In this article we discuss the cyclone dust collector: how and why it works, and what the advantages and disadvantages are for the home hobbyist.
Cyclones have been around for years, predominantly at sawmills, and feed mills. More recently, smaller versions of these dust collectors have become popular for the home workshop. You can purchase them in many different sizes and configurations. You can either purchase the cyclone alone, or as part of a system with a blower, filter and dust bag or box. A number of people that I have talked to over the years have either built one from scratch or tried to modify an existing unit.
The manufactured system typically costs over twice what you would pay for a traditional ‘bag over bag’ unit with the same horse power. On top of this cost you should also be prepared to spend extra money on piping, as cyclone units are stationary, while bag systems are typically portable. For most bag collectors you can simply connect your machines to it, plug it in and use it. The cyclone system requires more planning. To operate effectively you need to consider the design of the required airflow, volume and pipe sizes.
Bag collectors have a type of cyclone separator built into them to separate the heavy material from the airflow, and drop it out to the lower bag. While not a true cyclone they are semi-efficient; the heavy material does separate and the fine dust travels to a filter bag to be separated from the airflow. Since the heavy material does not pack into the lower bag, and the dust only drops off the filter when the machine shuts down, these units require more maintenance than a true cyclone.
Cyclones consist basically of a metal cylinder that sits atop a metal cone. Air with particulate (i.e. wood dust and shavings) enter a pipe in the side of the cylinder and exits through a vertical pipe. There are basically three principles involved in the functioning of a cyclone.
Centrifugal force comes into play as the air carrying dust and shavings enters the cyclone. The air is directed to spin by the design placement of the inlet pipe and the internal shape of the cyclone. The spinning action throws the shavings and dust particles against the wall of the cyclone and out of the mainstream of the air flow. Friction takes over and causes the shavings and dust particles that are riding along the surface of the cyclone’s wall to slow down. The cyclone cylinder size and height must be designed properly for the intended airflow and material to allow the shavings and dust the right amount of time to drop out of the airflow. This process carries on as the spinning action carries the shavings and dust down the inside wall of the cone.
As the air exits it must make an abrupt change in direction, turning up and into the vertical pipe located in the center of the cyclone. While air can make this abrupt directional change, the dust and shavings suspended in the airflow cannot. This tends to throw the rest of the particles out of the airflow and they drop down the outlet.
Most small, homeowner types of cyclones, are designed to sit directly over top of a waste container. The cyclone and container have to be sealed for the system to work efficiently, as both are under a vacuum. The cyclone outlet should connect vertically down to the center of the top of the waste container. The materials exiting the cyclone are spinning and will pack themselves into the waste container. To assist this process, the container should be round, and of equal diameter from top to bottom. That makes it easier to empty the waste.
Larger commercial units have rotary air lock vales at the bottom of the cyclone that allow them to be dumped continually into waste bins or trucks without loosing vacuum in the system.
There are a few advantages to using a cyclone in your dust collection system.
With a cyclone, nothing but air and very fine dust goes through the fan. So, with no bits of wood, nails, or screws ever making it to the fan blades, damage to the fan is eliminated, and any possibility of sparks in the waste is greatly reduced.
The discharged air is virtually clean, so the filter will last longer and need less cleanings. Also, since the waste enters spinning, it packs itself into the drum.
The major disadvantages to a cyclone system is that they require about 8 feet of head room, making them impractical if your workshop is in a basement. Also, because of its support structure, the footprint of most cyclones is larger than conventional portable bag over bag collectors.
As a rule, cyclones are not portable and therefore you will have to layout permanent piping to connect the unit to your equipment.
When purchasing a cyclone consider the following:
• The cyclone should be specifically rated for wood dust
• The CFM rating on the cyclone must be adequate for your machinery requirements
• The inlet header should be at least 6″ for a 1 HP motor
• The waste barrel should sit directly below the cyclone
• The filter should capture material between .2 and 2.0 microns
• Emptying the filter should not present a safety or health hazard to you
• The location in which the cyclone will be installed must be able to accommodate the weight and height of the unit.
Lastly, cyclones are not for everyone. If you have a small shop and a limited budget, then a small portable unit modified with a good filter bag is probably all you need. If that’s the case, then always remember that with all non-cyclone units, everything that enters the dust collection hose goes through the fan.
The manufacturer’s installed safety barriers should not be removed to improve performance. The added airflow does not make up for the loss of safety.
Many of the companies that sell cyclone dust collectors provide a free system design service when you purchase a system. They provide the correct layout, diameter piping and branch arrangement based on the size of your shop and the size and type of machinery you have. A properly tapered ducting system will ensure that a balanced airflow is delivered to your machines.