DonL
Jack of all trades Master of one
Do you have a pressure gauge on the tank? I put in a nipple and a Tee so that I can have both a gauge and a schrader valve to use with my compressor. Half a century ago, I used a bicycle pump to add air to the tank. The tank was tucked under the stair landing and there was no room to stand up so I had to work the bicycle pump sideways. Remember it like it was yesterday.
No gauge on the tank. Mine is mounted on the Pressure Regulator that controls the jet pressure.
When the pump is off , I would think that it is reading the tank pressure.
I could add another meter, but would have to worry about it freezing.
I have a heat tape to keep the regulator and Pressure switch from freezing.