A 3 port solenoid selector sends one supply line to either of two outlets, switched electrically. Flick a dash switch and the oil goes somewhere else — no lever to reach, no hoses to swap.

The common job is adding a second function to a machine with only one spare service: the diverter picks between the two.

Note the pressure difference. The 1/4" is rated to 310 bar; the larger sizes to 210 bar. If your system runs above 210, the small valve is the only one in this family that will take it.