I need to replace an old galvanized steel tank w/o a bladder. Trying figure out what size I need. Old tank is 48" high by 22" diam. So I am guessing about 30 maybe 40 gallons. I don't understand the replacement tanks with bladders stating, for instance, Simer brand pressure tank model VT36 states 35 gallon tank is equal to a 82 gallon tank but the tank size is only 36" high by 20" diam. Space is tight so smaller would be better but is this what I need or should I go bigger? Would like for my pump to run less often. Also I was told to avoid the smaller space saver horizontal tanks. Anyone know why?