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Expansion Tanks
Leaks at expansion tank inlet fittings are repaired the same way as other threaded
fittings. Generally, a crack in the tank wall at the inlet fitting indicates a need to
replace the entire tank.
Sometimes they can be welded, but it is rarely worth the effort and cost. Whenever
a tank without a diaphragm must be replaced, use one with a diaphragm.
Tank wall leaks are usually cause for tank replacement.
If the wall appears
corroded, check the condition of the fluid which caused it.
If the tank holds water, appropriate water conditioning may be needed. If the fluid is
a glycol, it may be acidic. In this case, the loop should be flushed and refilled with a
fresh glycol/water mixture.  Dispose of used solar fluids in accordance with local
If a diaphragm-type expansion tank has any fluid in the air compartment, it must be
replaced. This is usually found by momentarily depressing the stem of the schrader
valve. Any fluid discharged from the air compartment means the diaphragm has
broken, or is disconnected from the tank wall.
Be aware that sometimes fluid leaking from a loose connection at the top of the tank
will "sneak" down the back side of the tank. The dripping fluid at the bottom
schrader valve fitting may not really be coming out of the bottom of the tank.
Occasionally, a schrader valve will loosen up, releasing all the pressure from the air
compartment. Use an automotive valve stem tool to tighten up the schrader valve,
and repressurize the air side of the tank to the correct pressure listed in Table 5-5.
Refilling the air side to the appropriate pressure must be done when
there is no fluid pressure on the other side of the diaphragm. See
Table 5-5 for further information on system charging pressures.


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