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. We have several tools to enable you to achieve this. A dust collector must be able to overcome the piping resistance and pull vacuum from the machines you need to operate simultaneously.