Yuken DSG 01 is solenoid operated directional control valve. A Yuken hydraulic directional control valve comes fitted with 2 Yuken DSG 01 coils on both ends.  

How does a hydraulic directional control valve work?

A hydraulic directional control valve consists of electrically or mechanically actuated spools. These spools can be electrically actuated by installing hydraulic control valve coils on both ends. the inner dimensions of, in this case, yuken DSG 01 coil should perfectly fit the spool. The spool’s position allows or restricts the flow of fluid within the passageway. This process happens rapidly changing the speed of the fluid flow.