The main possible reasons for the negative leak detection value of the air tightness leak detector are as follows:

1.The tested workpiece has better sealing than the standard workpiece

The leak detector needs to display the leakage value (usually Kpa).Leak detectors using the direct pressure method and differential pressure method need to be compensated and calibrated before displaying the leakage rate.That is, finding the system zero point by getting infinitely close to the leak-free standard workpiece (some leak detection instrument manufacturers call this process zero-point calibration of the system, and some instruments call it the system zero-point offset) and after connecting the leak with a fixed leakage rate to this system that is infinitely close to the leak-free workpiece, the test results and the leak value of the fixed leak rate require corresponding parameter values ​​(this process is called calibration volume by some leak detector manufacturers, and calibration process by some leak detectors).Then the leak detection instrument calibrated using this method will be closer to the leak-free state, so negative values ​​will appear.This situation indicates that there is nothing abnormal about the leak detector.

Therefore, customers of automobile engines, lamps, cameras or parts are provided with leak-free standard workpieces.Standard workpieces are very important and should be almost air-tight.Before the test, compensate the workpiece and pipeline fixture system to a value of 0 (even if the workpiece and pipeline fixture system does not leak, there will definitely be pressure changes, because absolutely still air does not exist, and the air will also be affected by the gravity of the earth. For details, please refer to geocentric gravity. Therefore, it can be seen that there is always some pressure attenuation during the test phase of airtight leak detection equipment).

ifAir tightness testing equipmentDuring the test, there was a workpiece being tested that was better than the selected standard workpiece (the pressure attenuation was smaller than the selected non-leakage standard workpiece). Since we previously set the leakage value of the non-leakage standard workpiece as 0Kpa, the leakage value of the tested workpiece was displayed as a negative value.

Suggestion: Try to select the standard parts with the smallest leakage and the best sealing performance for air tightness testing.

2.Ambient temperature changes.

Ambient temperature refers to: the change in temperature around the leak detector.Or the temperature of the test workpiece itself changes.Or the temperature of the pipeline from the leak detector to the workpiece being measured changes.

Changes in temperature affect the test leakage value.If the conditions such as the test workpiece fixture remain unchanged, the temperature rise causes the gas to expand, and the expanded gas causes the pressure change to decrease, and the test value will be smaller than the original value. If the test workpiece has good sealing, this may occur.

Suggestion: There may be large temperature changes in the outside world in the morning and evening throughout the day. It is best to warm up the engine for ten minutes before doing the compensation calibration, or do the calibration at noon.Try to keep the temperature of the leak detection instrument and workpiece consistent with the ambient temperature.The temperature compensation system built into the air tightness leak detector of Shenzhen Hirays Automation Technology has improved the temperature difference in this area.

3.Change in product volume.

The volume of the product under test may change during the air tightness detector test. During the actual test, we found that when testing the engine oil passage, the customer mistakenly injected oil into the oil passage, resulting in a smaller volume.At that time, the test value showed a large negative value.Sudden changes in volume may cause test results to become smaller and negative.Volume changes can cause negative test results.

Suggestion: Pay attention to observe whether the volume of the product under test and the master (standard) workpiece are equal.

4.Deformation of clamps and pipelines used in airtight leak detection equipment.It may also cause the leakage value to appear negative.

Deformation of the fixture and pipeline may cause the entire test volume to change.It may also result in negative test results.For example, during the test, there is no leakage in the workpiece or the pipeline itself, but the clamp sealing rubber creeps at this time. The creep causes the internal pressure of the pipeline connected to the workpiece to rise, and a negative value may be generated at this time.Therefore, it is also important to customize special inspection tooling.

Shenzhen Hiraysi can provide professional seal leakage detection solutions, customize detection tooling as needed, and provide one-stop detection services.