Piston Filling Machines and the Right Piston Size

Piston filling machines are known for their ability to fill liquids by volume with very high accuracy rates. The reason for this is quite simple. The interior of the piston sleeve, or cylinder, never changes in volume, so the volume of product taken in to the cylinder will remain the same with each cycle. However, piston sizes for these machines rarely, if ever, are an exact match of the containers to be filled, and one piston is capable of filling more than a single container size, adding efficiency to the equipment.

To illustrate, let’s imagine a company that fills 8, 16 and 32 ounce containers along with one gallon bottles. Rather than use four different pistons for filling each of the container sizes, a single piston would be used to fill most containers. Manufacturing a machine with a 16 ounce piston would allow the above company to fill their 8, 16 and 32 ounce containers. The eight ounce container would be filled with a fractional movement of the piston. There are two ways to do this. Some piston fillers will retract to 8 ounces with each cycle, while others will retract fully and then fractionally push forward to allow for two fills with each retraction. The fractional retraction can help to protect the integrity of the liquid fillers accuracy by only allowing the amount being filled in to the cylinder. Full retractions with multiple forward pushes and fills can lead to product collapse or other issues that may slightly affect overall accuracy.

The 16 ounce containers would simply require a full retraction of the piston for each container to be filled. No fractional retractions or pushes from the piston would be necessary. While the 32 ounce container would require two strokes of the piston for each container to be filled. The ability to fill multiple containers with the same piston size increases efficiency by removing the need to disassemble and clean the machine while also changing out the piston and sleeve for each container.

The efficiency equation must be balanced, of course, with the size of the actual containers. Imagine the company above is now filling the gallon container. The 16 ounce piston would need to retract and push product out eight times to fill each gallon bottle! In this case, efficiency may be better served by taking the time to add a larger piston on the machine to reduce the amount of time taken to fill each container. In other words, the time to change out the piston will be less than the amount of time lost on requiring the piston to stroke eight times to complete a single fill.

The above scenario is definitely simplified for illustrative purposes. Many different factors will be analyzed to decide which piston size or sizes are best suited for the packaging project at hand. While container sizes will definitely be a factor, packagers will want to analyze their production demands, the product and any particulates in it (as piston fillers are ideal for thick products and chunky products such as pastes, sauces, jams and jellies), the level of automation required or desired and any other unique factors before deciding on the best machine and piston sizes to utilize.