A gas injector (10) has a valve assembly (12) and a solenoid actuator (14). The valve assembly (14) includes a spherical valve element (26) which locates against a valve seat (24). The valve element (26) is biased in a closed position by a spring (30), and can be disengage from the valve seat (24) by the action of a putrid (86) controlled by the solenoid actuator (14). The pushrod (86) acts in the same direction as gas flow between a gas inlet (20) and a gas outlet (22), and thus the spring (30) acts against gas pressure when in the valve assembly (12) is in the closed position.