It is a good idea to check their pressure at least annually or if you notice your pump coming on more frequently than normal.
Testing Accumulator: The blue tank is the accumulator. It can easily be checked. There is a Shrader valve (just like the valve on your tire) with a cap on it. Remove the cap. With shore water, off and water pump off AND a faucet open to drain off pressure, use a tire gauge to check the pressure. The pressure should be your pump cut-in PSI less 2 PSI. So for a 25 PSI cut-in pressure accumulator, set the pressure to 23 PSI. You can use your on-coach air or even a bicycle pump to properly pressurize it.
If, when you depress the valve on the accumulator, water comes out, the bladder is bad and the accumulator needs to be replaced. by Brett Wolfe 1993 U240
The accumulator contains a rubber bladder that is pre-charged with air in the factory. If the pressure is low (less than 20, but still pressurized), add a quick shot of air from a portable pump. Don Hay ’92 U-280
Winterizing: The accumulator has a bladder in it which is pressurized, When one empties the water system, the bladder pushes all the water out of the tank since there is no water pressure against the air pressure on the bladder.
You may remember that with no outside water hook up and the water pump turned off, one can turn on a water faucet and the water will run for a while. This is the water emptying out of the accumulator into the water pipes. Rudy Legett 1995 U320
Replacing Accumulator: Its a standard model, look for a gallon at Home Depot/Lowes.
You could also replace your pump with a variable speed model that doesn’t require one. Dave Head 95 U320C SE 40