Fuel injector with a ball valve for a two step servo valve

The injector has a servo valve with inner and outer control rooms (4, 5) which are closed/opened simultaneously via inner and outer valve bodies (2, 3) activated by an actuator. The bodies have inner and outer valve seats (31, 32) to seal the rooms from fuel, where the inner seat is spherically thickened with a radius (r). Nozzle needles are lifted from their other valve seats and spray holes are released by opening the rooms.