HYDRAULIC SYSTEM WITH A VARIABLE-DELIVERY PUMP AND A PRIORITY VALVE

摘要

A closed center, load sensing hydraulic system is disclosed which contains a primary work circuit which has priority in flow demand over a secondary work circuit. The system includes a variable displacement pump fluidly connected between a reservoir and a control valve with the primary work circuit. The primary work circuit includes a control valve which regulates fluid flow from the pump to a primary hydraulic function and which includes a feedback mechanism connected thereto. The secondary work circuit also includes a manually operable control valve for regulating fluid flow from the pump to a secondary hydraulic function. A priority valve is connected between the pump and the secondary work circuit and movable between an open and a closed position to regulate the pressure of fluid discharged by the pump. Pressurized fluid from the primary work circuit is conveyed through a load signal line to the priority valve such that the pressurized fluid will urge the priority valve towards a closed position thereby assuring that adequate fluid pressure is available from the pump to the primary work circuit. The system also includes a control valve for sensing pressure variations between the fluid discharged from the pump and fluid present in the load signal line. This valve controls fluid flow out of the primary hydraulic function, via the load signal line, when the pressure of the fluid discharged by the pump is less than the pressure of the fluid in the load signal line and thereby essentially eliminates kickback from the primary control valve.