I've never seen kegs like that before. I'm sure someone here will know what to do with them, but they certainly aren't the normal kegs most of us use for homebrew. Those ones are referred to as Corny kegs. If my calculations are right, it says the max pressure on them is 50psi as well. Most of the corny kegs i've seen have a 130psi max pressure. If you use them you'll want to be careful to keep them under 50psi at all times. That's well above serving pressure, but it wouldn't be that outlandish for someone to receommend or use 50psi to quickly carbonate some beer, so just be careful.