Low-cost HEPA filter leak detection solution

HEPA filter leak detection
The purpose of the HEPA filter leak detection test is to detect the leakage of the filter and find defects in the HEPA filter and its installation process so as to take remedial measures.
For laminar or turbulent clean rooms with cleanliness requirements of 10,000 or higher, including laminar flow workbenches, laminar flow hoods, self-cleaners, and high-efficiency filters on sterile tunnels and filling lines used in pharmaceutical factories, the above parts must be scanned and inspected on site.
Almost all clean room staff know that the current internationally accepted high-efficiency filter detection method is the DOP method. That is, DOP aerosol is emitted as a dust source on the upwind side of the HEPA air filter being tested, and a photometer is used to sample and detect on the downwind side. The scattered light generated by the dust-containing gas passing through the photometer is converted into electrical quantity through the photoelectric effect and linear amplification and is quickly displayed by the micro ammeter. The collected air sample passes through the diffusion chamber of the photometer. Due to the difference in light intensity caused by particle diffusion, the photometer can measure the relative concentration of the aerosol by measuring this light intensity.
However, the DOP leak detection instrument is expensive and is only widely used in some foreign-funded and joint venture enterprises. More domestic enterprises suffer from a lack of funds and find it difficult to equip DOP leak detectors. They are at a loss about the development of high-efficiency filters and think it is difficult to carry out the verification of purification systems.
Why do we need to conduct high-efficiency filter leak detection?
HEPA filters are ideal terminal filters for industrial clean rooms and biological clean rooms and are also commonly used supporting filters for other purification equipment. The filtration efficiency of the HEPA filter itself is generally tested by the manufacturer, and a filter filtration efficiency test report is generally attached when it leaves the factory. For enterprises, the purpose of leak detection is to timely detect possible defects in the HEPA filter itself and the installation by checking the sealing of the HEPA filter and its connection with the installation frame and taking corresponding remedial measures to ensure the cleanliness of the area.
Why do we need to conduct HEPA filter leak detection?
Once the HEPA filter leaks, the number of dust particles and bacteria in the clean room may exceed the standard, thus affecting the product quality. Leak detection of HEPA filters is to discover the defects of the HEPA filter and its installation to take remedial measures.
A leak detection test is the basis of particle determination, and its importance is no less than particle determination.
The leak test and air flow rate have met the specified requirements, the airflow uniformity is also within the specified control range, and the natural cleanliness is also guaranteed.
There are two main reasons for the leakage of the HEPA filter. One is that the HEPA filter is damaged during the installation process, and the other is that the installation seal is unqualified.
SX-L310S HEPA filter counting leak detector
The SX-L310S HEPA filter counting leak detector is designed according to the requirements of ISO14633-3 B.6.3 and IEST-RP-CC034.2 specifications. It is a special instrument for scanning and leak detection of high-efficiency air outlets in clean rooms (areas). It consists of three parts: an aerosol generator, a particle diluter, and a counting leak detector (equipped with a handheld intelligent scanning probe).
The SX-L310S HEPA filter counting leak detector uses the counting method to scan and detect leaks. The counting leak detector and the particle counter are used to detect the upstream concentration of the filter, and the downstream leakage point value is calculated according to the marked efficiency of the filter. The leakage point value downstream of the high-efficiency air outlet is detected by actual scanning and compared with the calculated leakage point value to achieve leakage detection of the high-efficiency air outlet. The Appendix B.6.3 of the third part of GB/T25915 "Clean Rooms and Related Controlled Environments", the procedures for scanning leak detection by counting method are detailed. GB50591 "Clean Room Construction and Acceptance Specifications" recommends that the counting scanning method should be preferred for leak detection.
Selection of test aerosol
The aerosol used for counting scanning leak detection of high-efficiency and super HEPA filters can be DOP, DEHS, PAO, etc., but not limited to these substances.
Make the upstream dust concentration much lower than the photometer method, which has little damage to the filter; the aerosol generated can be a monodisperse aerosol or a polydisperse aerosol.
However, no matter which type of aerosol occurs, the concentration and particle size distribution of the generated aerosol should be kept stable during the test.
When using monodisperse aerosol for the counting scanning leak detection test, the deviation between the counting median diameter of the test aerosol and the filter material MPPS should not exceed 10%. When using polydisperse aerosol for a leak detection test, the deviation between the counting median diameter of the test aerosol and the filter material MPPS can reach 50%.
Test air duct system
Test air regulation
The test air should be pre-treated before mixing with the test aerosol, and a suitable pre-filter (such as coarse-efficiency, medium-efficiency, and HEPA filters with performance in accordance with national standards) should be configured to ensure its cleanliness (should be at least ISO7 level).
Air volume regulation
The test air duct should have air volume regulation measures (such as changing the fan speed or using an air volume regulating valve). During the test, the test air volume should be maintained within ±3% of the rated air volume of the tested filter.
Air volume test
The air volume measurement should adopt standard or calibrated methods (such as using orifice plates, nozzles, and venturi tubes to test the air volume by pressure drop). The measurement error should not exceed 5% of the measured value.
Scanning system
The filter scanning leak test can be performed by manual scanning.
The equipped counting leak detector has a handheld intelligent scanning probe with a sampling flow rate of 28.3L/min and a recommended scanning speed of 3 to 5cm/s.
The downstream aerosol delivery pipe should deliver particles into the measurement chamber of the particle counter as quickly and without loss as possible. Therefore, the delivery pipe should be as short as possible without dead bends along the way. The surface of the pipe material is smooth and does not emit particles.