(1) to determine the nominal pressure, not to use Pmax to set PN, but to find the corresponding PN from the table by temperature, pressure and material, and be satisfied with the PN value of the selected valve.

(2) determine the valve type of the regulator, and the leakage quantity meets the technological requirements.

(3) the valve type is determined. The working pressure difference should be less than the allowable pressure difference of the valve. If not, the valve should be considered or selected from a special Angle.

(4) the temperature of the medium is within the operating temperature range of the valve, and the ambient temperature meets the requirements.

(5) consider the blocking of the valve according to the uncleanliness of the medium.

(6) considering the corrosion resistance of the valve according to the chemical properties of the medium.

(7) considering the erosion and wear resistance of the valve, according to the pressure difference and the hard material medium.

(8) performance and price ratio of comprehensive economic effects.