In the early 20th century, a salt merchant named Adelmer M. Bates signed too many orders exceeding his company's capacity, and the filling methods of the time limited his commission, so he invented the valve bag. After inventing the valve bag, Mr. Bates founded a company to develop filling equipment for his new valve bag. Since then, five basic machine types have evolved to fill various materials into valve bags:
• Airflow packer (also known as forced air)
• Auger packer
• Gravity packer
• Impeller packer (also known as jet)
• Vacuum packer
Although many granular or pelletized materials can be efficiently filled into valve bags, valve bags are most widely used 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 powders can be better controlled.
The earliest advantage of valve bags was self-closing, reducing labor for filling and closing (hand sewing) open-mouth bags. Despite several innovations in valve design, including film valves and double seals, the self-closing performance is far from airtight. Therefore, many bags used in chemical and food industries are ultrasonically sealed after filling. Other advantages of valve bags include tighter packing and a more rectangular shape for neater stacking on pallets (compared to other bag types such as open-mouth bags and form-fill-seal bags).
Originally, valve bags were sewn from cloth. Today, most valve bags are made of multi-layer paper, sometimes with an additional polymer layer. Although valve bags can also be made of polyethylene, paper is more common.
Of the five machine types, four are widely used. Gravity packers are relatively rare because they are suitable for granular or pelletized materials, which are better suited for open-mouth or form-fill-seal equipment. The application ranges of these different types often overlap.
To help you choose, we discuss the pros and cons of the remaining four types below:
Airflow packer (forced air)
Pros:
• Fast filling
• High accuracy
• Versatile – can handle fine powders and materials up to 3/8 inch
• No moving parts in the material stream
• Gentle material handling – no mechanical cutting, minimal material loss
• Easy to clean – has a live bottom for chamber access
Cons:
• Introduces air into the material during filling
• Pressurizes the bag during filling, risk of bag burst
• Not suitable for very lightweight materials (less than 10 lb/cu ft)
• Not suitable for sticky materials (e.g., baking mixes with fat content)
Auger packer
Pros:
• Almost no air incorporation during filling
• No bag pressurization during filling, so nearly no bag bursts
• Minimal adjustments needed – straightforward mechanical filling
• Versatile – handles a wide range of materials, including difficult sticky ones like baking mixes with fat
Cons:
• May require additional settling and vibration to achieve tight packing
• Fluidized powders may leak from the auger even when the machine is stopped
• Generally slower than other filling methods
• Limited adjustment options for different materials
• Prone to wear – material flow abrades parts
• May cause mechanical cutting and material degradation
Impeller packer (jet)
Pros:
• Fast filling for most fine powders
• Dense packing
Cons:
• Limited material range – requires 200 mesh or finer
• Difficult to clean (when changing materials)
• Prone to wear – material flow abrades parts
• May cause mechanical cutting and material degradation
• Introduces air into the material during filling
• Bag pressurization during filling may cause burst
• Some materials may cause impeller housing to heat up, risking material burn
Vacuum packer
Pros:
• Excellent for very lightweight materials (less than 10 lb/cu ft)
• Dense packing
• Gentle material handling – no mechanical cutting, minimal material loss
• No moving parts in the material stream
• If a bag bursts during filling, material is contained in the vacuum chamber
Cons:
• Not suitable for bags with polymer barrier layers
• Slow filling speed
• More expensive than other filling methods
• May cause bag bursts during filling
Overall, airflow and auger packers are commonly used for food, chemicals, minerals, and some feed filling. Impeller packers are mainly used for mineral filling, while vacuum packers are mainly for chemical filling. Although you should first consider machines traditionally suitable for your product, you may also consider the unique advantages of certain models when needed. Most equipment manufacturers offer testing services to help you determine which machine best suits your product needs.