Different nozzles for filling viscous products
There is a wide variety of viscous liquid products: from semi-viscous liquids (like some syrups) to very viscous liquids (like bitumen). To handle all viscosities, there is no one-size-fits-all solution. Depending on the characteristics of your products (more particularly the dynamic viscosity AND the dosing temperature), the manufacturers of dosing machines will offer you spouts suitable for filling viscous products. The most common unit of measurement for viscosity that you will be prompted for is the pascal second. For example, water, very fluid at room temperature, has a viscosity of 10^-3 Pa.s. For its part, molasses is around 10^2 Pa.s and bitumen 10^8 Pa.s!
Flap valves for fluid to semi-viscous liquids
“Simple” valve
In the case of fluid and slightly viscous liquids, manufacturers use so-called poppet nozzles. Flap valves are divided into several categories.
The “simple” flap valves are valves which are sealed by simply lowering the flap into the valve seat. The advantage of the simple valve is the absence of seals, which facilitates cleaning. It also allows the passage of spouts in autoclave without dismantling. If the principle of “simple” valves may seem trivial, their implementation is recent. It was only made possible by the use of numerically controlled lathes. Indeed, metal-to-metal sealing (more rarely plastic-to-plastic in the case of acidic products, for example), requires an impeccable surface condition: the slightest imperfection prevents sealing and causes a slight flow at the nozzle outlet at the end of the dispensing process.
Nozzles with “gasketed” valves are used for semi-viscous products. At the end of the dispensing process, if the liquid has a viscosity higher than a few tens of 10^-3 Pa.s, it will prevent the valve from regaining its place in the valve seat. It is the seal that allows the sealing between the valve and its seat. Very reliable on medium viscosities, blowing or “crenelated” systems can be used to increase its efficiency. Another advantage of the seal valve is that it can be used to dose liquids with small markings. Where a simple valve would be blocked by a marker, the seal will make the seal.
Valve “with joint”
Ball nozzles for viscous and pasty liquids
When the gasketed valve spout is not sufficient, for example for creamy honey, manufacturers use ball and socket spouts. The ball joint is a mechanical element similar to a tap body. Its action is particularly effective: the rotation of the ball joint cuts the filament completely. For the most viscous products, the ball joint should be driven by a mechanical system rather than a pneumatic one, otherwise the filament may not be cut properly. When controlled by the dosing system, the ball joint will not slow down the speed. Its weak point: its disassembly. Consisting of several mechanical parts, it can take several minutes to disassemble. Like the “gasketed” valve spout, it uses a gasket to seal with the upper part of the spout. It will not be able to pass “as is” in autoclave.
Conclusion
The filling of viscous products may therefore require several nozzles. The manufacturer of liquid dosing machines will guide you in the choice of the nozzle in order to meet the characteristics of your products and the conditions in which the dosing will be carried out (the temperature can have a strong impact). In any case, look for simplicity: the absence of a seal is a big advantage, especially for cleaning. Finally, do not hesitate to ask for tests of your products in your packaging. This will give you a better idea of the different equipment on offer.
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