Expansion tanks

JK_2

I am new to the service side of HVAC. I had to make a half dozen repairs this winter on water boilers that required me to drain the system. How do I test If I have the correct pressure on a bladder type and old stlye expansion tank? How many psi should the sytem go up from filling it to running it at 180 degree? If I have it set at 12 psi is it OK if it goes up to 16 psi? How do I know if I have a failed bladder in an expansion tank? Thank you for any help.

JK_2

Expansion tanks

I am new to the service side of HVAC. I had to make a half dozen repairs this winter on water boilers that required me to drain the system. How do I test If I have the correct pressure on a bladder type and old stlye expansion tank? How many psi should the sytem go up from filling it to running it at 180 degree? If I have it set at 12 psi is it OK if it goes up to 16 psi? How do I know if I have a failed bladder in an expansion tank? Thank you for any help.

steve_38

Extrol Tank

#30 average size in residential home...
if the diaphram inside the extrol tank is bad the tank
will become water logged and eventually the relief valve
will blow off. when i get a service call on a relief valve that blew out water, and lets say the system is 10 to 20 years old, Most of the time the extrol tank is bad but i also check over the rest of the system and to play it safe i check the feed valve and usually replace it, and put a new relief valve in too. When changing these parts most of the time you can hold the system on a vacuum.

Alan_6

expansion tanks

the bladder pressure should always match your system pressure. If the boiler pressure is at 16 psi, when the water temp is 180 F, the expansion tank pressure should be at 16 psi. Most common residental tank is a extrol #30. This is a 2.5 gallon tank, sized for the expansion of 30 gallons of water, at 180 F. Bladder tanks are sized for the expansion of water, based on size of system in gallons of water, at a design temperature of a system. As long as your system pressure does not go past 20 psi, 24 psi your pushing it. One of the best ways to see if a bladder is bad, while the burner is on, the system pressure increases very fast.

doug_10

System dumping

The water's out, don't mess around, anything you don't do is a potential callback.

"Old style" expansion tank (aka compression tank), drain it completely.

Extrol #30 most common size. If over 5 years old, replace it.

Relief questionable? Replace it.

Fill valve questionable? Replace it.

Much easier to do it all at once while the water's out. Nothing sucks more than going on a callback to your own job, and you have to dump the system again.

Also while it's empty, replace the air vents that mean something.

The books/engineering stuff will say your cold fill pressure should match your up to temperature pressure. This is true. But I say, as long as it doesn't go over 30 psi (your relief valve setting), it's fine. In the real world the pressure is always going to change as the system heats and cools down. As long as the relief valve isn't blowing off when it's up to temperature, get in the truck, head down the road, and get yourself a well deserved coffee.