Pitting on Jabsco face plate - is it electrolysis?

[Rivers & creeks]

I looked at the inside of the face plate on the Jabsco raw water pump on my new to me engine - it was a horrible mess, probably a lot of sediment in the water where it was used but worryingly there was a pitted area about 3mm across and 2mm deep and other smaller nicks, looked very much like corrosion - maybe from electrolysis? Is that possible and if so where else in the engine should I be looking for potential electrolysis issues? The engine was started and ran well just before delivery to me. It's a Mermaid J444 Dieselmax that doesn't have an engine anode.

 

[superheat6k]

Possibly a form of crevice corrosion / dezincification. The corrosion goes mad in the absence of oxygen due to the sealing effect of the rubber ones against the cover.

If so the problem is likely just with the pump.

What is the material ?

Can you post a photo.

 

[sailorman]

Is this the "wear plate" in the behind the impeller

 

[Rivers & creeks]

It's a standard Jabsco pump so I gues bronze. I forgot to take a photo of it I guess from what you said I should examine the rest of the pump housing inside. I replaced the face plate with an excellent Speedseal. I worried that there had been more widespread corrosion - are you saying it might just have been the pump insides?

 

[superheat6k]

It's a standard Jabsco pump so I gues bronze. I forgot to take a photo of it I guess from what you said I should examine the rest of the pump housing inside. I replaced the face plate with an excellent Speedseal. I worried that there had been more widespread corrosion - are you saying it might just have been the pump insides?

Most likely brass rather than bronze, and sounds like simple de-zincification. I would remove the impeller and see if the housing periphery is OK, or whether there are distinct lines of pitting where the lobes had sat unmoved for an extended period.

 

[sailorman]

I think the wear plate is brass

 

[Rivers & creeks]

Pump is definitely bronze so do they make the face plate brass to save the pump corroding?

 

[sailorman]

ask your installer

 

[vyv_cox]

Most likely brass rather than bronze, and sounds like simple de-zincification. I would remove the impeller and see if the housing periphery is OK, or whether there are distinct lines of pitting where the lobes had sat unmoved for an extended period.

Yes, that is my experience. Not certain whether Jabsco and Johnson fit the same plates but several that I have inspected were brass and had suffered dezincification. It is easy to differentiate brass and bronze by colour. Compare with a plumbing compression fitting, which will be brass. Bronze is very pink by comparison ('red brass' in American)

 

[sailorman]

spare plates are available from ASAP Supplies

 

[omega2]

turn it inside out for extra wear, and yes they do wear, a kit is readily available, at the jabsco shop.

https://www.jabscoshop.com/marine/

 

[sailorman]

turn it inside out for extra wear, and yes they do wear, a kit is readily available, at the jabsco shop.

https://www.jabscoshop.com/marine/

I also reverse the cover plate too, ignore the stamped lettering ( a rub with fine wet or dry will tale any burr`s off it ) on it, it will still work.

 

[Rivers & creeks]

Yes, that is my experience. Not certain whether Jabsco and Johnson fit the same plates but several that I have inspected were brass and had suffered dezincification. It is easy to differentiate brass and bronze by colour. Compare with a plumbing compression fitting, which will be brass. Bronze is very pink by comparison ('red brass' in American)

Thank you. So dezincification but most likely only localised electrolysis rather than a wider problem.

 

[sailorman]

Thank you. So dezincification but most likely only localised electrolysis rather than a wider problem.

Yes the pump is some what isolated, i had similar on my Nanni until i realised it was just the wear plate that was being gribbled

 

[vyv_cox]

Thank you. So dezincification but most likely only localised electrolysis rather than a wider problem.

Not electrolysis, no electricity is involved. Selective corrosion is the correct term for the mechanism that includes dezincification.