Their job is to grant a constant flow on a user line regardless to the working pressure. The compensation of the exceeding flow allows to feed a second line insensitive to pressure but not to flow. Regulation is made rotating clockwise or vice versa the higher nut, locking is granted by a second lower nut screwed clockwise. In this configuration a relief valve is mounted useful in case of pressure peaks, and an electric valve for installation customization. The external body is made of aluminium protected from oxidations by a black anodizing treatment. This treatment grants a big increase of the external hardness, a good resistance to wear, scraping and corrosion.