Valve mechanism for a combine hydraulic system

A hydraulic system for a combine and harvesting assembly having a valve mechanism that automatically routes fluid from a combine hydraulic line to a harvesting assembly hydraulic line when the harvesting assembly line is coupled with the combine hydraulic line, and automatically routes fluid from the combine hydraulic line to a hydraulic cylinder that controls the speed of a variable speed sheave of a conveyor drive system when the harvesting assembly hydraulic line is detached from the combine hydraulic line. The valve mechanism also includes a relief valve that allows pressurized fluid from the hydraulic cylinder to flow back to the combine's hydraulic system when the valve is routing fluid from the combine hydraulic line to the harvesting assembly.