The choice of filter testing methods is largely driven by standards by government or industry standards. Some test methods are for government certification (respirators are an example) other testing is required for quality control. Respirator standards require certification testing but also require a quality control plan that specifies the ongoing testing to assure that the filter products adhere to the requirements of the standard. For the highest efficiency filters the standard is 100% testing of the filters. While certification testing includes loading of the filters to determine the maximum penetration (minimum efficiency) this is a destructive test and cannot be used for quality control. Quality control tests therefore focus on measuring the penetration with aerosol and are typically fast tests that can detect defects in the manufacturing process such as cracks in filter media pleats, gaps in the adhesive and assembly defects.
For 100% testing the equipment for the testing of filters is often incorporated into the automated production line and is controlled by a PLC computer that also controls the manufacturing process. For high speed automated production the speed of the testing is critical and multiple test instruments may be required.
Testing of air filters requires airborne particles and detectors for those particles. Since efficiency of filters varies with particle size and different detectors respond differently to particle size the size distribution of the particles and the detector type (and response characteristics) will influence the test results in terms of percent penetration. This means that two test systems testing identical filters can give different results. For any particular filter type these differences will be consistent over time so different test systems can be used to monitor the consistency of filters.
The quality control tests of respirators are intended to detect mechanical failures and secondly to measure the filter efficiency or penetration. When filter defects occur the penetration of particles through the filter is typically much higher than the pass fail criteria for the filters. Different test methods will both show...
Session: G10 - Filter Test Systems II
Day: 23 October 2019
Time: 16:45 - 18:00 h