Anindya,

In my understanding...

Even though MTD guidelines does not address the issue of pressure rating directly, there is an indirect reference in para 2.3 of appendix A3 regarding unsupported mass. 600# and above valves and flanges are naturally heavy; consequently a heavier lumped mass at the free end will create vibration problems. Hence ur first statement!

And regarding asymmetry, I guess u r referring to the paper “AIV in high capacity pressure reducing systems” by Carucci and Mueller. My inference from this paper regarding asymmetry is; in case of small bore connections braced back to the main pipe, we are not restraining the vibrating main line pipe wall. Hence this case cannot be treated as an asymmetric discontinuity.

Pl. correct me if my reasoning is not correct.