You've invested in high-efficiency equipment and tools for Your woodworking shop, but is your dust extraction system working at peak efficiency? Find out about the most common mistakes when designing dust extraction and collection system and how to avoid them.
1. Wrong duct diameters
If the diameters are too small, the system will clog up quickly, while excessively large diameters will reduce the airflow velocity, which makes the extraction system operate inefficiently.
2. Use of 90-degree straight tees
When extracting dust, chips from soft trees, e.g. poplar or pine, you should avoid installing straight (equal) tees, as they can cause clogging of the system. This problem should not occur with finer dust (e.g. after welding), although using equal T-pieces will still result in more resistance. Instead, use reducing tees, Y-pieces or lateral tees, which result in a smoother flow.
It's recommended to limit use of equal (straight) tees, instead, use reducing or lateral tees.
3. Use of short radius bends
Wherever possible, use segmented fittings (elbows) of a larger radius – 2D, to ensure a gentle laminar flow.
4. Failure to keep ducts straight near the equipment and accumulation of fittings, i.e. tees, reductions, etc.
Keep the minimum required distance from the elements disturbing airflow, such as dampers, bends, tees, reducers, sound attenuators (silencers), etc., in order to ensure the correct operation of the dust extraction device, i.e. according to its declared efficiency. The minimum distance is 2.5 x of the nominal diameter. In the case of cyclones, keep a straight section – use a straight duct, since using other duct components e.g. a tee, reducer, or a 90° elbow early upstream will generate turbulence and resistance, which in turn can cause the transported material to be deposited inside the dust extraction system, thus reducing the unit's efficiency.
Apart from keeping straight sections, it is important to maintain the diameters for as long as possible. For example, if your dust collector has a suction port of a 200 mm diameter, use a 200 mm pipe, and run it for as long as it is practicable, before reducing the diameter to match it to the port of your woodworking machine. The use of a smaller diameter will result in a decrease in airflow, thus reducing the efficiency of the unit (the dust extraction unit, which was a considerable investment, will not be used at its full capacity), while the use of a larger diameter than the port of e.g. a cyclone will not increase the airflow.
5. Overuse of flexible ducting/ hoses
DON'T overuse flexible hose. Use only as much as necessary to connect the tool to the discharge pipe. Use only short sections – 1 m of a flexible duct can cause up to 10 x more flow resistance than a smooth rigid duct. Hoses generate high resistance, depending on the type of their corrugation. For this reason, we recommend keeping the use of hoses to a minimum. Since you cannot completely eliminate them in a dust extraction system, choose the best possible hose.
PUQT-AS / PUQT flexible hose.
What dust extraction hose should you choose?
If you can find a hose meeting these basic criteria plus made of a material that dissipates electrical charges, this will be a real advantage.
6. Wrong selection of the dust extraction system – material, thickness, etc.
When designing a dust extraction system, you must also consider the type of piping material. For safety reasons and as required by the OHS regulations, it is recommended to use steel pipes, preferably with a smooth inner wall, to minimise resistance, ensure unhindered airflow, and maintain the optimum speed. In practice, traditional spiral ducts, smooth pipes and plastic sewage pipes are used for extracting wood dust. Although all of these types have their pros and cons, the use of plastic piping is certainly cheaper but certainly dangerous. The use of such pipes involves the risk of explosion, which puts employees of the plant and your machinery at risk. Therefore, you have to analyse whether it will generally pay off to save on the piping.
The poorly selected duct system can significantly lower the efficiency of the whole dust extraction system.
It's recommended to use steel pipes with a smooth inner wall to minimize air resistance.
Explosion safety is not the only aspect to be taken into account when selecting piping, as minimising air resistance is another equally important aspect. It is recommended to use pipes with a smooth interior and duct fittings with soft curves and large radii to prevent blockages inside the dust extraction system. The best solution is a steel pipe with seam welds, or even better butt welds. The welding technique, as well as the selected type and thickness, will ensure the proper airtightness of the duct system and stiffness of the duct (if the sheet metal has a wrong thickness, the duct can sag).
Standard spiral ventilation ducts (so-called spiro ducts) are also used in dust extraction systems. While such a system is acceptable in terms of its airtightness (provided that good practices are observed), it is not optimal in comparison to smooth pipes, taking into account its flow resistance while transporting sawdust or wood dust. That is why we recommend using smooth ducts in the extraction lines (transport of dirty air), but you can use spiral ducts (special connectors/adapters are available to connect the two systems) in the return lines (transport of purified air).
Steel pipes can be equipped with grounding lugs as an additional safety element
The thickness of sheet metal is another aspect that you should observe when designing a dust extraction system. If selected correctly, the thickness of sheet metal will ensure a prolonged service life of the system, resistance to hydraulic impacts, protection against corrosion and excessive wearing of the galvanised layer when the extracted material rubs against the duct walls. Choosing piping with excessively thin walls can lead to the collapsing of the entire system.
7. Too long duct runs
DO NOT design too long lines of ducts. A single duct running through the entire plant reduces air velocity and increases the risk of dust accumulation. Instead, install one shorter main duct with lateral discharge branches to individual machines. The shorter the section, the better, as it means less airflow resistance.
8. Wrong dampers' selection
Two main types of air dampers are used in dust extraction systems – blast dampers and shut-off dampers. Both types play a specific role in the system and they are not interchangeable. Shut-off dampers are installed (and should only be installed) in a system returning clear air to rooms, while gate dampers are used in an extraction system, i.e. one for transporting polluted air. Installing a shut-off damper in a dust extraction line, i.e. the ductwork which transports material, e.g. sawdust and wood dust, will cause the material to accumulate on the damper's blades, and then block the system.
Gate dampers are used to open and close duct branches so that the airflow is directed only to those machines, which are in operation.
The operation of the sliding (gate) damper is quite simple: the gate slides up and down to open or close the pipeline. The dampers have a fully openable planar surface, without any pins or edges that could obstruct the conveyance of media through a pipeline, thus preventing the forming of blockages inside the dust extraction system. Due to its design, such a damper occupies much more space around the pipeline, as the gate protrudes well beyond its outline, which needs to be taken into account when designing the system.