Does a well pressure tank have to be empty to check and adjust air pressure?

Answer 1

No, it does not have to be empty. Most important, is to check the current pressure. There will be a valve at the top which resembles a bicycle or car tire inflation valve. It may be under a cap which either may pop on or screw on, to protect it from damage. If there is a cap on the valve stem, then remove the cap. Use a tire pressure guage to check the existing pressure, just like you would a car tire. I prefer to check it several times, to be sure I have an accurate measurement. The pressure in the tank should be within two psi of the reading where your pressure switch will cause your well pump to activate. So if your well switch is a 40-60psi, you would want your pressure tank to be at 38psi. If the reading is less than that, take an air compressor and add a little bit of air to the tank, being very cautious to not over-fill the tank which can cause permanent damage. Once you are done checking the pressure and adding any air (if needed,) be sure to replace the cap on the valve and then the protective cover to prevent any damage to the valve/tank. If the pressure registers zero, then there is a problem which may signify that there is a hole or leak in the bladder. At that point I believe it is best to replace the pressure tank. Good luck and best wishes!

Answer 2

YES, it is essential that the tank is empty (or very close) to set the air charge.
This tank where the water enters from the pump is a critical part of your system . It should have an 'air charge' of approximately 27-28 psi if the pressure switch is a standard 30/50 switch. (see note below about 40/60) If this air charge has gone down, then your water pressure will be lower. If this tank is very old, possibly silver or green in color, then it's a "galvanised tank" and is possibly 'waterlogged'. (meaning full of water and not enough air ) This means you have to recharge the air with a compressor (just like blowing up an auto tire) To do this, switch off the pump. Open a faucet near the tank and let most of the water out. When you think it's nearly empty, close the valve to house and pump in with the compressor till the needle on your tank gauge points to 27, 28 psi. Now switch on the pump and the pressure should be improved. -IF your tank is a pale blue one, then chances are it's a 'bladder' tank and low pressure means your bladder is leaking. -You can pump it just as I said already, but in this case it will only last 2-3 months. You basically need a new tank.
In all cases check the size of the pressure switch. It's printed somewhere on it . 30/50 as I've mentioned is common but some are 40/60. In this case pump in 38 psi of air. Both pressure switches are adjustable to a small degree by turning the central spring up or down. It's essential that lower limit of this switch is 2-3 psi above residual air pressure.
Always use a good round tire pressure gauge, (available in auto stores for about $5.) to check tank air pressure, Don't rely on the installed gauge, they soon get erratic.