18 at pressure p 2 the difference p 1 u2212 p 2 u03b4p representing the pressure drop across valve 10 actuator 12 is controlled by an electronic controller 20 and driver 22 control may be open loop or feedback closed loop as is well known in the prior art of flow control fluid 14 may be either a liquid or a gas fig1 provides structure for the discussion below of pwm and pdm control systems wherein reference numbers should be understood as coming from the components shown in fig1 referring to fig1 and 2 a representation of a pdm waveform 24 in accordance with the present invention consists of a fixed pulse width 26 and a variable repetition rate 28 pdm frequency the fixed pulse width with a fixed u03b4p gives a consistent quantity of fluid through valve 10 with each stroke of actuator 12 by varying the repetition rate 28 of actuator 12 the time average flow of fluid 14 through valve 10 can be controlled very precisely with good resolution over a desired flow range referring now to fig3 and 4 a comparison between the prior art pwm control and the present art pdm control is illustrative of the improvement and benefit of pulse density modulation in fig3 flow characteristics time average flow rate as a function of duty cycle at 125 hz are shown for a given valve 10 with varying u03b4p when using prior art pwm control for a low flow rate application box 30 and a high flow rate application box 32 at three different values of supply pressure p 1 for curve 34 p 1 300 bar for curve 36 p 1 900 bar.