expansion tanks

[GHRoberts]

We have a well. So I know about those.

The pressure tank acts as an expansion tank. I guess we could do some math on a typical tank. A 20 gallon tank set for a low pressure limit of 50psi and a high pressure limit of 100spi. (I think my tank is set for 60 and 80 but the math is more difficult.) The pump starts when the tank is empty and the pressure is 50psi. It pumps 10 gallons of water making the pressure 100 pounds and turns off. 1 gallon of water expansion would raise the pressure from 100 psi to 111psi (100*(10/9)). I don't think 110psi will trip the TP valve on the water heater.

 

[Dr. J]

100 psi is already over the limit (80 psi). The pump cut off needs to be lower than 80 to suck up the expansion without going over 80.

 

[M. Nieves]

when exactly are expansion tanks required on water heaters? type of fuel,capacity, closed system?

Hi, pwood, as far as I know, If your domestic hot water heating system doesn't have a functional expansion tank, swings in water pressure can take years off your tank’s integrity. This could cause leaking or bursting of your tank because the glass lining of the water heater gets stressed and damaged.

Also, your expansion tank should be checked annually if you want to avoid and prevent premature failures.

 

[Mr. Inspector]

I live in a community of 20 houses that are off 2 wells that fill a tank on top of a hill. I'm near the top of the hill so don't have a lot of pressure. The homes near the bottom of the hill are on a pressure limiting device because it get to about 100 psi. No one ever had any water hammering anywhere that I know of. Would anyone require itr here?