Basically there are 3 types of fundamental leak detection available for end users wishing to put their components through some degree of pre-sales testing.
Type A. The "underwater" test.
Type B. The standard "air pressure drop" test.
Type C. The sensitive "air leak decay" test
All the above tests are capable of finding the majority of standard leaks associated with the vast majority of components.
The water test "Type A" is the most basic of tests, comprising mainly of a tank filled with water. The operator then connects a hose (containing compressed air at a predefined pressure) to the component to be tested. The component and airline are then emerged in the water and the compressed air is allowed to fill the component. At this stage the operator looks for visible bubbles emerging from the components. This would then determine a failed component. The system as a whole is inexpensive a relatively easy to manufacture and install.
Air pressure drop "Type B" is the most common system employed by clients. Here a sensitive transducer is used to monitor a drop in air pressure over a predefined time. The machine is generally designed as a semi-automatic system, where the operator will place the component in a jig/nest, close the door and press a cycle start button. The biggest advantage of this type of machine is its relative cost to payback ratio and is also not subject to the visual skills of the operator, the transducer decides whether the component is a pass of a fail based on the machine setup parameters. It is also water free, thus no drying is required within the production process.
And finally The leak decay machine Test "Type C". This type of machine is used in circumstances where the client would be looking for very small changes in pressure to volume ratios, in such components as metal castings etc, this test would for example check for porosity (i.e. minute holes and cavities generated when a casting is made). these holes or cavities may or may not be leak paths to the external environment, but in any case they may well be extremely small and will require this type of test. Please be aware that although these types of machines can measure extremely small leak rates, once the specification starts to get down to the 0.1 cc/min mark with say a 10 bar pressure, environment conditions can start to play a part in the functionality of the machine. The advantage of this type of machine is its accuracy and versatility.