A leaking bottle or pouch can ruin an entire carton, damage a retailer’s shelf and harm a brand’s reputation. Leaks can be caused by poor sealing, damaged containers, loose caps or defective liners. Testing for leaks during production catches problems early, before they spread through the supply chain.
Why Leaks Happen
Common causes include:
- Incorrect capping torque
- Damaged bottle necks or threads
- Poor induction seals
- Weak heat seals on pouches
- Pinholes in containers
- Contamination in seal areas
Vacuum Decay Testing
Containers are placed in a sealed chamber, and a vacuum is applied. If the container leaks, the pressure in the chamber changes. Sensitive instruments detect even tiny leaks. Vacuum decay testing is non-destructive and widely used for quality control.
Bubble Testing
Containers are submerged in water inside a vacuum chamber. Bubbles reveal leak locations. This simple method is useful for checking sealing processes and finding the source of leaks, though it is usually used on samples rather than all production.
Pressure Decay Testing
Empty containers are pressurised and monitored for pressure loss. This method is common for testing bottles before filling, especially in blow moulding.
Squeeze Testing
On production lines, inline squeeze testers apply gentle pressure to filled containers and measure the response. Leaking containers behave differently and are rejected.
Inline Inspection Systems
High-speed lines may use inline leak detection based on pressure sensors, cameras or other technologies. These test every container without slowing the line.
Choosing a Method
Consider your container type, product, speed and the leak size you need to detect. Laboratory methods suit sample testing; inline systems suit 100 percent inspection.
Building Leak Testing Into Your Routine
Test samples at the start of each shift and after every changeover. Record results to identify trends. Investigate the root cause of any leaks found.
Setting Acceptance Limits
Every leak test needs a clear pass and fail limit. That limit should relate to the risk: a product that spoils quickly, a corrosive chemical or a sterile medicine requires tighter limits than a dry snack pouch. Work with your quality team to define the leak size that matters for your product and choose a test method sensitive enough to detect it. Validate the method using containers with known defects, such as bottles with deliberately created pinholes, to confirm that the test reliably catches them.
Testing Pouches and Flexible Packs
Flexible packs have long seals that can fail at any point. Burst tests, which inflate the pack until it fails, measure seal strength. Dye penetration tests show channel leaks in seals. Squeeze tests on the line can catch grossly leaking packs. Combining a routine inline check with periodic laboratory testing gives good coverage.
Linking Results to Root Causes
When a leak is found, check the capping or sealing settings, the condition of the containers and the closures. Keeping test records alongside machine settings helps identify patterns, such as leaks increasing after a changeover or with a particular batch of caps.
Prevention Is Best
Testing finds problems, but good machine settings prevent them. Correct capping torque, well-maintained sealing equipment and quality containers reduce leaks at the source.
Hilden supplies capping, sealing and inspection equipment and can help you build leak prevention and testing into your line.