Dryer basics can be broken down into four essential categories; neat, tumble, airflow and control. A good heat source is crucial for short heat cycles and efficient drying. Natural gas is most often used in the U.S. to provide these important criteria.

Natural gas burners are available in two main types, atmospheric and forced-air styles. Atmospheric designs provide a flame at atmospheric pressure for the air to pass through to become hot. Forced-air burners mix air and gas inside a chamber under pressure. This provides a very efficient and high-temperature burn, which brings the load to temperature set point more quickly.

Today’s most efficient dryers not only possess a forced-air gas burner, but they also have the ability to modulate the fuel input through use of a modulating gas valve. As the temperature set point is reached, these dryers can adjust the gas usage by slowing the fuel input.

Tumbling action is required to separate the load, allowing the hot air to penetrate the goods. Correct material drop moves the load from the basket top and dumps it through the basket center. To avoid tangling of large items, the basket rotation may be reversed, every minute or two.

As the products dry, lighter goods may cling to the basket sides and rotate around. Some dryers permit a change in basket rotation speed to assist with proper material drop for varying load types.

A forceful airflow is required in order to pull the moisture from the load. Dryer manufacturers use varying ways to introduce air into the goods… from the top-out the bottom, from the bottom-out the top, from the sides-out the bottom, or from the rearout the front. Which way is best? It comes down to performance.

With a quality heat source, tumble action and airflow, there must also be control over these functions. Microprocessors and PLC’s permit precise control over the burner modulation, formula set-ups, airflow and basket rotation speeds, along with many other features. Even smaller dryer designs now offer built-in controls to help determine the suitable time for heat termination.

Question your potential supplier. What dryer processes are programmable and what are not? How many programmable formulas are available? How does the dryer determine heat cycle termination? Is the burner system a simple Hi/Low fire system, or does the dryer modulate the gas input? Is the burner a forced-air type or an atmospheric design? Does the formula have control over basket rotation speeds or basket reversing? How is good airflow achieved?