38s and post valves

[James]

How many inch-pounds of torque did you install the burst disk with? Some (most) are real sensitive that way.

My guess is "Too Many" lol. Just replaced it (I'm wiped out and overdoing it, but who can say no to a 10 y.o. who wants to dive vinatge gear?) at 55 inch pounds... I only put a couple hundred psi in it so we could check the valve to bushing and bushing to tank interfaces for leaks. Very slow leak at the bushing to tank interface. So I'll tighten that tomorrow, and put some more in it and see how it goes. I'm using a DIY whip that goes through a 1st stage and HP hose for a guage, so it takes FOREVER! lol

[James]

Well, still have a super slow leak at the bushing/tank interface.... any suggestions? Tighten it more? Separate, use more teflon tape and try again? It's slow enough that I'd dive it no issue, but It would need to be filled day of the dive... not filled and left in the shop for a week.
Thanks in advance,
James

[antique diver]

Well, still have a super slow leak at the bushing/tank interface.... any suggestions? Tighten it more? Separate, use more teflon tape and try again? It's slow enough that I'd dive it no issue, but It would need to be filled day of the dive... not filled and left in the shop for a week.
Thanks in advance,
James

How much torque to use is a difficult thing to assess. There are no specs on torque per thread size that I know of, and you just have to learn to feel what's going on with the threads from lots of experience. Larger thread diameter needs more torque... so you might try a little more before removing everything to re-tape.

How many wraps of TFE did you use? It comes in various thicknesses, but even the thin stuff from Harbor Freight works great at 6000psi with enough wraps. I go through a lot of tape in a year. On 1/4" NPT threads I use 6 wraps of that type, but more is better on the larger threads like you have. I would use 8-12 wraps since you are having trouble now. Just my opinion, but it's hard to use too much. Excess will just squish into the thread gaps and help the seal. So far I have never seen too much tape ever cause a leak. Good Luck!

[James]

Thank you!.... I'll try to tighten a smidge more, and if that doesn't get it I'll redo it with more tape (used 6 wraps of cheap harbor freight thread tape this time).
Respectfully,
James

[luis]

Well, still have a super slow leak at the bushing/tank interface.... any suggestions? Tighten it more? Separate, use more teflon tape and try again? It's slow enough that I'd dive it no issue, but It would need to be filled day of the dive... not filled and left in the shop for a week.
Thanks in advance,
James

How much torque to use is a difficult thing to assess. There are no specs on torque per thread size that I know of, and you just have to learn to feel what's going on with the threads from lots of experience. Larger thread diameter needs more torque... so you might try a little more before removing everything to re-tape.

How many wraps of TFE did you use? It comes in various thicknesses, but even the thin stuff from Harbor Freight works great at 6000psi with enough wraps. I go through a lot of tape in a year. On 1/4" NPT threads I use 6 wraps of that type, but more is better on the larger threads like you have. I would use 8-12 wraps since you are having trouble now. Just my opinion, but it's hard to use too much. Excess will just squish into the thread gaps and help the seal. So far I have never seen too much tape ever cause a leak. Good Luck!

I totally agree with this. There is some religious cult (just kidding) that only believe in using only minimal amount of tape. That the tape is only a lubricant for the threads and that all the sealing only occurs in the metal to metal contact.

Well, in my personal experience I have never seen excess tape do any harm and I have seen it stopped plenty of stubborn leaks. I don't argue with success... and I am surely not going t take apart once I stop a leak, just for a "science fair".

I have also not sure you can actually over tighten a tapered thread... except when you start damaging the hex-flats with your tool. So I would also try a bit more torque while paying attention to the tool engaging surfaces.

[swimjim]

When I get a real stubborn leak I use pipe dope. I am told that the pipe dope needs to have PTFE which I believe makes it food grade. I also made a tank vise to help get valves and bushings tightened up.

[antique diver]

When I get a real stubborn leak I use pipe dope. I am told that the pipe dope needs to have PTFE which I believe makes it food grade. I also made a tank vise to help get valves and bushings tightened up.

Good point, Swimjim. I forgot to mention that when I run into a cantankerous thread leak on pipe threads I have often found it helpful to wrap with Teflon tape as usual, then spread the PTFE pipe dope evenly over the tape with finger tip. It seems to further lubricate the threads and less torque seems to be needed to get a seal, even at 6000 psi. It's especially helpful when the final alignment of a fitting is critical, like aiming a tee toward the intended next item in line. If you do a bunch of pipe thread fittings you will eventually have some that get too tight before they aim the desired direction. So if you don't mind a messy finger it won't hurt to do this on all your pipe threads. Don't let the dope get on good clothing as it just seems impossible to get out.

[SurfLung]

Sorry I'm so late to this conversation. I've had some experience with bushing tanks and with burst disks so I'll add my two cents in case there's a nugget that might be of help. Like you, I got a lot of help from the guys on this forum so, I might be repeating something they already said.

Paintball Burst Disks
- I'm interested to know if you got the 1800 psi paintball burst disks to work properly. I tried some a few years back and they didn't seem to be made for our vintage valve sealing method... My valves have a flat sealing surface and the paintball units are kind of like volcano orifice?
- I was never able to find any 1800 psi burst disk units. But I got some modern 2015 psi one piece units that go for flat seal scuba. I got them from Dive Gear Express. They're labeled to release at 3360 psi which is 5/3rds of 2015 psi. DGX says install them torqued 100-120 in-lb. Before I got a torque wrench, I used to install them snug, Then fill them full pressure and check for leaks by dunking. And if they leaked, I would gently tighten just until the leak stopped bubbling.

Sealing Bushing Tanks
- I've found that it's really important to clean the threads on these old tanks. In addition to rust, they may have hard residue from the old pipe dope method of sealing that was originally used. They may also have sand or abrasive residue from internal cleaning. I have scrubbed these threads with a toothbrush sized stainless steel brush using hot water with Dawn detergent and then scrubbed some more while rinsing.
- I DO have a home made strap type tank vice made from steel strapping and a 6 foot 2x6 board.
- I DO have a big box wrench to fit the bushing flats and also give good leverage.
- Finally, I've had very good luck getting these bushing tanks to seal on the first try.

[James]

Sorry about the late update... I see what you mean about the shape of the business end of the paintball burst disc. The first one popped at 1500 psi, but I think I over-torqued it. New one is in, and I trans-filled to 1200, but waiting to get it to the shop to verify it doesn't pop before 1800. If it pops, then I'll go the route you did. I did get rid of the slow leak on the bushing (just took a little more oomph on the wrench)... we'll see for sure once I get a proper fill.
I still need to get a second opinion on the vis for the second tank, but I'm not holding my breathe.
Respectfully,
James

[James]

Well,
SurfLung was right... the Paintball discs popped at about 1500 (both times), so I wasted time confirming he is right! It has a 2015 working pressure disc in it now, and is filled. Now my 10 y.o. can't wait to use it! We also came into a converted 1800 psi fire extinguisher (a bit shorter than a 72, bump bottom, bushing neck) that I need to get hydro'd. This keeps up, he'll have more tanks than me!