What Is The Difference Between Overflow and Gravity Filling Machines?

For newbie packagers or even those established ones who are just starting to consider buying an automatic packaging solution, the types of can filling machines may mean nothing at all. For example, among the most popular filling machine types are overflow and gravity filling machines. But to those who are not experienced in the industry of packaging, these two might look the same.

So in today’s discussion, we will be talking about the difference between overflow and gravity filling machines. This is to encourage new packagers to familiarize themselves with the different options they have when it comes to choosing a can filler.

Without any further ado, let us now start with our topic for today.

Overflow Filling Machines

When manufacturing bottles, there is an attempt to maintain the consistency of the process as much as possible. The obvious reason why is because packagers would want every bottle to look the same. This helps boost the appeal of the products on the shelves and makes small inconsistencies unidentifiable by the naked eye.

But when liquid products are filled into containers with slight interior volume variations, the fill levels can vary. Even if a consistent amount of the product is filled into each container. This is where overflow filling machines come in. These machines help combat volume inconsistencies by filling each container to equal levels regardless of each container’s interior volume.

Working Principle of Overflow Filling Machines

  • Overflow fillers use unique nozzles that do not only seal over the opening of the container. These nozzles also allow the product to flow back to the nozzle and to the reservoir or holding tank. Thus, eliminating the possibility of product waste.
  • The filling port opens as the nozzles seal over the containers, allowing the product to flow into the containers.
  • Once the fill reaches a specific level in the bottle, the liquid exits the container through the machine’s return port. Thus, “overflowing” from the container before going back to the reservoir or tank.

This working principle is commonly used for filling liquid products that are free-flowing into containers. But great container size variations may require nozzles of different sizes also for more efficiency.

As mentioned in the working process, the fill level of each container means that the actual volume of the product varies in each container. This might be a problem for industries with specific volume requirements like pharmaceuticals. But the majority of the industries have target volumes at acceptable ranges.

In many cases, there is only a slight change in the interior volume. So there is nearly no existing danger of going outside these acceptable ranges. But if this still concerns you, you can check with your container manufacturer to make sure that there are no great variations in the interior volume of the containers.

Gravity Filling Machines

Unlike overflow filling machines that fill to specific levels, gravity fillers fill each container with consistent product volumes. To do this, they use a filling principle that is time-based.

To solve the concern on the discrepancies regarding the containers’ interior volumes, gravity fillers will make sure that each container is filled with the same product amount. But this can result in some containers that look less filled or more filled compared to the others.

Working Principle of Gravity Filling Machines

Generally speaking, while a gravity filling machine can use different numbers of nozzles, all nozzles will open at a specified time. This allows the product to be dispensed from a reservoir into the containers.

  • Most gravity fillers have adjustable fill times for each nozzle to achieve greater accuracy. You can also set the fill times less than one second to improve the accuracy of the volumetric filling.
  • When the pre-set filling time is reached, the filling nozzles will stop the product flow into the containers.
  • For gravity fillers that are semi-automatic, they use switches to initiate the filling cycle. On the other hand, automatic machines will use PLC control systems.

Do note that aside from gravity and overflow fillers, liquid filling machines can also be categorized according to the type of operation.


The choice of either using an overflow filler or a gravity filler will depend on your application’s unique characteristics. Overflow filling machines are mostly used by packagers that use clear containers. For those who do not use opaque containers, gravity fillers offer a better option especially when your industry requires consistent volumes.

But some exceptions may apply when it comes to the unique characteristics of your product or containers. The best thing to do if you are new to the packaging industry is to understand your options first before buying a can packing machine. Because it is important to choose the right packaging machine for your application for your business to benefit from it.

Ask your packaging machine manufacturer. Better yet, choose a packaging machine manufacturer that offers machine customization. Through this, you can guarantee that the resulting machine is tailored to your specific needs.

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