Sorry to hear about your "odor" problem. Maybe there is a local public fountain you can take a dip into!!!
However, the problems you describe are fairly common, but may be tricky to isolate. Let's try some basics:
Relieve the pressure from the bladder completely. Let the well pump fill the tank completely and bleed any air from the system using the faucets with the pump running. Again, with the tank full of water, close all outlets and charge up the bladder to about 60PSI. Most systems work fine between 45 to 65 PSI. Anything over 70 is pushing it. The tank needs to be charged when full, not empty.
Monitor the pressure as you draw water. Does the pump kick on constantly when the pressure reaches the low limit, and off at the high limit? This will help tell if the regulator is working properly.
Is there any pulsating water pressure at the faucets?
When you are sure you have a full tank, no air in the system, is your second floor water flow ample when the tank is reading 60psi?
There are a few "if's" here. Depending on how the pump behaves and the pressure responds, you have to determine if the problem is with the pump and volume of water being delivered to the tank, or if the pressure regulator is properly operating.
If you are still seeing any pulsating water pressure at the taps, then the bladder is water logged again. If the bladder pressure drops too quickly, then most likely the volume of water from the pump is low. The pressure should remain fairly constant at the tank if all the functions of the pump and regulator are working properly. Good Luck
The tank should be charged to the pressure at the attachment point. If the tank is attached to a point in the system where the pressure is supposed to be 25 psi, the tank should be pre-charged to 25 psi. If the tank is attached to a point in the system where the pressure is supposed to be 55 psi, the tank should be charged to 55 psi.
When the water pressure raises above the air pressure in the expansion tank, the water will begin to fill the tank and compress the air further. As the water pressure decreases, the air pressure in the tank forces the water out of the tank. If the tank is charged too high, water will not be able to compress the air and fill the tank.
Note: Measuring the pressure in the tank while it's connected to a pressurized water system, will show the pressure in the water system not the pre-charged air pressure of the tank. To measure the air pressure of the expansion tank, you must isolate it from the system.
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Some mistakes I've made:
Did an initial test of plumbing changes by cracking a valve open(so if there's a leak it's not a big one...) then forgetting to finish opening it. Check that all the valves that should be open are actually fully open.
Banging things about loosened enough crud that the aeration screens and shower heads are filled with crud. Take them apart, clean and put back together.
May have gotten a bad gauge. To test the gauge:
Turn off power to the pump. Open a tap fairly low down in the house. (Outside tap works well) As the pressure tank drains, you should see the gauge go down. If it eventually gets down to zero or nearby, then the gauge is working. May not be accurate.
If the gauge still reads something significant after the water has stopped running, then the gauge is broken. Replace it. Easy to do. You will need a wrench and teflon tape.
Once you have a good gauge, try this: Run a garden hose to about the same height as the problem tap upstairs. Carrying the end up a ladder is one easy way. If you get good flow through the garden hose but still have problems with the upstairs tap, then you have a problem with the tap or the plumbing between.
You get about 2 feet elevation per psi. If your pressure tank is in the basement, and then the upstairs tap is about 20 feet up. 50 psi in the basement will be about 45 on the main floor, and 40 upstairs.
This should be enough to get reasonable flow.
Here the usual pressure switch has two adjustments: The high pressure, and the differential. One sets the cut off when the pump is charging the tank, the differential sets how much lower the cut in pressure is. It's not strictly linear. Adjust the high pressure first, then the differential. Instructions are usually on a label under the cover.
Note: The contacts are live. Either turn off the power before going in with metal tools, or do the adjustments with a plastic handled nut driver.
A large differential means the well isn't turning on and off as often -- better for both well and pump. A small differential is less nuisance in the house. We compromised at 70 psi for the high, and a 12 pound differential.