High efficiency filters must be inspected and installed one by one
The leakage point of high efficiency filter cannot be found by visual inspection. In high cleanliness occasions, a leaking high-efficiency filter is enough to fail the whole project. Therefore, each high-efficiency filter must be tested on a special test bench according to the standard before leaving the factory. Once the high-efficiency filter that has not been tested one by one is selected, the user will bear the risk of project failure.
Different manufacturers may adopt different test methods, and users may recognize or doubt specific methods. The bottom line of users is that each high-efficiency filter must be routinely tested in the manufacture of high-efficiency filter. In contrast, the test method is the second.
In foreign manufacturers that pay more attention to testing the high-efficiency filters just off the production line, 3% of the filters with leakage points can be picked out, some of which can be repaired into qualified products, while the other part can be scrapped because it cannot be repaired. A few years ago, the high-efficiency filter just off the production line of domestic manufacturers was tested, and the unqualified rate was 3% ~ 10%. In extreme cases, the unqualified rate could be as high as 30%. Sadly, among the hundreds of high-efficiency filter manufacturers in China, less than 10% have test methods, and few of them can adhere to the test one by one. A large number of untested high-efficiency filters flow into the market, and many users do not investigate.
Insisting on testing one by one will inevitably increase the production cost (test cost, waste products) and the product price will increase slightly. As long as you can prove that each high-efficiency filter has been strictly tested, users will not care about the resulting price difference.