Normally for all the effluent systems supplied by us, we use process side ball valves as socket weld till 40 NB and flanged end from 50 NB onwards.  We have indicated this in our offer
ref.TFS/08-194/Ranbaxy/O-4 dated 4/5/2009 under point no.3.26 of Scope of supply.  The standard that you have stated (BS 5351) is for fire safe ball valves. For all effluent applications we use the valves conforming to the BS 5159 standard. 
