How much CFM will my dust collector deliver?
There are many woodworkers that buy a dust collector on the basis of a CFM number. Unfortunately, the air volume they are given is called "free air delivery", which means there is not any pipe attached to the dust collector. This CFM number may very well be enough air to evacuate the machines, but when you add pipe to the collector you add resistance (static pressure). When resistance is put on a collector, the CFM delivery decreases. The actual air delivery of a dust collector is typically half of the "free air" factor once it is piped in. It is important to first find out your systems CFM and RESISTANCE (static pressure), then purchase the right collector. A dust collector must be able to overcome the piping resistance and pull vacuum from the machines you need to operate simultaneously.
What is Static Pressure?
Static Pressure is resistance to flow caused by friction and the channeling of airflow through a round pipe. If you turn on a dust collector without anything attached to it – spiral pipe, flexible hose, or filter bags, it will pull max volume at free air without any resistance. Attach filter bags and 10 feet of spiral pipe to the inlet and you have added resistance. Add 20 more feet of spiral pipe and so on – you increase resistance as you add more spiral pipe and fittings.
It is the dust collector’s job to overcome the duct work resistance and pull the proper amount of CFM when you open a branch or branches in a central dust collection system. When you drink a soda with a regular straw it does not take much effort. If you have ever seen kids trying to drink a soda with a curly straw, they strain trying to get the soda to flow. They are trying to overcome the resistance of the long run.
You can run as much duct work in a system as long as the resistance has been compensated for and the CFM is delivered as required.
“Inches of Water” on a scale is used to measure the resistance in a duct system. It can be equated to the resistance to lift water by inches in a tube.
Please see attachments for dust collector performance data and other airflow information.