Compensating pressure controller for fluid dispenser and method

A fluid dispensing system having a fluid dispenser supporting a barrel containing liquid to be dispensed. The barrel has a slidable piston therein with the liquid on a forward piston side and a chamber on a rear piston side. Positive and negative pressure fluid circuits have components operable to apply respective positive and negative fluid pressures to the rear side of the piston. A pressure transducer is operable to sense a fluid pressure in the chamber; and a dispenser control is operative to store a pressure-time relationship during an initial dispensing cycle and thereafter, operate a component in the positive pressure fluid circuit to maintain the pressure-time relationship during a subsequent dispensing cycle.