1/2 inch valve

[sthtxdiver]

Hello brothers i was thinking about exchanging valves on my tank with one with hp port but for some reason the healthways valve just did aboout 3 turns freely then it stopped . did not want to damage tank .I assume its the same tread size ? plz correct me if im wrong thanx in advance best regards








Fair Winds and Safe Vintage Diving

[antique diver]

Those valves both have the same threads, 1/2" NPT. It is not unusual for some variation in diameters on same pipe thread size that causes different valves to thread into the same tank differently.

In fact, I believe the allowed tolerances on NPT threads amount to one turn oversize or one turn undersize. That means that two different valves could have threads within tolerance, but still one could be threaded by hand into a given tank neck two full turns more or less than the other valve would.

Were you able to turn it in 3 turns by hand, or were you using a wrench? Three by hand is probably ok, since it will go further with a wrench. If that's all you got with a wrench, then probably not enough threads engaged. I'll try to find some specs on recommended thread engagement for that pressure, but I'll bet someone on this forum already knows....?

[antique diver]

I just checked the Mechanic Support website for information on acceptable thread engagement on NPT fittings. The answer for pipe thread sizes up to one inch call for 3.5 to 6 turns wrenchtight. Here is a partial quote:

"NUMBER OF ROTATIONS:
.... As a general guideline, after hand-tight engagement, tighten 2-3 full turns for sizes up to 1 inches for NPT thread fittings. You should have between 3.5 and 6 engaged threads. Any number outside of this range may indicate either under or over tightening of the joint or out of tolerance threads." (from http://www.mechanicsupport.com/articleFittingTight.html)

From experience I have found that 2-3 full turns from hand-tight is sometimes excessive. Depends upon "feel", a very subjective measurement but one that really must be used on pipe threads. I have often used as little as 1 full turn beyond hand-tight on 1/4 - 1/2 " NPT threads with compressed air up to 4500 psi, but note that I use more teflon tape than some advise, typically using 5 or 6 tight wraps on my 1/2" valves.

I hope this helps, and I look forward to hearing other suggestions as well.

[sthtxdiver]

Hello thanx for response i went three turns by hand easily vs the originall it went a few turns more easier so i just went with original i figured maybe the treads were messed up or had same size valve but diff thread .thanx best

[antique diver]

Hello thanx for response i went three turns by hand easily vs the originall it went a few turns more easier so i just went with original i figured maybe the treads were messed up or had same size valve but diff thread .thanx best

Charlie,
I would be totally comfortable using a valve that went smoothly into a tank neck for three turns by hand. Put plenty of teflon tape on it and put a full turn with a wrench (properly placed to prevent valve damage) and see how that feels. If it feels loose, snug it some more. The torque on a pipe thread is such a subjective thing that it is hard to describe; there are no real torque "specifications" for that. Just remember that over-tightening can damage your threads. If you end up with a slight air leak, you can always drain the air and snug it some more.

Yesterday I did a little test on a fire department fill system I was repairing. I was working with 1/4" NPT fittings and put 4 wraps on the male thread, turned it in hand tight, which ended up about 2.5 turns, then added only 3/4 of a turn with a wrench since it happened to aim the direction I wanted at that point. It held 4500 psi just fine.

I think your valve will be fine.

[sthtxdiver]

Thank U Truly for all ur troubles and hard work all is greatly appreciated best Regards