Ducting System
20
• Keep it simple, don’t over complicate the system.
• Keep it straight, ducting runs should all be straight with as
few bends as possible.
• Keep transfer duct as big as required by the extractor, this
should get larger towards the extractor.
• Keep flexible duct to a minimum. If the machine cannot be
connected to the system by solid ducting only then should
flexible ducting be used for the final connection.
Many manufacturers will state the volume of air required
for each machine in their manual. If not, note the size of the
extraction port and use the chart below
Example: for a single machine with a 100mm port an extractor
of a minimum of 700m³/hr will be sufficient. For multiple
Outlet size
Volume of air required
50
200 m³/hr
100
700 m³/hr
125
1100 m³/hr
150
1600 m³/hr
200
2800 m³/hr
Gerneral Info
Basic Design
• Keep branches joining the duct to a maximum of 45° When
branches join the main duct ideally they must enter at the
side or the top at an angle of a maximum of 45° towards the
direction of flow.
• Fit Blastgates to maximise efficiency and balance the system.
The negative pressure inside the ducting draws air into the
system. Incorrect sizing of the duct, too many bends coupled to
lots of flexible hose induces losses into the system and in badly
designed systems this is akin to leaving the hand brake on in a
vehicle.
machines count the number of extraction ports per size,
multiply the number of each size by the volume of air required.
Then add the results per outlet size to give you a total volume
of air required. This total is for all the machines operating at
the same time. You then must decide which and how many
machines will be used at the same time. Divide the total
volume of air required by this number and add 500m³/hr.
Choose an extractor that gives the airflow required by your
calculations. Look at the main inlet size of the extractor, this
is the size of the main duct to be used. In larger systems the
ducting should get larger towards the extraction unit as more
machines that are in use are added to maintain the correct air
speed in the duct. This is very important; if the airflow is too
low a build up of dust and debris will occur and is a fire and
explosion risk. If the air speed is high then the system will be
noisy but there will be no deposits in the ducting. Always use
blastgates to close off airflow to machines that are not in use.
