Captive Air Water Tank Model 273292200

[classicappraiser]

I just bought this unit to use for a water well. I am trying to find out what size it is (gallons). I tried to search with the model number to no avail, It is a green metal cylinder, about 4 feet tall and about 24" in DIAMETER. It appears to have one water inlet about 1 1/4" and a air valve stem as well as a threaded hole in the top. I am not sure what it is for. Help!!!!

 

[Valveman]

The threaded hole in the top is just to hang the tank for painting. That tank is about 40 to 50 gallon size which holds about 10 to 14 gallons of water.