You can use spiral (hvac) metal ducting or PVC pipes but for multiple reasons it is better to use industry standard metal ducting:
- The lock rings that come with industry standard metal ducting will give you a good galvanic connection with minimum loss of pressure. Flexibility: easy to re-configure your ducting if needed.
- Smooth inside (spiral ducting has a higher resistance and interconnections are not as smooth). PVC/plastic pipe is smoother than standard metal ducting but have two important issues: buildup of static electricity and no flange connection.
- If it comes to avoiding static electricity the metal ducting is the best option. Some metal spiral tubes use rubber insulated connection pieces so you need to ground wire each segment.
- The 6mm flange that is used on most standard metal ducting will attach to many accessories.
From a cost point of view standard metal ducting is slightly more expensive in general but it is the better option.
Pictures from left to right: spiro tube, standard ducting w flange, PVC tube.
Choose the right diameter
If chosen too wide you will lose airflow velocity, if it is too narrow there is a chance of the ducting clogging up. Rule of thumb: start with the diameter of your dust collector and try to run this diameter in a straight line as long as possible before stepping down gradually in diameter.
Use 30 degree angle for T-pieces
Each bend or T-piece will give resistance and therefore loss of airflow velocity. Using 30 degree T pieces will reduce the resistance as much as possible.
Use large radius when installing bends
The shorter the radius the higher the resistance. If possible use a large radius bend. When space permits, use multiple segments locked together to create a large radius. Use bends with minimal R = 2 x D ( radius is twice the diameter).
To avoid turbulence, keep your ducting straight as long as possible. When you connect to a dust collector or cyclone, use a straight section of at least 2.5 times the diameter of the ducting to avoid the buildup of material. Same for connecting to a machine; use a straight duct to avoid turbulence.
Use horizontal-vertical branches to the machines
Try to keep your main segment as short as possible and branch-out with a horizontal duct before going vertical with a bend to an individual machine. By first using a horizontal duct, you prevent material building up in the branch. This material will go airborne if the sliding damper in the branch is opened and may then clog up the inlet of the dust collector or, worse, it may damage the ducting because of its force.
Place the sliding dampers close to the main segment in the horizontal part of the branch and not close to the machine if possible. This gives less chance of pressure leakage as you close off the whole branch.
But for manual sliding dampers, you will want to position them close to the machine as that will be more efficient for the worker who has to open and close them by hand.
Use flexible hose as little as possible!It is almost unavoidable to use flexible hose as it lets you connect the rigid metal ducting to a machine with some flexibility. But flexible hose causes up to 10 times more resistance than standard smooth rigid ducting. Try to use a short length (1 meter maximum) of hose to connect to a machine and avoid bends or use a bend with a large radius.
Make sure to ground the system properly
Proper grounding is important for safety reasons. The airflow with dust particles may cause the buildup of static electricity. Once charged and given the right circumstances (an optimal mix of oxygen and dust particles), a spark may eventually lead to an explosion. This can all be avoided by using metal ducting and proper grounding:
- Always ground the system starting at the dust collector. The dust collector must be properly grounded at its mains connection. The ducting is grounded at the dust collector’s inlet.
- Make sure that each duct/section/segment in your ducting system is properly connected from a galvanic perspective. Lock rings with rubber inlays will prevent a good connection and must be bypassed with a ground wire to connect the next segment.
- When using a flexible hose:
- Avoid to use a (cheap) hose that does not have a metal wire inside.
- Connect the wire to the metal ducting
- At the final section where a machine is connected to the ducting (to avoid a ground loop), DO NOT galvanically connect the machine to the ducting.
An important reason why you should not use (cheaper) pvc/plastic ducting is that it builds up static electricity quickly and it is hard to ground such a system.
Always keep at least one inlet open
To prevent a vacuum in the system keep at least one inlet open. If this inlet is positioned at the end of the main duct it will help to keep the main duct free of material buildup. An "always open" inlet will, of course, influence the performance of the system. The SHUTR system gives you the option the keep one or more gates always open.
About explosion safety
In principle there is a danger of explosion with any dust collection system. The risk is highest in those areas where the density of dust particles is highest: in the dust collector/filter.
In the European Union, there are regulations for equipment used in explosion- hazardous environments. These regulations are part of the CE directives, and are called ATEX. If a manufacturer certifies its equipment for use in explosion-hazardous environments, it means several things:
- The term “zones” is used to specify the circumstances in an environment
- It is safe to use the ATEX certified equipment for the zone(s) for which it has been approved
- Utilizing ATEX certified equipment does not automatically mean your whole system is ATEX certified. It needs to be verified by an independent party that the ATEX equipment is indeed installed and being used as the manufacturer prescribes.
Very often, companies do go through the trouble (effort & costs) to certify the dust collector for ATEX but leave out the rest of the system. Not certifying the rest of the system means there the risk of explosion remains in the ducting and other parts of the dust collection system. There is certainly a risk here. Some insurance companies will demand ATEX certification for the whole installation.
But the main goal is to design and build the ducting and components in such a way that risks are minimized. That means sticking to the rule that everything needs to be properly grounded and use ATEX certified components as much as possible.