Air Compressor NPT fiting education needed

[TeamTruett]

I needed to reposition a coupler 90 degrees. The coupler is marked 1/4" NPT so I purchased a 1/4" NPT brass street elbow. It will not thread onto the compressor regulator like the coupler. It had red sealant on it that I thought was the issue and I removed it. It will start to thread but gets tight in one turn. I also needed a 45 degree angle (1/8") for my air gauge for better viewing. That too will start but not thread. Where did I go wrong?
Thanks

 

[csp]

How is the street elbow being tapered preventing it from threading into the regulator?

Is it literally incompatible threadwise, or will it not thread in tightly because of the taper?

 

[TeamTruett]

Just added close up pics, comparing the threads.

 

[tonyciambrone]

Are the female pipe threads in good shape? Are you just cross-threading them? Crossthreading NPT feels a little different than straight threads.

Also sealant is definitely not the problem...there needs to be sealant in NPT connections. l

 

[nadogail]

Pipe threads are tapered and they get harder to turn as they tighten.

 

[ColoMid]

TT, check the country of origin of the compressor. They threads may be BSP.
The default world "metric" standard. Not quite the same a NPT. I ran into this once.

 

[matt_i]

It sounds like the female thread might not be made to full depth OR its a straight pipe thread and gets tight very quickly as compared to the tapered male thread.

Also, BSPP threads will often work with NPT systems but its not ideal.

 

[sweetk30]

i know 1 time i got mixed up with 1/8" pipe and from NPT to BNPT its 1 extra thread . . .

i think someone got packaged wrong or you got british pipe stuff on your compressor parts .

when i found this out it was on a tire machine .

 

[TeamTruett]

These are what I bought, maybe I am missing something in the spec description?

https://www.amazon.com/gp/product/B007PD3M64/?tag=atomicindus08-20

https://www.amazon.com/gp/product/B01BYLXC76/?tag=atomicindus08-20

 

[lilredex]

Does the coupler fit the female end of that new elbow? Ditto for the gauge.

That will tell you if your original threads are NPT or something else.

 

[TeamTruett]

That's the funny thing, it will thread into the elbow no problem. The female turns 1 1/2 times and gets tight.

 

[tonyciambrone]

One of those parker fittings you bought says made to dryseal specs on parkers website I.E NPTF. I wouldn't be surprised if they were both NPTF spec threads and they don't play nice together

 

[TeamTruett]

Ah ha.... OK Thanks, so the lesson for me is NPT and NPTF are not the same? I thought the "F" was for female

 

[BukitCase]

Nope, the "F" in NPTF is for "fuel" - intended for higher pressure/quality uses... Steve

 

[TeamTruett]

Nope, the "F" in NPTF is for "fuel" - intended for higher pressure/quality uses... Steve

Thanks, threads can be confusing.

 

[BukitCase]

You're welcome; you might wanna dnl this
https://www.discounthydraulichose.com/mm5/thread_guide.pdf

Covers the British stuff mentioned earlier, as well as NPTF and a crapload of others -

Having 2 tractors, a full size backhoe, 2 manlifts and a dump truck (the common thing is hydraulics) I find that pdf invaluable, to the point that I keep a copy of it on my computer AND my phone...

As was also mentioned, some of the Brit stuff is ALMOST same as NPT, and will START to thread in but that stupid "one thread difference" will lock it up 'way too soon... Steve

 

[TeamTruett]

You're welcome; you might wanna dnl this
https://www.discounthydraulichose.com/mm5/thread_guide.pdf

Covers the British stuff mentioned earlier, as well as NPTF and a crapload of others -

Having 2 tractors, a full size backhoe, 2 manlifts and a dump truck (the common thing is hydraulics) I find that pdf invaluable, to the point that I keep a copy of it on my computer AND my phone...

As was also mentioned, some of the Brit stuff is ALMOST same as NPT, and will START to thread in but that stupid "one thread difference" will lock it up 'way too soon... Steve

great info

 

[crewchief888]

TT, check the country of origin of the compressor. They threads may be BSP.
The default world "metric" standard. Not quite the same a NPT. I ran into this once.

BSP pipe treads are the same thread pitch, (TPI) but are not tapered like US pipe thread.


I remember years ago adding a central grease system to Bomag vibratory rollers. we tapped out the BSP holes to accept US std tapered pipe threads.

that could be what the OP's experiencing.

 

[BukitCase]

"BSP pipe treads are the same thread pitch, (TPI) but are not tapered like US pipe thread"

NOT true; check out the thread guide I linked to earlier in this thread. There are both straight and tapered british pipe - tapered British 1/4" pipe is 1/4-19, NPTF and NPT a 1/4" pipe is 1/4-18.

Both male and female thread diameters are a few thou different than NPT also... Steve