Surface treatment process of a metering valve, said metering valve comprising a valve body and a valve sliding in said valve body, said process comprising a first step of forming a thin film of silicone by chemical grafting on at least one support surface of said valve body and/or said valve, and a second step of applying free silicone on said thin film of grafted silicone, such that said treated support surface simultaneously comprises grafted silicone and free silicone, siloxane chains of the grafted silicone and free silicone associating chemically together to reinforce the holding of the free silicone on said thin film of grafted silicone.
