Patent ID: 7731456

Claim:
A method for pumping powder, comprising: a. applying suction to a first annular chamber surrounding a first cylindrical filter element to create suction within a first volume enclosed by the first cylindrical filter element during a suction cycle to draw powder through a first pinch valve into the first volume; b. applying positive pressure air through a first positive pressure air conduit to the first annular chamber surrounding the first filter element to create a positive pressure condition within the first volume enclosed by the first filter element during a delivery cycle to push powder out of the first volume through a second pinch valve that was drawn into the first volume during the suction cycle; c. applying suction to a second annular chamber surrounding a second cylindrical filter element to create suction within a second volume enclosed by the second cylindrical filter element during a suction cycle to draw powder through a third pinch valve into the second volume; d. applying positive pressure air through a second positive pressure air conduit to the second annular chamber surrounding the second filter element to create a positive pressure condition within the second volume enclosed by the second filter element during a delivery cycle to push powder out of the second volume through a fourth pinch valve that was drawn into the second volume during the suction cycle; e. separating each suction cycle for the first volume from each delivery cycle for the first volume, and separating each suction cycle for the second volume from each delivery cycle for the second volume; f. using the applied suction and applied positive pressure to effect open loop control of the powder flow rate; g. monitoring the flow rate of air through the first positive pressure air conduit during the delivery cycle of said first volume; h. monitoring the flow rate of air through the second positive pressure air conduit during the delivery cycle of said second volume; i. increasing the flow rate of air through the first positive pressure air conduit if the monitored flow rate of air through the first positive pressure air conduit is below a reference air flow rate value; j. increasing the flow rate of air through the second positive pressure air conduit if the monitored flow rate of air through the second positive pressure air conduit is below the reference air flow rate value; k. wherein the steps of increasing the flow rate of air comprise increasing pressure to said first volume or said second volume over time to compensate for reduced porosity of said first cylindrical filter element or said second cylindrical filter element respectively so as to maintain a predetermined minimum flow rate of air through said first and second positive pressure air conduits.