A pump (104) is driven by a pump motor drive circuit (121-123) that produces a series of pulse width modulated signals. A closed loop system (110-113) is included to provide data indicative of any variation in the fluid flow. This is accomplished by using a Venturi (110) located in the fluid flow path to create a pressure differential indicative of the fluid flow. A pressure transducer (111) electronically measures this pressure differential which is then compared to a reference pressure differential indicative of the desired fluid flow. Any variation between the measured and desired fluid flow causes the pump motor drive circuit (123) to vary the width of the pulses that are transmitted to the pump (104).
