How to Test for Leaks in Product Seals Without Contacting Water: The Principles and Limitations of Air Leak Testers

Is it possible to determine whether a product is waterproof without exposing it to water, simply by measuring changes in air pressure?
This issue causes many engineers to furrow their brows when they first encounter a leak tester.

The answer lies in a real-world case study.

I. If the product isn’t submerged in water, how can you tell if it’s leaking?

First EncounterAir tightness testerAlmost every company asks the same question:Without using water, just by looking at changes in air pressure—can we trust the data?

Fully Enclosed Surveying InstrumentAir tightness testing equipment

The domestic brand JCGK (Jingcheng Engineering) gave a demonstration using a road surveying instrument.This equipment has a fully enclosed design; the airtightness of the housing and all sealing areas must be verified.. The customer's requirement is to test the pressure 15 kPa. Engineers select a suitable sealed test chamber based on the product's shape and internal dimensions, then adjust it to accommodate products of different sizes by replacing the internal filling modules. Once the parameters are set, the equipment is started, and the leakage value displayed on the screen stabilizes at 1PaThe

Getting a reading is only half the battle. This prototype has since beenPrecision EngineeringReal Water Leakage TesterA pressurized water immersion test was conducted, and no bubbles were observed throughout the entire process. The airtightness test showed low leakage values, and the water test revealed no visible leaks,Both paths lead to the same conclusionThe

Precision Engineering'sAirtight water leakage tester

There are three points to note. 1 Pa is the leakage value displayed by the instrument in this demonstration; it is not a universal pass/fail threshold for all products, nor is it equivalent to the absolute leakage rate. Whether a product passes or fails is determined jointly by product standards, test conditions, and the set threshold. This case demonstrates that, when test procedures and parameters are properly designed and validated, airtightness testing can provide assurance of sealing quality.Quantifiable criteria for assessmentThe

II. Why Can Atmospheric Pressure Be Used Instead of Water Pressure for Assessment?

Airtightness TesterThe principle is:Gas is introduced into an enclosed space at a set pressure, and the presence of a leak is determined by monitoring changes in pressure or gas flow rate.The

Road surveying instruments, outdoor surveillance equipment, instrument enclosures, and certain consumer electronics productsNo dedicated inflation port. During testing, a custom test chamber and sealing fixture are used to create a testable, sealed space for them.

The entire process consists of five steps. First, place the product into a test chamber that matches its shape to ensure a reliable seal. Next, set the pressure according to the product’s structure and testing requirements; in this demonstration, the pressure is set to 15 kPa. Then, fill the test chamber with gas and allow time for the pressure to stabilize. During the testing phase, the device monitors pressure changes and calculates or displays leakage data based on the corresponding algorithm. Finally, the device compares the results with the preset threshold and outputs a pass or fail result.

Air pressure can be used for leak testing because seal defects in a product create pathways for gas to escape; the instrument detects the passage of gas through these pathways, allowing the integrity of the seal to be assessed.

There is a boundary here:The permeation behavior of gases and water differs under all conditions.. Gas test results must correspond to actual waterproofing requirements; typically, immersion, water spray, or other applicable waterproofing validation methods are needed to determine appropriate test pressures and leakage thresholds. Therefore, airtightness testing does not simply involve converting water pressure to air pressure, but rather uses quantifiable gas data to establish quality control methods that align with the product’s waterproofing requirements.

III. How to Verify Accuracy: Four Dimensions, All of Which Are Essential

Determining whether aAir tightness testerYou can’t judge reliability based solely on a number on the screen or the stated minimum resolution. Check the following four aspects one by one.

1. The test results match the actual condition of the product.

In this case,The airtightness test results are consistent with the water immersion test results.... indicating that, under the current sample and test conditions, there was no apparent conflict between the two methods.

Mass-production projects require greater attention to detail:Select known good samples, known defective samples, or validated reference samples for comparison., to establish a correlation between the test results and the actual sealing condition.

2. Repeated testing of the same product yields consistent data

Under the same pressure, with the same test setup, the same test duration, and under similar environmental conditions,Test the same product multiple times to observe fluctuations in the dataThe

When data continues to drift, there are five areas to investigate:Elastic deformation of the product material, changes in gas temperature, tooling seals, stability of the gas lines, and whether the product has fully returned to its initial state. Complete test records must be kept for repeatability verification; you cannot simply select data from a single instance that performed well.

3. Resolution is not the same as accuracy

Resolution is the smallest change that an instrument can display or detect; it is not the same as the actual measurement accuracy of the entire test system.. The fact that the screen can display a 1 Pa change does not mean that every workpiece can achieve an accuracy of 1 Pa under every pressure and environmental condition.

Actual testing capacityDetermined by a combination of sensor performance, fixture design, product volume, temperature fluctuations, test duration, and leak thresholdsThe

4. The test fixture does not interfere with the results

Fully enclosed products such as road surveying instruments do not have a direct inflation port,The jig has two functions: to secure the product and to create a reliable, sealed test chamber.The

This Case StudyThe use of interchangeable internal filling modules to accommodate different sizes enhances the solution's versatility.. However, each time the model is changed, the seal condition, effective test volume, and test parameters must be reconfirmed.

IV. Water Testing and Leak Testing: One section of each pipe

The soaking method is intuitive:Place the product in water and observe whether bubbles appear under specified conditions. This method can directly pinpoint the location of a leak....that's what makes it valuable.

Once mass production began, the limitations of the immersion method became apparent:As a result, when relying on visual inspection, tiny bubbles are difficult to detect....Moisture must be addressed after testing, and it is difficult to directly generate standardized, quantifiable data.Airtightness TesterPrevent the product from coming into contact with water; use pressure, pressure differentials, or changes in flow rate to perform the test.... making it easier to integrate with automated workstations and quality data systems.

Comparison Program	Airtightness Tester	Traditional Soaking Method
Detection method	Monitoring of pressure or flow changes	Check for bubbles
Data logging	Can generate digitized test records	Typically relies on manual observation and recording
Product comes into contact with water	A standard dry air leak test does not require contact with water.	The product comes into direct contact with water
automation integration	Ideal for integration with machine tools, PLCs, and production line systems	The level of automation depends on the specific solution.
Detecting Minor Leaks	Determined based on the instrument's performance and validated thresholds	Due to factors such as bubble size and observation conditions
Scope of Application	The correlation between the gas detection results and the product's waterproofing requirements must be verified.	Visible bubbles can be observed directly under test conditions

The two methods are complementary:Leak testing is used for rapid screening, quantitative assessment, and process control during mass production, while water testing is used for visual localization and cross-validation.. The specific combination depends on product risk, testing standards, and process requirements; no single option can completely replace another.

V. Testing Protocol for Fully Enclosed Products

JCGK Jingcheng Engineering’s solution for this road surveying instrument consists of five key points.

• Custom Sealed Test Chamber, design the test space based on the external dimensions of the fully enclosed product.
• Replaceable Filling Modules...adapt to different sizes, reducing the need to redevelop an entire set of tooling whenever product specifications change.
• Parameters are set as needed, set the test pressure to 15 kPa and the corresponding test duration according to the customer's requirements.
• Real-time data display, Monitor leakage-related data during the test and make a determination based on the established criteria.
• Cross-verification with waterproofing validation...compare the airtightness test results with the water immersion test results to help establish reasonable test parameters and pass/fail thresholds.

These solutions can be used to evaluate outdoor meters, security equipment, smart devices, home appliance enclosures, and other products that require sealing.When there are specific requirements for production capacity and processes, it is also possible to evaluate automated loading and unloading via robotic arms, barcode scanning and binding, automatic result determination, and data traceability.The

The above outlines the design approach. Whether it is applicable will depend on the specific product structure, testing standards, and sample validation results. It may beContact Jingcheng Engineering for a free airtightness test and to schedule a one-on-one consultation with an engineer.The

VI. When to Introduce ItAirtightness Tester?

If any of the following six situations arise, it is worth evaluating an airtightness testing plan:

1. Products are subject to factory inspection requirements regarding sealing or water resistance;
2. Water immersion testing is time-consuming and slows down the production line's cycle time;
3. Manual observation of bubbles; results may vary from person to person;
4. After testing, the item must be dried or cleaned, which adds an extra step;
5. Test results for each product must be recorded to support quality traceability;
6. A single set of equipment is used to produce products in multiple sizes, with the goal of reducing changeover costs.

Start the selection process with these six pieces of information:Waterproofing requirements, test pressure, permissible leakage limits, product volume, test cycle time, and whether automation is required. Once the information is confirmed, select from Jingcheng Engineering’s direct-pressure, differential-pressure, or other methods.

Conclusion

Back to this road surveying instrument:At a set pressure of 15 kPa, the airtightness tester displayed a leakage value of 1 Pa; during the subsequent water immersion test on the same sample, no visible bubbles were observed.The

This case study demonstrates how a leak tester works:

The instrument detects leak signals by monitoring changes in gas pressure, then calibrates itself using actual products, ultimately establishing a repeatable quality control process.

For manufacturing companies, a valuable airtightness testing solution is not just about displaying a number on a screen; rather, it lies inUnder validated conditions, reliably distinguish between conforming and nonconforming products, and incorporate this into routine mass-production quality inspections.The

When a product requires waterproofing, sealing, or micro-leak testing, the appropriate testing method and fixture design can be evaluated based on the product drawings, test pressure, allowable leakage values, and production line cycle time.. Shenzhen Jingcheng Engineering Technology Co., Ltd.(JCGK) can discuss airtightness testing solutions and evaluate tooling compatibility based on specific product requirements, helping companies transition from sample validation to a practical mass-production testing process.

Original Statement: This article was written by ShenShenzhen Jingcheng Engineering Technology Co., Ltd.Written by the technical team, reproduced with attribution.Data sources: Precision Engineering internal test data and customer cases.