In the U.S. Air Force, we used 20-man life raft CO2 cylinders for our jump tanks. I have a set in my shed right now, but unfortunately they are 1/2 inch tapered threads, and I cannot get them sealed anymore with teflon tape. So they have not been used in about four years now.
Rick in Parascuba by John Ratliff, on Flickr These are the twins we set up with these CO2 cylinders. I at one point early in my career was tasked with removing the wire wrapping on a number of these cylinders. That was tough work, with a chisel, as I recall. (The wire wrapping was required in life raft cylinders carried on aircraft so as to minimize the possibility of a stray bullet hitting the cylinder and causing an explosion; I have no idea why our jump tanks were allowed on our aircraft without the wrapping.)
John Photos003 by John Ratliff, on Flickr Here is a set of our jump tanks being used with a non-USAF regulator (my Mistral) in Alexander Springs State Park, Florida in 1970, by me. They are painted black, with the lettering stating:
55th ARRSQ PARARESCUE
(It's kinda upside down in this photo.) We marked all our gear, including our life rafts, so that in a photo they cannot be said to be Navy divers (which happened with the Mercury flight of Scott Carpenter).
IMG_1453 by John Ratliff, on Flickr Here's what the converted CO2 cylinders looked like as a set of double 42s. They have a ICC setting of 2100 psi, as I recall.
I've since replaced them with a set of USD 52 cubic foot cylinders that I found at my LDS.
John Ratliff: "In the U.S. Air Force, we used 20-man life raft CO2 cylinders for our jump tanks. I have a set in my shed right now, but unfortunately they are 1/2 inch tapered threads, and I cannot get them sealed anymore with teflon tape. So they have not been used in about four years now."
John, what type of teflon tape are you using? Ordinary plumber's tape isn't thick enough to seal a worn pipe thread. I don't know what brand it is, but Jim Steele used 3/4" to 1" wide, very thick heavy duty white teflon tape on his steel 1/2" npt tank valves. That might be the solution to your problem.
Screw the manifold fittings tightly into the tank and check how many threads are proud of the tank neck. If the fitting threads completely (or nearly) disappear into it, the tank neck might be shot. Thick tape might help.
The following isn't much help, but the manifold fitting threads could be the problem and others might fit. Or other single valves?
If you have 1/4" or better of threaded valve body stem protruding from the neck, it'll work with the right tape. I know that hydro testers want to see a certain amount of thread protrusion, so you might have difficulty passing these tanks, but hopefully, you'll be able to do so.
Post by antique diver on Sept 7, 2023 6:16:20 GMT -8
Don't give up yet on the 1/2" threads. On hard to seal threads of that size I use 8-10 snug wraps of fairly light weight Teflon tape from Harbor Freight. After wrapping, work it down some into the male threads with your finger tips. I personally like it better than the thicker types, and been using it for 20+ years. Then I coat with a teflon thread seal paste, which helps lubricate the threads when tightening. Less torque is needed to get a good seal, and that saves stress on the threads. Can snug a bit more as needed if done soon... but strongly advise relieving all pressure before re-tightening.
I have used that combination on hundreds of 4500-6000 psi joints, with less wraps for smaller sizes, i.e. 5-6 wraps for 1/4" npt, 3-4 for 1/8" npt. Sometimes, but rarely, have to adjust wrap numbers if first try doesn't hold.
Good Luck, and hope to hear you have good results!