Float Sizing for flow contol

[mmaurigi]

I need to design a float that is attached to an arm that will open or close a butterfly valve that controls the water level in a retention tank. It is identical the way the float works in a typical toilet. As the level decreases, the float moves down and opens the valve allowing more water in. As the water level rises, so does the float and that closes the valve. I've contacted the valve manufacturer and he said the shut-off torque for the valve is 850 in-lbs. I was figuring that the lever arm from the centerline of the valve shaft to the float would be about 36in. How do I calculate the size of the float so that will in fact float yet be able to provide the required torque to shut off the valve. If you can give me a hand with this I'd really appreciate it.

 

[flamby]

torque = 850 lb-in
lever arm= 36 in
force required at float end = 850/36=23.6 lb
To have this force, flaot must have volume to displace this much of liquid.
Volume of float = 23.6/(density of water 0.036 lb/cubic inch) = 655 cubic inch.

The volume of your float = 655 + wt of its own/0.036

 

[MortenA]

Why dont you just buy it?

Dont try to overspecify a piece of equipment. Your concern would be to activate at a certain level - the vendor should provide the solution

Best Regards

Morten

 

[keyardee]

Directly controlled Float valves are slow and lethargic ones prone to problems.Try valves with pilot type float valves.The pilot could be as small as the one in the bath room and response will be far better and faster.You have one more advantage that the main valve need not be there near the tank controlled by the float- remote pilot.
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