Dear chavannilesh,

Particle size is the main factor for the selection of a filter.

The filter type (and the manufacturer) determines the allowable filter load in m/min.

The material properties, stickiness, electrostatic behavior and suspension velocity are also important.

The filter manufacturer has the experience.

The permissible can velocity is between 0.5 and 0.75 times the suspension velocity.

The can velocity is measured between the filter housing and the cross section of the filters and is thereby independent of the filter type.

The filter pulse interval/duration setting is also important to avoid under cleaning or over cleaning.

Be careful, which suspension velocity is used in a vacuum system or a pressure system with a back pressure. ■

Dear chavannilesh,

The suspension velocity (or terminal velocity) is calculated as:

v-suspension = SQRT((4*particlesize*materialdensity)/(3*dragfactor*airdensity)

v-suspension in m/sec

particle size in m

material density in kg/m3

drag factor in –

air density in kg/m3

For a filter, the smaller fraction of the material is collected by the filter cloth, until a layer has been built up.

At the moment that the dust layer reaches a certain thickness, the dust layer is blown of the filter material in dust agglomerations of a bigger size than the original dust particles.

Therefore, the cleaning pulse must not be too strong, to avoid that the dust agglomerations are destroyed to dust again. (Over cleaning)

v-suspension must be calculated under the most unfavorable conditions in the pneumatic conveying cycle.

Measuring is a good way to determine the v-suspension and calculate with the above formula to the actual situation. ■

Dear chavannilesh,

The function of a filter is to separate the dust from the air.

With secondary filters, you are apparently meaning 2 filters in series.

I never saw that configuration in my career.

When the first filter is not properly filtering the air and the secondary filter is, then it is better to not install the first filter anyway.

Sometimes a cyclone separator is followed by a filter, consuming both pressure drop.

In that case the cyclone has no real function and the filter alone must separate the fine dust. ■