PST Steel tank and U.S. Divers 7/8 valve questions

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SubseaSports

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@Rol diy depends on how bad. I mix either 50/50 if bad or 1/3 if mild. Just enough to cover the bottom of the tank to the straight wall. Time in the tank is what counts. As someone said earlier...too long and it will turn steel black. It will leave a light gray color if done properly.
Usually 20 minutes minimum with tank upright, static. Then lay it on its side and tumble, or roll for about 30 minutes or so to get the walls and under the bell of the tank. Be sure to plug the tank.
Dump appropriately, rinse, wash out with simple green or Dawn, rinse, rinse, and rinse some more.
Then blow it out.
 

rjack321

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Yep those a pain in the neck, I use 1/4 SS 1/8 thick punch outs as media,
Does a very good job, but going into the tank a pain in the butt on 1/2 npt.



What do you mix it at?
Phosphoric acid typically (but not always) comes at 85% strength. You want it about 20% strength. If it's too strong you quickly get ferric phosphate which is sorta easy to get out but its easier to use the right concentration in the first place.

So 1 part acid, 3 to 4 parts water. Remember from high school chem, add concentrated acid(s) to water not the reverse. Wear eye protection just in case you get a splash, plus gloves.

Rinse with boiling hot water and blow dry upside down with scuba air
 
OP
Diver Stan

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Checking back, I found a place in that cleaned up the tank and completed the hydro successfully. They did not tumble, they scoured it with acid which was mentioned by several folks.

The burst disks turned out to be fairly generic Harrison's mentioned by JimChris which are identical to the ones in the Luxfer aluminum tanks I have. The only difference is the pressure rating.

I set up a rig to whip the inside of the tanks using a plug made from a plastic plumbing fitting I had found at a hardware store. The plug fit these tanks very nicely, but the whip did not work well and I lost patience. In 5 years I may revisit the rig or phosphoric acid.

Thanks all
 

tbone1004

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Checking back, I found a place in that cleaned up the tank and completed the hydro successfully. They did not tumble, they scoured it with acid which was mentioned by several folks.

The burst disks turned out to be fairly generic Harrison's mentioned by JimChris which are identical to the ones in the Luxfer aluminum tanks I have. The only difference is the pressure rating.

I set up a rig to whip the inside of the tanks using a plug made from a plastic plumbing fitting I had found at a hardware store. The plug fit these tanks very nicely, but the whip did not work well and I lost patience. In 5 years I may revisit the rig or phosphoric acid.

Thanks all
The burst discs for AL80's and HP steels are likely the same regardless of what the stamp says. They're test pressures are only 5% apart with the AL's being 5000 and the HP steels being 5250. I use AL disc in all of my tanks.
 

rob.mwpropane

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quite a few, depends on how rusty they are as the acid reacts but easily a dozen if they aren't too bad.

I don't think they're too bad... haven't looked in them yet, but I can tap on the side and get a good "ting", no dull thuds.

I have exactly that to do, 12.
 

rjack321

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I don't think they're too bad... haven't looked in them yet, but I can tap on the side and get a good "ting", no dull thuds.

I have exactly that to do, 12.
I would mix up about 8 liters using 1.5L of 85% acid and 6.5L water that should handle 12 if they arent scaley rusty. You can always repeat some with fresh acid if you wear it out.

I would not try to tumble them unless forced to by scale type rust
 

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