3/2-way piston spool valve with differential piston and optional additional spring for piston return. The valve is normally closed from 1 to 2 and open from 2 to 3. The special feature of the B76 series is the mechanical return spring, i.e. the piston spool is returned to the rest position in the event of a pressure failure. On request, outlet 3 can be equipped with an exhaust air throttle.