If I understand this right, a 12 inch flapper valve at 40 ft depth........wow, that is 20 psi at that depth times the square inches of a 12 inch circle. That is over 2000 pound pull to open against 113 sq inches with almost 20 psi against it.
Am I figuring wrong or is there something amiss here????
I would expect it more likely to be a knife valve. I do not know how a person would ever open a flapper valve that large at that depth. For sure a diver would not want to be in front of it if it was opened as he likely would become the new permanant plug.
I don`t think you would have to worry about silt plugging at that depth and pressure. But some more solit debris such as rocks or sticks could be an issue.
Edit; I reread the original post. Maybe the piping is 12 inch but the drain flapper valve is smaller. That could be a more plausible situation. Also he said he needed to pump water against a 40 ft head. That does not mean the pond is that deep so the pressure at the flapper valve would be the pressure of the water depth, not the pipe outlet head height. If it is a 10 ft deep pond it would be only 5 psi at the valve, but still 20 psi at the 40' head outlet end if it were plugged.
Last edited by snrub; 11/13/17 09:34 AM.
