Addtime：2016/7/20

We usually use the PN, Class, are a way of pressure, the difference is that they represent the pressure on the corresponding reference temperature is different, PN European system is at 120 ℃ under the corresponding pressure, and CLass beauty The standard is the pressure at 425.5 ° C. Therefore, in the engineering exchange can not just be purely pressure conversion, such as CLass300 # pure pressure conversion should be 2.1MPa, but if you take into account the use of temperature, then it corresponds to the pressure increases, according to the material temperature pressure The test measurement is equivalent to 5.0 MPa.

Valve system has two kinds: one is Germany (including China) as the representative of the room temperature (China is 100 degrees, Germany is 120 degrees) allowable working pressure as the base of the "nominal pressure" system. One is the representative of the United States as a representative of the temperature of the working pressure of the "temperature and pressure system," the United States of temperature and pressure system, in addition to 150LB to 260 degrees as the benchmark, the other levels are based on 454 degrees . 150-psi (150psi = 1MPa) 25 carbon steel valve 260 degrees, the allowable stress is 1MPa, and at room temperature, the allowable stress is much larger than 1MPa, about 2.0MPa. Therefore, generally speaking, American Standard 150LB corresponding to the nominal pressure rating of 2.0MPa, 300LB corresponding to the nominal pressure rating of 5.0MPa and so on.

Therefore, can not be in accordance with the pressure conversion formula to change the nominal pressure and temperature and pressure levels. PN is a digital pressure-related code, is to provide a convenient round for the reference integer, PN is equivalent to the pressure equivalent to normal temperature MPa, is the nominal pressure commonly used in domestic valves. The control valve for a carbon steel valve body means the maximum working pressure permitted for applications below 200 ° C; for cast iron valve bodies, the maximum working pressure allowed for applications below 120 ° C; for valves with stainless steel bodies, 250 ℃ the following application of the maximum allowable working pressure. When the operating temperature increases, the valve body pressure will be reduced.

American Standard Valves in pounds to represent the nominal pressure, pounds for a combination of metal temperature and pressure of the calculation results, according to ANSI B16.34 standard to calculate. The main reason that the pound-level is not one-to-one with the nominal pressure is that the pound-grade is different from the nominal temperature of the nominal pressure. We usually use the software to calculate, but also know how to use the table to check ladder. Japan, mainly with K value that pressure level. For gas pressure in China, we generally use its mass unit "kg" (instead of "kg") in kg. The corresponding pressure unit is "kg / cm2", one kilogram of pressure is one kilogram of force on a square centimeter. Similarly, the corresponding to foreign countries, the pressure for the gas, commonly used pressure unit is "psi", the unit is "1 pound / inch2", is the "pound / square inch", English full name Pounds per square inch. But the more commonly used is the direct call to its mass unit, LB (LB), the actual LB. Is the aforementioned pound force. 1 psi = 1 lb / inch2 ≈ 0.068 bar, 1 bar ≈ 14.5 psi ≈ 0.1 MPa, Europe and the United States and other countries accustomed to using psi as a unit. In the Class 600 and Class 1500 corresponding to the European standard and American standard has two different values, 11MPa (corresponding to 600 pounds) is the European system requirements, which is "ISO 7005-1-1992 Steel Flanges" provisions; 10MPa (corresponding to 600 pounds Level) is a requirement of the Inter-American System, which is stipulated in ASME B16.5. So can not absolutely say that the corresponding 600 pounds is 11MPa or 10MPa, the provisions of different systems are different.

As the nominal pressure and pressure levels of the temperature reference is different, so there is no strict correspondence between the two. See the following table for the approximate correspondence between the two.

Pound and nominal pressure tables

Pounds (class) |
150 |
300 |
400 | 600 | 800 |

Nominal pressure |
2 |
5 | 6.3 | 10 | 13 |

Pounds (class) |
900 |
1500 |
2500 | 3500 | 4500 |

Nominal pressure |
15 |
25 | 42 | 56 | 76 |