Piston fillers are a popular filling machine for those packagers preparing thick, viscous products, or for packagers doing a range of viscosities. These liquid fillers are made to fill to an accurate volumetric level, with each piston covering a range of container sizes. In many cases, a single piston size will cover all containers for a packager, meaning less changeover time and efficient fills. However, when there is a large gap between the smallest and largest containers, a packager may have to compare fill times and changeover times to figure out the most efficient way to utilize the filling machine.
Piston fillers use a piston and product sleeve to draw product from a bulk source or hopper, depending on the set up of the filling process. The pistons themselves come in several different sizes. For instance, a packager may fill only sixteen ounce containers, in which case the filler would be manufactured with a sixteen ounce piston. For each container to be filled, the piston would pull back out of the product sleeve, allowing sixteen ounces of fluid to enter the piston. Upon returning to the product sleeve, the piston then pushes sixteen ounces of product in to the waiting container.
Of course, this scenario is seldom, if ever, found in the packaging world. Instead, packagers will fill a range of containers that may vary in size from a few ounces to a gallon or more. As the gap between the small and large bottle increases, a packager may have some choices to make. For example, imagine that the same packagers preparing the sixteen ounce containers above also fills eight ounce, thirty-two ounce and gallon containers as well. The sixteen ounce piston can be set up to do a fractional pull back for the eight ounce container, meaning no changeover is necessary other than the adjustment for the retraction. Rather than pull completely back to fill the eight ounce container, the piston would pull half way back to allow the product sleeve to be filled with the proper amount of liquid or product.
Some manufacturers will build piston fillers to retract fully with each cycle, meaning that in the above example, the piston would retract and allow sixteen ounces to pull in to the product sleeve. The piston would then push out eight ounces to do the fractional fill. At NPACK, piston fillers are instead manufactured to pull back a fractional amount to protect against product collapse or other issues that may occur when trying to push out only a fraction of the full amount of product in the sleeve, thus protecting the accuracy of the fills. NPACK machinery also uses O-rings on the product sleeve rather than a lip seal to further protect the integrity of the fill. So the sixteen ounce cylinder can now fill both eight ounce and sixteen ounce containers.
Thirty-two ounce containers provide a different challenge, in that they will require multiple strokes of the piston to fill the container. Obviously, to fill this larger container, the sixteen ounce piston would need to complete two full strokes. In some cases, it may be efficient to simply allow for the two strokes, depending on the volume and speed with which containers need to be filled. But when you consider the gallon container, there may be a better solution. Filling the gallon would require eighth complete strokes of the sixteen ounce piston! This can make the fill a time consuming process, especially if there are a large number of gallons to fill. In such a situation, a packager would most likely change out the sixteen ounce piston for a larger alternative. While the changeover will lead to some downtime, requiring eight strokes of the piston for one bottle will likely take even more time in the long run. Packagers must balance the changeover time with the longer fill times to decide which will provide more efficiency based on the process and volume being run.
Of course, this is a simplified example of how a piston filler may work. These machines can be manufactured as single head tabletop bottle fillers or with multiple heads to work with a completely automatic packaging line. The type of machine, the production demand, the containers, the product and many other factors will be analyzed to decide which and how many pistons will best serve the packager and the project. For questions about piston fillers or any of the other equipment manufactured at NPACK, simply call the offices to speak with a representative or contact NPACK via the forms on the website.