15 and the valve body 35 once the hose 41a is disconnected from the valve body 35 hydraulic fluid under pressure cannot enter the first hose 41 to effect an extension of the hydraulic cylinders 29 accordingly the only powered movement of the hydraulic cylinders 29 can be effected via the supply of hydraulic fluid under pressure through the second hose 42 which will result in a retraction of the hydraulic cylinders 29 one skilled in the art will readily realize that the displacement of hydraulic fluid from the end of the hydraulic cylinders 29 associated with the first hose 41 will flow into the return line 45 for return thereof to the reservoir 32 with the hydraulic fluid returning from the hydraulic motor 15 any extension of the hydraulic cylinders 29 which can be caused through gravity as described in greater detail below will draw hydraulic fluid from the return line 45 to maintain proper displacement of hydraulic fluid in the cylinders 29 as best seen in fig6 once the implement 10 has been mounted on the tractor t it is desirable that the hydraulic lift cylinders 29 be utilized only as a single acting cylinder having only a powered retraction which causes a lifting of.