Look at ASME B16.5 for flange details. Bottom line is that a gate valve rated for ANSI 150 will be able to withstand less pressure than one rated for ANSI 300 (the "lb" or "lbs" designation has fallen out of favor because too many people took it for a direct indication of a numerical pressure rating, now it is "class" as in "ANSI 300 Class" which is generally rated by application engineers between 600 psig and 750 psig)
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
Depending on the material group numbers involved your numbers will be different. For SA 105 flanges at 100 F, the corresponding pressure rating is 285 psig for 150# ANSI class ant 740 psig for 300# ANSI class.
ANSI has 6 major rating classes as follow:
150-300-600-900-1500-2500(psi)
these numbers represent the pressure and temperature rating.one thing which should be kept in mind is that these are nominal pressure classes.
for example class 150# can bear more than 150 psi.
ASME B16.34 have the exact working pressure and temperature for each material.
I have to ask, did you read the thread, or just read the question and assume that not a single one of the over 1 million eng-tips.com members could possibly know the answer so you just skipped to the respond panel?
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
Your question asks generally for the 'difference' between ANSI150 and 300 classifications, and then seemingly you want to know the difference between flanges (and building lengt?, topwork? other?).
I presume, as often is for 'open' questions, that there is a specifc problem causing you to ask the question. Perhaps you want to know if a specific valve, for a specific process, can be substituted with one of the different class, or if you should select the one or the other class for a specific application, etc. etc.
If you want more precise and detailed advice it is always a good idea to give as many details as possible.
This is, after all, as zdas04 says, a forum with a large number of specialists.
