valve 74 when its spool 152 is in the position shown in fig3 and solenoid feed line 124 is pressurized a feedback line 170 develops a pressure force on land 164 through orifice 172 which functions to prevent cyclic movement of spool 152 the maximum pressure that can be applied to any of the clutches or servos is the line pressure however clutch and servo pressure can be regulated down to zero p s i through operation of the actuating valve in order to regulate clutch pressure a pulse width modulated signal is applied to the winding of the solenoid which causes orifice 174 to open and close cyclically for variable and usually unequal periods thereby communicating vent port 162 to the valve chamber when orifice 174 is open differential pressure across orifice 154 causes an unbalanced pressure force to be developed on spool 152 moving the spool downward and opening line 146 to vent port 160 during the period when the solenoid winding is de energized spool 152 moves upward within the chamber to the position shown in fig2 and clutch pressure rises toward line pressure it can be seen from this that the duration of the period during which the solenoid winding is energized controls the magnitude of the associated clutch pressure and in this way the clutch is vented through vent port 160 when the solenoid winding is energized for an extended period referring to fig3 it can be seen that the second third and fourth.