Load sensing control for hydraulic system

In a system for controlling the flow of fluid from a variable fluid delivery source to a fluid actuated device, the system including main control means disposed in series flow relationship between the fluid source and the fluid actuated device, the main control means including a main flow orifice, the flow through the main control means normally being a function of the area of the main flow orifice, the pressure drop across the main flow orifice normally being substantially constant, the variable fluid delivery source including a load signal chamber and means responsive to changes in the fluid pressure within the load signal chamber to vary the delivery of the fluid source, the system further including means providing a load signal representative of the load on the fluid actuated device, and means communicating the load signal to the load signal chamber, the improvement comprising:

• valve means disposed within said load signal communicating means, said valve means including a first port in fluid communication with said load signal providing means, a second port in fluid communication with said load signal chamber, and a third port in fluid communication with a source of reference fluid, said valve means including a movable valve member having a first position permitting fluid communication between said first and second ports and isolating said third port, said movable valve member having at least one position permitting partial fluid communication between said first port and said second port and between said first port and said third port, the movement of said movable valve member being independent of the operation of the main control means.