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

[Diver Stan]

I have several PST steel 3,500 PSI 100 tanks with the U.S Divers 7/8" slant valves mentioned in a recent post.

These are great steel tanks, but figuring out parts for the valves is problematic.

What replacement burst discs do these take?
Sherwood lit. indicates that there are 3/8" 3-piece or 1/2" 1-piece. When I measure the disc hex nut it is actually 13mm. They are stamped 3300 PSI 20 Lbf-ft, 52-11.

Second question about Hydro and tumbling.

I took the tanks for hydro, 2 passed hydro. One tank required tumbling and was rejected. The same company that tumbled my tanks 5 years ago, now said they do not tumble tanks with the smaller 7/8" neck; the material they use to tumble is too big to fit through the neck.

What changed in 5 years? Have you heard about this? I now need to lug the tank around to AirGas or other place to see will tumble and hydro.

Jim Steele said that some places now use carbon to tumble and that is bad for steel tanks.

I appreciate any suggestions on tumbling.

--Stan

 

[rx7diver]

When I last checked (a couple of months ago), Northeast Scuba had replacement burst disc assemblies for those valves.

rx7diver

 

[tbone1004]

you can get burst discs from NESS and those 7/8 valves are a righteous PITA to tumble mainly because of getting the media out though getting it in is also somewhat annoying.
You may be able to get someone to sandblast the interior, but tumbling is something that I try to avoid on those bottles * I have 8 so I take very good care of them*

 

[Diver Stan]

you can get burst discs from NESS and those 7/8 valves are a righteous PITA to tumble mainly because of getting the media out though getting it in is also somewhat annoying.
You may be able to get someone to sandblast the interior, but tumbling is something that I try to avoid on those bottles * I have 8 so I take very good care of them*

Thanks for the info rx7diver and tbone. The NESS Sherwood or Harrison burst disc valves should work. Great.

Hydo: The same tank has needed to be tumbled at each hydro since I purchased it used 15 years ago. It has some recognizable pitting vs. my other tanks. There has been no increase in pitting that I can see in 5 or 10 years. Funny this was from a pair I bought and the other one is almost pristine.

I may need to take this to a back yard tumbler who uses sand.

I like the PST tanks due to their excellent buoyancy characteristics. I dove Worthington steel tanks in the Socorro Islands a few years back and didn't like those because they were too negative.

Diver Stan

 

[SubseaSports]

Yes these tanks are a PITA to tumble conventionally. Try vintage tanks with 1/2" NGT threads
If you have pits, I would look into an acid tumble using phosphoric acid. This will remove ALL bad material, aka rust. The pit you see now, might be bigger than you think. There are cleaning procedures to be followed along with a drying process, but it very effective and quick.
You don't even need tumbler to do it. I have done MANY tanks using this method.

 

[rjack321]

Yes these tanks are a PITA to tumble conventionally. Try vintage tanks with 1/2" NGT threads
If you have pits, I would look into an acid tumble using phosphoric acid. This will remove ALL bad material, aka rust. The pit you see now, might be bigger than you think. There are cleaning procedures to be followed along with a drying process, but it very effective and quick.
You don't even need tumbler to do it. I have done MANY tanks using this method.

Yep!
Despite having my own tumbler and media, I havent need to use my actual ceramic media in many many years. Phosphoric acid is the way to go to remove rust, just don't use to high a concentration or it will turn the steel black.

 

[Jimchris]

As stated above, Harrison makes replacement burst disks for Sherwood valves which are compatible with those valves. Replacement seats are available thru Trident.

PSI-PCI makes/sells a tumbling plug fit the 7/8 threading, but I just use a valve with bad din threads. For media I've used ceramic pellets and aluminum oxide.

 

[happy-diver]

Well it's still a punch made in China for me.

Pity people stopped doing copper rubbings

 

[rjack321]

PSI-PCI makes/sells a tumbling plug fit the 7/8 threading, but I just use a valve with bad din threads. For media I've used ceramic pellets and aluminum oxide.

You can also get a steel bolt at the hardware store for about $0.75

 

[bletso]

I used to sand blast the innards with fine glass media. A bit messy, but works like a charm.