This quarter turn isolating stop valve is used to turn off the flow in a run of MDPE water pipe. Made from tough and long-lasting polypropylene, our MDPE fittings utilise an acetal grip ring and a Nitrile rubber O ring.Pipe liners (or stiffeners as they are sometimes called) should always be used with this type of fitting.All of our MDPE fittings can be used on either blue (potable) MDPE pipe or black (non-potable) MDPE pipe.