Installing new 1/2" Valve into old tank.... questions....

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Culcuhain

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Just got my new 1/2" K-Valve from XS scuba. (going in a 1959 USD LP72)
We took out the old valve and cleaned the old teflon from the threads.
We trial fitted the valve and it would only go in like three threads.
So.....
we know we need teflon tape on the threads.
Will it make that much of a difference?
And I think we need a BFW on this too (Big Freaking Wrench)

Am I missing anything?
Thanks!
 

bletso

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Use three layers of tape and torque to 85 ft lbs. You need to have about 6 threads engaged. If it doesn't go in far enough you probably have thread damage in the cylinder.

Dale
 

captain

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I believe 7 engaged threads is the standard, there is no torque spec. And yes you will need a big freaking wrench and vice.
 

bletso

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The torque value is for gas cylinder 1/2 ngt threads. When torqued properly you should have the requisite thread engagement Over-torquing will damage the valve threads and on subsequent removal for hydro will render the valve useless. I have seen many over torqued valves here at the hydro station where there is no useable threads on the valve! I shudder to think what actually held the valve in the cylinder. IF you wish I can PM you a picture of such a valve.

Dale
EIS, Inc
DOT hydro facility
 

captain

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Culcuhain

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Without a Vise we got it down to 6 threads engaged. Good enough (seend 6 and 7 in this thread.)? I can post a pic. Worse case scenario is I take it to my friends shop and loaded it in his vise (LDS didn't have one).

thanks!

Hand/Finger tight ~3 turns
3 more turns from that is where I am now.
 
Last edited:

Culcuhain

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As seemed well. Tank got filled with no questions asked (except why it didn't get the + rating on the last hydro) and they filled it to plus rated pressure.
No champagne bubbles or anything... worked like a charm... I am loving these 72s!
 

flots am

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Just got my new 1/2" K-Valve from XS scuba. (going in a 1959 USD LP72)
We took out the old valve and cleaned the old teflon from the threads.
We trial fitted the valve and it would only go in like three threads.
So.....
we know we need teflon tape on the threads.
Will it make that much of a difference?
And I think we need a BFW on this too (Big Freaking Wrench)

Am I missing anything?

If you do it wrong you could be missing the rest of your life.

You should probably find a scuba shop that handles a lot of old tanks and does inspections and let them clean it, inspect it and install the valve if everything is kosher.

flots.
 

Culcuhain

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The scuba shop cleaned and vip'd the tank and had me do the tightening. According to some of the links, 2-3 turns past finger tight is good. So far so good. :-D
 
https://www.shearwater.com/products/perdix-ai/
https://cylindertrainingservices.com/training-program/

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