Tank thread/fitting/valve question

[HBoothe]

I recently bought 10 steel cylinders to replace the 13 or so I lost in a house fire. In that bunch I got 4 old tanks (original hydro '56, '58, '60, and '63) and I'm confused on one valve thread. The '56 and '58 have 1/2"NGT, the '60 has the now-common/standard 3/4"NPS, but the '63 has something I haven't found in scuba: 3/4" actual diameter straight w o-ring. XS Scuba has 1/2" NGT, they have 7/8" UNF (old HP 3,500 PSI tanks), and of course, 3/4"NPS. I used a micrometer, the thread diameter on the valve in question is 0.750" give or take a few thousandths and is straight thread and has an o-ring. I don't know what it is called and haven't seen any current-manufacture valves with a thread like that. It has a usable K valve on it and, if the tank passes hydro, I could use it, but I was hoping to switch everything to DIN. Anybody know what this thread spec might be? I didn't gauge the threads today, ran out of time. I can check it if it makes a difference.

As long as I'm asking about old tanks (maybe not old enough for this forum, apologies if this is in the wrong area), I got 4 LP 108s hydro'd today by a mobile guy @ a firehouse but he wouldn't touch the old ones because they didn't have an REE # on them and wouldn't touch the HP 3,500 PSI cylinders because he said he wasn't authorized/approved to check tanks with that DOT permit #. I've not had a HP 3,500 PSI tank hydro'd in about 8-9 years; did something change? I'm going to take the ones this guy wouldn't do to another place and just let them sort it out, but I might as well ask as long as I'm here.

Thank you.

--HC

 

[James79]

Your oddball thread is probably a 1/2 NPS (straight) thread. Sportsways and one or two others made them. I have one tank with a Sportsways 1/2 NPS... you can occasionally find valves on ebay, or check if The Scuba Museum has any (his stock varies). Or, you can have a modern valve machined down. See this thread: 1/2in NPS valve required for 72

Respectfully,

James

 

[tursiops]

ANSI B1.20.1 - NPS - American National Standard Straight Pipe Threads

NPS pressure tight straight pipe threads with lubricant or sealer.

www.engineeringtoolbox.com

 

[rob.mwpropane]

I recently bought 10 steel cylinders to replace the 13 or so I lost in a house fire. In that bunch I got 4 old tanks (original hydro '56, '58, '60, and '63) and I'm confused on one valve thread. The '56 and '58 have 1/2"NGT, the '60 has the now-common/standard 3/4"NPS, but the '63 has something I haven't found in scuba: 3/4" actual diameter straight w o-ring. XS Scuba has 1/2" NGT, they have 7/8" UNF (old HP 3,500 PSI tanks), and of course, 3/4"NPS. I used a micrometer, the thread diameter on the valve in question is 0.750" give or take a few thousandths and is straight thread and has an o-ring. I don't know what it is called and haven't seen any current-manufacture valves with a thread like that. It has a usable K valve on it and, if the tank passes hydro, I could use it, but I was hoping to switch everything to DIN. Anybody know what this thread spec might be? I didn't gauge the threads today, ran out of time. I can check it if it makes a difference.

As long as I'm asking about old tanks (maybe not old enough for this forum, apologies if this is in the wrong area), I got 4 LP 108s hydro'd today by a mobile guy @ a firehouse but he wouldn't touch the old ones because they didn't have an REE # on them and wouldn't touch the HP 3,500 PSI cylinders because he said he wasn't authorized/approved to check tanks with that DOT permit #. I've not had a HP 3,500 PSI tank hydro'd in about 8-9 years; did something change? I'm going to take the ones this guy wouldn't do to another place and just let them sort it out, but I might as well ask as long as I'm here.

Thank you.

--HC

Sorry to hear about your house fire, that sucks.

 

[HBoothe]

ANSI B1.20.1 - NPS - American National Standard Straight Pipe Threads

NPS pressure tight straight pipe threads with lubricant or sealer.

www.engineeringtoolbox.com

Replying to James and tursiops: thanks for the info. I'm new to this forum but not new to forums in general: nothing I write is intended to be rude, if it seems rude then I chose words poorly.

I will check the valve again just to be sure but I used a micrometer to check it...the NPS spec shows (on another site than tursiops linked to) that the OD of the threads is 0.823" +/- 0.0015" for 1/2" NPS. There's little chance I screwed up my measurement by 0.073"...but, I normally use a dial caliper not the micrometer, maybe I screwed up.

Unfortunately, I'm away for a couple days now and can't check it (tanks are in the car, headed to Koetter in Dallas w them, spending a couple days out of town in the process). I'll check my stuff again when I get home and I'll hit the threads w a set of gauges to see what the TPI is.

Thanks for the replies, I wish I could check right now but can't and didn't want to let your replies float unanswered for a couple days.

--HC

Sorry to hear about your house fire, that sucks.

Yes, it did. Lost a lot of stuff. Worst part was that there were 2 cats in the house and they died. That hurt me but it hurt my 6 YO son worse which hurt me even more. They were his cats; I can buy more stuff...can't buy those cats back.

--HC

 

[James79]

nothing I write is intended to be rude, if it seems rude then I chose words poorly.

I, for one, didn't see anything rude. And I'm sorry for the loss (both the replaceable stuff and the irreplaceable cats).

Best,

James

 

[HBoothe]

Thank you, James. I dunno...I swear I can sometimes tell someone the time of day and they'll take offense. I try to be polite and not step on toes and I don't want to be the new guy here who starts off offending folks.

In my travels yesterday I got within 30 miles of the house so I ran over and got some measurements of the thread in question. I got pictures, too, just to back up what I say. My final analysis is that the thread is 3/4" UNF. Per this link (and others):

UNC and UNF - Unified Coarce and Unified Fine Inch Threads

ANSI/ASME B1.1 Unified National Thread - UNC Coarse series and UNF Fine series.

www.engineeringtoolbox.com

The valve threads match the dimensions of 3/4" UNF.

I used both my micrometer and my dial caliper (I found one...there are several others in hiding). The threads are 16 TPI as determined by a thread gauge for US 60 degree threads. I've done a fair amount of machining for an individual hack and have some of the neat toys, thank God, so I had these things already. I had hoped this was a (sort of) common thread which would be easily identified here so I posted the question before I did the additional measurements. I post this now 1) to help anyone in the future (these posts online live forever) and 2) to complete my post with the final answer.

I don't know how attaching files will work (having not done it here before). I have one pic of the micrometer closed (proof of zero), one on the valve (proof of size), with the same for the dial caliper (closed/zero and on the valve threads), and one where I set the electronic dial caliper to metric, "just in case". Then I have one of the thread gauge on the threads where it should be visible that the tool is for US 60 degree threads and the one engaged to the threads is "16". The micrometer shows roughly 0.745" and the dial caliper shows 0.7465". The thread specs for 3/4" UNF 2A show a max OD of 0.7485" and a min OD of 0.7391" (Unified Screw Threads, Standard Series). 1A thread specs are kind of sloppy, 2A is "pretty darn good" and, I think, the most common fitment spec, and 3A is "NASA perfect", for reference.

0.7485

0.7391

I think the oddest part to me about this is: the 1956 and '58 tanks have 1/2" NGT...okay, I get it, old tanks, old standard...the 1960 tank has 3/4" NPS (the current "standard" for almost all, if not all, tanks in the US, I believe) which I checked by threading in a current (used) valve, but then, the 1963 tank has this 3/4" UNF. What the heck? The two HP 100s I got used which are marked/rated for 3,500 PSI (*not* 3,442 PSI), have 7/8" UNF which I've seen before on the 3,500 PSI HP tanks I had before. I don't recall ever running across this thread size before (I don't have tons of experience but these aren't the first tanks I ever bought used and changed valves on, including some from 1970).

Thanks for everyone's time. Hope this helps someone.

--HC

 

[James79]

Well, that is one of the Sportsways "1/2" inch valves. I don't have one pulled right now to be able to compare measurements (The specs I mentioned above were quoted from others... I apologize). Bright side, it's an easy valve to rebuild and should be fine. Downside is if you want din, looks like you'll have to machine a custom valve (turn it down from a 3/4-14 valve). If you decide to replace that valve, let me know... I wouldn't mind having a spare!

Best,

James

p.s. - You'll find most on this forum are thick skinned and or don't look for ways to be offended. Generally a pretty good crowd here!

 

[HBoothe]

Well, that is one of the Sportsways "1/2" inch valves. I don't have one pulled right now to be able to compare measurements (The specs I mentioned above were quoted from others... I apologize). Bright side, it's an easy valve to rebuild and should be fine. Downside is if you want din, looks like you'll have to machine a custom valve (turn it down from a 3/4-14 valve). If you decide to replace that valve, let me know... I wouldn't mind having a spare!

Best,

James

p.s. - You'll find most on this forum are thick skinned and or don't look for ways to be offended. Generally a pretty good crowd here!

James, the verdict is in: 3 pass, 3 fail. Ugh. Three of the LP 2,250PSI tanks were condemned. I don't know what test pressure they ran them to, it should be 5/3, but I couldn't ask the guy questions; his English is not very good, and he's the only one still wearing a mask in the whole place, and he doesn't talk much or invite conversation. One management-type guy said they failed to return to an acceptable volume after pressure was applied (they didn't spring back sufficiently). Anyway, the tank with the valve in question here is among those which failed. You mentioned being interested in having the valve. If you'll PM your address I will send it to you. No charge, thanks for your help/info.

--HC

 

[James79]

James, the verdict is in: 3 pass, 3 fail. Ugh. Three of the LP 2,250PSI tanks were condemned. I don't know what test pressure they ran them to, it should be 5/3, but I couldn't ask the guy questions; his English is not very good, and he's the only one still wearing a mask in the whole place, and he doesn't talk much or invite conversation. One management-type guy said they failed to return to an acceptable volume after pressure was applied (they didn't spring back sufficiently). Anyway, the tank with the valve in question here is among those which failed. You mentioned being interested in having the valve. If you'll PM your address I will send it to you. No charge, thanks for your help/info.

--HC

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