James
Lung Diver
Posts: 55
Joined: Thu May 18, 2017 7:54 am
First Name: James
Location: Lower Alabama

Re: 38s and post valves

Fri Jul 17, 2020 9:21 pm

ScubaLawyer wrote:
Fri Jul 17, 2020 8:45 pm
How many inch-pounds of torque did you install the burst disk with? Some (most) are real sensitive that way. 8)
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
Lung Diver
Posts: 55
Joined: Thu May 18, 2017 7:54 am
First Name: James
Location: Lower Alabama

Re: 38s and post valves

Sat Jul 18, 2020 4:51 pm

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

User avatar
antique diver
Master Diver
Posts: 2029
Joined: Sun Dec 10, 2006 12:50 pm
First Name: Bill
Location: North-Central Texas

Re: 38s and post valves

Sat Jul 18, 2020 5:10 pm

James wrote:
Sat Jul 18, 2020 4:51 pm
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!
The older I get the better I was.

James
Lung Diver
Posts: 55
Joined: Thu May 18, 2017 7:54 am
First Name: James
Location: Lower Alabama

Re: 38s and post valves

Sat Jul 18, 2020 5:30 pm

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

User avatar
luis
VDH Moderator
Posts: 1640
Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: 38s and post valves

Sat Jul 18, 2020 6:21 pm

antique diver wrote:
Sat Jul 18, 2020 5:10 pm
James wrote:
Sat Jul 18, 2020 4:51 pm
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". :P

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.
Luis

Buceador con escafandra autónoma clásica.

swimjim
Master Diver
Posts: 1596
Joined: Thu Mar 23, 2006 12:28 am
First Name: Jim
Location: Belgium WI

Re: 38s and post valves

Sun Jul 19, 2020 8:00 am

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.

User avatar
antique diver
Master Diver
Posts: 2029
Joined: Sun Dec 10, 2006 12:50 pm
First Name: Bill
Location: North-Central Texas

Re: 38s and post valves

Sun Jul 19, 2020 12:12 pm

swimjim wrote:
Sun Jul 19, 2020 8:00 am
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.
The older I get the better I was.

User avatar
SurfLung
Master Diver
Posts: 1550
Joined: Sat Jan 01, 2011 2:03 pm
First Name: Eben
Location: Alexandria, MN
Contact: Website

Re: 38s and post valves

Wed Aug 05, 2020 12:05 pm

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. :)
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

James
Lung Diver
Posts: 55
Joined: Thu May 18, 2017 7:54 am
First Name: James
Location: Lower Alabama

Re: 38s and post valves

Wed Aug 05, 2020 9:19 pm

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

Return to “Tanks and Valves”

Who is online

Users browsing this forum: No registered users and 5 guests