When it comes to performing a leak test, one of the key factors that can influence the test is the volume of the part being tested, as well as the internal volume of your testing equipment. These volumes directly impact the speed and efficiency of the testing process.
Let’s break it down and see how these elements play a crucial role, using a common example: a bike tire vs. a truck tire.
The Bike Tire vs. Truck Tire Leak Test: Which Empties First?
Let’s consider the scenario of a nail-sized hole in two different objects: a bike tire and a truck tire. Both tires are at the same initial pressure—let’s say 100 psi.
At first glance, you might think that because the hole size is the same, both tires would leak at the same rate. And in terms of the flow rate (i.e., how much air is escaping through the hole per unit of time), this is indeed true. The hole is the same size, so the air is leaving at the same flow rate, assuming both are at 100 psi.
But here’s where the real difference lies: the pressure decay.
- The truck tire has a much larger internal volume compared to the bike tire. As a result, it holds more air and will lose pressure more slowly when a nail-sized hole is introduced.
- The bike tire, on the other hand, has a much smaller volume and will experience a faster pressure decay—the air will escape quicker and the tire will empty faster.
So, while the flow rate at the hole is the same, the larger volume of the truck tire means it will take longer to empty, compared to the bike tire, which empties much faster. This is a perfect demonstration of how part volume influences the speed of the leak test.
The Importance of Test Circuit Design
Let’s look at another important factor: your test circuit. The diameter of your tubing, the routing path through the tester, and the path to the part being tested significantly affect the internal volume and therefore the speed of the test.
- Large-diameter tubing: While it may seem like it would make testing faster, in reality, large tubing can introduce extra volume and slow down the pressure decay. The larger the tubing, the more air is stored within the circuit, and this can distort the actual leak test results.
- Routing path: If the tubing has long or convoluted paths, additional volume is introduced into the system, which can again slow down the test. It’s important to plan out the shortest and most direct path for the air to travel.
The goal is to minimize unnecessary volume in the test circuit, keeping it as streamlined and efficient as possible.
Optimizing the Internal Volume of Your Leak Tester
The internal volume of the leak tester itself plays a huge role in the accuracy and speed of the test. You want the internal volume of your leak tester to be as small as possible—ideally under 1.0 cc. For example, Zaxis leak testers have a standard 0.8 cc internal volume, which can be reduced to 0.1cc on special order.
Why? Well, the more air your tester holds internally, the more it can affect the test. When your tester has a larger internal volume, it will cause a slower/less sensitive pressure decay, and you may not get accurate readings in a timely manner.
Designing Fixtures for Maximum Efficiency
Another factor that directly impacts the leak test speed is the design of your fixture. Proper fixture design ensures that your parts fit snugly, reducing dead space in the system.
- Close-fitting inserts and nests: These are crucial for minimizing gaps and dead spaces where air could accumulate. Any extra air in these areas can slow down the pressure decay, making the test less efficient.
By reducing dead space and ensuring that the parts being tested are securely and tightly held in place, you can improve the accuracy and speed of the leak test.
Conclusion: Volume is Key to Leak Test Speed
At the end of the day, leak test speed is greatly influenced by both the volume of the part being tested and the testing equipment itself. Whether you’re testing a 125-gallon tank or a miniature check valve, understanding how volume impacts pressure decay and flow rate can help you design a more efficient and accurate test.
From the test circuit design to the internal volume of your tester and fixture clearances, every element needs to be optimized for the best results. Keep these principles in mind to speed up your testing process and achieve more reliable results in less time.
