Why Are Gravity and Overflow Fillers Used Primarily With Free-Flowing Liquids?

With many different filling machines available to packagers, one of the areas that Liquid Packaging Solutions can assist is identifying and manufacturing the right machine for each individual project. Of course, one of the essential questions that must be answered in such a search is what products will the packager be running. As has been mentioned many times on the LPS website, certain machines are better for certain products, and with some exceptions, product viscosity goes a long way toward finding the best solution!

Of the four main filling machines manufactured by LPS, piston fillers and pump filling machines are typically used for higher viscosity products. When it comes to free-flowing, or water-like, liquids, both overflow fillers and gravity filling machines usually provide good solutions. But why are these latter two machines limited to free-flowing products? Understanding how the machines work help to explain why they are better suited to thin liquids.

Gravity filling machines, as the name suggests, places product in a tank above the nozzles and uses gravity to move the product through the pathway and in to the containers. In its most basic form, nozzles simply open for a set amount of time, allowing product to move through the pathway. Filling by volume, automatic machines may allow for the time to be set individually on each head, while semi-automatic machines may use a foot switch or finger switch with a timer to open and close all heads at once. Overflow fillers, on the other hand, will use a pump to recirculate product through the pathway.

The overflow filler, on the other hand, will fill each container to a specific level. Using a pump, this liquid filler pushes product in to the container through a special nozzle that allows product to "overflow" out of the bottle once the desired level is reached. These machines also work well with foamy products, where running the fill will generally push the foam out of the bottle as more liquid is released in to it.

So why would these two machines not work well with thicker, viscous products? For the gravity filler, the answer is fairly simple. It will take longer for gravity to have the desired effect on a thick product. Thick products flow slowly, meaning fill times would increase several times over, making a gravity filler an inefficient machine for thick products. while the overflow filler does use a pump, the recirculation of liquid causes the same issue as with the gravity filler, waiting for thick products to flow back through the return nozzle and into the holding tank will usually make the machine inefficient at best in its performance. So for both machines, the time it takes to accurately fill a bottle with thick liquid will simply make other types of liquid fillers more efficient.

While there is no cut-off line for thin versus thick products for overflow or gravity filling machines, where viscosity makes a product flow slowly, better solutions can usually be found with other equipment options. Seeing a product or products, knowing the viscosity, knowing any changes in viscosity due to temperature or other factors and understanding the needs of the packager will help guide LPS and the packager toward the best filling machine solution for any project.