A pressure control apparatus, comprising: a plurality of pipettes (101A-101D) configured to dispense a rinsing liquid for cleaning the pipettes from an outlet (103A-103D) of each of the plurality of pipettes (101A-101D); a manifold including a manifold chamber configured to supply the liquid to the outlets (103A-103D) of the plurality of pipettes (101A-101D) through flow paths (108A-108D) passing between the manifold chamber and the outlets (103A-103D); a flow control valve (110A-110D) in each of the flow paths (108A-108D) and configured to modulate a flow of the liquid in each of the flow paths -108D; a pump interconnected to a liquid source and configured to supply the liquid to the manifold chamber and maintain a target pressure (Pt) in the manifold chamber; a pressure sensor coupled to the manifold chamber and configured to provide a measured pressure (Pm) correlated to a pressure within the manifold chamber; and a flow controller configured to command an individual operational state combination from a plurality of operational state combinations, the flow controller further configured to: in a calibration mode, decrease a pump drive setting if the measured pressure (Pm) is too high, increase the pump drive setting if the measured pressure (Pm) is too low, and store the pump drive setting for the individual combined operational state if the pressure measurement (Pm) is within predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt), or in a testing mode, determine if the measured pressure (Pm) in the manifold chamber is within the predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt) for a previously-commanded state combination commanded prior to the individual operational state combination, and adjust the pump drive setting if not within the predetermined pressure threshold limits (UTP, LTP) for a next time the previously-commanded state combination is commanded. a plurality of pipettes (101A-101D) configured to dispense a rinsing liquid for cleaning the pipettes from an outlet (103A-103D) of each of the plurality of pipettes (101A-101D); a manifold including a manifold chamber configured to supply the liquid to the outlets (103A-103D) of the plurality of pipettes (101A-101D) through flow paths (108A-108D) passing between the manifold chamber and the outlets (103A-103D); a flow control valve (110A-110D) in each of the flow paths (108A-108D) and configured to modulate a flow of the liquid in each of the flow paths -108D; a pump interconnected to a liquid source and configured to supply the liquid to the manifold chamber and maintain a target pressure (Pt) in the manifold chamber; a pressure sensor coupled to the manifold chamber and configured to provide a measured pressure (Pm) correlated to a pressure within the manifold chamber; and a flow controller configured to command an individual operational state combination from a plurality of operational state combinations, the flow controller further configured to: in a calibration mode, decrease a pump drive setting if the measured pressure (Pm) is too high, increase the pump drive setting if the measured pressure (Pm) is too low, and store the pump drive setting for the individual combined operational state if the pressure measurement (Pm) is within predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt), or in a testing mode, determine if the measured pressure (Pm) in the manifold chamber is within the predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt) for a previously-commanded state combination commanded prior to the individual operational state combination, and adjust the pump drive setting if not within the predetermined pressure threshold limits (UTP, LTP) for a next time the previously-commanded state combination is commanded. in a calibration mode, decrease a pump drive setting if the measured pressure (Pm) is too high, increase the pump drive setting if the measured pressure (Pm) is too low, and store the pump drive setting for the individual combined operational state if the pressure measurement (Pm) is within predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt), or in a testing mode, determine if the measured pressure (Pm) in the manifold chamber is within the predetermined pressure threshold limits (UTP, LTP) of the target pressure (Pt) for a previously-commanded state combination commanded prior to the individual operational state combination, and adjust the pump drive setting if not within the predetermined pressure threshold limits (UTP, LTP) for a next time the previously-commanded state combination is commanded.