They are used in all those situations where the full flow in one way and the stop on the opposite way is needed. The sizes are from SAE4 to SAE32. The external body is made by high resistance steel and externally protected from oxidations by zinc treatment. On request we can sypply a zinc/nickel treatment to increase the oxidation resistance when the valve is located in external environments. Different opening than the standard one (7.5PSI) are possible: 43.5-65.25-87 PSI.