Drop the two unused hose ends below the surface of the acid. Turn on the pump,
and allow the dilute acid to circulate through the heat exchanger for 15 to 30
minutes. The time interval depends on the severity of scaling.
Turn off the pump, and allow the acid to drain out of the heat exchanger as much as
possible. Hold up the acid pump to allow it and the hoses to drain. Disconnect the
pump from the hose leading into the heat exchanger.
Dispose of the used acid properly. If it is phosphoric acid, such as Scalestrip, it is
biodegradable and can be flushed down a toilet. Reflush the toilet several times to
clear the acid from traps. If the acid is not biodegradable, dispose of it in
accordance with local requirements.
Connect the heat exchanger inlet hose to the fresh water supply. Flush the heat
exchanger for at least five minutes. Once every trace of acid has been purged out,
disconnect the hoses. Repipe the heat exchanger, and purge the air from it.
Rinse out both the acid bucket and hoses. Pump fresh water though the acid pump
briefly and drain it before returning it to storage. Dispose of the used acid-water
mixture in accordance with local requirements.
Most solar heat exchanger bonnets are bronze or cast iron. Cracks in the metal can
sometimes be repaired by brazing or welding. Leaks in the gasket usually require
replacing the gasket. Since the fluid against the gasket is water, no special
materials are required.
Corrosion or cracks at the inlet or outlet ports of the bonnet usually indicate the
need for a replacement bonnet.
The bonnet and associated piping should be adequately and completely insulated
after repairs are made.
Tubes and Bundles
Broken, corroded or burst tubes in coil-in-tank or tube-in-tube heat exchangers
cannot be repaired. Tube-in-tube heat exchangers must be replaced. Most coil-in-
tank heat exchangers are not removable, so the entire tank must be replaced.
Brass or copper tubes in shell and tube heat exchangers can be repaired by
plugging leaking tubes. Determine the internal diameter of the tubes. Have one
inch long plugs machined from brass or bronze 0.004" smaller than the tubes' i.d.. A
five degree taper over one-half inch of the plug aids insertion.
5.2 REPAIR PROCEDURES