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Educational Guide:

Introduction to Leak Detection

Educational Guide: Introduction to Leak Detection

Leak detection is the process of testing empty plastic blow-molded containers for leaks and defects. Leak detection helps:

  • Protect package integrity,
  • provide quality assurance, and
  • provide inventory protection. 

Every container that is produced has the potential to have leaks. By taking the time to incorporate leak detection into your production line, you are protecting your brand and providing the end-user with a high-quality product. Leak detection is a critical step in the manufacturing process that helps identify issues that lead to product leaking or contamination before they get to the consumer.

Leak Detection Systems for Empty Plastic Containers

Empty plastic containers are manufactured in high volume to keep up with demands. It is inevitable that some containers will have defects that will cause leaks once the bottles are filled and shipped. Inline leak testing equipment tests plastic bottles as they move through the production line and automatically rejects those with defects.

By performing empty container leak testing – you can identify issues before bottles make it further down the production line, minimizing the potential of recalls associated with bottle quality.

Importance of Leak Detection

Why Leak Test?

Leak testing provides a functional test and verifies that each container will seal and hold pressure. Containers that have been leak-tested will provide a variety of benefits including:

  • Verification that each bottle will seal and hold pressure.
  • Protection from random quality issues.
  • Monitor the blow molding process. Typically, the leak tester is positioned as the first machine after the blow molder, to detect and alert operators quickly to initiate corrective action.
  • Protection of inventory and prevention of costly return.

Leak detection also supports many of the market trends that are being implemented, including:

Consider the value of your inventory. Reflect on past quality issues you have experienced and ask yourself, “is my product leak tested and protected?”

Leak Testing for PET Containers 

Most blow molders use a one-step or two-step process to manufacture PET containers. The manufacturing method used in your molding facility determines the type of bottle leak testing equipment you require. You should also consider the bottle size and shape, as well as your production speed.

  • Testing One-Step Bottles: The one-step blow molding process is the slower of the two manufacturing processes, which makes it better suited for lower volumes. The one-step blow molding process is widely used to produce non-standard shapes, such as flasks and flat ovals because it achieves higher visual quality than the two-step molding process.
  • Testing Two-Step Bottles: The two-step blow molding process is much faster and scalable for larger volumes. Bottles. Bottles for food, beverages, and household cleaners are manufactured using a high-speed two-step molding process.

Both bottle molding processes produce high-quality containers, but neither method can guarantee your bottles will be defect-free

By introducing a pressure decay leak test procedure manufacturing companies can better guarantee a high-quality product, free of defects.

To learn more about blow molding, check out our Leak Detection Fundamental Series:

Reasons You Should Use PET Bottle Leak Testing

Bottle leak testing equipment is a valuable investment.

Many manufacturers rely on spot-checking by employees for PET bottle quality verification, but that is not always enough, especially if small leaks are present.

To learn more about PET container testing, visit: PET Leak Testing for Bottles

Identifying Common Defect Types in PET Bottles

Defective bottle with cocked neckA wide range of defect types can be found within the mass scales of PET bottle production. When performing a bottle leak test, ALPS seeks out the following types of defects:

  • Sealing related defects (short shots, nicks, cocked necks, etc.): The ALPS leak test equipment provides a functional test of every seal surface, by sealing and pressure checking every container.
  • Holes (gate leaks, gate cracks, contamination defects, malformed bottles): Pressure-based leak testing will detect leakage regardless of its location or appearance. The most common weak point for small leaks in a PET container is the gate. The gate is the injection point on the bottom of the container. Leaks can occur anywhere in the bottle if there are material issues (e.g., contamination from recycled material) or process problems affecting the proper formation of the container.
  • Bottle height and topload: Auxiliary inspections can be added to ALPS leak testers to inspect tall and short containers, and to verify that the container does not deform at a specific sealing force (topload).

To learn more about different defect types, check out our blog: What Causes Different Plastic Bottle Defects and How to Prevent Them

Leak Testing Methods

What Are the Different Leak Testing Methods?

Even the smallest of container leaks can cause challenges for bottle manufacturers. It becomes an even larger issue if leaks are identified after the containers reach your customer and end-users.

Testing empty containers for leaks and other defects is the most effective way for bottle manufacturers to ensure product quality.

Having a leak tester on your line is a great first step to ensure the container you are producing meets set quality standards – before it reaches the end-user.

How do you know what kind of leak test options are out there and which one is the best fit for my product? The answer depends on the type of product you are testing and wherein the process you are testing it.

Pressure Decay Leak Test

pressure-decay-leak-testFirst, you need to determine is if you want to test filled containers or empty containers.

If you are testing empty containers that are not required to have a vacuum seal, then pressure decay is the most efficient method.

Pressure decay is also beneficial in applications where the lack of container stability allows the possibility of an empty container to collapse during testing.

To learn more about the pressure decay leak test method and empty containers, read our blog, Pressure Decay Leak Test: Why it is ideal for empty container leak testing.

Vacuum Decay Leak Test

If you are testing a filled container or one that requires a vacuum seal, then the vacuum decay method might be your best solution.

Vacuum decay testing is a non-destructive test that detects leaks in nonporous, rigid, or flexible packages. This method ensures that packaging that contains items such as food or beverage are safe from possible container leakage after being filled and sealed.

What Are the Different Types of Leak Detection Systems?


Flex Pitch Linear Leak Detector Linear leak testers are ‘in-line” defense systems for non-destructive leak testing used for empty containers. 

Available as single or multi-test stations, these solutions are configured to test containers that are “in-line” on a conveyor system.

As containers move along a bottle conveyor system, a stationary or moving test head uses either vacuum decay or pressure decay to leak test each bottle.

Linear leak testers are flexible solutions that are ideal in a range of industries, from food and beverage to pharmaceuticals.

When tailored to the application, linear leak testers typically offer a more flexible and lower-cost approach for leak testing plastic bottles.


NexGen Rotary Leak DetectorRotary leak testers inspect containers as they travel around a turntable, using either pressure decay or vacuum decay leak testing methods.

Test heads check each bottle for leaks, and will automatically reject any defective containers as the bottles exit the machine.

Rotary leak testers are typically configured with multiple stations and are used to test empty containers of all sizes, ranging from small pharmaceutical vials to extra-large bottles.

Rotary leak inspection equipment provides the accuracy and speed required for high-volume leak testing applications. Containers are continuously fed through the rotary leak tester, with the speed and test time determined by the number of leak test stations.



Integrated leak testers are custom designed to be integrated into existing equipment and provide an alternative to purchasing and installing a full leak testing system into a production line. 

Integrated systems are used to test empty and filled containers of various sizes such as pharmaceutical vials, beverage bottles, food packaging, automotive oil bottles, and much more.

How to Select a Leak Detection System

When deciding which leak detector is right for your application, start by identifying a system that can handle these 4 things:

  1. the size and shape of the bottle
  2. quality specifications
  3. the speed of the production line
  4. your current blow molding equipment

To learn more about leak detection systems and application types, check out our blog: What type of leak inspection system is right for my application?

Additionally, factor in bottle handling:

  • How are the bottles presented to the tester?
  • Should the test-head move with the bottle or would an indexing conveyor suffice?
  • Will this platform need to have multiple test heads or require a rotary system to increase the allowed test time?
  • Think about how to minimize changeover time and complexity if you are running multiple bottle types on the same line.

Consider these factors, and for guaranteed success, now and in the future, partner with a company that manufactures multiple solutions that can be tailored for your applications and are supported by a service team that is available 24/7.

To learn more about what factors to consider in a leak detection supplier, read our blog, Comparison: How ALPS Inspection leak testing equipment stacks up against the competition.


Food and Beverage Industries 

Blow molders who manufacture plastic bottles for the food and beverage industry need to avoid product loss.

Leak testing bottles before they’re filled can ensure that defective bottles never reach the filling line. ALPS Inspection leak testers automatically reject defective bottles and machines can test up to 1200 bottles per minute.

Our food and beverage leak testing machines use pressure decay to test the integrity of all types of beverage bottles, including those with more complex, stylized shapes.

Household, Industrial, and Automotive

Loss of product is a concern for most manufacturers of household products, but when hazardous materials are involved, the integrity of blow-molded or injection-molded bottles is paramount.

Manufacturers of containers used for household, personal, automotive, or industrial purposes rely on leak testers to ensure the integrity of their containers – and prevent costly leaks.

Pharmaceuticals and Healthcare

Consumers will not buy pharmaceutical products from companies they cannot trust.

A big part of building trust with consumers is ensuring the integrity of the packaging that products come in.

Pharmaceutical manufacturers stand to lose a lot of money if bottles leak and lead to product loss. ALPS leak testers help pharmaceutical and medical manufacturers prevent product loss by automatically rejecting defective bottles.

For Brand Managers

Introduction to Blow Molding

Choosing the right blow molder partner can make or break your next product. While it may seem like a straightforward process, manufacturing containers to your specifications consistently and up to your quality standards is no small task.

How to select the right leak inspection system

There are several details about the production process that affect the speed & quality of your production process. For example:

  • Did you know that container volume, shape, and rate affect hole size sensitivity?
  • Do you know how you want to handle downstream jams, the way in which bottles are presented upstream, or how the machine integrates into your production line?
  • Did you know that ALPS also has a vision inspection solution that can be integrated into the leak detection platform to save you valuable floor space?

Key information brands need to provide a blow molder to get the most out of them

Understanding what information blow molders will need from you will help you become informed and help pick the best blow molding partner for your needs.  Key information usually includes:

  • Bottle drawings to clarify size, shape, and unique details
  • Hole size specification to ensure quality without jeopardizing speed
  • Your max-rate of production to ensure leak inspection does not slow you down
  • Post-Consumer Recycled Resin requirements

To learn more about how to select the right blow molding partner, visit our brand manager page that educates and walks you through key pieces of information to select the right partner for your needs.

Post-Consumer Recycling

If you are using Post-Consumer Recycled material, or PCR, in the blow molding process, there will be inherent risks.  While using PCR throughout the blow molding the questions then arises, “How do I protect my product while increasing PCR content?”

Using PCR can cause pinholes and leaks in containers.  During the blow molding process when the walls of the container are stretched, particles of contamination can cause weaknesses resulting in holes in the container wall.  The number of defects will depend on two things: 

  1. The amount of contamination in the PCR resin.
  2. The design and wall thickness of the preform and final bottle.

Leak detection is a guarantee that only containers meeting quality standards make it to the end-user.  100% in-line inspection will catch pinhole leaks, neck surface deformities and height irregularities, including short shots.

Commitment to sustainability does not have to mean sacrificing product quality. Leak inspection provides the assurance you need to keep up with market trends, including increased PCR content.

Leak detection and Post Consumer Recycling (PCR)

Educational Resources

Inspection Insights Blog

A collection of insightful content written by the leak detection experts at ALPS Inspection. The collection includes practical tips, best practices, and how to’s on leak detection and package integrity.

Read Inspection Insights Blog

Leak Detection Fundamentals

Read through our Leak Detection Fundamentals collection to learn about the best method and machines for leak testing your container type.

The Importance of Leak Testing in One-Step Stretch Blow-Molded PET Containers

The Importance of Leak Testing in One-Step Stretch Blow-Molded PET Containers

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Leak Testing PET Containers Produced by the Injection Blow Molding Process

Leak Testing PET Containers Produced by the Injection Blow Molding Process

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Leak Testing PET Containers Produced by the Two-Step High Speed Stretch Blow Molding Process

Leak Testing PET Containers Produced by the Two-Step High Speed Stretch Blow Molding Process

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