Getting ready to use the FT. I can't remember how to check the expansion tank. I know 25 lbs is the air pressure. Do I air it up before I add any water to the system and pressurize with the pump, or after it's all ready to go
If you are referring to the accumulator for the potable water system, with water pump OFF, shore water OFF and faucet opened to bleed off PSI, set to CUT IN PSI MINUS 2 PSI. So for the many pumps that have 25 PSI cut in, set it to 23 PSI.
Regular tire gauge and cycle pump work well.
But, start by pushing in the small plunger/valve stem core. If you get water, the diaphragm is bad and the accumulator needs to be replaced. If good, set to correct PSI.
Just as another piece of advise. You may have to let a bit of air out of the tank to see the water.
The first time I checked my accumulator, I just did a quick press on the valve. No water just air. Later I checked again holding the valve down for a few seconds and water came out that time.