I have a 4 diameter column of water 10' tall (filled with water). I need to find a flush valve unit to fit into the bottom of it so that it will flush all of the water out of the column in 1 flush. Essentially this will act as a large toilet but it is for a design project at school. My concerns are that the flapper will close before the water is completely flushed out of the column. Is there any way I can make the flapper stay open thus flushing all the water in column out without holding the chain connecting the float to the flapper valve?
Flapper valves are all about weight and pivot points and center of gravity. The air bubble inside the plug acts like a ping pong ball initially, holding the flapper open. When the water gets down to the level of the flapper, it tends to close too soon as you point out. But you can attach a smal plastic cup to the back of the flapper that fills with water and holds the flapper open when the water level is very low. You put a small hole in the bottom of the cup so that the water in the cup slowly drains out and finally the cg shifts and the flapper closes.
This is an interesting problem. I suggest you study the action of a toilet flush mechanism. Don't have the flapper on the outside, have it on the inside at the bottom of the column, in a small chamber. Use a flapper of very light material, such as a ping-pong ball, which will float on almost no water. (You don't say how fast the column has to drain.) A thought just occured - if the flapper were actually a floating ball, you could pull it up from above, and it would rise to the surface, then follow the water level down, and close it when empty with only a trace of water remaining. I can think of no simpler way to accomplish this challange. Good luck with the project.
