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argos59
May 13th, 2009, 09:10 PM
Can any one tell me the threan size for a HP 3500 psi Norris tank ?

NorthWoodsDiver
May 13th, 2009, 09:21 PM
It should be the standard thread for any other tank valve of 3/4"X14 Straight thread.

Only a select few tanks for scuba application (in America) were ever made with other threads.

Edit: Correction, some 3500psi tanks had 7/8"X16 straight threads

jswantek
May 13th, 2009, 09:21 PM
Wow, not sure on the specific brand. Most tanks are 3/4"-14 NPT. Older tanks sometimes had 1/2" tapered thread, but they're few and far between anymore.

NorthWoodsDiver
May 13th, 2009, 09:24 PM
Can you provide the tank stamping information?

H2Andy
May 13th, 2009, 09:25 PM
is there anything that makes you think the tanks would be anything other than 3/4"-14 NPT?

that's the overwhelming standard in the US

argos59
May 13th, 2009, 09:26 PM
Tank is 4 years old DOT E13483-3500 3216355y TP5250 HP100

SparticleBrane
May 13th, 2009, 09:27 PM
3500 psi cylinders are 7/8" threading, as far as I know.

dannobee
May 13th, 2009, 09:28 PM
If a quarter will fit in the neck hole, it's 3/4"-14 NPS. If the hole is too small, it's 7/8"-16 UNF.


.

argos59
May 13th, 2009, 09:29 PM
I think its 7/8

H2Andy
May 13th, 2009, 09:30 PM
3500 psi cylinders are 7/8" threading, as far as I know.

hmmmm ... you're right:

When Pressed Steel Tank Company began manufacturing the modern 3500 psi service pressure SCUBA cylinder, they elected to use a more modern thread form for the neck opening known as Unified National Standard Fine. The specific thread form used with the steel 3500 psi SCUBA cylinder is named 0.875-14 UNF, often referred to as "7/8 UNF."

SCUBA Valves: Regulator Fittings, 200 vs 300 Bar FAQ and Cylinder Neck Threads - Dive Gear Express (http://www.divegearexpress.com/library/valves.shtml)

jswantek
May 13th, 2009, 09:34 PM
Nice post Andy, I just learned something. Thanks!!!

argos59
May 13th, 2009, 09:36 PM
This site is the best, you guys know everything. Thanks for the info

H2Andy
May 13th, 2009, 09:36 PM
I think its 7/8

and you'd be right


Tank is 4 years old DOT E13483-3500 3216355y TP5250 HP100

So how do you figure out what you have? Look at the SCUBA Tank neck for the DOT stamp. If it reads DOT-3AL or DOT-3AA it has a 3/4 NPS threaded neck opening. (3AL means aluminum, 3AA means steel.) If it reads DOT-Exxxx-3442 it's a steel cylinder, also with 3/4 NPS threaded opening. If it reads DOT-Exxxx-3500, it's a steel cylinder with a 7/8 UNF threaded opening. (The xxxx is a manufacturer specific four or five digit exemption number.)

http://www.divegearexpress.com/library/valves.shtml

H2Andy
May 13th, 2009, 09:37 PM
Nice post Andy, I just learned something. Thanks!!!

thanks man ... thanks to the question, i learned something too

;)

Scared Silly
May 13th, 2009, 11:17 PM
Though the question has pretty much been answered - anything 3500psi and above are 7/8 UNF. Further, the valve must be DIN. Although, I have heard of some folks with yoke valves but these are about as rare as hen's teeth.

For 3442 PSI cylinders which are 3/4" NPS the valve can be either DIN or Yoke. So the 3500psi is a threshold for more than just the threads.

WD8CDH
May 14th, 2009, 02:15 PM
When the HP 3500 psi tanks first came out, they selected the 7/8" UNF thread both because it was different from the rest of the SCUBA tanks but also because it was already in current use for SCBA tanks so hydro stations could test them. There is no real technical reason to go to a smaller neck thread at 3500 psi. There are many higher pressure tanks used in other industries that have larger threads than the 3/4 NPS SCUBA threads. Many European tanks even at 4500psi use threads very similar (but not interchangeable) to 3/4" SCUBA threads.


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