zinc sacrificial anode

[Whidster]

Has anyone heard of putting in a zinc sacrificial anode when installing their swg? The pool place said most commercial pool installs put one in to protect the metal in the system from corrosion and electrolysis.

Should my husband install one? If so where in line with the swg would it go.

Thanks!

 

[chem geek]

If you have stainless steel that is not of high quality or you have aluminum touching the water, then connecting a zinc sacrificial anode to the bonding wire and burying it in moist soil can help protect such metals. The anode will corrode in place of the metal you are protecting. You will need to replace the anode every couple of years or so, depending on the rate of corrosion (check it annually). Most pools don't need such extra protection, but it does not hurt.

 

[blakeusa]

Why would you recommend burying the zinc rather than having it inline in the plumbing touching the water. I know the zinc will end up in the water but I don't understand how all the current will be pulled to the bounding wire. i.e. the heat exchanger in the heater will be getting current as salt water passes through would it not?

Thanks

B

 

[JasonLion]

You put the anode in the ground so you won't get zinc in the water. There needs to be a complete circuit. The bonding wire forms one leg of the circuit and the other leg goes from the anode, through the ground, through the pool wall, into the water, and to the metal being protected. Because of the differing electrical potentials, a current flows that charges the metal being protected so it won't corrode, and discharges the zinc so it corrodes more quickly. This all works as long as the pool is plaster. I believe the anode needs to be in the plumbing for vinyl and fiberglass pools.

 

[chem geek]

The ground acts as a "sink" where the ions diffuse. It's not fast electrolysis and the point is to put a voltage onto the bonding wire. It's not a complete circuit with the pool; corrosion occurs with the zinc and oxygen or acidity in the soil (i.e. the corrosion "circuit" is local) but the entire time there is a negative voltage on the bonding wire from zinc that has not yet corroded. If the zinc corrodes too quickly, then the zinc ions or zinc oxides could build up and the voltage on the wire drops so protection would then stop. Putting the zinc in the water (but still connected to the bonding wire) would prevent that build up but would also put zinc ions into the pool. The presumption is that there isn't fast enough corrosion to make this necessary.

You can think of it as having some zinc metal form zinc ions and putting more electrons on the bonding wire. This holds the metal in the pool more in place and less likely to corrode. This potential difference can be fairly static with minimal corrosion (if it were in an oxygen-free electrolyte), but in practice the zinc does end up corroding due to oxygen and acidity in the soil.

This is analogous to having a single electrical wire with a voltage with the other being connected to ground (not to the "ground" from the source). Yes, technically there is a circuit all the way back to the originating source, but in practice it's just that the ground is a huge sink/source of electrons so unless the current is high there is little build up of charge that would lower the effective potential difference.