What is the difference between the nominal pressure of GB valves and the pressure of ASME valves?

The nominal pressure is an important parameter of the valve, which is usually expressed by the letter PN and the nominal pressure value, the pressure corresponding to different reference temperatures. The pressure system of the valve is usually divided into two categories: the national standard pressure system and the American standard pressure system. What are the differences between them and how to simply convert them? Here are detailed instructions to help valve users better understand.

    The PN national standard system refers to the pressure corresponding to 20℃, while the Class American standard refers to the pressure corresponding to 425.5℃ (except for 150LB with a reference temperature of 60 degrees, all other levels are based on 454 degrees). For the 25-numbered carbon steel valve of the 150-pound class150psi = 1MPa), the allowable stress at 260 degrees is 1MPa, while the allowable stress at room temperature is greater than 1MPa, about 2.0MPa. Therefore, it is generally said that the corresponding nominal pressure level of the American standard 150LB 2.0MPa, and the corresponding nominal pressure level of the 300LB is 5.0MPa. Therefore, in engineering interchange, it is enough to simply convert the pressure, such as Class 300#, which should be 2.1MPa if it is simply converted by pressure, but if the temperature is considered, the corresponding pressure will increase, and according to the temperature pressure test of the material, it is equivalent to 5.0MPa.

    The pressure is not the actual pressure value, and the nominal pressure and the temperature pressure grade cannot be arbitrarily converted according to the pressure conversion formula. PN is a code representing pressure, which a convenient rounded number for reference. PN is approximately the equivalent of the MPa number of the normal temperature pressure, which is the nominal pressure commonly used in domestic valves. For example for gate valves with carbon steel valve bodies, it refers to the maximum allowable working pressure when used below 200℃; for valves with cast iron valve bodies, it to the maximum allowable working pressure when used below 120℃; for control valves with stainless steel valve bodies, it refers to the maximum allowable working pressure when below 250℃. When the working temperature increases, the pressure resistance of the valve body will decrease.

The American standard valve uses the pound class to indicate the nominal pressure, which is the calculated result of the combined temperature and for a certain metal according to the ASME B16.34 standard. The main reason why the pound class is not corresponding to the nominal pressure is that the temperature benchmark the pound class and the nominal pressure is different. We usually use software to calculate, but we should also know how to use the table to check the pound class. Japan mainly uses K value to indicate the pressure grade. For the pressure of gas, in China, we generally use its mass unit "kilogram" to describe (not "jin"), the unit is kg. The corresponding pressure unit is "kg/cm2", one kilogram pressure is one kilogram of force acting on a square centimeter. Similarly, to foreign countries, for the pressure of gas, the commonly used pressure unit is "psi", and the unit is "1 pound/inch2", that is "poundsquare inch", the full name in English is Pounds per square inch. However, it is more common to directly call its mass unit, that is, pound (LB.) in fact, this LB. is the pound force mentioned above. Convert all units into metric units to get: 1 psi = 1 pound/inch2 ≈ .068 bar, 1 bar ≈ 14.5 psi ≈ 0.1 MPa, and countries such as Europe and the United States accustomed to using psi as the unit. In Class 600 and Class 1500, there are two different values corresponding to the European standard and the American, 11 MPa (corresponding to 600 pound class) is stipulated by the European system, which is stipulated in the "ISO 700-1 Steel Flanges"; 10 MPa (corresponding to 600 pound class) is stipulated by the American system, which is stipulated in theME B16.5. Therefore, it cannot be absolutely said that 600 pound class corresponds to 11 MPa or 10 MPa, and the of different systems are different.

It is worth noting that although the national standard pressure and the American standard pressure can be simply converted, they are very different, and the dimensions are also completely different. In the actual use process, the valves used in the corresponding pressure system should be selected according to the corresponding standards, and should not be mixed