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Piston Volumetric

A piston filler measures and delivers the product to the container by the action of a single piston for each filler head. On the intake stroke, the piston draws the product from the supply tank or hopper, through the upper check-valve, and into the cylinder of the piston chamber or product cylinder. On the down stroke, the product flows through the lower check-valve, and the product is forced from the chamber through the valve and into the container.

The volume of the filling chamber in which the piston is operating determines the volume of product delivered into the container. The larger the product cylinder, the more available volume for filling. Adjusting the length of the piston’s stroke can change this volume. As the stroke is lengthened, the volume of the chamber is increased, and as the stroke is shortened, the volume of the chamber is decreased.

Accuracy is dependent on what percentage of the overall volume of the product cylinder is used. The greater the volume, the more accurate. The SVF series filling machines are accurate to +/- .5% when used in the recommended fill volume ranges for each specific size cylinder.

In some applications, double filling is used to deliver two discharges from the filler into each container. This technique works effectively, but it is considerably slower and is generally used for short runs. 
The filling speed is dependent on four factors:

• The piston draw speed based on product viscosity and draw length 
• The piston stroke speed based on nozzle pressure, foaminess, fill level 
• The size of the container, or dose size 
• The operators experience

An experienced operator filling 6oz. of a water-thin liquid that does not foam into an 8oz. container using a SVF1-8 – 30 per minute – 1,800 per hour – 14,400 per 8 hour shift 

An intermediate operator filling 16oz. of mayonnaise into a 17oz. container – 
20 per minute using a SVF1-16 – 1,200 per hour – 9,600 per 8 hour shift 

• The method that is used to keep the product from leaking out around the piston as it moves back and forth is the use of an O-ring. The O- rings are placed in grooves around the circumference of the piston head. These rings may be made of a number of different materials that are selected to work best with the characteristics of the products being filled. Testing the chemical compatibility with the different types of elastomers is required to verify compatibility. The different elastomer that may be used is also dependent on the temperature range and abrasiveness of the product being filled. The different elastomers that are commonly used are:

• floroelastomers 
• Buna 
• Silicon 
• Encapsulated Silicon 
• Teflon 

Different types of products require different nozzle designs and sizes. The nozzles used for filling an ampule with 10cc. of thin fluid obviously would not be appropriate for filling a five-gallon can with paint, and there are numerous sizes and shapes available between these two extremes.

• The diameter of the nozzle should be selected to provide a smooth flow. If it is too small, the velocity of the material will be too high as it enters the container and there may be splashing and foaming. If the nozzle is too large, the product may drip at the end of each fill. When the nozzle diameter matches the surface tension of the product, a film or bubble is naturally formed in the tip of the nozzle at the end of each fill. This keeps any material left in the nozzle from dripping out. If the nozzle diameter is too large, the film cannot form and there may be a few drips at the end of each fill. This can make it necessary to either run the process slower so that all the drips are caught in the container or to require frequent cleaning of the containers and the machine.

• Filler nozzles are designed in different sizes and shapes to prevent splashing, foaming, or excessive aeration of the products during filling. Some nozzles direct the flow downward in a solid stream, others break it up into a spray, or direct it to the side of the container so that it will run down the sides. Screens may also be mounted inside the nozzles to break up foamy products so that they will flow smoothly. Each filling machinery manufacturer has a large selection of nozzles available, and not any one of them is appropriate for all products. The best way to select a nozzle for filling a new product is laboratory testing with a number of different types of nozzles to find the type and size that works most efficiently and effectively. Using an improper nozzle can cause slow operation, loss of product, uneven fills, and a messy machine.

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