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Re: Air velocity is too low

Barry Irby
The velocity through the duct is related to cross section area. Since the ares of the 6" duct is more than twice that of a 4" duct, the velocity of the air will drop to less than half as it enters the larger duct. Velocity of the air must have enough energy to keep the particles flying.

It's unlikely your DC actually moves 2400 cfm, with the possible exception of if you disconnect the ducts and run the machine naked. As you are aware just about everything about the system restricts the air flow, more or less.

I have a 1100 CFM system and it does well in my tiny shop with 6" mains and 4" drops (plastic SD pipe.) With one gate and sometimes two open. My runs are significantly shorter than yours but nearly as complicated.

Its very difficult for any DC to suck enough air through a single gate on a four inch drop to service a 6" main. Particles in motion tend to stay in motion. Particles at rest tend to stay at rest. (Physics). It's easier to keep them moving than to get them moving after they drop out. I think what you need to do is to open a second gate to allow copious air flow through the main.

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