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Air filter leak detection

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air filter

According to the \"Code for Clean Room Construction and Acceptance\", its efficientair filterThe following methods are available for leak detection:

1. Scanning by leak detector method

The air filter to be detected for leaks must have been tested for air volume, which is between 80% and 120% of the design air volume.

When there are multiple filters on the same air supply surface, if the structure allows, it is advisable to use the method of exposing only one filter at a time.

When several or all filters must be exposed to aerosol at the same time, in order to cause uniform mixing of all filters, it is advisable to introduce leak detection aerosol into the suction end of the fan or the branch pipe in front of these filters, and immediately The concentration on the upwind side is measured directly in front of the filter.

2. Leak detection by particle counter method

The air volume of the leak-tested filter must have been measured, and the air volume must be between 80% and 120% of the design air volume.

The instrument is a light scattering particle counter capable of measuring 0.5 micron with a sampling volume of 1-3L/min. For leak detection, a mass particle counter is not suitable.

What I want to explain now is:

On-site leak detection using the DOP method is neither easy nor necessary, and even less intuitive, because it reflects the relative concentration rather than the amount of particles. In addition, DOP brings pollution to the filter, and whether it is carcinogenic is still a question.

It turns out that these two leak detection methods require a certain upstream concentration, which is based on the minimum scale of the instrument, the efficiency of the high-efficiency filter is defined as 99.97%, and the minimum reading of the particle counter is 1 particle.

However, the latest research and measurement practice show that the upstream concentration does not need to be as large as it should be sufficient to bring danger to the work area, and it does not matter if it cannot be detected.

According to experiments, efficientair filterThe upstream concentration may be around 3000 grains/L. Calculations show that for leaks as small as 0.2mm, at a distance of 25mm from the surface of the filter (this is a common requirement of relevant standards at home and abroad), when sampling at a flow rate of 2.83L/min, a concentration of about 25 particles/L will be obtained , This is completely measurable.

3. The construction acceptance specification stipulates that the number of particles measured by the particle counter during leak detection is not more than 3 times or 2 times the theoretical number of particles that can pass through (the latter is for ultra-high efficiency filters). The basis for this is the calculation proposed by the author.

However, according to the above-mentioned latest research, for ordinary 0.5 micron high-efficiency filters with 100 as the highest target, if the number of particles measured at 25mm from the filter surface does not exceed 3 particles/L, it will not bring to the work area There is a danger of exceeding the standard, so this can be used as a leak detection standard for ordinary high-efficiency air filters.

4. Confirm

It must be efficient for a hundred placesair filterA comprehensive leak detection qualification report on site before installation (allowing to include a qualified report after repair), and a border scanning qualification report after installation (allowing to include a qualified report after repair).

For places below grade 100, there must be a high-efficiency air filter after installation (including repair and plugging) frame scanning sampling inspection qualification report (each room shall have no less than one air outlet, and when there are many air outlets, the sampling rate should be no less than 20%)


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