Pump with suction and pressure control for dry particulate material

Abstract

A pump for particulate material includes a pump chamber wherein material flows into the pump chamber under negative pressure and flows out of the pump chamber under positive pressure. A plurality of pinch valves are provided to control flow of material into and out of the pump chamber. The pinch valves are operated independent of each other and of the pump cycle rate. A modular design of the pump is provided. A pump control feature is provided for air flow rate control during positive and negative pressure conditions.

We claim: 
     
         1 . A method of pumping dry particulate material comprising:
 applying suction to a volume at time T 2 , opening an inlet flow path to the volume at time T 3  which is after T 2  so that material flows into the volume under suction, closing the inlet flow path to the volume, opening an outlet flow path from the volume, and applying positive pressure to the volume so that material flows out of the volume.   
     
     
         2 . The method of  claim 1  wherein the step of applying suction at time T 2  produces and initial higher suction force in the volume that reduces to a lower suction force before the step of closing the inlet flow path. 
     
     
         3 . The method of  claim 1  wherein just prior to time T 2  the inlet flow path and the outlet flow path are closed. 
     
     
         4 . The method of  claim 1  wherein the step of closing the inlet flow path begins at time T 4  and the inlet flow path is fully closed before the outlet flow path opens. 
     
     
         5 . The method of  claim 1  wherein after an initial higher suction force is applied to the volume at time T 2  the suction force reduces but is a sufficient suction force to suck material into the volume. 
     
     
         6 . The method of  claim 5  comprising the step of maintaining sufficient said suction force as the suction force reduces over time by monitoring a flow characteristic associated with the suction force. 
     
     
         7 . The method of  claim 6  comprising the step of monitoring flow rate of air out of the volume when suction is applied to the volume and compensation for decreased flow rate over time by increasing suction force so as to maintain a predetermined minimum flow rate. 
     
     
         8 . The method of  claim 7  comprising the step of adjusting positive pressure to a venturi pump that is used to produce the suction force so as to maintain said predetermined minimum flow rate. 
     
     
         9 . The method of  claim 4  wherein the time period from T 2  to T 4  occurs about in the middle of a vacuum portion of a pumping cycle, wherein a pumping cycle includes a pressure portion and a vacuum portion. 
     
     
         10 . A method of pumping powder comprising:
 applying suction to a volume to draw material into the volume and applying positive pressure to push material out of the volume, opening an inlet flow path at time T 3  and closing the inlet flow path at time T 4 , applying the positive pressure at time T 5 , time T 5  being after the time T 4  plus a delay for response time has elapsed to ensure the inlet flow path is fully closed before time T 5  occurs.   
     
     
         11 . The method of  claim 10  wherein the step of closing the inlet flow path at time T 4  comprises applying positive air pressure to a portion of the inlet flow path to pinch the inlet flow path closed. 
     
     
         12 . A method of pumping powder, comprising:
 applying suction to a volume during a suction cycle to draw powder into the volume, applying positive pressure to the volume to push powder out of the volume during a delivery cycle, wherein within each suction cycle is a suction duration period during which suction force is applied to the volume, the suction duration period being shorter than the suction cycle and is approximately centered within the suction cycle.   
     
     
         13 . A method of pumping powder, comprising:
 applying suction to a volume at time T 2 , opening an inlet flow path to the volume at time T 3 , the time T 3  being after the time T 2  plus a delay so that when the inlet flow path is opened an initial higher suction force spike is applied to draw powder into the volume.   
     
     
         14 . A method of pumping powder, comprising: applying suction to a volume to draw powder into the volume, and controlling the flow rate of air from the volume during a suction time period. 
     
     
         15 . The method of  claim 14  wherein the step of controlling the flow rate of air comprises increasing suction force applied to the volume over time to maintain a predetermined minimum flow rate. 
     
     
         16 . The method of  claim 15  comprising the step of monitoring flow rate by determining pressure drop across an orifice disposed in a flow path for air sucked from the volume.