Pressure Decay Leak Testing: A Buyer’s Guide

A test program compares the measured change with the application’s acceptance limit. The method is non-destructive when the selected pressure and fixture are appropriate for the part. It is commonly considered for sealed components with an accessible port; a chamber arrangement can extend the approach to parts without a convenient internal connection.

Pressure decay is a measured pressure change, while leak rate expresses gas loss over time under stated conditions. For a practical pressure-decay estimate, the relationship is proportional to test volume multiplied by pressure change, divided by the test interval: leak rate ∝ V × ΔP / Δt. The correct conversion depends on the chosen units, absolute pressure reference and stated conditions.

Use the Zaxis leak-rate calculator to work through volume, pressure drop and time. A calculated value is only as representative as the controlled part volume, test pressure, temperature and fixture condition behind it.

A fixture is part of the measurement system. Keep connection geometry repeatable, minimize dead volume, select seals for the part and test pressure, and verify that clamps and fittings return to the same condition. Create a routine for checking the fixture independently before changing a tester limit.

Common false failures come from a fixture leak, unstable material after fill, temperature change, inconsistent incoming air, an unaccounted-for volume, or a program that starts measuring before the system settles. The existing pressure-decay article and common methods overview provide additional method context.

A pressure-decay program is a sequence, not simply a pressure setpoint. Begin with the part in its production condition and identify every volume connected to the test port. Include adapters, hoses, manifolds and fixture cavities. The result represents the complete sealed test volume, so changes in any of those elements can change the result.

During fill, the pressure source brings the connected system to the programmed condition. The fill stage must be long enough for the available supply, valves and fixture path to reach the intended pressure. A restriction, blocked passage or inconsistent connection can make fill behavior look different from one cycle to the next. In applications where a flow path itself is being evaluated, mass-flow testing or occlusion testing may answer the more direct question.

Stabilization follows fill because gas and materials respond to the pressure change. A flexible part can stretch; a seal can seat; and compressed air can change temperature. Measuring before those effects have settled can produce an apparent leak that is not a part leak. Conversely, an unnecessarily long settle stage may consume cycle time without improving the decision. Establish the timing from representative parts and the intended production environment.

During the test stage, the source is isolated and the instrument applies the programmed measurement logic. The acceptance limit should trace to the application requirement and the agreed test conditions. The vent stage then returns the part or fixture to a condition where it can be safely disconnected. Keep the four stages documented with the recipe so that maintenance, quality and automation teams can recognize a material program change.

Fixturing should locate the part consistently, seal only where the design allows, and present a repeatable internal volume. Choose sealing interfaces that match the part geometry and intended pressure. A seal that moves from cycle to cycle, a connection that is cross-threaded, or a hose that is changed without revalidation can become the dominant leak path.

Before rejecting a production batch, isolate the question. Check a known fixture condition, fittings and hoses; confirm the part is seated; review the pressure and time recipe; and compare the change with environmental or material events. This disciplined process helps distinguish a part-related signal from a station-related signal. Zaxis also offers leak test fixture information for teams planning a dedicated station.

Document the part revision, fixture configuration, selected pressure condition, timing stages, acceptance logic and required station outputs. Train operators to recognize normal loading and seal engagement, while giving maintenance a defined check for fittings, seals and tubing. When a part or fixture changes, review the complete test volume and rerun the application checks rather than assuming the existing limit transfers unchanged.

For automated lines, clarify the handoff between the tester and controller: start permissives, part-present signals, cycle-complete output, pass/fail handling, fault states and record retention. Channel count should match the fixture and desired diagnostic result. When multiple cavities are tested, independent reporting can help the station identify the relevant cavity instead of treating the assembly as a single undifferentiated result.

Use the production review to compare stable reference behavior with representative good and failed conditions where available. That record supports a controlled launch discussion and establishes a baseline for future troubleshooting.

Keep the selected method, test conditions and acceptance decision together in the application record. When a test is questioned later, the team should be able to identify the part revision, fixture, program and production condition that produced the result. This supports orderly troubleshooting and helps prevent a temporary adjustment from becoming an undocumented process change.

See the leak-testing glossary for definitions used in this guide.