A boom control system includes a pair of pressure reducing valves forcommunication with lifting circuits of a boom. The pressure reducing valvemaintainsa set point pressure in the respective lifting circuit. An elevation monitor,for examplean ultrasonic sensor, monitors elevation of the boom. A controllercontrollably variesthe set point pressures of the pressure reducing valves responsive toelevation of theboom structures for maintaining the elevation of the boom structuressubstantially at adesired elevation level.
