Bag fillers can be divided into two main categories:

Nett Weighers and Gross Weighers

Nett Weighers

Nett weighers offer the most flexibility and provide advantages in terms of speed and accuracy. The product being weighed is pre-weighed into a holding hopper and then emptied into the waiting bag.

Traditional gravity fed weighers use a two-position, pneumatically activated feed gate. The main gate closes when 80% of the required weighment has been reached and thereafter a trickle feed continues until the target weight is achieved. Pneumatic activators are relatively slow and operation is inconsistent if the air pressure fluctuates or ambient conditions change significantly.