The invention in question is a sealing method for injection molded polypropylene plastic valves, allowing simple and safe sealing of the valve in closed, semi-open and open positions without having to manually add the sealing material, as well as the sealing rib related to the method. The type of valve comprises of two parts (see FIG. 1): a) The Valve Body (2) with inlet (7), outlet (8) and a chamber for the Valve Core (1) b) The Valve Core (1), with the handle (4), valve opening (6) and sealing material (3) The invented method is using double injection techniques to shape the polypropylene Valve Core (1) of the valve in the first injection stage and then apply the thermoplastic elastomer sealing material (3) to the surface of the polypropylene Valve Core (1) in the second stage. In this way the Valve Core (1) and the Sealing Material (3) is made as one part in one single process, but with two separate injection stages. The Sealing Material (3) which is adhered to the surface of the Valve Core (1) is creating a sealing barrier where there is interference between the Sealing Material (3) and the Valve Body (2). The actual sealing is made by a protruded Sealing Rib (5) at the edges of the area of the Sealing Material (3). The elastomer Sealing Rib (5), which will seal against the inner surface of the Valve Body (2), is carefully measured to ensure proper sealing in all open/closing stages, while at the same time not adding too much friction between the parts. This way proper sealing is achieved, without having to increase the torque required to open and close the valve.