Indicating valve (Butterfly vs Gate Valve) Requirement in Fire Water Mains:
NFPA 24, Section A.220.127.116.11 (Edition 2019), suggests to use OS&Y gate valves, butterfly valves, and underground gate valves with post indicators.
I understand that any type of valve are acceptable to use and I've seen frequent use of butterfly and gate valves in underground main. OS&Y requirement is quite clear.
Based on my understanding, butterfly valves are less prone to corrosion and ferritic buildup when compared to gate valves due to its body design.
My understand is that gate valves, due to buildup, might be prevented from closing and would require an entire systems or section of a system to do any maintenance. Yet, direct-buried gate valves are still preferred for underground mains and I'm not sure why.
The cost difference does is not enough in my case to use gate valves specially for 8", 10" 14" or higher sizes.
Is there some reason for gate valve preferences over butterfly valves?
If a butterfly is used I could possibly see a pit being required for maintenance, but NFPA standards do not address pit requirements for a butterfly valve.
Is there any other consideration would be helpful to consider when using butterfly vs gate valves, for underground or even aboveground applications?
Any suggestions would be much appreciated.
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