Stupid bladder tank question

[Taylorjm]

So I bought a house with a 4" submersible well that leads into the basement of the house and into a tank with an air bladder. There's a 40/60 pressure switch to control the pump. Not having any problems, but recently turned off the pump and drained the bladder tank and started thinking. So if this bladder tank, fills up from the bottom while the pump is running and pressurizing all the house pipes, how does any air get out of the water part of the bladder tank? Seems like the tank would end up with a pocket of air at the top against the bladder. What am I missing?

 

[Reach4]

So if this bladder tank, fills up from the bottom while the pump is running and pressurizing all the house pipes, how does any air get out of the water part of the bladder tank? Seems like the tank would end up with a pocket of air at the top against the bladder.

When the water pressure is zero, the diaphragm (probably, rather than bladder) will be all of the way down, squeezing out water and air.

If air did get in somehow, the air would come out of a faucet, or dissolve in the water. It is not a problem, unless you have a rare gas-producing well that brings up carbonated water or some such.

 

[Sponsor]

 

[Taylorjm]

Ahhh, I see whats your saying. Since there's air pressure on the one side, when you drain the water out of the other side, the diaphragm pushes down towards the water. So is that diaphragm really that flexible that it will push down to the bottom of the tank when the water is left out?

 

[Taylorjm]

And yes, you are correct in your terminology. I have an ao smith pre-charged diaphragm tank. I thought a bladder tank and diaphragm tank were the same thing, but in looking up the definition, I see there's a difference. Thank you.

 

[Reach4]

Ahhh, I see whats your saying. Since there's air pressure on the one side, when you drain the water out of the other side, the diaphragm pushes down towards the water. So is that diaphragm really that flexible that it will push down to the bottom of the tank when the water is left out?

Note that the diaphragm is not like a stretched flat thing, but made to be a low tension barrier between water and air.

 

[Taylorjm]

Wow, there seems to be a lot of wasted space inside that particular one. I expected it to be filled with more water, but then I guess you need enough volume of air at a pretty low pressure to do anything.

 

[Valveman]

Rule of thumb is a pressure tank holds 25% water. Even a large 80 gallon tank only holds 20 gallons of water. You water doesn't come from the tank, it comes from the pump and well. All a pressure tank is for is to reduce the number of on/off cycles while your pump is pumping maximum flow. Cycling is bad for the pump system and bounces the pressure up and down. This is why constant pressure systems can use a smaller tank, as they vary the pump output to match the demand.