Volumetric or Gravimetric Feeder?

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I recently received this question…

 

JC

How do I decide whether to choose a volumetric
or gravimetric feeder?

 

Note: A gravimetric feeder measures the flow’s weight and adjusts the feeder output to
maintain the desired set point. On the other hand, a volumetric feeders, by
definition, do not measure the weight of the flow.

 

My Response

Having said
this, volumetric feeders are inexpensive and simple but are open loop devices.
They will not detect or make adjustments for changes in material density. Because
they are open loop devices, volumetric feeders are also unable to measure the
flow for data acquisition. A volumetric feeder may be good for your application
if your material has little variation in density and pellet uniformity.


Most
materials do have variations in density great enough to warrant the use of a
gravimetric feeder.


Most feeder
manufacturers have the resources to determine whether a given material can be
fed volumetrically at a required accuracy or if a gravimetric feeder is
required.


You must
also consider what you will be feeding based on cost and concentration. If you
need to feed a material in at 1% by weight a gravimetric feeder is almost
always a must. Also, for expensive additives, the material saved by having a
gravimetric feeder may pay for itself.

 

-Andy

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