Why does the pressure, attached to a submersible well, keep increasing?
Per your other thread, it sounds like you're measuring the pressure in the tank's bladder. If this is the case: don't. In fact, if you're releasing pressure to get it to 28, you've actually screwed up the calibration of your tank, your pump is likely going to be cycling faster than it should be, which will wear out the pump faster as well as cause fluctuations in the water pressuring in your house.

The tank pressure is irrelevant while the system is running. The valve at the top of the tank is for setting the pre-charge pressure.



The pressure you should care about is on the gauge at the base of your tank: this is the water pressuring going to your house.





To set up the pre-charge correctly for a 40-60 PSI range:


Turn off the power to the pump, then open a tap until all the water drains out (so your system pressure is 0). 
Via the valve on top of your tank, set the pre-charge pressure in the tank to whatever the manufacturer recommends: typically 4 PSI below the low pressure limit (so, 36 PSI). 




Now you can adjust your pressure switch, if needed:


Turn off the valve to the rest of the house, and turn the pump back on. Your goal is for it to stop at 60 PSI. 
If it goes higher/lower, adjust the big nut until it shuts off at 60. 
You may have to open the valve to release pressure so the pump kicks in again, and repeat several times.
Now open the valve to the house (run some water). The pump should turn on at 50. If not, adjust the small nut until it does.


Keep in mind to adjust the pressure switch, the big nut (green arrow) adjusts the overall pressure, while the little nut (red arrow) adjusts the range between the on and off values.