Care and feeding of captive-air tank

I haven't had a C-A tank since 1984 but installed one (used but clean) over the weekend when my galvanized tank started to leak after I had pumped it down to cut recycle time. The new tank seems to work fine, with greater pressure than I've had for years (crud in old lines, I found). My questions are simple: Is there any maintenance I have to do on the C-A tank? Also, the gauge reads about 43 PSI, but a label says factory set for 40. Should I worry? My old non-C-A tank's gauge would fall and rise between 40 and 60 as water went out and was pumped back in. Should the C-A tank's gauge do the same thing? It seems to not move much except when it was at zero when empty. All advice appreciated.

Does the tank have a bladder. Where is the guage you are talking about. On the water line or on the top of the tank?

Details on C-A tank

I guess I assumed the tank has a bladder. I know it's not a regular steel tank -- it's one of those that, if I'm correct, doesn't have to be repressurized as the old galvanized tanks do. The pressure gauge is on the line coming out of the tank, not on the tank itself. There is an air valve on top of the tank, but I think that's just for factory charging. I hope this helps. Sorry for lack of details in original message.

Shut the pump off. Open a valve until the pressure is released. Check the air pressure in the tank. Set it 2# less than the turn-on pump pressure setting.