After checking my water tank for water coming out of the air valve I discovered none, however noticed that there is an in-line pressure gauge that reads ZERO. This is without any water running i nthe house and may be the way it should read unless water is running. My common sense tells me that there should always be pressure in the line regardless of the tanks bladder being busted. Maybe not if the pump is not running. Could the electrical box thing installed close by the pressure tank be bad and not telling the tank what to do. Not sure what it purpose really. I call it a regulator. It is a small 4"x4"x4" plastic box. It was alte at night and I forgot to take my air pressure gauge with me when checking the tank so I don't know how much pressure was really in it other than air was coming out when I pushed the pin in on the air stem of the tank.
Zero pressure means zero water, the gauge could be bad but normally when they do go bad it will show pressure when you have none. The box you talk about would be the pressure switch that controls the pump, the tank just stores the water.
I guess there was another thread I missed. Blue Jay has the parts description right on. The tank stores the water but also allows for some expansion and contraction.
If the problem is low water pressure you may have a rupture in the bladder in the tank. You could try adding air to that valve. No water pressure at all (no water) would indicate a pump issue, switch or electrical issue..