vectus ALNOR Balometer Jr. Manuel Du Propriétaire page 21

6. LoFlow Adapter—This screen assembly makes use of the standard
area and velocity principles mentioned above. The adapter reduces
the effective area through which the air flows, causing a
corresponding increase in velocity past the manifold. The screen
blocks 50% of the standard opening, increasing the velocity to twice
the original. This means, for example, that with the adapter a volume
of 200 cfm will create the same velocity as 400 cfm without the
adapter. The lowest volume range on the Velometer Jr. is calibrated
to be used with the adapter, on the most sensitive range setting.
Note that the adapter provides higher sensitivity at low flow rates, but
can more easily upset the system being measured at flow rates above 125
cfm (200 cmh, 60 l/s) because of additional back pressure. It is therefore
suggested that measurements above these flows be taken without the
adapter.
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