Thanks anindya!
but it would help if you could explain it a bit.for i believe if there is a jet from elbow(curved)the reaction force would be vertical as is covered in the code and not horizontal.Please forgive my ignorance..i may be quite wrong.
I also came across one formula for horizontal reaction force, but it had no mention of the source.

Dear habib!

please clarify one doubt, for the closed system, shall he consider the reaction force at the first elbow(8")after exit from safety valve or at the last/silencer end(20")(where it meets the atmosphere).

Manvender [:)]