Theory of Operation

Our competitors' equipment may look similar to the Press - Relax Dryer™, but our process is unique.

The Press - Relax Dryer™ uses two parallel shafts, with one rotating clockwise and the other counterclockwise. Each shaft is equipped with individual paddles that can be rotated to increase or decrease the pitch to allow more or less time for drying. The screw flight shafts are housed in the "U" trough, which is heated by electric elements running the length of the trough. The pitch of the paddles can be adjusted to suit the volume and dryness of the product being processed. Each paddle pitch is set to the desired angle, determining how fast the material moves through the hot "U" trough. Screw flight shafts rotate with a unique ratchet drive. This is where the "Press - Relax Dryer™" action begins.

A hydraulic cylinder stroke pushes a ratchet drive one measure per stroke, and the fixed end of the hydraulic cylinder anchor pin is on an eccentric shaft driven by a variable speed drive. This relaxes the product, reducing the compression and allowing the material to expand, releasing the moisture. As the ratchet wheel is advanced, with the pawl engaged to the hydraulic cylinder, the paddle forces the product forward. The pressure exerted on the product presses the moisture to the surface of the product. As the ratchet resets for the next stroke, hot air is injected between the two screw flight shafts, which helps to vaporize the moisture.

During the relax period, the vapor is sucked away with an exhaust fan to remove condensation from the dryer. Odor control and solids separation happen further down the air handling system. The unique drive uses the energy of hydraulics for the process and requires just a small horsepower motor. It is a low-energy method of drying, and the design keeps operating costs low with simple maintenance.


Material is loaded into the holding tank and pre-warmed using heated air recovered from the drying process. The preheated material is then fed into the dryer using a speed controlled feeder that allows the operator to maximize dryer efficiency. Material moves toward the dryer discharge via the paddles, which are set slower at the inlet and then faster as the material approaches the discharge as it dries. Because the paddles can be set to a variable pitch, the dryer can be optimized for each customer's particular conditions. If the product being dried goes through a "sticky stage," an additive feeder is used to inject 1/4" diameter steel balls into the dryer to prevent buildup on the shafts and paddles. These steel balls are removed at the discharge with a rotary screen system and are reusable.

Finished Product

The dried, granulated sludge will be inert and free of pathogens with a moisture content of 8-10%. The volume is reduced by approximately 90% from the initial input. The product can be safely bagged and used for soil enrichment or trucked to a disposal site.