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Here is my dilemma. I am an Imaginary engineer( Industrial )  so please bare with my explanation of the problem.

We are airveying coffee beans from one lower level to a higher level. Coffee is transferred from a vat up to a hopper on the roof. The coffee beans enter the side of the hopper and fall down the hopper where as the air is sucked further up into the system. As a precaution there is a dust collector after the hoppers to collect any beans or chaff that might have been sucked with the air. After the dust collector there is a bag house unit ( Final Safety ) and after the Baghouse  is a fan and obviously the exhaust  stack.

There are 4 Hoppers on the roof and they feed one line going into the dust collector . there is a damper above each hopper which closes every 30 seconds or so to allow the coffee beans to fall down . My problem is that if I am using 3 hoppers, no coffee is sucked into the bag house or the dust collector, however if I run all 4 hoppers it's creating too much suction and its plugging up my dust collector.  I am installing  screens below these dampers and will see if i run all 4 hoppers without plugging those screens.

What are some of the solutions I can look into? How do i make sure that coffee beans fall down and still have enough suction to take them up to the hoppers? I looked into NPSH and am i correct in assuming that it this net positive suction that is creating this ?

I would love to talk to someone about this ?

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