Motionwell Automation builds leak testing machines in Singapore. Pressure decay and pressure hold systems combine the measurement circuit with part-specific sealing fixtures, controls and result handling. For a multi-channel design, main air preparation and station-level regulation work with the test valves and sequence to limit interactions between channels. Cross-channel disturbance is checked while neighbouring stations fill and vent.
The design specifies the pressure range, sensor and gauge checks, valve arrangement and timing for each station. Record the measurement interval with the result: pressure changes taken over different intervals need the appropriate conversion before they can be compared.
Interchangeable bases and clamps can support several tube formats. Position sensing confirms the clamp’s motion; pressure and fixture checks establish that the test volume can be measured. Identify the sealing elements by controlled part number so replacement seals match the designed material and geometry.
We build air pressure decay and pressure hold testers with the fixtures, seals, handling and reject path around them. Method selection starts from part volume, permissible pressure, reject threshold and cycle time, followed by a trial on representative parts and reference leaks. Related station design is on the automated test equipment page, and the joint being tested is covered on the capping and sealing systems page.
What Does a Pressure Decay Test Actually Measure?
It measures a pressure change over a fixed time in a sealed volume, and it infers a leak from that change. The part is filled to a test pressure, the fill valve closes, the pressure is allowed to settle, and the controller then watches the pressure for a defined dwell. A valid test passes when the measured decay stays within the specified limit; excessive decay produces a reject result.
The word inferring matters. The instrument never sees a leak. It sees a pressure drop, and a pressure drop has several possible causes, only one of which is a hole in the part. Trapped volume that has not finished settling produces one. A seal that is still seating produces one. Air that is still equalising in temperature after compression produces one. Most of the engineering in a leak tester is the work of removing every cause except the one you want to measure.
That is also why the cycle has a settle phase between fill and measure. Compressing air heats it, and heated air in a fixed volume shows a falling pressure as it returns to ambient, which reads exactly like a leak. The settle time is not padding. It is the interval during which the machine allows a physical effect to finish so that it does not appear in the answer.
| Cycle phase | What happens | What it is protecting against |
|---|---|---|
| Clamp and seal | Part located and sealed against the test port | Seal seating movement appearing as decay |
| Fill | Part brought to test pressure | Undershoot producing inconsistent starting points |
| Settle | Fill valve closed, pressure allowed to stabilise | Adiabatic heating from compression |
| Measure | Pressure sampled over the dwell window | Separates the decay measurement from fill and stabilisation transients |
| Vent and unclamp | Part depressurised and released | Operator exposure to a pressurised part |
When Is Pressure Decay the Right Method, and When Is It Not?
Pressure decay suits parts that seal against a port, hold a moderate pressure without distorting, and have an internal volume small enough that a real leak moves the gauge. It is fast, it uses shop air, it needs no consumable gas, and the measurement is direct enough that operators trust it.
Large internal volumes reduce the pressure signal and can require an impractical measurement interval. Flexible parts can change volume under pressure, which also changes the reading. Fully sealed packages without a test port need a chamber-based method or another suitable approach instead of direct connection to the part’s interior.
| Method | Typical use | Why you would not use it here |
|---|---|---|
| Air pressure decay | Small to medium rigid sealed parts, in-line production | Loses resolution as internal volume rises |
| Vacuum decay | Suitable sealed packages and parts tested under a pressure differential created by vacuum | Requires a suitable fixture or chamber and pump; cycle time depends on the method and part |
| Helium mass spectrometry | Very low leak rates, hermetic devices | Tracer gas handling and recovery, higher cost |
| Bubble immersion | Manual verification, failure analysis | Operator dependent, wets the part |
| Leak-flow measurement | Measures the flow needed to maintain a specified test pressure in a sealed part | Requires suitable flow range, pressure regulation and stabilisation time |
| Through-flow testing | Parts with an intended passage, such as a valve or channel | Tests passage flow or restriction against its specification; distinguish it from a sealed-part leak test |
The summary worth carrying away is that air decay covers a wide band of ordinary industrial parts well, and stops being the answer at the bottom of the leak rate range. Knowing where your part sits in that band is the first engineering decision, and it is made from the part volume and the reject threshold.
Why Does Part Volume Decide the Resolution?
At the same leak rate and test conditions, a larger enclosed volume produces a smaller pressure change over a given measurement interval. Include the part, fixture and connected tubing in that volume. Sensor resolution matters alongside temperature stability, part deformation, valve leakage and the time available to measure.
A tester specification therefore needs the part volume and test method as well as the nominal leak threshold. Better sensing or a longer interval can improve detectability, but the complete fixture and part must demonstrate sufficient separation between acceptable parts and reference leaks under production conditions.
Start with the enclosed volume, allowable test pressure and reject threshold. Trials then establish the fill, settle and measurement times using the actual part and fixture. If the resulting cycle misses the required output, compare parallel stations, reduced fixture volume and alternative test methods against the same detection requirement.
Why Does the Fixture Decide the Result More Than the Sensor?
Fixture leakage and inconsistent sealing can obscure the part’s own leak signal. Check those alongside the sensor, test valves and temperature conditions when results drift or become intermittent.
The seal has to close on the same surface, with the same compression, on every unit. If the part is located loosely, the seal lands differently each cycle and the settling behaviour changes with it. Correct that fixture variation before reviewing the threshold; widening the limit can allow unacceptable leaks to pass.
Dowel-located bases, format-specific pockets and controlled O-ring specifications help keep the sealing condition repeatable. Cylinder position sensing confirms that the clamp reached position before filling begins. Guided fixture motion controls the approach path; the pressure sequence checks whether the sealed test volume is ready for measurement.
| Fixture element | What it controls | What goes wrong without it |
|---|---|---|
| Dowel-located part base | Repeatable part position | Seal lands differently each cycle |
| Specified O-ring set | Repeatable seal compression | Drift as mixed seals enter the machine |
| Clamp position sensing | Confirms the clamp reached its commanded position before filling | A missing or misplaced part can invalidate the cycle; pressure and fixture checks establish whether the test volume sealed |
| Linear bushing guidance | Consistent approach path | Side loading, uneven seal compression |
| Format-specific tube base | Correct fit per product | One base forced to fit two products, sealing on neither |
Seals are consumables. They should appear on a replacement schedule with a part number and an interval, and the interval belongs in the handover pack, not discovered later when reject rates climb.
What Does Temperature Do to a Leak Test?
It corrupts it, quietly, in ways that get blamed on the machine.
Air warms when compressed and cools when expanded. A part filled to test pressure contains air that is briefly warmer than its surroundings, and as it equalises the pressure falls with no leak present. That is what the settle phase absorbs. A part that arrives on the line warm from an upstream process carries the same problem in the other direction, and a part handled by an operator gains heat from the hand.
The countermeasures are ordinary but they have to be decided at design stage. Give the settle phase enough time for the part volume in question. Keep the test station out of direct airflow from fans and air conditioning outlets. Where parts arrive from a heated process, either buffer them so they equalise or accept a longer settle. Where the ambient temperature in the hall swings across a shift, a reference part run at intervals will show the drift before the reject rate does.
None of this is exotic. It is the reason a leak tester that passes factory acceptance in an air-conditioned assembly area can behave differently on a production floor next to a shrink tunnel, and it is worth raising before the machine is placed.
How Many Stations Are Worth Building?
Build as many as the dwell time and the required rate together demand, and no more than that.
The cycle includes loading, clamping, filling, settling, measurement, venting and unloading. Establish the measurement interval from the required detection performance, then examine which other steps can be shortened or overlapped. Parallel stations are useful when measurement time remains the capacity constraint.
For an illustrative nine-station batch with a 30-second measurement interval, the measurement-only ceiling is 1,080 parts per hour: 9 × 3,600 / 30. Actual output is lower once filling, settling, handling and interruptions are included. Size the stations from the complete cycle, and include each channel’s valves, regulator, sensor, fixture and control wiring in the cost comparison.
| Rate driver | Effect on the machine |
|---|---|
| Measurement time at the required leak threshold | Established with the part, fixture, sensing method and environmental conditions |
| Required parts per hour | Guides station count using the complete cycle and handling arrangement |
| Load and unload method | Decides whether stations idle while an operator works |
| Format count | Adds change parts per station, multiplying with station count |
The load and unload method deserves attention at this point, because a nine-station machine loaded by one operator can spend more time waiting for hands than measuring. Where that is the case the answer is either a two-batch arrangement, so one set tests while the other is exchanged, or automated loading, which is covered on the part feeding and presentation page.
What Does the Controller Have to Record?
It has to record enough that a rejected part can be explained a month later, and no more than your quality system will actually read.
The minimum useful record is per part: the station that tested it, the starting pressure after settle, the ending pressure, the calculated decay, the threshold in force at the time, the pass or fail result, and a timestamp. Where parts carry an identity, the record binds to that identity. Where they do not, it binds to the station and the cycle, which is enough to trace back through a tray.
A reference-part routine checks known-good parts and reference leaks at defined intervals, with the results logged for drift review. Recipe management stores the test pressure, settle time, dwell and threshold for each format. Set access permissions and allowed ranges for parameter changes, and record the recipe version used for each test.
For regulated production the record has further requirements around audit trail, access control and signature, which are set out on the electronic batch record page and are decided by the predicate rule.
Which Parts of a Leak Test Cell Are Safety Rated?
The required safety functions follow from the cell’s hazards, operating modes and access needs.
A leak tester closes a fixture around a part and applies pressure. Assess the clamping motion and stored pneumatic energy, including a failed part or fitting. Guard locking may be required while hazardous pressure remains after a stop. Size and control the clamp’s force and speed, and define how pressure is released and safe access is confirmed.
Where a guard interlock or a two-hand control forms part of the protective measure, the performance level required comes out of a risk assessment and is calculated and validated against ISO 13849-1, and it has to be documented that way. The wider treatment of guarding, interlocks and the safety file is on the machine safety and compliance page.
Pneumatic energy needs its own attention in the documentation. A lockable isolation point, a defined venting sequence and a residual pressure indication belong in the machine and in the lockout procedure your EHS team will adopt.
How Does Leak Testing Fit the Quality Process?
Pressure decay gives an integral result for the sealed volume. Use a separate localisation method, such as a bench investigation, when a failed result needs to be traced to a particular joint or sealing surface.
Place the test after the joints and seals it needs to verify have been completed. An earlier test can still check an intermediate assembly, with its own acceptance criterion.
Review the sealing-face dimensions when parts fail at the fixture interface. A dimensional error can prevent a valid leak measurement, so distinguish a test fault from a confirmed product leak in the result handling. Dimensional verification belongs on its own station, covered on the inline dimensional measurement page.
Confirm the detection threshold with representative reference leaks before fixing the production cycle.
What Shapes the Leak Test Specification?
The following information guides fixture design and trials. We can help develop the specification from the drawings, samples and quality requirements already available.
| What to send | Why it changes the machine |
|---|---|
| Internal volume of the part | Contributes to the pressure signal and measurement time, alongside fixture volume and test conditions |
| Test pressure the part tolerates | Sets the regulator range and the safety case |
| Reject threshold and its units | Decides whether the method is viable at all |
| Every format to be run, including planned ones | Sets change parts and recipe count |
| Required parts per hour | Guides station count using the complete cycle and handling arrangement |
| Sealing face drawing and tolerance | Decides the fixture seal design |
| Part temperature on arrival at the station | Decides settle time and buffering |
| Where the results have to go | Decides the data route and the record format |
| Destination market for the machine | Decides the electrical build standard |
A sample part is worth more than the drawing on this particular machine, because the sealing face and the way a real part seats are the two things a drawing describes least well. Send parts that seal well and parts that are known to leak. A leak tester tuned only on good parts has not been tested.
Machines are designed, assembled and tested at our Woodlands Link facility. Motionwell has operated in Singapore since 2014, with ISO 9001:2015 certification and bizSAFE Level 3. Testers destined for medical device production are covered further on the medical device industry page.
Frequently Asked Questions
How small a leak can a pressure decay tester actually find?
At the same leak rate and test conditions, a larger enclosed volume produces a smaller pressure change over the measurement interval. The volume includes the part, fixture and tubing. Sensor resolution, temperature stability, part deformation, valve leakage and measurement time also affect detectability. We assess the required threshold against representative parts and reference leaks, then establish a cycle that separates acceptable parts from leaking ones under production conditions.
Why use individual regulation on a multi-station leak tester?
Individual regulation lets each station establish its test pressure. During pressure-decay measurement, the test volume also needs to be isolated from the supply by the test valves. Regulators alone do not provide that isolation. A multi-channel arrangement can use station-level regulators and pressure sensors, with the pneumatic circuit checked for disturbances while neighbouring stations fill and vent. Parallel capacity is verified with the complete loading and test cycle.
Can the same machine test more than one part size?
Yes. Different tube formats can use interchangeable bases and clamps located on dowel pins. Each format also needs a reviewed test recipe: pressure, settle time, measurement time and the conversion between the specified leak limit and measured pressure decay. The permissible leak rate may remain the same across formats even when the pressure-decay threshold changes. We can work through current and planned formats with your team.