Pressure tank problem?

[LLigetfa]

You can attach a 12V air compressor to a hydro-pneumatic tank and force out quite a bit of water after a power outage. Usually about 1/3rd of a hydro tank is wasted space. But that space is full of water if you have a way to force it out during a power outage.

That may be true for the old style galvanized tanks but some HP tanks are "supercharged" so as to perform more like captive air tanks and as such they are almost empty when the pressure drops to cut-in. I deliberately shortened up the AVC (12 inches) on my second (inline) tank so it acts more like a contact tank for the iron filter. The AVC on my tanks release air very slowly so cannot expel the sudden expansion of air when the pump doesn't come on. That was why I mentioned the air moving forward to the media tanks and displacing the water it them.

Also, you would need to add air faster than the AVC can purge it.