Butterfly or gate valve for siphon spillway?

[mlib]

I am designing an 8-inch dimaeter siphon spillway for a small reservoir (about 5 acre-feet). The spillway will be for emergency draw-down only. Under normal conditions the flow is regulated through a spillway channel at one end of the dam. This siphon will only be operated once a year and in emergencies if the spillway channel is overwhelmed. My two main design considerations are vandalism resistance and zero leakage, but I also care about torque & ease of operation. I am considering a gate valve and a butterfly valve. Maybe I'm missing something but I don't see why one would be better than the other, except it seems the butterfly valve would give quicker operation. Is there a technical reason to prefer one over the other in this application?

 

[dale100]

Assuming you plan to use line size valve. B/F valves have lower pressure drop (Higher Cv)and with constant head will have greater flow rate. Gate valves are generally more rugged. Soft (rubber) seated B/F valves and wedge gate valves will both give bubble-tight shut off. B/F easier and quicker to actuate. There are very secure key interlocks to prevent unauthorized operation. For low pressure drop applications you could use valve with direct lever operation and padlock. I hope this helps. Let me know if you would like further info. dale100.

 

[Hench]

Is there the possibility of entraining debris into this spillway? This is also something, which would need to be considered when making your valve selection. Making the assumption that you may have to contend with debris. The butterfly valve may not be you best bet. The disk of the butterfly valve could catch some of this debris, making the operation of the valve almost impossible

You may want to consider looking at a Knife Gate type valve.

Good Luck!

H

 

[mlib]

I'm including a fish screen on the intake, so any debris that did get in would be pretty small and would probably pass on through with the flow. Thank you both for your replies! It sure does help to have a forum to bounce things around in.

 

[NGiLuzzu]

MLIB,
I think a triple eccentric, metal seated, butterfly valve could work... for more information, see thread408-26451 (if haven't already read it) in this forum.
Regards, 'NGL