expansion tank and glycol solutions

R. Taliano

I have a hydroair system with a MZ-40 boiler an Amtrol Extrol (model 60 I think) external expansion tank. The system runs through an unheated attic so it has the "MZ" glycol solution in it. I have continued to have system pressure swing problems and the tank was replaced (it was 2 years old) last March. I have ruled out the water fill valve (problem still exists with the fill valve off) and external high pressure relief valve. The new tank seemed to fix the problem until October...now same problem again. The tank is not waterlogged but it seems to be behaving as if the membrane has become inflexible. I know that tank diaphram could go bad but what are the odds of having two bad tanks. Could the glycol be ruining the tank diaphragm? I don't use the system for hot water...could non-use of the system contribute to tank diaphram problems with or without glycol? Could it be a concentration problem? If so how would I measure concentration and is the MZ antifreeze/anticorrosive proprietary?

Thanks
Ross T

Einsiedler_2

potential

is the expansion tank for heating? The domestic tanks won't hold up to high temps and come precharged quite a bit higher than the heating tanks. The Heating Tanks have a butyl diaphram so glycol shouldn't be an issue.

I'd suggest checking the precharge on the tank (do this with the system side at 0 psi). match the tank precharge to your idle fill pressure setting. If the tank is sized right, it should not be causing flucuation problems, it should cure them.

If you have the old tank around, cut it apart and locate where the failure was. This may help in determining problem.

EIN