Every type of conveying system has its application and its place in the material handling industry. Selecting just the right one for your specific needs can be daunting. Here’s some information about two types of conveyors, the pneumatic conveyor and the tubular drag cable and disc conveyor, to help you make your decision.

A pneumatic conveyor is a practical way to move large amounts of  materials including powders, grains, soils, sands, pills, pellets, tablets, rocks, metals, carbon black, coal, gravel, chemicals, textiles, food, plastics, powders, and wood chips. 

Pneumatic conveyors don’t leak a lot of the material they transport, which is particularly important in industries that call for the transport of hazardous materials like toxic waste and asbestos.

Also called air conveyors, pneumatic conveyors use air to move materials from one location to another. This is done by generating air pressure levels that are either above or below the atmospheric pressure to transport the materials to their destinations through horizontal or vertical tubes or pipes in the conveyor system. Materials can be conveyed at short or long distances. An inert gas such as nitrogen can be used to convey a material if that material reacts with oxygen.

There are a number of components in a pneumatic conveying system including compressors, fans, blowers, and vacuum pumps to convey the air or gas supply; the conveying line consisting sections of straight horizontal and/or vertical pipe lines; elbows and other components like valves; a feeding mechanism like a screw feeder or rotary valve to feed the materials to the conveying line; and separation equipment at the end of the line to separate the material from the gas or air stream that transported it.

There are two main types of pneumatic conveyors: the dilute phase conveyor and the dense phase conveyor, which differ by rate of speed and pressure.

Dilute phase conveyors move materials at high velocities by creating a vacuum. They use low pressure air levels to transport materials through the system at a high rate of speed.

Typical velocities for dilute phase conveyors range from 2,200 ft/min for fine powders to 3,200 ft/min for fine granular materials, and higher velocities for denser materials and larger particles. However, this high rate of speed means that your power requirements will be high as well.

This type of pneumatic conveyor, which is much faster than the dense phase conveyor, is used to convey smaller, lighter non-abrasive materials like powders and grains. Because the dilute phase conveyor operates at high velocities the particles being moved are separated from each other and are suspended in the tube as they are blown through the pipeline.

Dense phase conveyors use air compressors to generate high pressure levels to move materials slowly through the system. They are mainly used for conveying abrasive, friable or heavy materials such as cement, sands, soils, minerals and rocks. Air velocities for dense phase conveyors can be as low as 600 ft/min or even lower in some instances.

Sometimes in dense phase conveying with high loadings or when materials are moved over long distances, variations in pressure can cause line plugs. To counter this problem, some vendors have developed boosters to inject additional air into the pipe if necessary.

Of the two, dilute phase conveying is the easiest, most cost effective, and flexible to use.

Because pneumatic conveyors are completely enclosed systems, you can reduce or eliminate contamination, dust emissions, and loss of material. Eliminating or reducing dust emissions means a pneumatic conveyor is a good choice for transporting hazardous materials. In addition, because they run cleaner than some other types of conveyors and there is less product contamination, recycling materials is easier.
.
Pneumatic conveyors are more advantageous to use than other conveying systems like mechanical conveying systems because of the flexibility of the installation. Pneumatic conveyors can economically transport materials via the pipeline to distant areas of your plant that would be more expensive to reach via mechanical conveyors.

Additionally, you can use pneumatic conveyors to pick up the bulk materials from multiple sources and/or move them to different destinations. A pneumatic conveyor is usually very reliable and easy to maintain because there are few moving parts, so it’s a good choice for companies looking into various conveying methods.

However, there are some drawbacks with pneumatic conveyors. One of the main problems is the high power consumption. In fact, pneumatic conveying is the most expensive method of moving materials based on the cost per unit weight per unit distance conveyed. But sometimes the higher price is necessary if other systems can’t be used because of the limitations of the plant layout, or if containment and cleanliness are important.

In addition, if the system is not designed properly, the equipment will wear out and the bulk solid particles being conveyed will degrade. The size of the particles affects the rate at which the pipeline will wear out so larger particles will cause more wear than smaller ones. In general, reducing the velocity will decrease this problem.

Another problem with pneumatic conveyors is that sticky materials are difficult to transport. That means that materials that are wet enough to stick to the sides of the tube can’t be conveyed effectively. In addition, materials that contain a lot of fat or oil can build up in the tube making it difficult to convey them. However this problem can sometimes be handled by installing flexible pipelines and temperature controls.

A tubular drag conveyor is an enclosed mechanical conveyor that uses a cable-and-disc assembly to continuously move materials through a tube at high speeds. The speeds, however, can be adjusted on some systems to fit various applications.

A tubular drag conveyor handles material gently, so friable and other delicate materials can be transported without degradation. Blended materials can also be moved with very little segregation. A tubular drag conveyor can also transport hot or highly abrasive materials and it can move foods and other materials that need to be kept sanitized.

Depending on a company’s application, the conveying tubes can have diameters of 2 inches, 4 inches, 6 inches, or 8 inches or greater. The materials in tubular drag conveyors are transported to discharge points in enclosed conveying tubes, so harmful dust, and toxic or flammable materials don’t escape into the environment. And the materials are protected from the atmosphere because they are completely sealed within the tube.

Tubular drag conveyor systems can have a wide variety of configurations and options, so they’re very flexible. The conveying tubes come in a variety of lengths, can be straight or curved, and can be laid out in various configurations including vertical, horizontal or angled parallel lines; a loop; or multiple-corner shapes. The drive unit provides power to move the cable-and-disc assembly through the conveying tubes and the tension turnaround unit maintains the proper cable tension.

A tubular drag conveyor can include multiple inlets and outlets and can move material vertically, horizontally, around corners and at an angle so you save space, energy and money because you don’t need multiple conveyors.

Tubular drag systems gently convey dry bulk materials including powders, chunks, flakes, pellets, prills, parts, shavings, crumbles, granules, fluff, regrind and dust through an enclosed tube without the use of air. These systems can convey up to 1,500 cu. ft/hour.

Tubular drag conveyors, like Cablevey conveyors, control dust, so you can save money on dust collection systems. In addition there are no filters to clean and product degradation and separation are virtually eliminated as well.

And, like Cablevey conveyors, tubular drag conveyors operate on low horsepower – 1- 5  horsepower – single- or variable-speed motors, saving you money on energy. They’re quiet, so they reduce the noise level in your plant and they’re self-cleaning, so they eliminate the build-up inside the tube.

Tubular drag conveyors offer many advantages to material handling over pneumatic conveying systems or traditional mechanical conveying systems like a screw conveyor or bucket elevator system.

According to Dick Matthews, Air Process Systems & Conveyors Co. Inc., the advantages of using a tubular drag conveying system, like Cablevey’s system, as opposed to a pneumatic conveying system include:

The bottom line, according to Matthews, is pneumatic conveyor systems have higher maintenance requirements, higher horsepower requirements and are not as user friendly as tubular drag systems like the Cablevey system.