Thermal Expansion Tank Primer

rob

Using this site as a resource.... Dispatched to heating call, more like a plumbing call actually, but I think I can handle it.:) SatAM leaking expansion tank on cold water inlet to HWT. HO installed water heater 50g/40K. Seems he is very upset with the big orange guy HomerDepew, he keeps getting "defective" tanks that leak... I see the tank Watts heating expasion tank like a #15. I isolate the tank, pull the #15 and pressure test the incoming line @ 60 psi. I know the problem as soon as I see it. I call the parts mgr and order a domestic pressure rated thermal expansion tank, fabricate a bracket to support it and invoice the client.
Sometimes (more often the better) I can be compensated for what I know as well what I do.. Anyway, not being a plumber per se and wanting the learn from the best... just what is the function of this "expansion tank" ?? Check valve in main water, true expansion (why the cold water line?, Thanks.

Constantin

Because water expands as you heat it...

... being a fairly incompressible liquid, the cold water heating inside a water heater will cause the pressure to rise. With a check valve preventing expansion out into the cold main, the pressure simply builds in the "hot" part of the domestic water system. It may or may not break anything, but it's not a good thing because it can cause scalding as water shoots out of faucets under pressure.

Putting an expansion tank on the system allows the water to expand into the tank, compressing the air bladder inside. Therefore, the hot water pressure in the home will remain fairly constant. However, the bladder tank has to be sized correctly and have the right pressure, otherwise the water will simply squish the bladder into the opposite end of the expansion tank, and the same carnival ride begins again.

This is also the reason that dripping T&P valves can be an indicator of a expansion tank whose bladder has ruptured or is leaking.

I presume the reason that the manufacturers want the bladder tank on the cold side of the DHW system is that rubbers for the bladder material that can withstand high temperatures cost a lot more than rubbers that work at room temperatures. Plus, migration of water molecules through the bladder material may be lower at low temperatures than at high temperatures.

Big Ed

Thermoexpansion

> Using this site as a resource.... Dispatched to

> heating call, more like a plumbing call actually,

> but I think I can handle it.:) SatAM leaking

> expansion tank on cold water inlet to HWT. HO

> installed water heater 50g/40K. Seems he is very

> upset with the big orange guy HomerDepew, he

> keeps getting "defective" tanks that leak... I

> see the tank Watts heating expasion tank like a

> #15. I isolate the tank, pull the #15 and

> pressure test the incoming line @ 60 psi. I know

> the problem as soon as I see it. I call the

> parts mgr and order a domestic pressure rated

> thermal expansion tank, fabricate a bracket to

> support it and invoice the client. Sometimes

> (more often the better) I can be compensated for

> what I know as well what I do.. Anyway, not

> being a plumber per se and wanting the learn from

> the best... just what is the function of this

> "expansion tank" ?? Check valve in main water,

> true expansion (why the cold water line?, Thanks.



With a check valve on the main it will close the domestic system off from the outside.As the water is heated in the tank it will exspand. Water can not compress so it will turn into pressure.Air can compress ,so with the tank in the system the compressing air takes up the building pressure. It works like a spring in the system ,the thermo tank in a closed system will compress on temperture rise and it will decompress when soneone runs water or temperture drop....

It is installed on the line between the tank and the checkvalve .If someone opens the cold water with the thermo espansion tank after the hwh , the decompression (spring)tank will back alittle hot water up the cold line...

Big Ed

Thermoexpansion

With a check valve on the main it will close the domestic system off from the outside.As the water is heated in the tank it will exspand. Water can not compress so it will turn into pressure.Air can compress ,so with the tank in the system the compressing air takes up the building pressure. It works like a spring in the system ,the thermo tank in a closed system will compress on temperture rise and it will decompress when soneone runs water or temperture drop....

It is installed on the line between the tank and the checkvalve .If someone opens the cold water with the thermo espansion tank after the hwh , the decompression (spring)tank will back alittle hot water up the cold line...

Dave Yates (PAH)

Boyle's Law as it relates to thermal expansion

http://wwwboard.masterplumbers.com/plumbviews/2002/Boyleslaw.asp

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