With its lands a, valve spool 1 divides the inner space into two chambers: chamber b, connected by port d to the high-pressure system main, and chamber c, connected by port e to the low-pressure system main. When spool 1 is in its extreme right-hand position (as shown), port g is connected to the high-pressure main and port f to the low-pressure main. When spool 1 is shifted to its extreme left-hand position, port f is connected to the high-pressure main and port g to the low-pressure main. The spool is shifted to the left by pressing roller h, and to the right by helical spring 2.
$3656$SHP,FC$