Reads like the airflow needs to be reversed. ■

Particles at 45 um fall at about 200 mm/s.

At 20 um they fall at about 32 mm/s.

At 7 um they fall at about 4 mm/s.

So the smaller the particle size the longer is the retention time in a vessel with still air.

You are saying that your dust extraction system acts like a particle size classifier, distorting the results at the sampler by sucking away all the minus 45 fines. If you cut the velocity down in the duct you get blockage.

1 - It seems like the capture velocity at your hood is too high. Probably this is not a duct velocity issue - but what is being sucked in at the dust extraction point. If the capture velocity is too high you will be sucking product in as well which will block your ducts - particularly if you reduce the transport velocity.

2 - The next question to ask is what is happening in the void space above your product in the bin. Do you have any air leaks bleeding air in?

3 - Where is the sampler, and how does the air flow work at the sampler?

I start with a schematic diagram of the system, detailing all the significant points, and then ask "what if...?" questions. What is the fan doing? What is the Bucket Elevator doing? What if you get high suction pressure? What if you have low suction pressure? and so on. Seeing the total picture on one sheet of paper often helps the mind to zero in on the most likely cause of the problem and a way forward to solve it. ■

U need to

reduce the suction in the air slide system....do U have a relief/balance valve on top of the silo - standard practise.

Also..U need an air tight sampler..say thief type...screw types are not OK if u have an air path

U main problem is the sampler design/configurations...esp. in the current location - if u are stuck...relocate to low suction area eg in the bagfilter chute to air lock??

Cheers

James ■