flow sensor monitors the air flow within the system.
If air escapes through a leak in the test specimen, a measurable air flow is generated, which is detected by the flow sensor. In this way, any existing leak can be reliably detected.
Detect Test Gases with Precision
Sniffing Method
Instead of compressed air, suitable test gases—such as helium or an air-helium mixture—can also be used with certain electrical measurement principles.
Using appropriate detectors, escaping gas can be located by sniffing it out. This allows for the precise detection of leaks.
Using appropriate detectors, escaping gas can be located by sniffing it out. This allows for the precise detection of leaks.
Select the appropriate method
Choosing the Right Leak Test Method
The choice of leak testing method depends on various factors.
These include, in particular:
These include, in particular:
the design of the workpiece
the permissible leakage limit
the required measurement accuracy
the test speed
the cost-effectiveness of the testing facility
the respective production conditions
For each testing task, the method that best meets the technical and economic requirements should therefore be selected.
Discuss Your Situation NowProvide personalized advice and review
Finding the Best Solution Together
The selection of the appropriate leak testing method is always based on the specific application.
With extensive experience gained from a wide range of completed projects and a diverse lineup of equipment, we can help you find the right solution for your leak testing needs.
Our equipment lineup includes, among other things:
With extensive experience gained from a wide range of completed projects and a diverse lineup of equipment, we can help you find the right solution for your leak testing needs.
Our equipment lineup includes, among other things:
70pro Leak Tester
Request NowFlow meter 3925-0160
Request NowVolume Tester 3925-0360
Request NowLeak Calibrator 3925-0201 / -0202
Request NowWe would be happy to consult with you personally and work with you to develop the optimal solution for your leak testing needs.
Ensuring Leak-Tightness Cost-Effectively
Our Conclusion on Leak Testing Procedures
Leak testing methods are an essential part of industrial quality assurance.
Different testing methods make it possible to reliably inspect components for leaks and ensure the required product quality.
Whether it’s the bubble method, absolute pressure method, differential pressure method, flow measurement, or vacuum leak detection—each method has specific characteristics and is suitable for different applications. The choice of the appropriate leak testing method always depends on the technical requirements of the respective workpiece as well as the conditions of the testing process.
We would be happy to assist you in selecting the appropriate testing technology and work with you to develop a cost-effective and reliable solution for your leak testing needs.
Different testing methods make it possible to reliably inspect components for leaks and ensure the required product quality.
Whether it’s the bubble method, absolute pressure method, differential pressure method, flow measurement, or vacuum leak detection—each method has specific characteristics and is suitable for different applications. The choice of the appropriate leak testing method always depends on the technical requirements of the respective workpiece as well as the conditions of the testing process.
We would be happy to assist you in selecting the appropriate testing technology and work with you to develop a cost-effective and reliable solution for your leak testing needs.
HeMaTech Prüftechnik GmbH & Co. KG
Submit a Request Now
Whether you need a leak tester, testing system, calibration, or technical consultation – we assist you in finding the right solution for your application.
Describe your requirements to us, and we will get back to you personally.
HeMaTech Prüftechnik GmbH & Co. KG
Siemensstr. 7
D-71409 Schwaikheim
FAQ on Leak Testing
Frequently Asked Questions
What is a leak test procedure?
A leak test procedure is used to check components for possible leaks. The goal is to ensure that workpieces reliably fulfill their function of separating media.
What leak testing methods are available?
A general distinction is made between leak testing methods that use positive pressure and those that use negative pressure or a vacuum. Well-known methods include, among others, the bubble method, the absolute pressure method, the differential pressure method, pneumatic flow systems, and vacuum leak detection.
What does "boundary leakage" mean?
Since absolute leak-tightness does not exist in practice, a permissible limit value is defined for each workpiece. This is referred to as the leakage limit and serves as a criterion for assessing leak-tightness.
Why is compressed air often used for leak testing?
The air leak test takes advantage of the low viscosity of the test medium. This allows even very small leaks to be reliably detected.
How do positive-pressure and negative-pressure methods differ?
The difference lies in the pressure inside the test specimen. In a pressure test, the pressure is higher than atmospheric pressure; in a vacuum test, it is lower.
Which leak test method is the right one?
The selection depends on the workpiece, the permissible leakage rate, the required measurement accuracy, and the economic requirements of the respective testing process.