Pump 1 delivers fluid through a groove of valve spool 2 to the left end of cylinder 3, moving piston 5 to the right. From the right end of cylinder 3, fluid is discharged through speed regulator 4 to the tank. End a of spool 2 is connected to the right end of cylinder 3 so that the back pressure in the cylinder is transmitted to spool 2. When the back pressure exceeds the design value, spool 2 shifts to the left, compressing spring 6 and connecting chambers b and d. At this, a part of the fluid delivered by the pump is discharged to the tank and the back pressure drops. Upon an increase in the load acting on piston 5, the back pressure drops and spring 6 shifts spool 2 to the right. This increases the resistance to the flow of fluid from end a to chamber b because the clear opening, formed by notches f of spool 2, is reduced. As a result, the working pressure increases to a value sufficient to overcome the resistance.
$4190$CHP,Dr$