on topic: scuba tank fittings

[AngryScientist]

Quarantine project!

I have in the shed a couple old scuba tanks. i would like to re-purpose one of them for a "field" tubeless tire booster.

what i want to know is what fitting size threads into the tank?

the idea would be a set-up like this

obviously, my air compressor or floor pump is WAY under the rated pressure for the tanks, so i'm confident this is safe.

anyone know?

https://i.ebayimg.com/images/g/BG0AAOSwlJ1ayI25/s-l1200.jpg

[Seramount]

I own 14 tanks, but still had to google the valve thread size...

The specific thread form used with most SCUBA cylinders is named 0.750-14 NPSM, often referred to as "3/4 NPS." This thread form is seen on both steel and aluminum SCUBA cylinders with service pressures of 2400+ (2640), 3000, 3180+ (3498), 3300 and 3442 psi.

[AngryScientist]

I own 14 tanks, but still had to google the valve thread size...

The specific thread form used with most SCUBA cylinders is named 0.750-14 NPSM, often referred to as "3/4 NPS." This thread form is seen on both steel and aluminum SCUBA cylinders with service pressures of 2400+ (2640), 3000, 3180+ (3498), 3300 and 3442 psi.

ahh, if it's really just 3/4 nps, that's easy!

grumble, i wish i could just go to the local plumbing supply house and dig around their bins, or home depot even. this is colossally annoying.

[jischr]

ha, last month I threw out about 5 lbs of 1/2" and 3/4", black iron and SS fittings that have been in my garage for a decade or two. Could have sent you a couple.

[AngryScientist]

ha, last month I threw out about 5 lbs of 1/2" and 3/4", black iron and SS fittings that have been in my garage for a decade or two. Could have sent you a couple.

haha, i've joked that home projects lately are like an episode of "junkyard wars" - i've been scrounging through stuff to come up with pieces and parts ive needed that i would have otherwise just run to the store to get.

[htwoopup]

Not to derail your project, but are you planning to get the tank filled at a scuba store or a local FD? Reason that I ask is that if it is an old tank and it has not had a hydrostatic inspection within the last five years they won’t refill it. Of course, it might be that you pay them, they do the inspection, refill it, and you are good for 5 years. But if it fails the inspection... (I have only had two tanks fail in decades of diving. And those were tanks that had been sitting in the basement for a few years without very much pressure in them.) So I just wanted to throw that out there.


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[AngryScientist]

Not to derail your project, but are you planning to get the tank filled at a scuba store or a local FD? Reason that I ask is that if it is an old tank and it has not had a hydrostatic inspection within the last five years they won’t refill it. Of course, it might be that you pay them, they do the inspection, refill it, and you are good for 5 years. But if it fails the inspection... (I have only had two tanks fail in decades of diving. And those were tanks that had been sitting in the basement for a few years without very much pressure in them.) So I just wanted to throw that out there.


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no no, i'd just fill it to 140 pounds or so with my air compressor, just want that "shot" to pop the tubeless beads. way way under scuba pressure.

[Steve in SLO]

I’m thinking AS is going to just fill at home off his compressor. If he goes to high pressures that require hydrostatic testing, then he will need to put a primary regulator in line to step down the pressure or will colossally blow up everything when he tries to inflate the tire.

[Steve in SLO]

Oops, you beat me to it.

[Seramount]

Not to derail your project, but are you planning to get the tank filled at a scuba store or a local FD? Reason that I ask is that if it is an old tank and it has not had a hydrostatic inspection within the last five years they won’t refill it. Of course, it might be that you pay them, they do the inspection, refill it, and you are good for 5 years. But if it fails the inspection... (I have only had two tanks fail in decades of diving. And those were tanks that had been sitting in the basement for a few years without very much pressure in them.)

fwiw, many LDS won't fill certain tanks and/or made before a specific date, regardless of whether they have a currently valid DOT hydro stamp.

here's a partial list:

ll DOT-3AL tanks manufactured under one of the following exemptions or special permits: 6498, 7042, 8107, 8364, 8422
All composite cylinders manufactured under one of the following exemptions: 7235, 8023, 8115
All Walter Kidde DOT-3AL scuba tanks.
All Cliff Impact DOT-3AL scuba tanks made before July 1990.
All Luxfer 80.8 cu. ft. scuba tanks (S80.8) made before May 1987.
All Luxfer 72 and 100 cu. ft. scuba tanks (S72, S100) made before August 1987.
All Luxfer 80 cu. ft. scuba tanks (S80) made before January 1988.
All Luxfer 50 and 92 cu. ft. scuba tanks (S50, S92) made before April 1988.
All Luxfer 30 and 63 cu. ft scuba tanks (S30, S63) made before May 1988.
All Luxfer 40 cu. ft. scuba tanks (S40) made before June 1988.
All other scuba tanks made in the US before February 1990 (except Catalina).

pro tip: don't go to a dive shop for hydros...take cylinders to a facility that tests fire extinguishers. usually much cheaper...as the do the same test procedure.

[Seramount]

ooops, OP you can ignore everything I just posted...

[Steve in SLO]

Good tip on the hydros, Seramount.

[DWColiins]

I did something similar with a stainless fire extinguisher. Then changed it to water plants with a misting nozzle.

With the volume of a scuba tank (assuming the full size one) 140psi is probably overkill. I don't think you would need to go over 100psi.

The head from a refillable water fire extinguisher should get you sorted.

[AngryScientist]

I did something similar with a stainless fire extinguisher. Then changed it to water plants with a misting nozzle.

With the volume of a scuba tank (assuming the full size one) 140psi is probably overkill. I don't think you would need to go over 100psi.

The head from a refillable water fire extinguisher should get you sorted.

excellent, good tip.

looking now.

[DWColiins]

This is the head you want. With a Schrader valve built in.