Common leak detection methods for high efficiency filters

I. Sodium flame method

 

The test dust source for the sodium flame method is a polydisperse phase sodium chloride salt mist, the "amount" being the brightness of the hydrogen flame when the salt mist is burned.

 

The brine is stirred by compressed air and splashed, dried to form tiny salt crystal particles, and enters the air duct, which is sampled before and after the filter respectively.

 

The salt mist containing the gas sample causes the hydrogen flame to turn blue in color and increase in brightness. The brightness of the flame is used to determine the salt mist concentration of the air and to determine the filtering efficiency of the filter for salt mist.

 

The main detection instrument is the flame photometer, the method can only sponge detection sensitivity is not high, and can not be detected on the ultra-high efficiency filter.

 

II. Oil mist method

 

Oil mist method of testing the dust source for oil mist, "amount" for the turbidity of the air containing oil mist, before and after the filter to determine the difference in turbidity of the air sample to the filter on the filtering efficiency of oil mist particles.

 

Germany requires the use of paraffin oil, an oil mist particle size of 0.3 to 0.5 microns. The oil mist method in the detection of filters, easy to cause damage to the filter, and can not directly read the value, wasting time.

 

III. DOP method

 

This method used to be a common method for testing high-efficiency filter sponges internationally.

 

Its test dust source is 0.3-micron monodisperse phase dioctyl phthalate (DOP) droplets, also known as "hot DOP", "amount" for the degree of turbidity of air containing DOP.

 

The DOP liquid is heated to a vapor, which condenses into tiny droplets under certain conditions, leaving particles of around 0.3 microns after removing the oversized and undersized droplets, which enter the duct.

 

IV. Fluorescence method

 

The test dust source for the fluorescence method is sodium fluorescein dust generated by the nebulizer.

 

The test method is to first sample before and after the filter sponge, then dissolve the sodium fluorescein on the sampled filter paper with water, and then measure the fluorescence brightness of the aqueous solution containing sodium fluorescein under specific conditions, the brightness responds to the weight of the dust, from which the filter's filtration efficiency is calculated.

 

V. Particle counting method

 

This method is common in Europe, and the United States ultra-high efficiency air filter test method is relatively similar and is currently the mainstream of the international sponge test method.

 

The dust source is polydisperse phase droplets or solid dust of defined particle size. Sometimes filter manufacturers have to use atmospheric dust or other specific dust according to the specific requirements of the user.

 

If a condensation counter is used in the test, a monodisperse phase test dust source with a known particle size must be used. The main measuring instrument is a high-flow laser particle counter or a condensation counter.

 

The counter is used to scan the entire air outlet surface of the filter and the counter gives the number of dusts at each point and also allows the local efficiency of each point to be compared.