Patent ID: 7850431

Claim:
A method for controlling fluid pressure in a multiple stage pump comprising: operating a feed pump to reduce a volume of a feed chamber at a first predetermined rate; opening a barrier valve to allow a fluid in the feed chamber to enter a dispense chamber while keeping an outlet valve closed so that none of the fluid entering the dispense chamber is dispensed; taking a first pressure measurement of the fluid in the dispense chamber using a pressure sensor disposed to measure pressure in the dispense chamber; determining whether the first pressure measurement is greater than a predetermined pressure; in response to the first pressure measurement being greater than said predetermined pressure, operating a dispense pump to increase a volume of the dispense chamber at a second predetermined rate; taking a second pressure measurement of the fluid in the dispense chamber using the pressure sensor, wherein the second pressure measurement is taken while the dispense pump is operating to increase the volume of the dispense chamber; determining whether the second pressure measurement is greater than the predetermined pressure; in response to determining that the second pressure measurement is greater than the predetermined pressure, operating the feed pump at a decreased speed; in response to determining that the second pressure measurement is not equal to or greater than the predetermined pressure, operating the feed pump at an increased speed; determining whether the operation of the dispense pump has caused the volume of the dispense chamber to reach a predetermined volume; in response to determining that the volume of the dispense chamber has not reached the predetermined volume, repeating the method from the step of measuring the second pressure; and in response to determining that the volume of the dispense chamber has reached the predetermined volume, stopping the operation of the feed pump and the dispense pump.