An ink jet printing device is disclosed in which a bore providing a nozzle for the ejection of droplets of ink is closed by a pin to prevent ejection of ink. The pin is movable into a retracted position in which the pin is withdrawn from the bore to permit ejection of droplets of ink from an ink chamber in communication with said bore. The pin is connected to a piston movable within a chamber. A spring acts on the piston to urge the pin into the bore. Withdrawal of the pin from the bore is effected by pressure of ink acting, against the spring force, on the piston. Ink is supplied selectively under pressure to the ink chamber from an ink supply. Alternatively the piston may be moved by selective application of positive and negative gaseous pressure in the chamber.