Setting the right allowable leak rate isn't always straightforward, especially when you're leak testing a final assembly made up of multiple subassemblies or components.
A final product will only pass leak testing if all the individual components and the completed assembly are tested with the final leak rate requirement in mind. If subassembly leak limits are too lenient, their combined leakage can exceed the final assembly specification, even when every individual component passes inspection.
This concept, known as leak rate stack up, is critical in industries such as automotive, EV battery manufacturing, HVAC, refrigeration and industrial fluid and cooling systems.
What is Leak Rate Stack Up?
Leak rate stack up is the combined leakage of multiple components or sealing interfaces once they are assembled into a finished product.
Although every individual part may pass its own leak test, each allowable leak contributes to the total leakage of the completed assembly. However, establishing a leak rate limit for the final assembly isn’t as simple as adding up the allowable leak rates of the subassemblies. This is because the final allowable leak rate based solely on stack up could likely far exceed the allowable leak limits for its function.
For example, imagine a final assembly consisting of 20 cooling plates.
Each cooling plate is individually leak tested with an allowable leak rate of:
5 sccm at 100 psi
If every cooling plate passes at its maximum allowable limit, the theoretical worst-case leak rate of the completed assembly would be:
20 cooling plates × 5 sccm = 100 sccm
However, suppose the finished cooling assembly must be watertight, and thus is only allowed to leak at a max allowable rate of 10 sccm during its final leak test. Although every cooling plate individually passed inspection, the combined leak rate could be 10x higher than the final assembly specification.
How to Prevent Leak Rate Stack Up Problems
The best way to avoid leak rate stack up is to consider a combination of all the individual components and the final assembly requirements when establishing your leak testing process.
Test Subassemblies More Stringently
Subassemblies should typically be tested more stringently than the final assembly. This may mean testing at a higher pressure, a lower allowable leak rate, or both.
For example, individual cooling plates may be tested at 100 psi, while the completed assembly is tested at 30 psi. Testing subcomponents under more demanding conditions helps detect small leaks before assembly and reduces the risk of leak rate stack up causing failures at the end of the production line.
Test Throughout the Manufacturing Process
Don't rely solely on the final assembly leak test. Leaks can be introduced during assembly through seals, fittings, welding, or handling, even if every subcomponent passed inspection.
By leak testing both subassemblies and the finished product, manufacturers can identify where leaks are occurring, reduce troubleshooting time, and improve overall product quality.
Need Help Developing Your Leak Testing Process?
Whether you're developing a new leak test or optimizing an existing production line, establishing the right leak rate limits and testing strategy can significantly improve yield, reduce false rejects and scrap, and ensure your products meet the highest quality and performance requirements.
Contact us today to learn how we can help you design a leak testing process that delivers reliable results and ensures the highest-quality final assemblies.