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How Leak Testing Works

Leak testing is a broad term that includes a multitude of technologies. For the purposes of this article, different leak test methods will be referenced but not described in full detail. This article defines the broad term leak test and takes a closer look at the pressure decay leak test method. Furthermore, this article will describe how a pressure decay test works, considerations for the pressure decay method, and how recent technological advancements have impacted manufacturing environments.

What is Leak Testing?

A fixed head leak tester is a procedure used to determine if an object, product, or system functions within a specified leak limit. A leak occurs when a gas or liquid flows through an object via an imperfection or manufacturing defect such as a hole, crack or weak seal. These imperfections create high- and low-pressure zones within a product, forcing the gas or liquid to flow from the high-pressure area to the low-pressure area. The primary leak test method discussed in this article uses pressurized air to identify leaks.

Leak Testing Methods

There are many different types of leak test methods, which have different detectable leak rate limits. This article will primarily discuss the pressure decay leak test method. A pressure decay test identifies if a part is leaking or not within a predetermined leak rate limit. The smallest detectable leak rate for the pressure decay method is 10-4 mbar*l/s or 0.0059 SCCM.

The benefits of pressure decay leak testing include:

Economical

Fast (depending on the internal test volume of a part)

Easy to set up

Only requires compressed clean,

dry air

Quantitative

Nondestructive

No pre or post processing required

Determining a leak rate is vital to selecting the best leak test method. 

Typical industries for pressure decay leak test methods include:

Automotive

Sealed Electronics

Medical Devices

Packaging

Consumer Goods

How a pressure decay test works

During a pressure decay test, a product is attached to a leak test system and filled with air. Once pressurized, the air source is closed off and the pressure is allowed to settle. During the test any decrease in air pressure over time signifies a leak.

Variations of pressure decay methods

Pressure Decay – Measures the pressure change of an object under positive pressure

Vacuum Decay – Measures the pressure change of an object under negative pressure

Occlusion – Checks for a blockage in the gas flow path of an object

Burst – A destructive or nondestructive ramping pressure test that measures the point at which the device opens or has a catastrophic event (rupture).

Crack – Typically performed on check valves to detect weeping prior to reaching the opening pressure. A downstream sensor monitors for weeping.

Chamber – Finds leaks in sealed packaging or devices that do not include an opening for filling.

Depending on the functional use of an object or part, any of the above tests may be required.

Considerations for leak testing:

What is the intended use of the part?