SYSTEM / Hydraulic System Priority Valve Circuit (When steering is in neutral) • When the engine is stopped, the priority valve spool is pushed rightward by the spring force. • When the engine is started, pressure oil from the main pump flows to the steering valve through the priority valve spool, and also flows to ports LS1 and LS2 through orifices 1 and 2 respectively at the same time. • When steering is in neutral, as pressure oil to port LS2 flows to the hydraulic oil tank through orifice 3 and the steering valve spool, port LS2 is not pressurized. • As pressure at port LS1 is larger than the spring force, the priority valve spool moves leftward, and all pressure oil from the main pump flows to the control valve. • The priority valve spool is provided with a notch to lead pressure oil from the main pump to the steering valve and a notch to lead pressure oil to the control valve, which are both connected to the main pump delivery port constantly. • When the priority valve spool moves leftward, the notch to lead pressure oil from the main pump to the steering valve moves until the delivery port on the steering valve side in the priority valve is closed. The pressure balance is obtained and the spool stops moving.
T2-2-6
NOTE: Orifice 2 of the priority valve is installed in order to warm up the circuit by flowing pressure oil to the hydraulic oil tank from port LS2 at neutral of the steering valve. Although diameter of port 2 is small and temperature of the oil passing through it rises rapidly, pressure is not raised enough to influence movement of the priority valve spool.
