Water submersal leak detection/location using a dunk tank for complex assemblies and parts
Water submersal or dunk tanks are a widely used method for location of leaks in complex assemblies and products with air bubbles present around the leaking area.
Most often, differential pressure or vacuum decay is used first to qualify a “tight” part beforehand, one may then need to locate the leak afterwards using this underwater method to repair the identified leaking area. If the part leaks, simple decay of pressure does not show the leakage path. If a part fails the quantifiable test then one method of detecting the leak path is to submerge in water and look for bubbles.
All of these examples shown use the technique of submerging the part in water. Some of these examples were used as the only leak test method. All of these examples had complex sealing requirements prior to the pressure being applied.
When submerging a part the force required to push the part underwater against bouyency may be significant. To work out the force first, calculate the volume of the water displaced by the part, multiply by 10N (1KgF) per litre and then subtract the mass of the part. This calculation will indicate the submersal force require to hold the product underwater.
Each of the systems locate the part or assembly into a fixture. The assembly is then clamped into place either by hand operated toggle clamps or automatically. Some sealing areas and the length of seal are considerable, requiring significant seal forces to both compress the seal and overcome the forces generated by the internal pressure.
In all instances an operator makes a subjective visual check as to whether the part is good or bad. Clearly a bubble has to be formed, released and identified by observation so this technique is limited in its suitability.
Ultrasonic Bubble Testing
There is a technique applied by TQC where by bubbles leaving a part can be sensed and mapped using ultrasonics. The technique is similar to SONAR but on a smaller scale.