A plug assembly is provided for a high-pressure valve of the type with a tubular body extending along a longitudinal axis and in which, under the action of a piloted actuator, a needle moves longitudinally between a closed position and an open position. The plug assembly includes a plug having a flat part able to be fixed onto the body transversally to the longitudinal axis, and a spring intended to apply to the needle a force biasing it axially towards the closed position. The spring is fixed to the plug forming with it an integrated assembly.