In the early 20th century, a salt merchant named Adelmer M. Bates signed more orders than his company could deliver, and the filling methods at the time limited his ability to earn more sales commissions, so he invented the valve bag. After Mr. Bates invented the valve bag, he founded a company to develop filling equipment specifically for his new valve bag. Since then, five basic types of machines have evolved to fill a wide variety of materials into these valve bags:
• Air packer (also called forced air)
• Auger packer
• Gravity packer
• Impeller packer (also called jet)
• Vacuum packer
Although many granular or pelletized materials can be filled efficiently into valve bags, the most widespread use of valve bags is for fine powders or mixtures containing fine powders. Because the valve opening is much smaller than that of open-mouth bags, the flow of fine powder can be better controlled.
The earliest advantage of valve bags was their self-closing feature, which reduced the labor required for filling and closing (hand sewing) open-mouth bags at the time. Although the valve design has undergone several innovations, including film valves and double seals, the self-closing performance is far from airtight. Therefore, many bags used in the chemical and food industries are ultrasonically sealed after filling. Other advantages of valve bags include tighter filling and a more rectangular bag shape, allowing for neater stacking on pallets (compared to other bag types such as open-mouth bags and form-fill-seal bags).
The originally invented valve bags were sewn from cloth. Today, the vast majority of valve bags are made of multi-layer paper, sometimes with an added polymer layer. Although valve bags can also be made from polyethylene, paper is still the most common material.
Of the five machine types mentioned, four are widely used. Gravity packers are suitable for filling granular or pelletized materials, but these materials are better suited for filling with open-mouth or form-fill-seal equipment, so gravity packers are relatively rare. The application ranges of these different machine types often overlap.
To help you choose, we discuss the pros and cons of the remaining four types below:
Air Packer (Forced Air)
Pros:
• Fast filling
• High accuracy
• Versatile – suitable for fine powders and materials up to 3/8 inch
• No moving parts in the material flow
• Gentle material handling – no mechanical cutting, minimal material loss
• Easy to clean – bottom access for chamber entry
Cons:
• Air is mixed into the material during filling
• Pressure is applied to the bag during filling, posing a risk of bag burst
• Not suitable for very light materials (less than 10 lb/ft³)
• Not suitable for sticky materials (e.g., baking mixes containing fat)
Auger Packer
Pros:
• Almost no air incorporation during filling
• No pressure applied to the bag during filling, so bag burst is rare
• Minimal adjustments required – straightforward mechanical filling method
• Versatile – can handle a wide range of materials, including difficult sticky materials such as baking mixes containing fat
Cons:
• May require additional settling or vibration to achieve tight filling
• Fluidized powders may leak from the auger even when the machine is stopped
• Generally slower than other filling methods
• Limited adjustment options for optimizing different materials
• Susceptible to wear – material flow can abrade parts
• May cause mechanical cutting and material loss
Impeller Packer (Jet)
Pros:
• Can quickly fill most fine powders
• Tight filling
Cons:
• Limited material applicability – requires 200 mesh or finer material
• Difficult to clean (when changing materials)
• Susceptible to wear – material flow can abrade parts
• May cause mechanical cutting and material loss
• Air is mixed into the material during filling
• Bag burst risk due to pressure during filling
• Some materials may cause heat buildup inside the impeller housing, potentially burning the material
Vacuum Packer
Pros:
• Excellent for very light materials (less than 10 lb/ft³)
• Tight filling
• Gentle material handling – no mechanical cutting, minimal material loss
• No moving parts in the material flow
• If a bag bursts during filling, material is contained in the vacuum chamber, preventing environmental contamination
Cons:
• Not suitable for bags with polymer barrier layers
• Slow filling speed
• More expensive compared to other filling methods
• May cause bag burst during filling
Overall, air and auger packers are mostly used for filling food, chemicals, minerals, and some feed. Impeller packers are mainly used for mineral filling, while vacuum packers are primarily used for chemical filling. Although you should first consider the machine traditionally suited to your product, you may also consider unique advantages of specific models if needed. Most equipment manufacturers offer testing services to help you determine which machine best fits your product and needs.