Pencil Anodes

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lampshuk

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I've a rather old Martec heat exchanger on my VP 2003.
It seems to get through pencil anodes rather quickly.
The pencils are 8mm diameter, and the cavity in the cap/nut is smooth.
Is there any reason not to use "plating anodes" (which seem to exist in 8mm size from Amazon) as sacrificial anodes?
Zinc Rod Anode/Electrode (10 cm x 8 mm) for zinc Plating Solution: Amazon.co.uk: DIY & Tools

It seems a terrible waste to keep buying bronze nuts just to get a little bit of zinc - though Martec are perfectly keen to supply them.
 
lampshuk said:
I've a rather old Martec heat exchanger on my VP 2003.
It seems to get through pencil anodes rather quickly.
The pencils are 8mm diameter, and the cavity in the cap/nut is smooth.
Is there any reason not to use "plating anodes" (which seem to exist in 8mm size from Amazon) as sacrificial anodes?
Zinc Rod Anode/Electrode (10 cm x 8 mm) for zinc Plating Solution: Amazon.co.uk: DIY & Tools

It seems a terrible waste to keep buying bronze nuts just to get a little bit of zinc - though Martec are perfectly keen to supply them.
Click to expand...

Anodes for cathodic protection are made of a special high purity zinc with a few small additions. Usually to a US military specification.

A very low iron content is important and even that is only made tolerable by the addition of a small %age of cadmium ( see below)

You can buy rod that conforms to the relevant spec

. Zinc anodes are made to MIL-A-18001K​
(Output 780 Ampere hours per Kg.)​
Cadmium . . . . 0.025% - 0.07% (no cadmium alloys are being investigated)​
Copper . . . . . . .0.005% Max.​
Iron . . . . . . . . . 0.005% Max.​
Lead . . . . . . . . .0.006% Max.​
Aluminium . . . . 0.1% - 0.5%​
Zinc . . . . . . Remainder (special high grade 99.995%)​
 
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Hmm. So "99% pure zinc" is several orders of magnitude off.

Is it fair to say that if I try it, and it's disappearing, then it's doing its job?
 
lampshuk said:
Hmm. So "99% pure zinc" is several orders of magnitude off.

Is it fair to say that if I try it, and it's disappearing, then it's doing its job?
Click to expand...

I think so, but if you find severe corrosion in your heat exchanger you'll know it's not

Why muck about with material that may not be suitable when you can get zinc rod of the correct specification
 
" ...when you can get zinc rod of the correct specification "
I may not be googling the right thing, but I keep getting galvanizing rod, not cathodic protection - certainly not in 8mm.

To Alahol's point: I've been in touch with one of the generic anode suppliers, so going that route is on the cards.
I can see why nobody wants to sell the rod on its own when they can sell something more complex.
 
Colour me stupid, but I did reallise the Volvo Penta 2003 indirect cooled HAD an anode! I understood the anodes were only fitted to the raw water cooled variant?
 
rszemeti said:
Colour me stupid, but I did reallise the Volvo Penta 2003 indirect cooled HAD an anode! I understood the anodes were only fitted to the raw water cooled variant?
Click to expand...
I think you will find that the anode is in the seawater side of the Martec HE. AFAIK the HE normally supplied by VP does not have or need an anode ( cannot see one in the parts catalogue anyway)

 
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Pfft ... far too deterministic.

You need to specify it as something Delphic like "1/4 inch NPQLGBT" or "1/4 inch gas" which - as far as I can tell - means about 13mm. As Asterix would say "you plumbers are crazy toc, toc, toc".

Meanwhile - in spite of Vic's assertions to the contrary - 8mm cathodic protection zinc rod seems to be made of 100% pure Unobtainium for mere mortals like me.
Or perhaps I'm using the wrong search in Google.

When I called one of the anode guys I was told "Can't make 'em that small - they would snap. It must be 10mm."

I had a brief moment of hope when I saw an "8mm unthreaded Onan pencil" ('scuse me???) on Anode Outlet - but it turned out to be a 10mm pencil turned down to 8mm at the base.

If I didn't have the spare one from Martec sitting in front of me with a micrometer clamped around it, I would believe it must actually be 10mm.

1583789773325.png

Anyway: this thread is becoming rather onanonistic, so I'll sort something out.
And if anyone's interested will let you know, including when/if the heat exchanger bursts.
I may even resort to asking Martec where they get their rod from.
 
I'm about to rebuild my original Volvo Penta exchanger, as one of the tubes rotted out from the inside ... if one has gone, there will be others getting close. Should be a fun little project.
 
lampshuk said:
Anyway: this thread is becoming rather onanonistic, so I'll sort something out.
And if anyone's interested will let you know, including when/if the heat exchanger bursts.
I may even resort to asking Martec where they get their rod from.
Click to expand...
Did you mean onanistic.

The smallest rod I can find is in fact 10mm but it would be simple enough to turn the end down to suit .
I'd suggest making it such that if you heated the brass holder and cooled the rod the holder would contract as it cools to grip the rod securely
 
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I know what I meant! :)

Thanks, Vic. I was worried I was walking into a "Let me Google that for you" moment.
I don't have access to a lathe, so will pursue other options.
 
lampshuk said:
I know what I meant! :)

Thanks, Vic. I was worried I was walking into a "Let me Google that for you" moment.
I don't have access to a lathe, so will pursue other options.
Click to expand...
Stick the rod in a drill chuck lash drill to something solid hold a flat file against the bit of rod you want reduced .
 
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