They are used as fix set one-way flow regulator, it allows free flow in one way and works as flow regulator by means of a calibrated orifice on the opposite one. The sizes are from 1/4 BSPP (1/4 G) to 1 BSPP (1 G). The external body is made by high resistance steel and externally protected from oxidations by zinc treatment. On request we can supply a zinc/nickel treatment to increase the oxidation resistance when the valve is located in external environments. Different opening than the standard one (1 bar) are available: 3-4.5-6 bar.