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Del Williams


Food Processors: Tubular Drag Conveyors Double the Volume

8-in. cable and disc systems are comparable to belt or bucket systems

Published: Thursday, July 28, 2022 - 12:02

Food processors have long sought a safer, more energy-efficient means to convey product with less spillage, breakage, or downtime due to necessary cleaning and maintenance. Although tubular drag conveyors have offered these desired attributes compared to belt, bucket, or pneumatic systems, many in the industry selected the traditional options to move higher volumes or larger-sized products.

Now, however, 8-in.-diameter tubular drag conveyors have become widely available and can almost double the volumes of smaller 6-in. units. This provides comparable volumes and pricing to conventional industrial systems and enables transport of much larger product sizes than previously possible.

8-in. tubular-drag cable conveyors can move up to 2,000 ft³ and 80,000 pounds per hour depending on the bulk density of materials.

The tubular drag cable pulls the solid circular discs attached to the cable at low speed through a loop, which requires less energy than conventional methods but still allows the conveying of a large volume of material.

Tubular drag-cable conveyors gently move product through a sealed tube using a coated, flexible, stainless-steel drag cable pulled through on a loop. Solid circular discs (called flights) are attached to the cable and push the product through the tube without using air. These conveyors excel in transporting delicate, precise blends for a wide variety of food types in versatile layouts and configurations.

“Today, 8-in. tubular drag-cable conveyors can move up to 2,000 cubic feet and 80,000 pounds per hour depending on the bulk density of materials,” says Clint Hudson, engineering manager at Cablevey Conveyors, a mechanical conveyor manufacturer that serves the specialty food, coffee, nut, powder, produce, and pet food markets. “The units can transport product as large as whole potatoes and midsized grapefruit, and are increasingly used to convey pet food, cereal, nuts, and whole fruit.”

Optimizing food processing

According to Bob Owen, director of product performance at Cablevey, the primary reasons why industry professionals are turning to the higher volume tubular drag-cable conveyors include improved power use, safety, product preservation, product quality, and production uptime.

Power consumption

As energy prices continue to rise, food processors are paying more attention to reducing the power required to convey materials. Within plants, the motors needed to convey large volumes of food materials can vary greatly in power consumption. At the high end are pneumatic conveyors that use air to move product at high velocity through an enclosed line by creating air pressure above or below the atmospheric level. High-volume pneumatic conveyors generally require larger, power-hungry motors with 20–50 horsepower or more that run fans, blowers, and rotary valves.

At the midrange of power consumption are belt conveyors and bucket elevators. In a typical conveyor belt system, a belt forms a closed loop and stretches across two or more pulleys with a drive pulley that enables it to rotate continually. Bucket elevators move material using buckets attached to a rotating belt or chain. The buckets pick up material, move it to an endpoint, discharge material, and return to the starting point to pick up a new load. To convey a similarly high volume of material, belt conveyors and bucket elevators would typically use motors with approximately 25 horsepower, says Owen.

At the low end of power consumption are 8-in. tubular drag-cable conveyors, which would usually use a 5.5 or 7.5 horsepower motor to move a comparable volume of material. Figures 1 and 2 below compare Cablevey energy usage to other types of systems.

Fig. 1: Typical Cablevey motor sizes and annual cost

Figure 2: This chart shows typical motor sizes for chain conveyors using 2.5 times more energy, and with pneumatic conveyors often using 10 times more power.


Open systems such as bucket elevators and belt conveyors are common in the food industry but have substantial drawbacks in terms of potential for contamination. With either type of system, any product that is left uncovered can potentially be exposed to contaminants and moisture in the surrounding environment. Open systems also allow product spillage onto the plant floor, which can present a slip-and-fall hazard if not promptly addressed.

Unlike open systems, closed systems like tubular drag-cable conveyors and pneumatic units effectively seal off product from the outside environment and any potential contamination from that source. The enclosed nature of the systems ensures that no dust escapes that could lead to an unsanitary and potentially dangerous coating of dust on the floor or process equipment. The result is a safer, cleaner, dust-free work environment and reduced risk of dust explosions if the product is in powdered form.

The enclosed systems also eliminate the inherent risk of slip-and-fall incidents due to product discharge onto the processing area floor.

Product preservation

Enclosed conveyors prevent the product loss intrinsic to open systems such as belt or bucket units. Once food product is in the enclosed tube, it can’t fall out, and no powdered product is lost in the form of escaped dust.

Preventing product loss can offer considerable benefits to the food processor’s profitability, with surprisingly quick ROI in some cases.

For example, an international pet food manufacturer that processed dog kibble used a bucket elevator that created excessive product loss due to spillage.

“When the pet food manufacturer switched to an 8-in. tubular drag-cable conveyor, they minimized product spillage and reported a one-year ROI for the system,” says Owen.

Product quality

For product that is delicate or presents a higher value in undamaged form, preserving product integrity is important. However, the rough mechanical action of scooping or dumping product from buckets can cause incidental damage that lowers product value. So can the high-velocity conveyance of pneumatic systems through tubing, turns, and sweeps, which can batter product during the process.

In contrast, tubular cable conveyors offer a gentler alternative. When the systems move product through a sealed tube using a coated, flexible, stainless-steel drag cable pulled through on a loop, the solid circular discs attached to the cable push the product through the tube at low speed without using air. This preserves product integrity and minimizes waste.

“After a cereal manufacturer turned to a high-volume tubular cable conveyor, it was able to reduce product damage,” says Owen.

The premium for processing high-value products whole and unblemished can be even greater for products like nuts.

“One food processor that used almonds in its recipe was only able to sell its product for 40 cents a pound if the almonds were damaged. The same product sold for $4 a pound if the almonds were whole and undamaged,” says Owen. He notes that the processor chose to use a tubular cable conveyor to minimize product damage and optimize the sales price.

Production uptime

To reduce production downtime, food processors also increasingly expect conveyor systems to be designed for easy cleaning and maintenance. In this regard, bucket elevators are particularly difficult to clean in preparation for production line changeovers. To clean them, each bucket must be removed and cleaned inside and out to remove accumulated residue. Belt conveyors are usually cleaned with scrapers, but this can still leave product residue that must be removed by a more thorough method. If not cleaned properly, the food product conveyed must be discarded due to contamination, which equates to lost profit. Worse, consumers could be harmed, resulting in costly recalls, damage to brand and reputation, or even potential litigation and liability.

With closed conveyors, cleaning is also a mixed bag. Pneumatic conveyors can still be relatively time-consuming to clean and sanitize if any manual procedures are involved. With regard to maintaining cleanliness, tubular drag-cable conveyor systems generally offer more options for dry and wet tube conveyor cleaning. These include brush boxes; urethane wipers; air knives; in-line sponges; in-line bristle brushes; and multistep, essentially automated clean-in-place (CIP) wet cleaning.

“Using more automated forms of cleaning like in-line wipers, sponges, and air knives, or CIP wet cleaning, can result in hours of additional production uptime after every product change, compared to conventional manual methods,” says Owen.

Food processors are generally more familiar with traditional belt, bucket, or pneumatic systems than with tubular drag-cable conveyor systems. Previously, processors had selected these familiar systems when they required higher capacity. Today, however, 8-in. tubular drag-cable units can basically match the high-volume output of the traditional systems, but with significant advantages in power consumption, safety, product preservation and quality, and production uptime.


About The Author

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Del Williams

Del Williams is a technical writer based in Torrance, California. He writes about business, technology, health, and educational issues, and has a master’s degree in English from California State University-Dominguez Hills.