failed diaphram expansion tank

Unknown

Could improperly draing a boiler system with cast iron radiators tear the bladder in the tank?  I know it is possible to capsize a compression tank.  We have a customer who thinks draining his boiler to do a repair caused the failure of the expansion tank.  I wasnt sure if this was the case.  Any feed back would be appreciated.

Mark Eatherton

Nah....

But, you touched it last, now anything that goes wrong is your fault :-)



ME

Brad White

Failed Diaphragm? Hi Dad!

Oops. Wrong one. NEVER let your cat play with the one in the top dresser drawer.



The heating system kind- Not very likely.



The butyl diaphragm in most expansion tanks is remarkably flexible.  What can make it fail is a collection of rust or sediment with sharp edges wearing on it,  or some chemical interaction (unlikely in a hydronic system). The replacement diaphragms (one of the few times you will actually see one), are pretty tough to tear and do stretch a good deal. I cannot imagine tearing one with my bare hands and absent a defect, cannot imagine a drain down even to vacuum, tearing it. I could be wrong but handled the material and it is tough.



Just one point of terminology, a diaphragm tank has a stretched "drum head" across the middle of the tank which bulges toward lower pressure of course. A true "bladder" tank is like a bag and has a higher percentage of acceptance volume, often 100 percent of tank volume.

kcopp

There is a good....

possibility it was on the way out. You probably just put it over the edge. Too bad you have a customer like that.... might be time to tell them to find someone else.

croydoncorgi

Diaphragm positions

If you look into the neck of a diaphram EV fresh from the factory, you'll be able to see the diaphragm pressed hard against the end of the tank by the preload pressure!  The stretching and movement of diaphragms (IMHO) makes them fail sooner than the bladder type of EV - AND you can often replace the bladder without disturbing the plumbing (much!).  Another benefit of bladders (while they remain intact) is that the steel tank wall is NOT wetted, so no possibility of corrosion.



Since the diaphragm is designed to stretch all the way to virtually filling the water-end of the vessel, I can't see how draining the system could affect it at all - unless it was on the point of failure already.  And they DO often fail.  How did the customer KNOW it hadn't failed long before? It can take a very long time for all the trapped air to leak through a small hole in the diaphragm and dissolve into the water.

icesailor

Expansion tanks:

First, how old is the tank? There's a date code on it.

Second, in MY experience, Amtrol's last the longest. Far longer than some out there. I've seen some that went in two years. Just after the warranty ran out. I just replaced one that was offered by my supplier when Amtrol had some problem a few years back and it was sold in NE but was made in China when you looked. There are others that as soon as I see them, I know that they are gone. If you have a tire gauge, it's easy to check. If the boiler pressure gauge says 8# and a tire gauge says 8# and you drop the system pressure to 0#, the tank is gone.

How old is the heating system? The tank is as old as the system.

If it has a Cast Iron PRV/fill valve like a Watts 1156F, it was probably clogged up in the strainer or the valve was stuck so it didn't matter what was happening in the system. When you drained it or added water, it wouldn't fill. Once you operated the fast fill lever, you removed the obstruction. Then, the pressure was too high in the system for expansion.

It's a trough call on what's to do. I would probably wish this person health, happiness and long distance. Sounds like a predatory customer. You are they prey.

Because they are so easy to change, I always change them on the fly, maybe change the tank with the cheapest POS you can find, and tell them to get someone else next time. 

Shame on me if I get into the same problem with the same customer the second time.