Whitepaper: Piston Fillers

Last month I discussed cosmetic or level style fillers. These fill a container to a certain level and fill volume is determined by the volume of the container. This is fine for many products, but others need more precise volume control. Volumetric fillers provide precise fills independently of the container. They do this by measuring physical volume, as in a piston filler. Other architectures measure the product by weight, mass or flow.

Level filler precision is typically rated by the distance from the top of the container. Volumetric fillers precision is typically rated by percentage accuracy. A volumetric filler rated at 1% accuracy would be expected to fill a 10oz container to +/-0.1oz. Some high precision models can fill to +/- 0.1% accuracy. This precision can be critical when filling a high value product like a pharmaceutical that might cost thousands of dollars an ounce. This rating is typically expressed as six sigma. This means that 99.7% of all fills will be within specification absent any extraneous factors.

Piston Filler Design

The most common volumetric filling technology is based on cylinder/piston combinations of various types. Regardless of details, all piston fillers include a piston, cylinder, and inlet and outlet valves. Most pistons used for filling are single acting and that will be the focus of this paper. Single acting means that they fill and discharge one dose per stroke.

There are a few companies that make double acting piston fillers that discharge one end of the cylinder while simultaneously filling the other. This allows them to fill 2 doses per fill cycle. This increases speed but adds complexity that is not usually necessary.

The dosage volume of a piston filler is a function of the diameter and stroke (linear travel) of the piston. A 5cm cylinder has an area of 19.6cm² If the piston travels 10cm the total volume displaced will be 196cc (cubic centimeters). Fill volume is controlled by adjusting the length of the piston stroke.

Download the complete Piston Fillers Whitepaper to continue learning about the typical piston filler design.

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