Piston Volumetric

The filling speed is affected by these three factors:

 – The piston draw speed depends on product viscosity and stroke length 

 – The piston exhaust speed depends on the nozzle and product characteristics

 – The operator’s experience

O-rings keep product from leaking around the piston as it moves back and forth. The O- rings are placed in grooves around the circumference of the piston head. The O-ring and tubing material must be evaluated for chemical compatibility with the product. The fill temperatures and product abrasiveness will also dictate the elastomer type needed. Some common types of elastomers used are: 

– Fluoroelastomers 

– Buna

– Silicon

– Encapsulated Silicon

– Teflon 

Different types of products require different nozzle designs and sizes. The nozzles used for filling an ampule with 10 ml of thin fluid would not be appropriate for filling a five-gallon can with paint.

Laboratory testing with a number of different types of nozzles is needed to find the type and size nozzle that works best with a particular product. Each product requires a different nozzle configuration. For instance, a bubble forms at the tip of a nozzle when the nozzle diameter is matched to the surface tension of the product. This bubble prevents dripping at the end of a fill. In other cases a screen can be mounted inside a nozzle to prevent foaming. 

Products compatible with SVF fillers