What is the limiting factor of a Class 150 valve that has 125 psi working pressure stamped on it.

Looking in the ASME/ANSI B16.34 you will find the ratings (Pressure/Temprature)for different groups of materials

 If your valve is of Group 1.1 then class 150 has a working pressure of 125 psi at 650 Deg F.But if you are using this valve at a temprature less than 650 F then you can go above 125 psi.For example at 300 F ,the working pressure is 230 psi.

you have a butterfly valve of 150 pressure class then how will you get the pressure rating,shell test pressure,seat test pressure?

you first confirm that the valve's pressure testing is as per a valve standard such as MSS SP67 OR API 598.Then go to ANSI B16.34 150 #class to check the pressure rating for the particular material(body and disc).Under that you have diff. pressures for diff. temp. ranges,Confirm your medium's min to max.temperature then you can get the line pressure for your valve.Go back to MSS SP67 OR API 598 and see the shell test rating(it will be 1.5 times the rated pressure)and seat test pressure(it will be 1.1 times the rated pressure).

In your case the seat test pressure is 11 bars(160 psi)and the shell test pressure is 15 bars (220 psi).

Of course,I am assuming the valve standards and that the valve is operating at room temp.If it is any other temp. then you have to follow what SHAHIN 71 has already described in his response.

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