Abstract: A dryer control system for controlling the drying of polymer plastic pellets within a dryer hopper is provided. A series of temperature snap switches and pressure switches are strategically located within the dryer control system to cause a variety of passive fault lights to be activated to signal faults while the system continues to operate or to cause an alarm light to be activated which stops the drying cycle. The passive fault lights indicate a situation within the drying cycle which should be corrected but which is not sufficiently serious to stop the drying cycle. An alarm being activated, on the other hand, indicates a situation which requires shut-down of the drying system until the problems which caused the alarm are corrected. A programmable logic controller and a temperature controller control the operation of the system by receiving signals from the snap switches and pressure switches throughout the system.

Abstract: A reciprocating gate valve for controlling the flow of particulate material is provided. The gate valve has a metal valve gate with an angled leading edge and also has a groove in the center of the angled leading edge. The valve body is formed from a metal cover plate that has a plurality of plastic body parts fixed to the cover plate so that the metal valve gate reciprocates between plastic body parts. The plastic body parts are preferably formed of self-lubricating plastic such as nylon or Teflon. The valve body has a rectangular recess which intersects the circular passage through the valve body with the rectangular recess having its long dimension positioned transverse to the direction of movement of the valve gate. The rectangular recess provides space for the particulate material to be moved ahead of the valve gate angled leading edge as the valve gate closes.