How much does it cost to tighten NPT fittings?

I helped a friend install a new compressor at his house. It has a 3/4" NPT female fitting on the side, and I installed a 3/4" street elbow, reducer bushings to 1/4" NPT, then a T style QD. I used teflon tape and tightened to around 75 foot pounds to get the right orientation, but it leaks ever so slightly. I need the fitting to point in a particular direction, so to get it any tighter I'll have to turn it another 360 degrees. Is this even possible? All the fittings are black iron. When I look at NPT piping it always seems to go in directions that are intended and none leaks, so there must be a way to wind up with a particular direction without leaking. What am I missing? Or is it ok to use my 24" pipe wrench to twist that elbow around another full turn?

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Author: mwr (IN)

A wiseman gave me this advice when I asked about how many turns past hand tight is sufficient?

"Author: hj (AZ)
IF it doesn't leak, then you used enough torque. Tightness does not depend on some formula about how many turns past "hand tight", whatever that is."


I was looking at this page
[sizes.com]

and they actually give a figure for how many turns past handtight!

Now I am paranoid, because it says 3/4 fittings need 3 turns past handtight.

Well I recently did a 3/4 nipple into a ball valve and there is no way I got 3 full turns past hand tight, maybe a turn and half at very most.

I must be a real weakling.

So I would love to hear your opinions on this.

How many threads should be left to see after making up a 3/4 joint?

If I didn't get those 3 turns, should I expect my joint to leak in the forseeable future?

Does a turn mean a full 360 degree rotation?

Is a NPT joint something that would leak immediately if it wasn't torqued sufficient or would it surprise me with a leak at a later time?



Edited 2 times.

Author: bernabeu (SC)

ALL 1/8" through 2" NPT threads theoretically are 7 turns total.

'Rule of thumb' :

3-5 turns for 'hand tight' then 2 -3 turns 'power makeup'.

So, in the real world (unless working to NRC specs), 5-8 turns total will do.

A little 'short' is preferable to 'too long' - the worst case is driving the pipe in so hard that the wedging action of the taper splits the fitting.

ps. for 1/2 & 3/4

14 tpi - thread cut 3/4 long, 11t, 4 threads (1/4&quot showing after make-up

Author: mwr (IN)

Is a "turn" a full 360 rotation?

typically how many exposed threads are left when its made up properly?

"14 tpi - thread cut 3/4 long, 11t, 4 threads (1/4" showing after make-up"...

so 11 threads are on a 3/4 fitting and 4 should remain after makeup?

If there is no drips after a day, is it safe to call it good or does an improperly made threaded connection develop leaks at a later time?



Edited 3 times.

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full turn = 360

all 1/8"-2" fittings have 7 threads

different pipe sizes may have different tpi and 'length of thread' but ALL will make up (if perfect) 7 turns total

1/3 of thread should remain OUTSIDE of fitting

to repeat: 3-5 hand tight - 2-3 power

the seal is formed by the metal to metal wedging action of the tapered threads

a 'perfect' seal would be obtained by 7 total turns, 2 or 3 of which would be under power/wrench tightening

Author: mwr (IN)

I think I am out of luck justifying my work in this manner.

If all fitting threads are different than I wont be able to judge by exposed threads then with my 3/4" brass nipple into my ball valve. Which I was just down in the basement measuring the threads (about 1/4" exposed) and 4 total threads exposed.

I also did not count turns either when I made it up.

So it comes down to if it leaks or not.

After 48 hours, not (knock on wood)... can I call it good after that amount of time and get on with my life?

Author: hj (AZ)

quote; Is a "turn" a full 360 rotation?
YES

typically how many exposed threads are left when its made up properly?
I have absolutely no idea because I have never checked it and would depend on how the pipe was threaded, anyway.

"14 tpi - thread cut 3/4 long, 11t, 4 threads (1/4" showing after make-up"...
If you say so and it makes you happy. But, you are assuming that the thread IS exactly 11 threads and/or an inch long.

Author: bernabeu (SC)

Quote

If all fitting threads are different than I wont be able to judge by exposed threads then with my 3/4" brass nipple into my ball valve. Which I was just down in the basement measuring the threads (about 1/4" exposed) and 4 total threads exposed.

You miss the point.

ALL 1/8" through 2" fittings have EXACTLY 7 threads.

ALL 1/8" through 2" fittings require 7 turns for full contact.

In our imperfect world 5 through 8 total turns is 'acceptable'.

3-5 turns by hand then 2-3 turns by wrench = 5-8 turns total

ps. the first 2 threads 'cut' are imperfect 'starter threads' so it is critical to have at least 3 threads 'showing' else the 'starters' will wedge the fitting off the good threads and break the seal

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