Reprinted with permission from MLS Machinery, Inc.
Dust collectors come in numerous sizes depending on the application. They come from say 1 HP internal units used inside a plant which are used on individual machines in small shops. These have a canvas bag on the top with another canvas bag on the bottom which collects the sawdust. They are on wheels and can be moved around the shop wherever needed. Larger units will go to, as an example, 125 HP and bigger. These units can be seen standing outside larger factories and look like big round cylinders. They normally sit on legs and are truck level so that a truck with a container can go underneath to unload the dust that has been collected and stored in the storage section of the dust collector. Once a container or truck is under the unit, the gates at the bottom are opened and all the sawdust will fall into the container. The gates can be slide opening, hydraulic opening, or clam gates, which open like a clam.
The dust collectors have a filter section at the top, called the filter media, which separates the dust and cleans the air to filter it back into the factory. The sawdust from each machine is sucked through a network of piping into the dust collector, separated by the filter media (bags) the dust falls into the storage section while clean air that has now been filtered goes back into the factory through the air return. The law in North America states that you must return as much air into the building as you take out. The air return system often has a silencer to dampen the noise when the air returns back into the building. Most dust collectors have a shaker to shake the bags clean so they do not get full and clog up, thereby reducing the efficiency of the dust collector. The storage is determined by the customer's needs when they originally purchase the dust collector. Units can stand anywhere up to 70' off the ground. Dust collectors from say 25 HP onwards would normally have safety ladders and rails attached to protect anyone if they have to climb up for maintenance. Some have motors mounted on the top of the machine while others might be on the ground. Systems are called either positive or negative systems. Negative systems suck the air through the filter bags and then blow the clean air back into the factory. The positive system blows air into the filter bags and then back into the building. In this case the dirt and sawdust go through the fan, which is not good for the fan and therefore these types of units are becoming less common.
The continuous clean or pulse jet or reverse air clean have a very unique way of cleaning the bags. They do not use shakers but a continuous pump that blows air into each individual bag for cleaning.
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