Removing black/hard scale on inside of pumps?

[RickFlorida]

I have one of these well made irrigation pumps from Sta Rite. But mine is over 25 years old I estimate. I'm moving the location of it and decided I should rebuild it. The Artesian well water has created a thick and hard shell of black scale on inside of the pump. I think I should remove it or the shattered pieces could jam up the pump during operation. Is there an efficient method to remove it? I'm using rust dissolver but that really only works once the exposed cast iron is free. I can take a chisel and hammer chunks of it off but it's very slow and inefficient. Is there a chemical bath that works well for this? A new pump of this quality is 900 bucks (they actually still sell these according to the internet) so I don't mind putting a lot of time and effort in this. I'm going to enamel paint it when done.

 

[MicEd69]

Assuming the black scale is mineral deposits from the water, it should be able to be removed with an acid. I don't know if you have easy access to all of the scale, but if you do, a weak HCl solution would be fastest. If not, a long soak in vinegar would help.

And of course, you need to take the normal precautions when working with an acid.

 

[RickFlorida]

Assuming the black scale is mineral deposits from the water, it should be able to be removed with an acid. I don't know if you have easy access to all of the scale, but if you do, a weak HCl solution would be fastest. If not, a long soak in vinegar would help.

And of course, you need to take the normal precautions when working with an acid.

Thanks, yeah a pump guy just told me that its sulfur and that makes sense as it smells. The hard suflur scale is difficult to remove. He says he normally sandblasts it but he said another option is to build a coal fire in the yard or in old grill and then let it heat soak overnight in the coals. This breaks up the hard scale sulfur and makes it easer to remove he says. I like your idea about acid but if I were to use muratic acid, it could eat too much of the good metal and ruin the threads and tolerances I would think. I will try the heat soak method first and then see if I can manually remove the rest first. Thank you.

It's really thick, like 4 or 5mm thick hard scale. I don't thing soaking it in vinegar would really do anything but maybe if in really hot vinegar over a long period of time?

 

[MicEd69]

Opps, I glossed right over the Artesian well comment. No, sulfur cannot be dissolved in anything and must be mechanically removed. If you have a large air compressor, you could use a needle scaler to make faster work of it, or as the pump guy said, sandblasting.

And when I thought you had mineral deposits, I didn't mean you could soak the pump in HCl, but that you would have to "paint" it on in areas. The only thing you could "soak" the pump in would be the vinegar.

 

[RickFlorida]

Opps, I glossed right over the Artesian well comment. No, sulfur cannot be dissolved in anything and must be mechanically removed. If you have a large air compressor, you could use a needle scaler to make faster work of it, or as the pump guy said, sandblasting.

And when I thought you had mineral deposits, I didn't mean you could soak the pump in HCl, but that you would have to "paint" it on in areas. The only thing you could "soak" the pump in would be the vinegar.

Okay thanks. Yeah I was thinking it would be cool if I had a small "needler" but I don't have airtools. And if I tried to use a big hammer chisel, it would be difficult to access the hard to reach areas with a large tool. Do you think heat soaking it would break up the hard sulfur scale like the pump repair told me? Would be interesting if that breaks it up good by just heat soaking it over night in an spare old grill. I'm a public school teacher so I have more time than money. And since these Sta Rite cast iron pumps are so well made, it's worth it to me to restore it.

 

[MicEd69]

Do you think heat soaking it would break up the hard sulfur scale like the pump repair told me?

The pump guy apparently has experience with this, so it might work.

I'm not sure as to the theory behind the heat soak, but as sulfur melts at around 235 F, I assume it is to drive out all the moisture and melt the sulfur into a glassy coating that might be easier to remove mechanically. Another thing that might be an option would be a propane torch. Again, care must be used as too much heat in one spot can crack cast iron. And the fumes from sulfur would not be pleasant.