Answer by
LeheckaG (1826)
Water-ressure-tanks usually have a flexible-sealed-bladder of air;
when your water-pump is running,
it pumps the water-pressure-tank full of water,
compressing the sealed-air-bladder.
When your pump turns off,
the air-bladder is still compressed applying pressure to the water
which forces a few gallons water out of the tank when you open a faucet.
Water-pressure-tanks ease the start/stop load on your water-pump.
Some old style tanks were fitted with a schrader valve so you could put pressure on the tank to push water through the system. Others had an air pressure pump that pressurized the tank, often connected to a pressure switch that would cut it on automatically when pressure got low. add a comment