Do water pressure tanks have bladders or lungs?

Answer 1

NOT lungs, but bladders, yes. Most new style well pressure tanks have a large tough balloon known as the bladder to contain the water as it's pumped in from the well. This bladder will expand to fill about 2/3 of the tank volume. The other third is the air charge, usually of 28psi. It is this air charge that gives the water it's pressure, and as the water depletes through normal usage the pump will switch on at 30 psi and refill the tank. (It's vitally important to balance the tank air pressure and the pressure switch settings.) These bladders can become pinholed through long use and often bleed water into the air chamber and slowly become useless as there is less water pressure. Bladders in tanks over 120 gallon can be replaced, smaller than that is possible, but not cost effective.

Older style tanks, called 'galvanised tanks' did not have a bladder, and once the tank contained a small amount of water, a compressor is used to install 28 psi of air charge. The disadvantage of these is obvious when power outages occur and people use water and deplete the air charge because the pump does not switch on. When power returns there is no, or very little water pressure. (in a good bladder tank this will not happen as the air charge is separate.) Under this condition, the pump will operate for a very short time every time a faucet is opened or a toilet flushed, leading some people to think they have a pump problem. I have known unknowledgable people, and even some plumbers to have bought and fitted a new pump, when all it needed was an air charge. -This is why bladder tanks were invented.