It does seem strange that the air pressure in the tank would be 35 while the water pressure is 48. As I understand it, the bladder holds the water and the tank holds the air. So, higher water pressure in the bladder while the air pressure in the tank is lower suggests to me that the bladder has stretched to its elastic limit and cannot expand any more to bring the air pressure up to the water pressure. I would expect that to happen if there was not enough air in the tank. Maybe I should add air to the tank to bring the air pressure up to the same as the water pressure when it is at 48 psi? Then when water is released from the bladder by turning on a faucet, the air pressure in the tank should come down as the bladder contracts.
Steve,
I believe that you are looking at the pressure tank operation incorrectly.
The bladder contains the air, from the top of the tank. The bladder expands downward to "PUSH" the water out of the open end of the tank at the bottom. When all the water has been expelled from the tank, the bladder is fully expanded and there is no water inside the tank to "PUSH" back against the bladder. At this point, the precharge psi is limited to the air pressure you fill the bladder with. So, in your case 33 to 35 psi. The bladder is fully stretched out at this point.
When you turn your pump on, the water starts to fill the pressure tank and compresses the air bladder within the tank. As the bladder compresses, the air pressure inside it has to increase because your pressure switch doesn't shut the pump OFF until the water pressure that the switch senses reaches 50, 55 or 60 psi, wherever you have the pressure switch cut out point set at.
Therefore, the air pressure in the bladder rises from its minimum psi of 33-35 up to the 50, 55 or 60 psi where the pressure switch shuts the pump off.
If you precharge the bladder to a pressure higher than the cut-in pressure of the switch, you will confuse the switch. The pump will then turn on only when you have reached a much lower volume of water in the tank. This reduces your reserve of water available in the tank before the pump turns on. If you go too high, the pump may not turn back on before you run out of reserve water because the switch may sense the precharge air pressure in the tank as the actual water pressure.