Pond Boss Forums GENERAL QUESTIONS Help Need help: Pond Leak with No Really Good Way to Fi

If it's cranked down, it's probably a gate valve. There may be a piece of debris under it, and opening it a little bit may dislodge the debris, allowing the valve to close fully.

If it's 12 inch SDR 26, I have a few scrap pieces of that, and it's pretty thick and double gasketed at the bells. Rated for forced sewer mains at a maximum of 160 PSI. If it's SDR 35 or higher, it's not rated for pressure, but gravity feed only.

SDR35 is what my ponds have for overflow pipes. I would imagine the 400 feet of drain would not require pressure rated pipe, but they may or may not have used it.

He said a flapper valve operated by a pull lever. If that is the case I would think it might be a smaller valve like maybe a 4 or 6 inch. I can't imagine a 12" flapper valve as the amount of pull to initially open it would not be practical.

We are still trying to read between the lines of the design but my best guess now is that the flapper valve is smaller then the drain pipe is 12".

I looked online, and cannot find a flapper valve larger than 4 inches. They are listed as check valves. I cannot imagine why an engineer would spec a flapper. Most, if not all small lakes that have valve towers have gate valves.

The OP may have some seepage around the valve. Such valves are rated for gravity flow at low head. As I said before, 480 gallons per day is not much for a 12 inch valve to leak. You could gravity flow that much through a garden hose in two or three hours with much less head.

FWIW...Not saying this is the case but, if the "flapper" valve is an offset pivot disc design, it would be pressure balanced to where it would not take that much force to open it even with 20 psig water pressure against it.

The designer and/or installer of the system should be able to provide details on the valve used.

Snrub
I get the same figures as you.
I do not know I think I would try and plug it. But if it starts coming around the pipe you have big problems.
Is there any way to have your diver plug off the inlet? Sorry for your troubles.

I sure would not want to be anywhere near the opening if someone opened a 12" valve 40' under water. It might be the divers last dive.

A 2-4" open end might be manageable. A 6" open hole operating at 17 psi negative pressure would be dangerous. Anything bigger and being within two or three feet of it when it opened would likely be fatal if it opened all at once.

Diving around lake dams always made me nervous. I know we were a quarter mile away, but you could still hear those turbines plain as day and they were not quiet under water.

The easiest thing to do first would be to open the valve and see if debris was blocking full closure the valve....If this lake was engineered, go to the engineer and see what the plans called for on the valve...was there and trash rack installed to prevent large limbs, etc from plugging the inlet? If not, I'd be billing the engineer for all repair work done....