An apparatus is provided for injection of a fluid for an exhaust gases treatment device of an internal combustion engine arrangement. The apparatus includes a fluid injector fed from a source of fluid under pressure through a fluid conduit, a feed valve in the fluid conduit between the source of fluid the said injector, a purge system including a gas conduit connecting a source of pressurized gas to the fluid conduit, a pressure limiter within the gas conduit, and a check valve downstream of the pressure limiter. The pressure limited by the pressure limiter is lower than the pressure of fluid delivered by the source of fluid.