Vehicle hydraulic system with single pump

In a work vehicle of the type having at least two hydraulic load circuits,

• one of said circuits including a first control valve and a first hydraulic motor operatively connected with a first utilization device and adapted to be energized in response to actuation of the first control valve,
• another of said circuits including a second control valve, and a second hydraulic motor operatively connected with a second utilization device and adapted to be energized in response to actuation of the second control valve,
• a positive displacement hydraulic pump,
• a changeable speed prime mover connected with the pump,
• said second hydraulic motor being operable at a higher value of hydraulic flow than said first hydraulic motor,
• said pump being adapted to supply the hydraulic flow required by the second hydraulic motor when the prime mover is operated in a high speed range and to supply the flow required by the first hydraulic motor when the prime mover is operated in a low speed range,
• a priority demand valve having an inlet port connected with said pump, a primary outlet port, a secondary outlet port and a normally closed valve means between the inlet port and the secondary outlet port,
• the first control valve having an inlet port connected with the primary outlet port,
• the second control valve having an inlet port connected with the secondary outlet port,
• and speed control means operatively coupled with said prime mover for causing the prime mover to operate in said low speed range when only the first control valve is actuated and to operate in said high speed range when only the second control valve is actuated and when both control valves are actuated together,
• said priority demand valve including means for supplying to the primary outlet port all of the flow required by the first hydraulic motor when the first and second control valves are actuated individually or together,
• said priority demand valve including means for opening said valve means when the inlet flow exceeds that required by the first hydraulic motor when said first and second control valves are actuated together,
• and means for diverting the excess flow from the primary outlet port to the secondary outlet port,
• whereby the inlet flow in excess of that required by the first hydraulic motor is supplied to the secondary outlet and thence to the second hydraulic motor.

For use in a hydraulic system having a pump and having first and second hydraulic load circuits, the second load circuit being adapted for operation at higher pressure than the first load circuit,

• a priority demand valve having an inlet port adapted to be connected with the pump, a primary outlet port adapted to be connected with the first load circuit, a secondary outlet port adapted to be connected with the second load circuit, and normally closed valve means between the inlet port and the secondary outlet port,
• flow rate responsive means urging said valve means toward opening in response to inlet flow,
• pressure responsive means for urging said valve means toward opening when the pressure in the first load circuit exceeds a predetermined value,
• and means for diverting the excess flow from the primary outlet port to the secondary outlet port,
• said valve means being opened in response to the inlet flow or the pressure in the first load circuit or the combination thereof whereby the flow required by the first load circuit has priority and the inlet flow in excess of that required by the first load circuit is supplied to the second load circuit.