How do I know if an expansion tank is working properly?

gsherm

Hello All,



I work as an energy auditor in New York City and we perform energy audits on many small to large multifamily properties. We come across numerous hydronic heating systems equipped with old expansion tanks. A few questions:



1) How does one determine if an expansion tank has a bladder without having to look up the make and model?

2) How does one know if an expansion tank is flooded or waterlogged without a guage glass? Is knocking on the outer wall of the tank a viable strategy?



Any other tips or investigative procedures would be helpful for me and our team of energy auditors. Thanks in advance.

Mark Eatherton

Loaded questions...

If you really want to learn more about hydronics, invest the time and money to purchase Dans books.



Gnereally speaking, if it is mounted to the ceiling above teh heat source, it is a non captive tank. No bladder or diaphragm. Residentially, unless it is a HUGE mansion, the expansion tank will be a diaphragm type, not a bladder type.



If it is the old ceiling hung type, there can NOT be any automatic air removal devices in the system.



If it is the newer style of diaphragm tank, there SHOULD be automatic air vents.



As for checking a tank, unless you have a infrared camera, knocking on the side of the tank only tells you that it is there, because you are knocking on it.



Keep an eye on the pressure. If it remains relatively stable, the tank is fine. If it climbs quickly while boiler is firing, it could be partially water logged.



As for determining the volume of the tank, if it is hung from the ceiling, the volume is called out in gallons, so you have to do a little math to determine that.



Pi times the radius, squared, times the length = cubic inches. Cubic inches divided by 1728 = cubic feet. Cubic feet times 7.5 = gallons. Most small residential systems have a 30 gallon tank on them, and the actual volume of water (if you happen to be lucky enough to have sight gages on the tank) are usually 1/3 to 1/2 full cold, and 1/2 to 2/3's full hot.



If it is hanging from piping and has a lot of rounded corners, it is a diaphragm tank and there is usually markings on the tank showing the model number.



No 2 systems are the same.



Good luck.



ME

icesailor

Expansion Tanks:

Mark,

Plumbers' math is easier.

MA Journeyman Plumber Test question:

What is the volume in gallons of a water tank 12" in diameter X 5" high (or 60")

D(iameter)2(squared) in inches X length in feet (") X .0408= US gallons.

If it is the length in inches, (like 60"), the constant is.0034.

Thus, a 12" diameter tank (12"x12"= 144) x 5' = 720 X .0408 +29.37 or 30 gallons.

How much does the water weigh in the tank?

Mark Eatherton

Only one correct answer regarding what it weighs...

It DEPENDS! How full is the tank? 8.3 lbs per gallon, but you obviously knew that. :-)



Your mathechusetts is a different means to the same end. I learned mine in high school. And it has stuck with me and served me well all these years.



Kinda like the difference of R value versus U value, and which one works better doing a heat loss. They are the same thing, just expressed in different ways. Different means to the same end.



ME

icesailor

Expansion Tanks:

Well, our plumbing issues always evolve around "How much water is in a water tank 12' in dia. X 60" high. And how much does the water weigh. Not "half full".

Or, one of my Master Plumber test questions:

What is the total pressure of water in PSIG at the base of a 4" soil stack 40' high with 2-4" branch intervals with 1' risers on each. How much does the water weigh. How much is the total weight at base of the stack filled with water if it is 4" XH soil pipe?

I guess I studied too hard. I still remember a lot of those questions.

But I use it every day.