Leak testing is a process used to detect manufacturing flaws and to verify the integrity of the products. Various methods can be employed to test the work, depending on the system at hand. These tests ensure the proper functioning of the components and improve consumer safety.
Each leak testing method has its own sensitivity; highly leak prone systems require high sensitivity methods. Other factors considered while selecting a method are the size of the products, materials used, the temperature and the presence of any type of coating on the surfaces.
Before we go further into leak testing, let us first see the basic principles of leak testing. Starting with the fundamentals:
What is a leak?
A leak is the flow of liquid or gas through the walls of a product due to an imperfection or defect such as a crack, hole or bad seal. In order for a leak to occur, a pressure difference needs to be generated. The flow of the gas or liquid is always from higher pressure to lower pressure.
Leaks are generally considered to go from positive pressure to atmospheric pressure. The pressure inside an object is considered positive pressure and the pressure outside is atmospheric pressure. All the units of measurement and models are based on this consideration.
The units of measurement for leak testing
A standard unit of leakage that takes into account air pressure is mbarl/sec (milibar-litre/second). A leak of 1 mbarl/sec into the atmosphere is equivalent to a leak of 1000cm³/sec in volume. The units used for leaks of air are mm³/sec or cm³/sec. A bubble is usually measured as 30-50 mm³, 1 bubble/sec is 30mm³/sec or 2 cm³/min.
Leak test selection criteria
To select a leak tester for testing your products certain factors have to be considered so that you may select the right tester. These factors are:
- Size of the component
- Internal volume
- The leak limit
- Temperature of certain parts of the product
- Surface finish of any sealed surfaces
- Hidden internal volumes that may affect leak measurement
- Cleanliness and dryness of all the parts
Two of the most popular systems used in leak testers are helium systems and the pressure/vacuum systems. Both the systems are explained in brief below.
- Helium System
The test chamber and the test piece are concurrently evacuated to a pre-set vacuum using a vacuum pump and then they are isolated. To create a positive pressure variation the pressure in the chamber is lowered further.
Helium gas is introduced into the test piece and a mass spectrometer analyses a sample of air from the chamber. The spectrometer measures the helium leakage and decides whether the product has passed or failed the test.
- Pressure/Vacuum System
The system uses a differential pressure transducer to detect changes in pressure. The sensitivity and accuracy of the system are defined by the method of presetting the pressure together with the control valve and the transducer.
The test piece and reference volume are simultaneously pressurised or evacuated to a preset pressure. With the supply valves closed the air in the system is allowed to stabilise and the transducer is automatically set to zero. After stabilization, the pressure change in the test piece is compared with the pressure change in the reference volume. If there is a leak in the piece, the difference will increase and the leak will be measured.
Leak testing is required in a wide range of industries such as medical, engineering, food industries and automobiles, among others. The pressure vacuum system is commonly used in air leak testers that are becoming popular in all the industries these days. Mikro Innotech provides innovative and cost-effective air leak testers for various applications. These highly accurate leak testers are fully automated and have the facility to mark the products as leak-proof.