Working Principle of Dosator Type Capsule Filling Machine to Filling Powder into Low Fill Weight Capsules

Working Principle of Dosator Type Capsule Filling Machine to Filling Powder into Low Fill Weight Capsules

Most encapsulating machines use either the tamping pin or dosator technology. However, for the scope of this article, I’ll focus mainly on the dosator type capsule filling machines.

Below is an image showing how a dosator capsule filling machines works (I’ll explain this shortly).

dosator capsule filling machine
Figure 1: This is a dosator capsule filling machine

Background Information about Dosator Capsule Fillers

The dosator capsule fillers are popular in the pharmaceutical industry and they’ve been around for over 60 years.

Since their invention, there has been consistent improvement on these machines to increase accuracy, efficiency and reliable.

In fact, most capsule filling machine manufacturers are more concerned on how the machine behaves during powder dosing process.

It has forced most dosator type capsule filler manufacturers to focus on the potency and dose weight that tend to vary. That is, they have to research and understand the bulk properties of powders more so, during the formulation stage.

As you’ll learn shortly, a dosator type capsule filling machine has two main sections – pin part and body section. With these, it obtains small doses of powder from the bulk container and transfers to the packaging equipment (capsules).

This is a technology that guarantees flexibility when it comes to powder filling. A reason why you can use it for mass production and clinical trials.

Having said this, let’s explore the working principle of dosator capsule filling machine.

NOTE: You can use a dosator systems to fill powders, pellets or tablets.

The Working Principle of Dosator Type Capsule Filling Machine

For a fact, there are several options of dosator capsule fillers available in the market. This variation could be due to the:

  • Experience and expertise of your manufacturer hence, the ability to produce a sophisticated machine.
  • The behavior or nature of the filler material. That is, it could be powder, pellets or tablets.

So, how do these machines work?

Here is a simple step by step explanation of the entire process:

working principle of a dosator machine

Figure 2: This image illustrates the working principle of a dosator machine.

Let’s review each of the five stages:

  • Stage 1

Switching on the encapsulator machine will force the dosator into the powder bed. This forces the powder to fill the cavity at the tip of dosator.

Normally the size of the cavity will depend on the level of the dosator plunger (section in color red). Remember, the arrows indicate how the dosator components move.

  • Stage 2

The powder fills the cavity and the plunger compacts it within the dosator. This locks the powder in the dosator cavity.

  • Stage 3

The dosator retracts from the powder bed carrying with it the powder in the cavity.

  • Stage 4

At this point, the tip of the filled dosator should be free from excess powder. A process referred to as “doctoring”.

That is, cutting off the excess powder that hangs at the tip of dosator.

  • Stage 5

Dosator can now eject the powder in the capsules.

As you can see, the working principle of dosator type capsule filling machine is quite simple and straightforward thou, it may seem complicated after assembling the machine.

SaintyCo Z series dosator capsule filling machine

Figure 3: SaintyCo Z series dosator capsule filling machine

In typical applications, the capsule filling machine manufacturer may modify the machine to suit a wide range of applications.

For instance, let’s review a specific example:

The Working Principle of SaintyCo Dosator Capsule Filling Machine

A dosator machine may have two segments. The system is such that, the powder bed is on one side while the empty capsule body is on the opposite side.

A dosator machine with two segments – powder and capsule sections

As the dosing block moves downwards, the dosator on the first segment penetrates through the powder bed. It fills the cavity at the tip of the dosator after which the pistons compress the powder forming a slug.

One end of the dosator fills the capsule, one end is being filled with the powder

One end of the dosator fills the capsule, one end is being filled with the powder

The dosator system moves up, then it rotates in the opposite direction. It is such that the section with the powder moves over to the section with capsule body while the empty dosator moves above the powder bed.

The dosator alternate (The rotation is a continuous process

The dosator alternate (The rotation is a continuous process?

As the dosator block moves down, the second segment penetrates the powder to be filled while the second segment ejects the capsule to the empty capsule.

All these processes take place concurrently.

Remember, this is a continuous process and it takes place so fast that you may hardly notice this change. For instance, a dosator type capsule filling machine may have an output rate of 180,000 capsules per hour.

With all these in mind, now let’s explore how to use the dosator capsule encapsulating machine to fill low weight capsules.

Using Dosator Encapsulator Machine to Fill Powder into Low Fill Weight Capsules

In this section, you’ll learn about the fundamental aspects on how to fill low weight capsules using a dosator type capsule filler. To achieve this, you’ll adjust the dosator nozzle.

Remember, the design of these capsule filling machines is such that, the nozzle should match the diameter of the capsule.

In the available designs, the smallest nozzle can handle about 40 to 80 mg of powder. However, there are certain applications, where the dosator type capsule filling machine should handle 5 to 20 mg.

This is a very small quantity, hence the need to adjust the nozzle accordingly.

For such applications, the most practical option will be to redesign the dosator nozzle – that is, reduce the diameter of the nozzle. By reducing the nozzle size, you’ll definitely alter the overall performance of the dosator capsule filler.

To avoid this, there are a number of factors you should consider. You’ll learn about these in the next sections.

But first, why do you think the use of dosator nozzles is popular in filling powder into low fill weight capsules? Here are the main reasons:

Advantages of Dosator Nozzles in Low Weight Filling

These include:

  • Equipment performance and output is predictable
  • Guarantees a high production output, hence, suitable for large scale production
  • Easy to automate and integrate with the existing systems
  • Scalability of the filling process
  • High level of accuracy and precision due to enhanced production control

Apart from these, you need to have a clear understanding about all aspects that can affect the overall quality of the capsule filling process. Generally, there are three aspects you need to consider and they include:

Characteristics of the dosator type filling machineThe surrounding environmental conditionsPhysical properties of the filler
Powder layerRelative humidityThis will vary depending on the type of powder you’d like to fill. Analyze both chemical and physical properties of the powder
Diameter of dosator
Powder filling speedChange/fluctuations in temperature
Nature of the dosing chamber

For capsule filling machine manufacturer, this is a rigorous process that involves so many experiments. They have to fabricate and validate the machine performance specifications.

That is, they have to assess all the factors listed in the table above.

Unlike other processes that have been tried before, dosator nozzle is likely to be the best technology when dealing with low fill weight.


From above, it is quite clear that the dosator type capsule fillers are flexible machines you can adapt to nearly all applications in the pharmaceutical industry. You can use it to fill powder into low fill weight capsules, which is not possible in other machines.

Moreover, the working principle of dosator capsule filling machine is simple and can easily be adapted to most capsule filling projects.

Sources of information

  1. Manufacturing of Low Fill Weight Capsules Using a Nozzle Dosator Capsule Filling Machine – Source: The Global Home of Chemical Engineers.
  2. Pharmaceutical Machine Products (Z – series machines) – Source: SaintyCo
  3. Modelling of Dosator Filling and Discharge– By Angulo Pinzon
  4. The Filling of Granules into Hard Gelatine Capsules – Source: NCBI
  5. Increasing Manufacturing Efficiencies in Capsule Filling Systems– By John Van Tol, Harro Höfliger Packaging Systems
  6. Pharmaceutical Capsules – by Fridrun Podczeck, Brian E. Jones

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