How to perform leak detection on high efficiency filters?
Time:
2021-11-12
Source:
Leak detection of high efficiency filter is an essential task before the clean room project is put into use. From clean wall panels to purification equipment, every detail needs to be carefully checked to ensure that it meets acceptance criteria. Among them, the investigation of air cleanliness, that is, whether the filtering effect of the high-efficiency filter meets the standard, requires leak detection. So, what are the common and reliable methods for leak detection of high efficiency filters? The following are some of the methods shared by high efficiency filter manufacturers.
Generally speaking, there are five kinds of leak detection methods for high efficiency filters: sodium flame method, oil mist method, DOP method, fluorescence method and particle counting method. Here, we mainly introduce the DOP method.
The DOP method is a method that has been widely used to test the efficiency of high-efficiency filters. The method uses 0.3 micron monodisperse dioctyl phthalate (DOP) droplets as a test dust source. The DOP liquid is heated into steam and then condensed into tiny droplets to screen out 0.3 micron particles for testing the filtration efficiency of the filter. The specific high-efficiency filter leak detection process mainly includes the following steps:
1. Preparation:
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Ensure that the test environment meets the requirements, including temperature, humidity, etc.
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Prepare a DOP test solution, typically a 0.3 micron droplet of monodisperse dioctyl phthalate (DOP).
2. Aerosol generation:
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The DOP liquid is heated to produce a vapor, which is then condensed into tiny droplets under specific conditions.
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Through screening, particles of about 0.3 microns are retained as a source of test dust.
3. Aerosol Injection:
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The aerosol is uniformly injected into the upstream side of the high efficiency filter.
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For HEPA in HVAC systems, aerosols can be introduced directly from the negative pressure side of the system fan, or at least 10 duct diameters away from the filter with minimal turning.
4. Aerosol concentration regulation:
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The concentration of the upstream aerosol was measured using an aerosol photometer.
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Adjust the aerosol generator to make the upstream aerosol concentration reach 10~20 μg/mL.
5. filter scanning leak detection:
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Remove the diffuser plate of the high efficiency filter and scan the entire filter surface, between the filter and the frame, between the frame and the frame, and between the frame and the static pressure box.
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When scanning, the sampling head is about 1 inch (about 2.54cm) away from the filter surface, and the scanning speed does not exceed 5 cm/s.
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During the test, if there is an alarm sound (I. e.% LEAKAGE (leakage rate) exceeds 0.01%), it indicates that there is a leak.
6. Leak treatment:
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For leaks, use special glue to repair.
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The area of a single leak cannot be greater than 1% of the total area, and the area of all leaks cannot be greater than 5% of the total area.
7. Result judgment:
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If the leakage rate of the high efficiency filter does not exceed 0.01% at all points during the test, the high efficiency filter is judged to be qualified.
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If there is a leakage rate of more than 0.01%, it is judged as unqualified and needs to be repaired or replaced.
8. Records and Reports:
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Record test results and prepare test reports.
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