Understanding the Role of Bulk Density in Pneumatic Conveying System Design

Each pneumatic conveying system should be designed according to the specific characteristics of the material it will convey. That includes particle size, size distribution, shape, composition, and bulk density.

The bulk density of your product influences the size of components such as vacuum receivers and air sources. It’s also a key factor in determining the amount and velocity of air required to move your product through your conveying lines. As such, understanding bulk density is vital to designing an efficient and profitable pneumatic conveying system.


What is bulk density in pneumatic conveying?

The term bulk density refers to the weight per unit volume of product. It’s usually expressed in pounds per cubic foot (PCF) or grams per cubic centimeter (g/cc).

You can use the following equation to calculate bulk density:



In pneumatic conveying, there are three types of bulk density:

  • Loose bulk density: Also called poured bulk density, this is the weight per unit volume as measured when the sample is in a loose, non-compacted, or poured state. Since loose bulk density can be close to the bulk density during conveying, this is the preferred measurement for pneumatic conveying system design.
  • Packed bulk density: This refers to the weight per unit volume of the product as measured when the sample has been packed or compacted in a silo, bin, or other vessel after containerized transportation. It doesn’t compare to the conditions that would be found inside the pneumatic conveying system, and so isn’t referenced during design.
  • Fluidized bulk density: The apparent bulk density of the product in its fluidized state. This is generally lower than both loose and packed bulk density as there is a great deal of air within the voids between particles.

When designing a pneumatic conveying system, it’s important not to confuse bulk density with particle density. Particle density, also called specific gravity, assumes there’s no air present between the particles, which is impossible in real-world applications.


The role of bulk density in pneumatic conveying system design

If the air volume or velocity within your conveying line is insufficient, your product won’t be picked up and carried through to its destination. Instead, it will fall out of the airstream and pack at the bottom of your pipes, causing blockages that require downtime to remove.

On the other hand, when air volume or velocity is too great, both your product and your system will experience greater abrasion and impact damage. This can lower the quality of your materials or even make them unusable, while also increasing your maintenance expenses.

The bulk density of your product is vital for determining how many cubic feet per minute (CFM) and ft/min of air are required to move your material through your conveying line. Materials with bulk densities of 25-55 PCF are easy to convey. But heavier materials require more power and larger vacuum receivers.

When moving fine powders with low bulk density, such as fumed silica, you might require more filtration than medium-density powders. That means you could require larger vacuum receivers to prevent the material from falling out of the air stream.


How to build a high-efficiency pneumatic conveying system

By figuring out the bulk density of your dry bulk materials, you can design your pneumatic conveying system with the ideal air volume and velocity. That means you can efficiently transport your materials without excessive energy costs or maintenance cycles, letting you maximize your profits.

But building a highly efficient system is about more than getting the math right. You also need to use durable, high-quality components that let you minimize downtime while maintaining high product integrity. That’s why manufacturers around the world rely on the experience, knowledge, and industry-leading products of Progressive Products Inc.

For more than 40 years, driven innovation in the pneumatic conveying sector by providing incredible components at affordable prices. Add to that our fabrication, painting, and machining services, and you can get top-quality pneumatic conveying support all in one place!

Take a look at the industries we serve to see how we can help you construct an efficient and profitable pneumatic conveying system.

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