Due to their small size, these valves are often installed on tanks in low-clearance areas. They begin opening at the set pressure. Nylon valves fully open at about 10% over the set pressure and steel valves fully open at about 50% over the set pressure. Valves begin closing as pressure drops and fully close when the system pressure is restored below the set pressure. All have a vent outlet to exhaust discharge directly. Set pressure is not adjustable. Nylon valves have better corrosion resistance than steel valves. They are color coded based on the set pressure for easy identification.