Double 38's

[gj1963]

From what I can tell - these are 38's correct? New project I picked up. Valve/manifold is in good shape but is getting a good overhaul. Then need to get bands and a harness.

[captain]

You may run into problems having them filled at a dive shop. The tanks have reducing bushings and although that is perfectly safe and legal many shop are ignorant of that fact and will refuse to fill them.

[8dust]

Captain (or anyone else...),

Have you had to replace any of those bushings? I have a set I was starting to fool with a while back and found that very little was rated for pressures in the range we would need for these tanks. I must have talked with at least a half-dozen industrial pipe and supply houses. What was available was ex-pen-sive! Brass was reported to be too soft and I wasn't going to pay the coin for SS, and as I remember that only left bare steel which I figured would rust as bad as what I wanted to remove. Had an absolute devil of I time finding the right thread patterns too.

What's the best approach & source on these???

Fred

[captain]

A forged steel bushing is the best choice.
Mc Master-Carr 1 X 1/2 . . 4,500 PSI . . # 50925K362 $4.92 each

http://www.mcmaster.com/#catalog/118/72/=fvpyhd

If you want 316 stainless 1 X 1/2 3000PSI #4443K757 $14.25

http://www.mcmaster.com/#stainless-stee ... rs/=fvq1gt

[gj1963]

Luckily I am in fairly well with the dive shops and my crazy gear at this point. Overhauled manifold and put in new burst disks. It still had the lead plugs. Looked inside with the bore scope and they are pretty clean. Here they are on a Scubapro pack for now.



Fred thanks for asking about the bushings, and Captain for the info... These are in hydro - but when the time comes I will put in new bushings while it's apart.

[8dust]

A forged steel bushing is the best choice.
Mc Master-Carr 1 X 1/2 . . 4,500 PSI . . # 50925K362 $4.92 each

http://www.mcmaster.com/#catalog/118/72/=fvpyhd

If you want 316 stainless 1 X 1/2 3000PSI #4443K757 $14.25

http://www.mcmaster.com/#stainless-stee ... rs/=fvq1gt

Well I'll be a bare-assed monkey...

I'm sure I looked at McMaster, and Granger, and at least 4 other places... can't imagine what or why I was finding what I did, but galv. @ 3x the operating pressure for < $5.00 sounds AOK to me. I swear what I was finding wasn't plated, had an operating pressure ~ 750psi, and were like $16.00/ea.??? and the SS were like $25.00 or more?...

maybe I was just intoxicated, but not for a solid week, not since college anyway...

Thanks! Very glad to be pointed in the right direction if I decide to get back into that set one day.

[eskimo3883]

Mixing brass, zinc and steel is not a good thing. Also, I do not think you should go with galvanized surfaces in contact with highly compressed air. $20 extra for SS sounds like a bargain.

[captain]

Mixing brass, zinc and steel is not a good thing. Also, I do not think you should go with galvanized surfaces in contact with highly compressed air. $20 extra for SS sounds like a bargain.

I guess that's why we don't have galvanized steel tanks with brass valves.

[Bryan]

When you go to re certify with PSI to keep current you have to set though about 30 minutes of back and forth over this issue....Almost as much over what to use and what not to use on valve threads....I'm glad you can do it on line now!
I don't know how many valves I have removed from scuba cylinders, boilers, gas manifolds etc and the only ones I can remember having a problem with were copper to steel when a dialetic union was not used. I do see a lot of valves in scuba cylinders that have more grease on them than threads

[Douchebag]

Mixing brass, zinc and steel is not a good thing. Also, I do not think you should go with galvanized surfaces in contact with highly compressed air. $20 extra for SS sounds like a bargain.

I guess that's why we don't have galvanized steel tanks with brass valves.

That's right we don't, at least we don't with galvanizing on the inside. Galvanizing inside the tank, including threads, is a recipe for possible disaster. Air purity is a big one. Don't know about you guys but I'm not to keen on inhaling Zinc.

[kgehring]

I had a set of tanks hot dipped and I still do not have the insides of tanks smelling usable. Not sure if some chemical got inside during process or there was some type of coating in the tank that caused the problem when heated in the dip. Tanks have been tumbled and cleaned. Still have a trick or 2 to get them back in service.

[eskimo3883]

Hi Captain,
I think tank threads on galvanized tanks are left bare because otherwise the thread's sealing surface would be sacrificial zinc and prone to leaks after the galvanic reaction in salt water. I think internal surfaces like the inside of the tank and inside of bushings are not zinced to prevent inhalation of zinc oxide.

Is there a down side to using a SS bushing other than $$$? Would the harder SS be more likely to gall the tank threads?

[captain]

When a threaded stainless anything galls it usually leads to both threads being ruined even if one is not stainless. Normally you can use an anti-seize compound to help prevent it but in the case of tank you don't want to because of contamination of the air and teflon tape is no guarantee of it not galling.
I didn't just fall off the turnip truck. I know why the interior and threads of a tank are not galvanized but just saying you shouldn't mix galvanize, steel and brass isn't telling the whole story and gives the uninformed the wrong impression. They hear or read something in one context and repeat it in an entirely different content.and turns into someone saying you can't use a brass valve in a galvanized steel tank. The three mix mix quite well in the proper application. There is just so much misinformation about tanks that it boggles the mind and I don't like to see more added to it.

[Bryan]

When a threaded stainless anything galls it usually leads to both threads being ruined even if one is not stainless. Normally you can use an anti-seize compound to help prevent it but in the case of tank you don't want to because of contamination of the air and teflon tape is no guarantee of it not galling.
I didn't just fall off the turnip truck. I know why the interior and threads of a tank are not galvanized but just saying you shouldn't mix galvanize, steel and brass isn't telling the whole story and gives the uninformed the wrong impression. They hear or read something in one context and repeat it in an entirely different content.and turns into someone saying you can't use a brass valve in a galvanized steel tank. The three mix mix quite well in the proper application. There is just so much misinformation about tanks that it boggles the mind and I don't like to see more added to it.

I go though some scenario or Q-A or You Don't Know What You Are Talking About situation on a weekly basis regarding aluminum cylinders / thread grease/ O2 cleaning/ steel cylinders have stress load cracking in the necks/ 1/2" cylinders cannot be used because hydro testing equipment no longer attaches to it... etc....
Last week I was told by a customer I could not fail his aluminum cylinders on a visual inspection. He had taken a side grinder and wire wheel to them and some of the pits were still more than 3/32" deep on the outside....His comments was...A visual inspection is for the inside....No one cares what the outside looks like

I will agree 110% that when I put stuff on the form it makes sense in my head but does not always make sense when others read it....
This is one of the reasons the main page looks like it does....Get to the facts, cut out the BS and have a good time.
Oh and someone please invent a sarcasm font and also a marker by peoples names that don't get sarcasm.....It will save a lot of feelings

[gj1963]

Continuing on this -- I had a leak from under the J-Valve plug. The rebuild pdf mentions the USD diagrams show no seal. A very perished one came out though. So I am looking for a suitable replacement - if it is supposed to have one. I dont see how it would seal effectively without. The rebuild guide mentions adding an O-Ring. Just looking for any input on this from someone with previous experience. I dove through a bunch of washers and o-rings and the LDS. Did not find a good washer that will fit. Got an O-Ring - but to me it seems more that it would have taken a washer. Worry about an O-ring bunching or pinching.