I have to analyse a steam piping system with safety valve. The safety valve discharges to atmosphere.I study B31.1 appendix II and search through this forum also. The recation forces in B31.1 are the reaction at the discharge elbow. While searching through this forum and in Caser manuals I could not see any reference to raction force due to valve opening. Is this rection force mentioned in Valve vendor drawing is balanced itself in the system and is not worth considering for analysis?( this appears to be discussed in the topic Relief valve loads 1985 - 08/09/04 , but not clear to me)
In my case the recation force mentioned in the vendor drawing is 14820 lbs.Inlet is 6" 600 # and outlet is 10" 150 #, set pressure 43.1 Barg.
Senior memebrs kindly guide.
Regards
lee

The reaction force quoted on your vendor drawing is almost certainly calculated in accordance with API RP 520. It is an instantaneous force and thus is considered an impact type of load with an associated dynamic amplification factor. Once established flow is reached, this force is balanced.