Before you get into the size you need, I think it`s important to make sure you understand the different types of equipment to reduce the amount of sawdust in your store. Each of these devices has a specific role, which can sometimes lead to confusion in the number of new carpenters. Dust collectors provide dust collectors with air volume requirement tables and air velocity requirement tables so that these companies can design commercial air systems that transport materials without obstructing or building piles in the ducts. Air engineers working for these manufacturers, like many universities, have done a considerable job of building meticulous charts that show how much air needs to be moved and how fast for each type of material. Most small store duct designs are inappropriate reduced versions of large commercial designs. Commercial stores rarely use beam valves and configure their dust collection systems with huge blowers that can power all open sewers at the same time. This requires each channel to be large enough to support the airflow of all bypasses connected to it. As a result, commercial duct constructions begin with nets large enough to carry the airflow for the entire store. The power grid shrinks when the branches break. Each branch shrinks until it reaches the size of the falling drop at its end.
Each drop descending provides exactly the airflow needed for the connected machine. When discounted for small stores, these models sell well because they look pretty and give a small store a professional-looking department store feel. These commercial designs, with all their channels of different sizes, do a great job of collecting chips, but do a terrible job of collecting particles and putting us and our businesses at serious risk. Unlike commercial stores, most hobby blowers are too small to even provide good particle collection from one machine at a time, let alone an entire workshop full. Unlike our in-store vacuum cleaners ten times more powerful, the air barely compresses to typical dusting pressures. We should think of our dust removal more like a water system than an oversized vacuum cleaner. Almost every small pipe, machine connection or obstacle kills the airflow. This means that these pretty commercial designs are a terrible solution in our stores that only use one fan that can support operation at a time. We finish all but this one with explosive doors. As a result, our individual runs stay with the airflow, which is limited by the smallest pipe. This small pipe is usually the descending drop that leads directly to the tool. While this provides the speed required for each specific tool, what happens when that significantly reduced airflow hits a larger main flow is bad news.
For example, a downsize that fits on a 4-inch port reduces the airflow of a fan from 800 CFM to only 349 CFM. When these 349 CFMs hit the Main, the air velocity drops well below what we need to prevent the Main from accumulating piles of dust. The piles of dust in the power grid are just waiting to pass and pose a potential explosion hazard. When the Main finally gets enough airflow, the batteries come off. Normally, small dust collection systems almost never flow with a concentration of dust large enough to present a risk of explosion, but if a large pile comes off, any spark created by cutting off a piece of staple, for example, could cause an explosion that could level a magazine. Although this risk of explosion is low, these piles hit hard and can ruin our ducts, dividers, blowers, wheels, engine mounts and filters. We can open other doors or use special weighted hatches called hyperbaric shock absorbers that open when the pressure becomes too high to avoid these dust pile problems, but most find that we get the best dust separation when we all use equal-sized sewer pipes, tool terminals, and flexible hoses to avoid these problems. Similarly, for tools with multiple connections, it is better to divide our Down Drop into two pipes of equal size and length, because pipes of unequal size require balancing to maintain the airflow where we want it.
On some tools, the internal resistance confuses the airflow between the connections so much that we still have to balance with an outlet valve and test gauges. The total resistance of our dust collection system, known as static pressure, defines the size of a fan we need to drive our system and move the desired air. Our total static pressure is a sum of the resistance of our channels plus all the other resistors in our system. Most amateur sellers never mention general resistance, as their blowers usually don`t have the strength to move the air they need and overcome resistance for a small store, so despite advertising claims, a bad job is done to collect particles. We perform a resistance calculation to obtain a reasonable approximation of the total resistance of our system.
