Whether BS 5351 specifies drain & vent connection for floating ball design?
BS 5351 specifys the requirement for drain tappings for ball valves of sizes NB 2 and above.
Drain tapping sizes as follows:
NB 2,3 & 4 - tapping size = 1/2"
NB 6 & 8 - tapping size 3/4"
NB 10 to 16 - tapping size 1".
This is regardless of type (floating or trunnion mounted) or pressure class.
Threads in accordance with ASME B1.20.1 - taper thread and of the following valve Nominal size, and drain to be at the bottom of valve.

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