Leak testing is the checking of every valve, pump or battery case for leaks as it is made, with instruments and software that keep the record of each test. A product that leaks can fail in use, so the plant tests all of them and does not rely on a sample.
The simplest method uses air. The tester seals the product, fills it with air to a set pressure, and then waits. If the pressure falls, air is escaping. The instrument measures the fall in pressure very precisely, so that it can find leaks too small to see.
The pressure test is sensitive to temperature, because warm air in a sealed case expands and raises the pressure by itself. This is why the tester waits for the air to settle before it measures. Other methods exist. A case can be put under water and watched for bubbles, which is cheap but slow. For extremely small leaks, such as those in a sealed electronic part, the tester fills the product with helium and uses a sensor that detects helium gas escaping.
Imagine a plant in Sanand that makes battery cases for electric vehicles. Each case must keep out water. The tester seals the case and raises the air pressure inside to 0.3 bar above the outside. It waits 10 seconds for the air to settle, then measures the pressure for another 10 seconds. If the pressure falls by more than the limit, for example 5 pascals, the case is rejected. The whole test takes about half a minute.
The software stores the result of each test with the case's serial number. If a battery pack is later found to leak, the plant can look at the original record. This is a part of traceability. The records go to the MES and the quality management system.
The test is used for the battery cells and battery packs of vehicles, and for valves and pumps. It sits with machine vision and the coordinate measuring machine as one of the three ways of checking quality in a plant.