FILL
Connect the part with a fitting or fixture and pressurize it to the desired test pressure.
Leak Test Method
Pressure Decay Leak Testing
A pressure decay leak test pressurizes an internally pressurized part, isolates the air source, and measures any pressure drop over time to make a pass/fail decision.
Pressure decay is one of the most widely used leak-testing methods in manufacturing. It is suited to a sealed component with an access port and starts by connecting the part to a leak tester with a fitting or fixture.
After the part is pressurized, the air source is valved off and the pressure is allowed to settle. The test then measures the change in pressure over time against the programmed reject value.
Part volume and test time work together. Larger internal volumes need a longer cycle to reach a useful sensitivity, while smaller volumes can use shorter cycles and support higher production throughput.
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Use the leak-rate calculator and unit converter →What is a pressure decay leak test?
A pressure decay test answers one question: does this part hold pressure? The part is connected to the tester, filled to its test pressure, then sealed off from the air supply. From that moment the tester watches the pressure. Air escaping through a hole, a bad weld or an imperfect seal shows up as a falling pressure reading.
It is the most widely used leak test in manufacturing because it needs nothing more than air, a fitting and a repeatable sequence. There is no tracer gas to buy, no chamber to evacuate, and the part comes off the fixture unharmed, so every unit on the line can be tested rather than a sample.
The result is a pass or fail against a reject limit you set for that part. A pressure decay test tells you a part leaks more than you allow — it does not tell you where the leak is. When the location matters, a helium sniffer is the tool for that job.
How a pressure decay test runs
SETTLE
Allow the part to settle after fill. This stage accommodates part stretching, flexing and thermodynamic stabilization before measurement.
TEST
The pressure sensor measures any drop in pressure during the test interval.
VENT
Vent the remaining system pressure to atmosphere; venting has no bearing on pass/fail and is for operator safety.
A non-leaking part remains within its specified pressure-decay limit and passes; a part that decays beyond its lower limit fails.
When pressure decay is the right method — and when it is not
Pressure decay is a fit when
- ✓A sealed part with an access port
- ✓A non-destructive test of the part
- ✓Small internal volumes where a low cycle time supports high production throughput
- ✓A test based on air pressure change after the source is isolated
Choose another method when
- →A part with no accessible opening — Use chamber leak testing.
- →A need to locate the physical leak site — Use sniffing leak testing.
- →A sensitivity requirement beyond air-based testing — Use trace gas leak testing.
- →A flow-through part or a need to check for blockage — Use mass flow testing or occlusion testing.
- →A need to determine whether a passage is blocked — Use occlusion leak testing.
Sensitivity, cycle time and part volume
Zaxis testers resolve pressure to 0.00001 PSI. That resolution is what makes short cycles possible: the smaller the pressure change you can see reliably, the less time you need to spend watching for it.
Sensitivity is a negotiation between the part's internal volume and the time you give the test. The same leak bleeds a large volume slowly and a small volume quickly, so a big assembly needs a longer test interval to produce a measurable drop, while a small sealed component can be judged in a fraction of the time. That is why small-volume parts run at high throughput on the same tester that needs a patient cycle for a large one.
Settle time exists because parts move. A flexible part stretches when it is pressurised, and that expansion looks exactly like a leak to a pressure sensor. Settle gives the part time to stop moving so the test interval measures leakage instead of elasticity.
Temperature and fixturing deserve the same attention. Compressed air warms as it fills and cools as it settles, and a fixture that flexes adds volume of its own. A stable fixture, a consistent fill and a settled part are what turn 0.00001 PSI of resolution into a trustworthy production decision.
Which Zaxis testers run pressure decay
Every Zaxis air leak tester runs pressure decay. They differ in channel count, interface and enclosure, so the choice comes down to where the tester has to live and how many parts it has to handle.
Z8Up to four channels, an 8-inch touchscreen, and pressures to 1000 PSIG for automated production lines.
Z5The benchtop workhorse: 5-inch touchscreen, the same 0.00001 PSI resolution, in a 6.5-inch-wide cabinet.
Z12.6 inches wide with an optional detachable touchscreen, built to live inside a machine.
Z5LSingle-channel entry point, 0–30 or 0–100 PSIG, with single-screen test setup.
Z8NZ8 capability inside a sealed NEMA enclosure for dusty or washdown areas of the plant.
VM3Generates its own fixed air volume with a plunger, so a station needs no house air supply.Applications for pressure decay testing
Catheters and medical tubing
Balloon catheters, IV sets, infusion sets and needleless injection components are pressure decay's home ground: sealed, low volume, and required to hold pressure in use.
Implantable and drug-delivery devices
Devices that carry fluid inside the body are tested unit by unit, which suits a non-destructive method that leaves the part fit to ship.
Sealed electronics and wearables
Enclosures that must keep moisture out are checked through a single port, with the tester generating its own air volume when no plant air is available.
Sealed packaging and bagged product
Bags, pouches and sensor housings without a usable port are tested inside a chamber fixture, where the same decay measurement is made on the space around the part.
Automation cells
A single-channel tester mounts beside its fixture and runs one recipe on cue from the machine, which is how pressure decay ends up embedded in an assembly line rather than beside it.
Multi-cavity assemblies
Parts with several sealed cavities are tested on separate channels so a failure points at a specific cavity instead of the whole assembly.
Pressure decay vs other leak test methods
| Method | Non-destructive | Needs an access port | Locates the leak | Typical use |
|---|---|---|---|---|
| Pressure decay | ✓ | ✓ | × | Sealed parts with a port |
| Vacuum decay | ✓ | ✓ | × | Parts and packaging |
| Mass flow | ✓ | ✓ | × | Flow-rate limits |
| Occlusion | ✓ | ✓ | × | Blocked passages |
| Burst | × | ✓ | × | Failure pressure |
| Pressure cracking | ✓ | ✓ | × | Valve opening pressure |
| Chamber | ✓ | × | × | Sealed parts, no port |
| Sniffing | ✓ | ✓ | ✓ | Finding the leak site |
| Hard vacuum | ✓ | ✓ | × | Hermetic, safety-critical parts |
| Accumulation | ✓ | ✓ | × | Large parts, total leak rate |
| Bombing | ✓ | × | × | Sealed parts, no fill port |
| Differential pressure | ✓ | ✓ | × | Large volumes, low leak rates |
| Trace gas | ✓ | ✓ | ✓ | Very small leaks, quantified |
Pressure decay leak test FAQ
What is a pressure decay leak test?
It pressurizes a sealed part, isolates the air source, and measures the pressure change over time. A drop in pressure during the test signifies a leak.
How sensitive is pressure decay testing?
Zaxis testers resolve pressure changes to 0.00001 PSI. What that converts to as a leak rate depends on your part's internal volume and how long the test interval runs.
How long does a pressure decay test take?
Cycle time depends on part volume and the time needed to reach the required sensitivity. Typical production cycles are often 7–10 seconds; larger volumes need longer cycles and appropriately sized valves to fill and vent efficiently.
Does part volume matter in pressure decay testing?
Yes. Large internal volumes require more cycle time to reach useful sensitivity; smaller internal volumes can support faster cycles.
What is settle time in a pressure decay test?
Settle time follows fill and allows the part to accommodate stretching or flexing before pressure decay is measured.
How does pressure decay differ from vacuum decay?
Pressure decay applies positive pressure and measures a pressure drop. Vacuum decay applies negative pressure and measures an increase in vacuum pressure.
Can a pressure decay test find where a leak is?
No. It makes a pass/fail decision from pressure change. Sniffing leak testing is used when the physical leak location is needed.
Is pressure decay testing destructive?
No. It is a non-destructive method for sealed components.
What test pressure does a pressure decay test use?
Test pressure is chosen for the part and its application, not by the method. Across the Zaxis range the available spans run from 2 PSIG up to 1000 PSIG of positive pressure, plus vacuum to roughly -14.7 PSI, and the tester is configured for the span your part needs.
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Planning a production station? Read the Pressure Decay Leak Testing Buyer’s Guide and compare alternatives in the leak test method chooser.
For standards scope context, see the ASTM F2095 and ASTM E2930 explainers.
