i 've started my job as operations engineer in fertilizer sector. i wanna ask(explanation) why does the pipe sizes increases after pressure control valve?? actually i have different opinion and my seniors have somewhat different opinions regarding this point... the particular pressure control valve i m talking about reduces pressure of natural gas from 40kg to 5kg which is to be used as fuel in furnace. and the pipe dia increases from 6" to 14".

Calculate the downstream velocity for both cases (6" and 14") and see why.

This query is almost identical with that in:

http://www.cheresources.com/invision/index...amp;#entry23312

and the response given by Ankur is valid for both.