The definition of leakage is an unintended hole, crack, or the like, through which liquid, gas, light, etc., enters or escapes.
A resultant leak volume differs according to the difference of pressure across the opening and relates with the ease of fluid flow through the opening; this is termed conductance. This can be expressed by the equation Q = C (P1-P2)
Where Q is a leak volume, P1-P2 represents the difference between two pressures and C is conductance.
The ease of fluid flow depends upon a variety of factors; when a leak is the subjective problem, including the configuration of opening, length, etc. It is, therefore, difficult to apply one type of equation to all cases. In this section, an explanation is finishing with a generally applicable equation.
It must be accepted that everything which is manufactured has some level of leakage. The expected working life of a component or shelf life of a packaged product can be used to calculate an acceptable leak rate based on fitness for purpose. Even NASA, responsible for sending astronauts into space have to set an acceptable leak rate, quote ‘ A leak is zero if a certain gas leaks at a certain ate under a certain pressure, for example Nitrogen 1.4 x 10-8 cm sec at 300 psig.’
Accurate leakage testing has a great impact on the safety and reliability of a product. Reliable leak testing reduces cost by decreasing the number of warranty repairs and liability claims.
Leak tests may be carried out for an environmental reason, or what is contaminated by the environment. Or simply successful leak Testing can protect against the loss of costly materials.
leakage is measured by how much fluid it will pass under a given set of conditions. It is thus important to state both the leak rates and operating conditions to define a leak properly.
Leak rate is often expressed as a product of pressure and volume per unit time.
A true leak would not occur if the conditions were the same either side of the crack or hole, i.e. the gas or liquid would only diffuse through, thus for a leak to occur there must be a driving force.