Definition of leakage
The definition of leakage is an unintentional opening, hole, crack or similar through which liquid, gas, light, etc. enters or escapes.
The resulting leakage volume depends on the pressure difference across the opening and is related to the fluid's ability to flow through the opening; this is called conductance and can be expressed by the following equation: Q = C (P1-P2)
Where Q is a leakage volume, P1-P2 is the difference between two pressures and C is the conductance.
The fluid flow depends on a variety of factors, including the configuration of the orifice, length, etc. Therefore, it is difficult to apply one type of equation to all cases. This section concludes an explanation with a generally applicable equation.
Everything has leakage
It must be accepted that everything that is manufactured will have some degree of leakage. The expected life of a component or the shelf life of a packaged product can be used to calculate an acceptable leakage rate based on serviceability. Even NASA, which sends astronauts into space, must determine an acceptable leak rate, quote, "A leak is zero if a given gas escapes at a given pressure in a given time, e.g. nitrogen 1.4 x 10-8 cm/s at 300 psig.
Accurate leak testing has a major impact on the safety and reliability of a product. Reliable leak testing lowers costs by reducing the number of warranty and liability claims.
Why leak testing?
Leak testing may be carried out for environmental reasons or because the environment is contaminated. Or a successful leak test may simply protect against the loss of costly materials.
How to measure leakage?
Leakage is measured by how much liquid is allowed to pass under certain conditions. Therefore, it is important to specify both leak rates and operating conditions to properly define a leak.
The leakage rate is often expressed as the product of pressure and volume per unit time.
A true leak would not occur if the conditions were the same on both sides of the crack or hole, i.e. the gas or liquid would just diffuse through, so for a leak to occur there must be a driving force.