A method for pumping powder, comprising: a. applying suction to a first annular space 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 air passage to the first annular space 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 space 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 air passage to the second annular space 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. alternating each suction cycle for the first volume from each delivery cycle for the first volume, and alternating each suction cycle for-the second volume from each delivery cycle for the second volume; characterized in that it further comprises the steps of f. monitoring a condition related to air flow rate through the first air passage during the delivery cycle of said first volume and adjusting air pressure accordingly by means of a flow rate controller (720, 730); and g. monitoring a condition related to air flow rate through the second air passage during the delivery cycle of said second volume and adjusting air pressure accordingly by means of a flow rate controller (720, 730). a. applying suction to a first annular space 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 air passage to the first annular space 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 space 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 air passage to the second annular space 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. alternating each suction cycle for the first volume from each delivery cycle for the first volume, and alternating each suction cycle for-the second volume from each delivery cycle for the second volume; characterized in that it further comprises the steps of f. monitoring a condition related to air flow rate through the first air passage during the delivery cycle of said first volume and adjusting air pressure accordingly by means of a flow rate controller (720, 730); and g. monitoring a condition related to air flow rate through the second air passage during the delivery cycle of said second volume and adjusting air pressure accordingly by means of a flow rate controller (720, 730).