Patent ID: 8167517

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. monitoring a condition related to air flow rate through the first positive pressure air conduit during the delivery cycle of said first volume to generate a first signal, wherein said condition changes with reduced porosity of said first cylindrical filter element; g. monitoring a condition related to air flow rate through the second positive pressure air conduit during the delivery cycle of said second volume to generate a second signal, wherein said condition changes with reduced porosity of said second cylindrical filter element; h. comparing said first signal to a reference value and if the comparison indicates that reduced porosity of said first cylindrical filter element has occurred, adjusting air pressure in said first positive pressure air conduit in response to that comparison; and i. comparing said second signal to a second reference value and if the comparison indicates that reduced porosity of said second cylindrical filter element has occurred, adjusting air pressure in second positive pressure air conduit in response to that comparison.