A shut-off member of a pressure reducing valve of a pressure regulator device, such as a diaphragm-type first stage for scuba diving, includes an enlarged head connected to a shaft and cooperating with a valve seat that separates a chamber supplied with high pressure gas from a chamber in which gas is at a lower pressure. The enlarged head and an end section of predetermined length of the shaft, connected to the enlarged head, are seamlessly coated with at least one layer of elastomeric material. Such coating of elastomeric material is limited to an end portion of the shaft connected to the enlarged head and the coated shaft portion is entirely contained in the high-pressure chamber in any operating position of the shut-off member.