Understanding Filling Principles - Thin Liquids versus Thick Liquids

Those doing research on filling machines have likely run across information stating that certain machines are ideal for thin products while others are better for higher viscosity liquids. This is true based simply in how containers are filled, or what principle is used to move liquid from the bulk tank or supply to the containers. Let's look at the four most popular filling machines manufactured by Liquid Packaging Solutions and explain why two are better for thin liquids while two others are preferred for thicker products.


Overflow Filling Machine

Overflow machines fill containers to a specific level, rather than a specific volume. Filling to a level does not in and of itself require a thin liquid, but the process by which the level fill is achieved using an overflow filling machine is better suited to thin products. Overflow nozzles will lower themselves in to a bottle, creating a seal over the bottle opening. Product is then pumped in to the bottle until it reaches the desired level. Once that level is reached, the liquid will "overflow" out of the bottle and back in to the supply tank through a second opening in the nozzle itself. The overflow filler works better with thin products because fill times would become lengthy if thicker products had to be pumped not only in to the bottles but also pushed back through the overflow port and into the supply tank. While possible, the fill times simply become inefficient.

Gravity Filling Machine

Gravity fillers, as the name suggests, fill bottles by taking advantage of one of the most well-known forces. These machines will typically be built with overhead tanks to hold product. Nozzles open and product, by force of gravity, flows to the waiting containers. Usually simple ball valves will open and close to allow product to run through the nozzles and in to the containers. The timed fill, with each head able to be timed individually, will produce an accurate volumetric fill. Simply understanding gravity will help to understand why thin or free-flowing products work best with gravity fillers. Hold up a glass of water, turn it upside down and it flows quickly to the ground. Do the same with a jar of honey and you may be standing for some time until the thick product all makes its way to the ground. Thick products on a gravity filler simply take too long, making the machine inefficient.


Pump Filling Machine

Pump fillers will usually use a single pump for each fill head on a machine. Also filling by volume, these machines can be set to fill by time or by pulse, pulse being a certain movement of the pump. For example, if a machine uses a gear pump, a pulse may be a full turn, half turn or even quarter turn of the gear. The pumps found at each fill head make these machines ideal for thicker products. Pumps help push the thicker product through the pathway on the way to the containers, and unlike the overflow filler, there is no need for a return to a supply tank. Therefore, thicker products can be moved while still keeping fill times efficient.

Piston Filling Machine

Another volume based filling machine, the piston filler allows product to flow in to an empty cylinder, at which time the piston enters the cylinder and pushes product out through the nozzles and in to bottles or other containers. While piston fillers are capable of running thin liquids as well, the open area of the cylinder makes the machine ideal for thick products and especially products with bigger particulates, such as jams and jellies that may contain large pieces of fruit. The cylinder can fairly quickly be filled with product, with many machines utilizing a hopper, and the piston can quickly move product out at consistent volumes, given that the cylinder volume never changes.


Of course, the above are general rules regarding thin and thick products, and exceptions to every rule exist. Some medium viscosity products run efficiently on any one of the four machines. By taking in to account the needs of the packager, the bottles or containers being used, the production demand and other factors, LPS can help determine the best filling principle for any product. We encourage packagers to take advantage of the years of expertise accumulated by LPS employees and give LPS a call to discuss the best option for your own packaging project.