NPT/NPTF Threads?

Exile_D

Exile_D

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I have this little DIY project (distilled water reservoir) that instructed to use a NPT threaded fitting and a NPT locknut. If I understand the basics of how NPT threads work, the threads on the locknut and/or the fitting will deform as you tighten them together.
My concern/confusion is regarding how far the locknut will actually travel along the fitting threads because it needs to clamp down on a fairly thin material and there is a long way to go. Will the locknut make it almost all the way up the threads?

In the picture, the locknut is now finger tight and won't turn anymore, so that is as far as it goes without getting out the wrenches.

0220241618.jpg

I haven't tested it yet, because these are the only ones I have and if I destroy the threads trying to take it off again I gotta buy more. Or should I just get some straight threaded ones and use a bunch of silicone sealant and/or tape, lol.
 
First question, do you have to have NPT fitting?

NPT threads are taper and the threads made a wedge type connection. You'll need a washer or stack to take up the extra room there

You can go to Lowes and make a bulkhead fitting or get one from McMaster Carr. These have IPS threads which are straight pipe thread. Just get a 2 washers, sealant and nut.


www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com www.mcmaster.com
 
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Not sure what kinda material you are going though but seems like that is going to be prone to leaking and not sure how you'd get it tight enough to seal.

I'd use something like this
www.thebucketcompany.com

3/8" MPT w/ Nut & Gaskets - 3/4" Straight Barb | The Bucket Company

The Bucket Company's 3/8” Male Pipe Thread (MPT) with Nut and Gaskets to 3/4” Straight Adaptor Fitting works with the 1.2 Gallon and 3 Gallon Ez-Pz Buckets and growing systems. Cultivators can use this drainage fitting especially well when assembling individual buckets for home growing applications!
www.thebucketcompany.com www.thebucketcompany.com

If you have to have it in metal, look at Thru Hall fittings for boats, they are usually stainless
 
Exile_D said:
Or should I just get some straight threaded ones and use a bunch of silicone sealant and/or tape, lol.
Click to expand...

Just an FYI on teflon tape. It does nothing as far as sealing threads. It actually works as a lubricant on interference threads, ie pipe thread, to let you tighten a fitting tight enough to seal. Teflon pipe dope or even loc- tight have the same effect.
A fitting with regular old SAE threads will seal with crush washers, o-rings, plastic washers or stat-o-seal washers, etc. But tape or pipe dope is nothing more than a placebo and will not actually seal the threads for anything above a single psi of head pressure.
 
Djstorm100 said:
First question, do you have to have NPT fitting?

NPT threads are taper and the threads made a wedge type connection. You'll need a washer or stack to take up the extra room there

You can go to Lowes and make a bulkhead fitting or get one from McMaster Carr. These have IPS threads which are straight pipe thread. Just get a 2 washers, sealant and nut.


www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com www.mcmaster.com
Click to expand...
Don't think it has to be NPT fittings, that was just what the instructions used. It listed NPT fittings because it "prevents leaks", but it also used silicone sealant on both sides of the connection.
Does it matter what type of washers and nut for that fitting from Lowes?

NCMedic said:
Not sure what kinda material you are going though but seems like that is going to be prone to leaking and not sure how you'd get it tight enough to seal.

I'd use something like this
www.thebucketcompany.com

3/8" MPT w/ Nut & Gaskets - 3/4" Straight Barb | The Bucket Company

The Bucket Company's 3/8” Male Pipe Thread (MPT) with Nut and Gaskets to 3/4” Straight Adaptor Fitting works with the 1.2 Gallon and 3 Gallon Ez-Pz Buckets and growing systems. Cultivators can use this drainage fitting especially well when assembling individual buckets for home growing applications!
www.thebucketcompany.com www.thebucketcompany.com

If you have to have it in metal, look at Thru Hall fittings for boats, they are usually stainless
Click to expand...
Not sure it has to be metal either, just needs to be for a 3/8" ID (10mm) hose. Do those plastic ones hold up well to putting the hose on and taking it off often?

Johnny said:
Just an FYI on teflon tape. It does nothing as far as sealing threads. It actually works as a lubricant on interference threads, ie pipe thread, to let you tighten a fitting tight enough to seal. Teflon pipe dope or even loc- tight have the same effect.
A fitting with regular old SAE threads will seal with crush washers, o-rings, plastic washers or stat-o-seal washers, etc. But tape or pipe dope is nothing more than a placebo and will not actually seal the threads for anything above a single psi of head pressure.
Click to expand...
So skip the teflon tape, got it! Honestly never knew that, always thought it was for sealing the threads!
 
Am I understanding that the npt fitting is not threading into anything but the nut?
In that case either rubber or soft plastic washers on both sides or possibly a snug o-ring with cup washers on both sides is what I would be using for that if given no other choice of fittings.
In my world (racing/aircraft stuff), I would be looking for a part called a bulkhead fitting but I honestly have no clue if that is a "thing" in the home plumbing, big box store world.

Sorry, I'm probably adding more confusion to this than necessary. 😁
 
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Exile_D said:
Don't think it has to be NPT fittings, that was just what the instructions used. It listed NPT fittings because it "prevents leaks", but it also used silicone sealant on both sides of the connection.
Does it matter what type of washers and nut for that fitting from Lowes?


Not sure it has to be metal either, just needs to be for a 3/8" ID (10mm) hose. Do those plastic ones hold up well to putting the hose on and taking it off often?


So skip the teflon tape, got it! Honestly never knew that, always thought it was for sealing the threads!
Click to expand...

It doesn't matter everything is in the same isle, metal washer, they do have rubber washer you can put in between the tank and metal washer. You could go plastics instead of brass. I would put sealant on the washer that goes on the outside of the tank.

Important question, where you plan to put the fitting, is the tank flat? Will the whole washer be flat against the tank?
 
Johnny said:
Just an FYI on teflon tape. It does nothing as far as sealing threads. It actually works as a lubricant on interference threads, ie pipe thread, to let you tighten a fitting tight enough to seal. Teflon pipe dope or even loc- tight have the same effect.
A fitting with regular old SAE threads will seal with crush washers, o-rings, plastic washers or stat-o-seal washers, etc. But tape or pipe dope is nothing more than a placebo and will not actually seal the threads for anything above a single psi of head pressure.
Click to expand...
IMG_0605.gif
 
Lots of great advice above, which I totally concur with. Use a bulkhead fitting and add a ball valve.

If you’re removing the hose frequently, I’d consider a quick connect fitting such as this one. It’s stainless steel and includes some replacement o-rings. It’s setup for 1/2” line on one side, so you’d also need a brass hose barb reducer (available on Amazon if you search on that term). One end has 1/4” pipe threads which could interface directly with the ball valve output.


The reason why is that removing and installing hoses over barbed nipples usually puts a lot of side flex on the nipple. If it’s protruding from a plastic tank, this can cause the tank to crack over time.

.
 
Exile_D said:
Not sure it has to be metal either, just needs to be for a 3/8" ID (10mm) hose. Do those plastic ones hold up well to putting the hose on and taking it off often?
Click to expand...

Late to the reply party, but what others said... barbed fittings aren't great for multiple removals before either the tank, barb or hose gives out.

I was going to suggest some type QD connection like @Scsmith42 suggested
 
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